Process for producing a water-absorbing resin derived from a biological raw material and the resulting water-absorbing resin

Abstract

The present invention solves the problem of obtaining a water-absorbing resin with the same or higher performance and less impurities than the conventional water-absorbing resin derived from fossil raw materials at a low cost by using renewable bio-raw materials in the production of the water-absorbing resin. The technical solution is a method for producing a water-absorbing resin derived from bio-raw materials, comprising the following steps (i)-(vii): step (i), obtaining acetone from bio-ethanol; step (ii), obtaining isopropyl alcohol from the acetone; step (iii), obtaining propylene from the isopropyl alcohol; step (iv), obtaining acrylic acid from the propylene; step (v), polymerizing a monomer aqueous solution containing the acrylic acid to obtain polyacrylic acid and / or its salt; step (vi), drying the polyacrylic acid and / or its salt; and step (vii), surface cross-linking the polyacrylic acid and / or its salt.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a water-absorbing resin. More specifically, it relates to a method for producing a water-absorbing resin with good productivity and low cost, using renewable biological raw materials, that exhibits properties equal to or better than those of water-absorbing resins derived from fossil raw materials, but with fewer impurities. Background Technology

[0002] Superabsorbent polymers (SAP), absorbent gel materials (AGM), and water-swellable polymers are also known as superabsorbent polymers, superabsorbent polymers (SAP), and absorbent gelling agents. They are widely used in hygiene materials such as diapers, sanitary napkins, and incontinence pads, as well as in agricultural and horticultural water-retaining materials, fragrances, deodorants, dehumidifiers, and cable waterproofing materials. Known superabsorbent resins include partially neutralized cross-linked polyacrylic acid polymers and starch-acrylic acid graft polymers. Representative polymerization methods for superabsorbent resins include aqueous solution polymerization, reverse suspension polymerization, and gas-phase polymerization. For example, aqueous solution polymerization involves processes including preparing an aqueous solution of monomers such as acrylic acid, polymerization, gel pulverization, drying, granulation (pulverization / grading), micronized powder recycling, surface cross-linking, and additive addition (Non-Patent Literature 1).

[0003] Superabsorbent polymers are typically synthetic polymers represented by cross-linked polyacrylates. Acrylic acid, their monomer, is generally obtained through the oxidation of propylene, which is derived from the cracking of naphtha, a fossil fuel. Superabsorbent polymers are primarily used in hygiene materials such as diapers, which are used extensively for single purposes and are therefore discarded as disposable hygiene products. In recent years, these fossil-derived polyacrylate superabsorbent polymers have been classified as petrochemicals that have an environmental impact from a sustainability perspective. Therefore, in replacement of conventional fossil-derived (petroleum-based) polyacrylate superabsorbent polymers, superabsorbent polymers grafted or mixed with polyacrylates have been proposed (Patent Document 17), and superabsorbent polymers derived from natural polymers obtained by cross-linking or carboxyl modification of natural polymers (Patent Document 18), etc.

[0004] However, in the water-absorbing resins of natural polymers (such as starch-grafted or starch-mixed polyacrylic acid crosslinkers, modified starch crosslinkers, carboxymethyl cellulose crosslinkers, polyamino acid crosslinkers, etc.), the natural polymers have low heat resistance. Therefore, in the manufacturing process of water-absorbing resins, there are not only coloring problems (yellowing and browning of products due to low heat resistance), but also difficulties in processing under high temperature conditions and low productivity. In fact, due to the use of natural polymers, the water absorption performance is far worse than that of the previous polyacrylate water-absorbing resins.

[0005] Therefore, instead of using natural polymers with poor performance and heat resistance in water-absorbing resins, a method has been proposed to produce water-absorbing resins by obtaining acrylic acid derived from conventional fossil raw materials from biological raw materials (bioacrylic acid) (Patent Documents 1-16, 19, 20). In water-absorbing resins made from bio-derived acrylic acid, the manufacturing process of conventional polyacrylic acid water-absorbing resins can be used as is, thus offering advantages over water-absorbing resins using natural polymers in terms of performance, productivity, and heat resistance (coloring) issues.

[0006] Specifically, methods for obtaining absorbent resins from bio-acrylic acid include: methods using acrylic acid derived from glycerol (Patent Documents 1-4); methods using acrylic acid obtained by dehydrating lactic acid and 3-hydroxypropionic acid (Patent Documents 5-8, 20); methods using acrylic acid obtained by dehydrating polyhydroxypropionic acid (Patent Document 9); methods for obtaining acrylic acid from β-propiolactone (Patent Document 10); and methods using bio-naphtha based on natural oils and / or fats (Patent Documents 11, 12), etc. Furthermore, methods using carbon isotopes for these absorbent resins are also known. 14 C quantity, 13 The C-quantity specification refers to the content of raw materials derived from biological materials and the method using bio-acrylic acid water-absorbing resin (Patent Documents 7, 13, 14).

[0007] However, in the methods for manufacturing bio-acrylic acid without using propylene (Patent Documents 1-10, 19, 20), existing acrylic acid manufacturing equipment that uses fossil fuel propylene as a starting material cannot be used, requiring entirely new manufacturing equipment. Therefore, from the perspective of equipment cost, it is also likely to become expensive acrylic acid. Furthermore, it is known that in the manufacture of bio-acrylic acid, although biological raw materials that are more expensive than fossil fuel propylene are used (in the aforementioned Patent Documents 1-14, 20, lactic acid, 3-hydroxypropionic acid, glycerol, and bio-naphtha based on natural oils and / or fats), impurities are more likely to increase compared to acrylic acid derived from fossil fuels. For example, even when using bio-propylene, propylene contains a large amount of propane during the thermal decomposition of bio-naphtha. The increase in propane in bio-propylene will cause an increase in non-polymerizable propionic acid in the acrylic acid obtained through oxidation reaction (Patent Document 11). Bio-propane is also likely to contain sulfur, phosphorus, and nitrogen derived from biological raw materials (Patent Document 12). Furthermore, the following problems exist: Bioacrylic acid, not limited to that derived from biopropylene, contains a significant amount of formic acid (Patent Document 15); bioacrylic acid derived from glycerol contains a significant amount of hydroxyacetone, making the absorbent resin prone to staining (Patent Document 16); when acrylic acid is obtained from glycerol, organic acids such as propionic acid, acetic acid, and formic acid are easily produced as byproducts, especially propionic acid produced as a byproduct via propionaldehyde; and when acrylic acid is obtained from 3-hydroxypropionic acid, organic acids from fermentation byproducts may also be introduced. In particular, the byproduct propionic acid has a boiling point approximately the same as that of acrylic acid, at 141°C, making separation difficult. To remove organic acids such as propionic acid from acrylic acid, repeated purification is required, but even with repeated purification at the expense of yield and cost, the removal of organic acids, especially propionic acid, may not be sufficient.

[0008] Compared to conventional acrylic acid derived from fossil raw materials, the increase or new generation of impurities in bio-based acrylic acid not only reduces the purification cost and yield of bio-based acrylic acid, but also causes problems when using bio-based acrylic acid with these impurities in superabsorbent resins (odor, discoloration, reduced performance, etc. of superabsorbent resins).

[0009] Therefore, the current situation is that the manufacturing cost of any bio-acrylic acid is very high, and the polyacrylic acid (salt) superabsorbent resin using this bio-acrylic acid is also very expensive. Furthermore, when the starting biological raw materials are expensive or their production is limited, there are limits to the use of superabsorbent resins derived from biological raw materials to replace the large quantities consumed from fossil-derived superabsorbent resins. Moreover, although the polyacrylic acid (salt) superabsorbent resin derived from bio-acrylic acid is the same polyacrylic acid (salt) superabsorbent resin, compared to superabsorbent resins derived from acrylic acid from fossil-derived raw materials, the actual situation is that due to the unique impurities of various bio-acrylic acids (e.g., the increase in propionic acid in acrylic acid), the superabsorbent resins derived from these impurities tend to have inferior odors (e.g., the sour smell of propionic acid) and poorer coloring.

[0010] Existing technical documents

[0011] Patent documents

[0012] Patent Document 1: WO2006 / 092272

[0013] Patent Document 2: WO2006 / 136336

[0014] Patent Document 3: WO2008 / 023040

[0015] Patent Document 4: WO2010 / 066513

[0016] Patent Document 5: WO2006 / 092271

[0017] Patent Document 6: WO2008 / 023039

[0018] Patent Document 7: WO2007 / 109128

[0019] Patent Document 8: WO2013 / 155292

[0020] Patent Document 9: WO2013 / 185009

[0021] Patent Document 10: WO2018 / 085254

[0022] Patent Document 11: WO2014 / 079785

[0023] Patent Document 12: Japanese Patent Application Publication No. 2018-083866

[0024] Patent Document 13: WO2011 / 136237

[0025] Patent Document 14: WO2011 / 136238

[0026] Patent Document 15: WO2011 / 040575

[0027] Patent Document 16: WO2009 / 130915

[0028] Patent Document 17: WO2007 / 098932

[0029] Patent Document 18: WO2002 / 096953

[0030] Patent Document 19: WO2010 / 090324

[0031] Patent Document 20: WO2010 / 090322

[0032] Non-patent literature

[0033] Non-patent literature 1: Modern Superabsorbent Polymer Technology (1998); pp. 69–117 Summary of the Invention

[0034] The problem the invention aims to solve

[0035] The technical problem of the present invention is to use renewable biological raw materials in the manufacture of water-absorbing resins to obtain water-absorbing resins with the same or better performance and the same or further reduced amount of impurities as conventional water-absorbing resins derived from fossil raw materials at low cost.

[0036] Solution for solving the problem

[0037] To address the aforementioned technical problems, the inventors have, for the first time, focused on using ethanol as a starting material for the monomer constituting the main chain of the absorbent resin, and developed a method for manufacturing absorbent resins derived from biological raw materials. This method replaces the method of using natural polymers with poor performance and heat resistance in absorbent resins, and replaces the conventional representative manufacturing method of bioacrylic acid (starting materials include glycerol, bio-naphtha, lactic acid, 3-hydroxypropionic acid, bio-naphtha based on natural oils and / or fats, etc.). The inventors have also studied the method of obtaining absorbent resins from ethanol, which is mainly used as fuel.

[0038] That is, the inventors have devised a method that replaces the expensive biological raw materials (and the biological raw materials with limited production) of the past, using bioethanol, which can be produced in large quantities, as the starting material, and synthesizes propylene through a specific process, thereby suppressing the generation of propane and the like, thereby suppressing impurities (such as propionic acid content) in bioacrylic acid.

[0039] Furthermore, in this invention, it was discovered that by preparing a monomer from bioacrylic acid obtained from bioethanol through a specific process (bioethanol → bioacetone → bioisopropanol → biopropylene → bioacrylic acid), the bioacrylic acid derived from bioethanol through the specific process does not cause problems with water absorption performance or various problems caused by impurities (e.g., coloring, odor). As a raw material for water-absorbing resin, the acrylic acid is preferably equivalent to or higher than conventional acrylic acid derived from fossil raw materials, thereby solving the above-mentioned technical problems and completing this invention.

[0040] That is, the present invention is a method for manufacturing a water-absorbing resin derived from biological raw materials, which includes the following steps (i) to (vii):

[0041] Process (i) involves obtaining acetone from bioethanol;

[0042] Step (ii) involves obtaining isopropanol from the acetone;

[0043] Step (iii) involves obtaining propylene from the isopropanol;

[0044] Step (iv) involves obtaining acrylic acid from the propylene;

[0045] Step (v) involves polymerizing an aqueous monomer containing the acrylic acid to obtain polyacrylic acid and / or its salts;

[0046] Step (vi) involves drying the polyacrylic acid and / or its salts; and

[0047] Step (vii) involves surface crosslinking of the polyacrylic acid and / or its salts.

[0048] Furthermore, the present invention relates to a water-absorbing resin obtained by the manufacturing method described above.

[0049] Invention Effects

[0050] Renewable biological raw materials can be used in the manufacture of absorbent resins to obtain absorbent resins with performance equal to or better than conventional absorbent resins derived from fossil raw materials, and with the same or further reduced impurity levels, at low cost. Since biomass absorbs CO2 from the air during its production, using bioethanol as a raw material to manufacture absorbent resins can lead to carbon-neutralized, high-performance absorbent resins. Furthermore, bioethanol is also a cheap and readily produced biological raw material; therefore, the absorbent resin of this invention, manufactured from bioethanol, as a bio-based absorbent resin, can widely replace the large-scale consumption of absorbent resins derived from fossil raw materials. Detailed Implementation

[0051] [Explanation of Terminology]

[0052] (Biomaterials (biomass))

[0053] In this invention, biological raw materials (biomass) can be any organic resource derived from living organisms, such as animal-derived biological raw materials (e.g., wool), but renewable plant raw materials are preferred. Specifically, biological raw materials with plant components such as sugars, starches, and cellulose as starting materials are preferred.

[0054] In this invention, bioethanol, bioacetone, bioisopropanol, biopropylene, and bioacrylic acid refer to ethanol, acetone, isopropanol (also known as 2-propanol, isopropyl alcohol), propylene, and acrylic acid obtained by using biological raw materials in their raw materials or further upstream raw materials, except for carbon isotopes. 14 Apart from the amount of carbon, its chemical structure is no different from that of known ethanol, acetone, isopropanol, propylene, and acrylic acid.

[0055] In the following text, to emphasize that ethanol, acetone, isopropanol, propylene, and acrylic acid are obtained from biological raw materials, they are sometimes referred to as bioethanol, bioacetone, bioisopropanol, biopropylene, and bioacrylic acid, respectively.

[0056] In this invention, a bio-derived absorbent resin refers to a resin in which the monomers constituting the main chain of the absorbent resin include monomers derived from bio-derived materials.

[0057] In this invention, unless otherwise stated, the terminology relating to the properties of absorbent resins is defined in the 2005 edition of the WSP (Worldwide Strategic Partners) standard in the EDANA Recommended Test Methods. The following properties are specified in WSP: pH (WSP200.2), Residual Monomer (WSP210.2), Particle Size Distribution (WSP220.2), Loss on Drying (WSP230.2), Free Swelling Capacity or FSC (WSP240.2), Centrifugal Retention Capacity or CRC (WSP241.2), AUP (Absorption Up to Load) or AAP (Water Absorption Up to Pressure) (WSP242.2), Flow Rate or PDAUP (Pulse Up to Load) (WSP243.1), Flow Rate (WSP250.2), Loose Density or Density (WSP260.2), Water-Soluble Components or Extractable Components (WSP270.2), Attracted Particles (WSP280.2), and Dust (WSP 290.2).

[0058] In this invention, AAP is sometimes measured at a pressure of 0.7 psi (4.8 kPa), and sometimes the AAP at this pressure is recorded as AAP0.7.

[0059] In this invention, the "moisture content" of the water-absorbing resin or particulate hydrogel is the value when the mass of the sample is set to 1g and the heating temperature is set to 180°C in the "loss on drying" (WSP230.2) determination.

[0060] In this invention, the weight-average particle size (D50) is based on the data of "particle size distribution" (WSP220.2), and is obtained by marking the proportion R% of particles remaining on a sieve with a specified mesh size on logarithmic probability paper and reading the mesh size (particle size) with R=50.

[0061] (Other) In this invention, mass and weight are treated as synonyms. Furthermore, "X~Y" indicating a range means "X or more and Y or less". Furthermore, "X" in "X~Y" indicating a range can serve as a basis for the reasonableness of setting it as "X or more" or "X or less". Furthermore, "Y" in "X~Y" indicating a range can serve as a basis for the reasonableness of setting it as "Y or more" or "Y or less". Moreover, unless otherwise specified, "%" and "ppm" refer to "mass %" and "mass ppm". Furthermore, "~acid (salt)" refers to "~acid and / or its salt", and "(meth)acrylic acid" refers to "acrylic acid and / or methacrylic acid". Furthermore, regarding the determination of physical properties, etc., unless otherwise specified, the determination is performed at room temperature (20~25°C) and relative humidity 40~50%RH. Furthermore, regarding a specific component, when there is a description related to content, concentration, usage amount, or amount added, if the specific component consists of two or more, it is the total amount.

[0062] [Method for manufacturing the water-absorbing resin of the present invention]

[0063] (Bioethanol)

[0064] The most significant feature of this invention is that it is the first time that bioethanol has been used as a raw material for absorbent resins, and absorbent resins are obtained from bioethanol, which has been primarily used as fuel in the past.

[0065] Global bioethanol production exceeded 113 billion liters (approximately 89 million tons) in 2022. Compared to petroleum production of approximately 4.6 trillion liters, bioethanol represents about 3%. As a biological feedstock, it is readily available inexpensive and in large quantities. Its primary use is as fuel (approximately 85% for automobiles, etc.). In addition, it is mainly used as a solvent in industrial applications and in food-related applications such as beverages and disinfectants. While examples of bioethanol being used in chemicals such as ethyl acetate can be seen, this invention is characterized by its use as a starting material for superabsorbent polymers, a function primarily intended for fuel.

[0066] Bioethanol can be obtained from glucose, sucrose, etc. through well-known fermentation methods, using molasses (waste molasses) after separating refined sugar as fermentation raw material, for example, through the following reaction formula.

[0067] C6H 12 O6→2CH3CH2OH+2CO2

[0068] First, in the first stage, one molecule of glucose is broken down into two molecules of pyruvate by multiple enzymes in the glycolysis system. From the second stage onwards, it is a reaction unique to alcohol fermentation. One molecule of carbon dioxide is removed from one molecule of pyruvate to produce acetaldehyde. Then, acetaldehyde is rapidly reduced to ethanol by electrons from reduced NADH (Nicotinamide adenine dinucleotide).

[0069] Ethanol aqueous solutions obtained through fermentation (ethanol concentration of several to several 10% by volume, particularly about 5 to 20% by volume) contain a large amount of water and fermentation raw materials (sugars, proteins) as well as fermentation products other than ethanol (organic acids, alcohols, etc.). Therefore, they are purified by distillation. However, due to the azeotropic phenomenon of ethanol and water, even after distillation purification, they will still become hydrous ethanol containing a small amount (about 4 to 10% by weight) of water. The purity (especially the concentration) of the distilled hydrous ethanol can be appropriately selected, with 90 to 96% by weight being representative. In this high-concentration hydrous ethanol, most of the impurities are water, with a small amount of other impurities.

[0070] Then, to further dehydrate and purify the hydrous ethanol obtained by distillation, azeotropic distillation is performed using hydrophobic organic solvents such as benzene or hexane, or dehydration is carried out using dehydrating agents such as zeolites or calcium oxide, or reverse osmosis membranes, to obtain commercially available anhydrous ethanol (typically with a purity of 99.5% by volume or higher). For example, anhydrous ethanol, which has high compatibility with gasoline, is widely used as a fuel when mixed with gasoline.

[0071] Both aqueous ethanol and anhydrous ethanol can be used as the bioethanol of this invention. It should be noted that in step (i) of obtaining acetone from bioethanol, as described later in Formula 1, the ethanol is reacted with water as described later, so there is no obstacle even if the ethanol contains water. One of the features of this invention is that the use of aqueous ethanol, which is cheaper than anhydrous ethanol, as a raw material. On the other hand, using anhydrous ethanol incurs higher purification costs, which is disadvantageous, and the residual hydrophobic organic solvent used in the azeotropic distillation during dehydration may contribute to the odor of the absorbent resin. Furthermore, aqueous ethanol has a higher flash point than anhydrous ethanol (the flash point of anhydrous ethanol is 13.0°C, while the flash point of 50% by volume ethanol is 22.2°C), therefore, from the perspective of ethanol operability, the use of aqueous ethanol is sometimes preferred.

[0072] (Water content of bioethanol)

[0073] In the use of aqueous ethanol in this invention, the lower limit of the water content of the aqueous ethanol can be 3% by weight or more, 4% by weight or more, 5% by weight or more, 6% by weight or more, 7% by weight or more, 8% by weight or more, 10% by weight or more, or 12% by weight or more, and the upper limit of the water content can be less than 50% by weight, less than 40% by weight, less than 30% by weight, or less than 20% by weight. The lower limit of the ethanol concentration is appropriately selected within the range of 40% by weight or more, 50% by weight or more, 60% by weight or more, 70% by weight or more, or 80% by weight or more. Ethanol with higher water content is preferred because it requires less energy for distillation purification, but the water content of the aqueous ethanol is appropriately selected considering impurities, cost, or reactivity. For example, aqueous ethanol with an ethanol concentration of approximately 97–50% by weight, 96–60% by weight, or 96–70% by weight, or within the range of the above upper and lower limits, can be reacted by adding only water and ethanol from the aqueous ethanol, or by adding water (water vapor) as needed, thereby obtaining acetone. For example, in step (i) of obtaining acetone from bioethanol as described later, when acetone is obtained from ethanol as in Formula 1 described later, based on the weight ratio of 2 moles of ethanol to 1 mole of water in Formula 1 (ethanol / water = 92 / 18), the water content of the reaction system is approximately 16% by weight, based on the theoretical value (100% reaction in Formula 1 described later). Therefore, the ratio of water to anhydrous ethanol or aqueous ethanol, and the water content of ethanol, can be selected as needed, taking into account the reaction rate of ethanol, recovery rate, acetone yield, energy, etc. When the water content of the ethanol is too high (ethanol concentration is too low), it is not only energy-disadvantageous for acetone synthesis in Formula 1 described later, but also disadvantageous in terms of the transportation cost of aqueous ethanol containing a large amount of water. Consequently, during distillation purification from the fermentation broth, the removal of fermentation products (organic acids, alcohols) other than ethanol may be insufficient. It should be noted that the water content (volume% or weight%) of aqueous ethanol can be determined appropriately, for example, it can also be calculated based on the density (g / ml) of aqueous ethanol (20℃) as an inherent value.

[0074] In this invention, the water content of the aqueous ethanol can be adjusted under the distillation conditions of the aqueous ethanol solution (the concentration of ethanol after fermentation is a few volume% to a few 10 volume%, particularly about 5 to 20 volume%), or by adding a specified amount of water to the distilled aqueous ethanol or anhydrous ethanol for dilution, or by mixing multiple anhydrous ethanol solutions for adjustment.

[0075] (Trace components in bioethanol)

[0076] In this invention, when using anhydrous ethanol or aqueous ethanol, as trace components other than water, ethanol sometimes contains lower alcohols with 1, 3 to 5 carbon atoms, such as methanol, 1-propanol, isopropanol, 1-butanol, 2-butanol, 2-methylpropanol, and 2-methyl-1-butanol, as well as lower aldehydes or ketones, such as acetaldehyde (2 carbon atoms) and acetone (3 carbon atoms). The content of lower alcohols with 1, 3 to 5 carbon atoms, acetaldehyde, and acetone in anhydrous ethanol or aqueous ethanol is, for example, less than 1% by weight, less than 0.1% by weight, or less than 0.01% by weight, respectively. The content of these trace components can be determined, for example, by gas chromatography.

[0077] In this invention, acetone and isopropanol are obtained from bioethanol. Therefore, ethanol may contain or contain residual acetone or isopropanol. Considering the yield and cost of ethanol, it is not necessary to remove all acetone and isopropanol through ethanol purification. In this invention, bioethanol (and aqueous ethanol) containing acetone and / or isopropanol can be used as a preferred starting material. Considering cost and the performance of the resulting absorbent resin, the content of acetone and / or isopropanol in ethanol, calculated as the total amount of acetone and isopropanol, is preferably 1 ppm or more, 5 ppm or more, 10 ppm or more, or 20 ppm or more, more preferably 1 ppm or more, 5 ppm or more, 10 ppm or more, or 20 ppm or more, respectively. Furthermore, the upper limit of the content of acetone and / or isopropanol in ethanol can be high. Considering the balance with other impurities, for example, it can be selected within the above range as less than 1% by weight, less than 0.1% by weight, or less than 0.01% by weight. It is further preferred to use ethanol containing acetone and isopropanol, the total content of which is within the above range. Ethanol containing acetone or isopropanol can also be obtained as crude ethanol.

[0078] In this invention, ethanol obtained from biological raw materials can be used, preferably ethanol obtained from plant raw materials, and more preferably bioethanol obtained from the fermentation of one or more plant raw materials selected from sugarcane, corn, and sugar beet. One or more of the sugarcane, corn, and sugar beet can be further crushed or juiced before fermentation.

[0079] The plant material can be a genetically recombinant plant (represented by genetically recombinant corn) or a non-genetically recombinant plant. However, in the application of this invention, since it follows the pathway of bioethanol, acetone, isopropanol, propylene, and acrylic acid, it is different from the case of directly using or consuming bioethanol. It is not limited by genetic recombination and can widely use genetically recombinant plant materials, so it is preferred.

[0080] It can be determined using radiocarbon dating.14 C / 12 C is used to confirm that it is bioethanol. Alternatively, traceable ethanol can also be obtained. It should be noted that acetone, isopropanol, propylene, and acrylic acid, obtained sequentially from bioethanol in this invention, can also be determined using radiocarbon dating. 14 C / 12 C or records of acquisition and generation pathways can be used to confirm that the compound is derived from biological raw materials.

[0081] The bioethanol content can be determined in the following manner.

[0082] 1. The ethanol used in the raw material gas is burned and completely converted into carbon dioxide.

[0083] 2. Carbon dioxide is separated and purified using a vacuum pipeline.

[0084] 3. Carbon dioxide generated from ethanol is completely reduced with hydrogen using iron as a catalyst to produce graphite.

[0085] 4. Use 14 C-AMS measuring devices (e.g., those manufactured by NEC) are used to measure graphite derived from ethanol. 14 C concentration and 12 The ratio of C concentration ( 14 C / 12 C).

[0086] 5. Oxalic acid (hereinafter also referred to as standard sample) produced from ethanol provided by the National Institute of Standards and Technology (NIST) in the same year was also determined using the same methods as described in 1-4 above. 14 C concentration and 12 The ratio of C concentration ( 14 C / 12 C).

[0087] 6. Graphite derived from raw material ethanol 14 C / 12 The value of C divided by the standard sample 14 C / 12 The value of C is multiplied by 100 to obtain the bioethanol content.

[0088] (Process (i) for obtaining acetone from bioethanol)

[0089] In the method for manufacturing the absorbent resin of the present invention, in order to obtain acrylic acid from bioethanol, a step (i) of first obtaining acetone from bioethanol is necessary. Methods for manufacturing acetone from ethanol are known, and to obtain acetone from bioethanol, known methods can be applied, for example, by synthesizing acetone from bioethanol using methods such as WO2022 / 244797, Japanese Patent Application Publication No. 2012-240913, Japanese Patent No. 5747326, WO2009 / 110413, and Japanese Patent Application Publication No. 2022-178043. The disclosures of these publications are referenced and are incorporated herein by reference in their entirety.

[0090] It should be noted that while these well-known patent documents describe the synthesis of acetone from bioethanol, acetone is typically used as a solvent and also as a raw material for methyl methacrylate. None of the aforementioned documents on acetone preparation methods suggest the manufacture of absorbent resins from ethanol, nor do they suggest the manufacture of acrylic acid from ethanol via steps (i) to (iv). The present invention is characterized in that, among the numerous uses of acetone obtained from bioethanol, after steps (i) to (iv), absorbent resins are further manufactured from bioacrylic acid obtained from ethanol via steps (v) to (vii).

[0091] More preferably, in step (i), acetone is generated by the following reaction formula (1) between ethanol and water. With this configuration, the absorbent resin can be obtained more efficiently from renewable natural raw materials.

[0092] Equation 1) 2CH3CH2OH + H2O → CH3COCH3 + CO2 + 4H2

[0093] That is, in this invention, anhydrous or aqueous bioethanol is reacted with water (and water in aqueous ethanol) to obtain a mixed gas containing acetone, water vapor, carbon dioxide, and hydrogen. Furthermore, acetone and isopropanol, as fermentation byproducts, may also remain or be present in the bioethanol.

[0094] (Water used in the reaction)

[0095] In the reaction of Formula 1 in step (i), the selectivity of acetone is increased when water (water vapor) is present. The molar ratio (water / ethanol) of water (water vapor) to ethanol (ethanol gas) is preferably 0.1–10, 0.5–10, 0.5–5, and 1–5, respectively, and can be 1–3. When using aqueous ethanol as bioethanol, the total amount of water contained in the aqueous ethanol that is introduced into the system and water added as needed is preferably the above molar ratio relative to 1 mole of ethanol. As an example, 95% by weight (about 96% by volume) of aqueous ethanol contains 0.14 moles of water relative to 1 mole of ethanol. In order to make the molar ratio of water to ethanol 0.1–10, water may not be added, or 9.9 moles or less of water may be added relative to 1 mole of ethanol.

[0096] Apart from the water in the ethanol, there are no particular restrictions on the water added as needed, and tap water, industrial water, pure water (RO water, ion-exchange water, distilled water), etc., can be used. These waters can be groundwater, river water, or water obtained by treating them. In addition, water generated in at least one of the steps (i) to (iv) can be reused.

[0097] (catalyst)

[0098] The catalyst used in step (i) is not particularly limited, but preferably comprises at least one metal (Me) selected from the group consisting of magnesium, calcium, manganese, copper, and zinc, iron, and zirconium. The state of the metal element contained in the catalyst used in step (i) is not particularly limited; for example, it can be a metal oxide containing the metal element, a support containing the metal element, a support bearing the metal element, or a support bearing the metal oxide. The metal oxide can be a composite metal oxide. Examples of composite metal oxides include spinel type, perovskite type, magnetoplumble type, and garnet type, with spinel type being preferred.

[0099] From the viewpoint of catalytic activity, the catalyst used in step (i) preferably contains iron. More preferably, in addition to iron (Fe), the catalyst also contains one or more metals (Me) selected from the group consisting of magnesium (Mg), calcium (Ca), manganese (Mn) and zinc (Zn).

[0100] As a catalyst that contains, in addition to the aforementioned iron (Fe), one or more metals (Me) selected from the group consisting of magnesium (Mg), calcium (Ca), manganese (Mn) and zinc (Zn), the iron composite oxide (sometimes called ferrite) shown in the following general formula (1) is preferred.

[0101] MeO·nFe2O3 (1)

[0102] (In general formula (1), Me represents one or more metals selected from the group consisting of Mg, Ca, Mn and Zn, and n represents a number from 1 to 6.)

[0103] As iron complex oxides, examples include MgO·Fe2O3 (MgFe2O4) and ZnO·Fe2O3 (ZnFe2O4).

[0104] When the catalyst used in step (i) is a catalyst formed by supporting a metal element or metal oxide on a support, the support can include: activated carbon, silica (SiO2), alumina (Al2O3), silica-alumina, zeolite, silica-calcium oxide, zirconium oxide (ZrO2), cerium oxide (CeO2), magnesium oxide (MgO), and diatomaceous earth. More preferably, the support is selected from one or more of activated carbon, silica-calcium oxide, zirconium oxide, cerium oxide, and magnesium oxide, with zirconium oxide being particularly preferred. The shape of the support is not particularly limited, and spherical, granular, and honeycomb shapes are also possible. The BET specific surface area of ​​the support is preferably 20 to 200 m². 2 / g, more preferably 40-200m 2 / g. By using a support with a high specific surface area, the catalyst components can be easily supported in a dispersed state, resulting in higher catalytic activity, which is therefore preferred.

[0105] The state of zirconium contained in the catalyst is not particularly limited. It can be a compound containing zirconium as a single metal, a composite metal oxide containing zirconium along with other metal elements, or a support. Examples of compounds containing zirconium as a single metal include zirconium oxide (ZrO2). Examples of composite metal oxides containing other metal elements (Me) include composite metal oxides of zirconium with Sn, Pb, Zn, Cu, Fe, Mn, In, etc. As a support, zirconium oxide (ZrO2) and composite metal oxides of zirconium with Zn and Fe are preferred; from the viewpoint of catalyst performance, zirconium oxide (ZrO2) is more preferred.

[0106] The amount of metal (Me) in the catalyst is preferably 0.4 to 0.7 moles of iron (Fe) per mole, more preferably 0.4 to 0.6 moles, and even more preferably 0.45 to 0.55 moles. Good catalytic activity is obtained when the amount of metal (Me) is within the above range. The amount of zirconium (Zr) in the catalyst is preferably 0.01 to 0.5 moles of iron (Fe) per mole, more preferably 0.05 to 0.5 moles, and can also be 0.1 to 0.4 moles. The durability of the catalyst is improved when the amount of zirconium is within the above range.

[0107] The total amount of metal (Me), iron and zirconium in the catalyst is preferably 50 to 100% by mass relative to 100% by mass of the catalyst, more preferably 80 to 100% by mass.

[0108] (Reactor / Reaction Conditions)

[0109] The reaction in process (i) is not particularly limited and can be either batch or continuous; however, from a productivity point of view, a continuous reaction is preferred. The reaction is preferably a gas-phase reaction. Examples of gas-phase reaction methods include fixed-bed, moving-bed, and fluidized-bed reactions; the simpler fixed-bed method is preferred.

[0110] In a fixed-bed reaction configuration, ethanol gas can be mixed with water vapor and fed into the acetone synthesis reactor to contact the catalyst, or ethanol gas and water vapor can be fed separately into the acetone synthesis reactor to contact the catalyst. Alternatively, ethanol gas and water vapor can be produced directly from aqueous ethanol, or water vapor can be added separately. It should be noted that ethanol gas and water vapor are obtained by heating aqueous ethanol or anhydrous ethanol and water in a gasification unit, respectively. Besides ethanol gas and water vapor, inert gases such as nitrogen and helium can also be supplied to the acetone synthesis reactor.

[0111] The concentration of ethanol gas is preferably 3 to 66 mol% relative to the total amount of gas supplied to the acetone synthesis reactor (100 mol%), and more preferably 5 to 50 mol%. With this ratio, acetone can be produced at a high productivity.

[0112] The pressure in the reaction of step (i) can be any of reduced pressure, atmospheric pressure, or pressurized pressure, but is preferably 0.07 to 2 MPa, more preferably 0.1 to 1 MPa. The temperature in the reaction of step (i) is preferably 250 to 600°C, more preferably 300 to 550°C, and even more preferably 330 to 500°C. In the case of a gas-phase reaction, the space velocity of the feed gas is preferably 300 to 10,000 (L / h), more preferably 400 to 8,000 (L / h), and even more preferably 500 to 6,000 (L / h).

[0113] (Purification of acetone)

[0114] If the acetone obtained in step (i) has high purity, it may not need to be purified or separated and can be used as is in the subsequent step (ii). Alternatively, steps (i) and (ii) can be combined. However, if the acetone-containing mixture obtained from the aforementioned bioethanol contains gas, it can be separated into a gas mixture mainly composed of hydrogen, carbon dioxide, etc., and a liquid mixture mainly composed of acetone using a known gas-liquid separation method (sometimes referred to as gas-liquid separation). The pressure during the gas-liquid separation operation is preferably 0.1 MPa to 2 MPa, more preferably 0.2 MPa to 1 MPa.

[0115] Furthermore, acetone can also be absorbed from gases primarily composed of hydrogen and carbon dioxide. The method for acetone absorption is not particularly limited; the gas can be introduced into an absorption tower, where the acetone is absorbed by an absorbent supplied from the top of the tower, and recovered from the bottom as an acetone-containing liquid. Water is preferred as the absorbent. There are no particular limitations on the type of water used; tap water, industrial water, pure water (RO (Reverse Osmosis) water, ion-exchange water, distilled water), etc., can be used. Additionally, water used or generated in other processes can be used or reused. The acetone-containing absorbent obtained from the bottom of the absorption tower can be combined with an acetone-based liquid mixture obtained through gas-liquid separation. This improves the acetone recovery rate.

[0116] Next, purified acetone can be obtained by distilling the acetone-based liquid mixture. Distillation can be carried out using known methods. Examples of known distillation methods include thin-film distillation and rectification. Distillation can be continuous or batch; from a productivity point of view, continuous distillation is preferred.

[0117] Purification can involve only gas-liquid separation, gas-liquid separation and distillation, or distillation only, but more preferably, it includes gas-liquid separation and distillation in sequence. This yields more thoroughly purified acetone (sometimes referred to as purified acetone).

[0118] (Impurities in bio-acetone)

[0119] When the acetone obtained above is used in the next step (ii), it is preferable that the aldehydes, alcohols, and ketones (excluding acetone) in the acetone have been reduced. In particular, ethanol and acetaldehyde may become acetic acid after steps (i) to (iv), so it is also preferable to reduce them from the viewpoint of the odor (acidic smell) of the absorbent resin.

[0120] (Purity of bio-acetone)

[0121] The purified acetone obtained by the purification process has an acetone content of at least 90% by mass, more preferably at least 95% by mass, and even more preferably at least 98% by mass, relative to 100% by mass of the purified acetone. Preferably, when the acetone obtained above is used in the next step (ii), the aldehydes, alcohols, and ketones (excluding acetone) in the acetone have been reduced. Particularly preferably, ethanol and acetaldehyde are reduced because they may be converted to acetic acid after steps (ii) to (iv). The total content of ethanol and acetaldehyde in the acetone is preferably 20,000 ppm or less, more preferably 10,000 ppm or less, and even more preferably 5,000 ppm or less. The total content of ethanol and acetaldehyde in the acetone is preferably low, for example, 100 ppm or more, or 500 ppm or more, and even more preferably 1,000 ppm or more, considering the relationship between the yield of purified acetone and the purification cost. The total content of ethanol and acetaldehyde in the acetone is, for example, 100 ppm or more and 20,000 ppm or less. Using high-purity acetone with purity and impurities within the aforementioned range as raw material, the acetone reduction reaction in step (ii) is carried out, and the isopropanol contained in the obtained product is separated from the gas by gas-liquid separation, thereby easily obtaining high-purity isopropanol. It should be noted that if the combined content of ethanol and acetaldehyde in the acetone obtained after step (i) is already within the aforementioned range, it is preferable not to perform any special reduction operation. It should be noted that as long as acetone is obtained with the above-mentioned purity, the adverse effects on the absorbent resin are very small or practically non-existent; therefore, considering the purification cost and yield of acetone, the obtained acetone may contain residual or present isopropanol (e.g., 1 ppm or more, or 10 ppm or more). It should be noted that the content of these trace components can be determined, for example, by gas chromatography.

[0122] (Process (ii) for obtaining isopropanol from acetone)

[0123] In the method for manufacturing the absorbent resin of the present invention, step (ii) of obtaining isopropanol from acetone in order to obtain acrylic acid from bioethanol is necessary. Furthermore, industrially, isopropanol is obtained from acetone using the cumene process for producing phenol. In the method for manufacturing the absorbent resin of the present invention, to solve the technical problem, it is characterized in that acetone obtained from bioethanol in step (i) is used in step (ii). Methods for manufacturing isopropanol from acetone are known. To obtain isopropanol (also known as 2-propanol, isopropyl alcohol) from the acetone obtained in step (i), known methods can be applied, for example, isopropanol can be synthesized from acetone using methods such as Japanese Patent Nos. 5197637, 5300392, 4321838, 2762591, 2723621, and WO2022 / 244797. The disclosures of these publications are referenced and are incorporated herein by reference in their entirety.

[0124] It should be noted that while these patent documents describe the synthesis of isopropanol from acetone, isopropanol is typically used as a solvent and as a starting material for glycerol in chemical products. None of the aforementioned documents on isopropanol preparation methods suggest the production of absorbent resins from bioethanol, nor do they suggest the production of acrylic acid from bioethanol via steps (i) to (iv). The present invention is characterized by, among the numerous uses of isopropanol obtained from bioethanol, further utilizing bioacrylic acid obtained from ethanol as a raw material via steps (v) to (vii) after steps (i) to (iv) to produce absorbent resins.

[0125] In this invention, more preferably, in step (ii), isopropanol is generated by hydrogenation of acetone according to the following reaction formula (2).

[0126] Formula 2) CH3COCH3+H2→CH3CH(OH)CH3

[0127] That is, the acetone obtained in step (i) is reacted with hydrogen to obtain a mixed gas containing isopropanol.

[0128] (catalyst)

[0129] The catalyst used in step (ii) is not particularly limited, and examples include Raney catalysts. Other catalysts include solid catalysts containing metal elements such as Ba, Co, Cr, Cu, Fe, Mn, Ni, Pd, Pt, Zn, Zr, Ru, and Rh. Among these, solid catalysts containing at least one metal element selected from the group consisting of Pt, Ru, Ni, Fe, and Co are preferred, and solid catalysts selected from the group consisting of Ru catalysts, Ni-Pt catalysts, Ru-Pt catalysts, and Ni-Ru catalysts are more preferred. By using solid catalysts containing these metal elements, the activity inhibition effect caused by carbon dioxide in the acetone reduction reaction using hydrogen in step (ii) can be suppressed, and acetone hydrogenation to produce isopropanol can be carried out efficiently.

[0130] As the catalyst, catalysts in the form of elemental metals, alloys, oxides, etc., can be used. Furthermore, the catalyst can be a mixture of elemental metals, a mixture of elemental metals and metal oxides, a mixture of metal oxides, or a mixture of metal oxides.

[0131] Furthermore, the catalyst can be a catalyst in which a metal element is supported on a carrier such as activated carbon, silicon dioxide (SiO2), alumina (Al2O3), titanium dioxide (TiO2), zirconium oxide (ZrO2), cerium dioxide (CeO2), magnesium oxide (MgO), or diatomaceous earth. Among these, the carrier is preferably either silicon dioxide (SiO2) or zirconium oxide (ZrO2). The above-mentioned catalyst can be used alone or in combination with two or more types.

[0132] These catalysts can be in any shape, such as rings or spheres, without any particular limitation.

[0133] In step (ii), one catalyst may be used alone, or two or more catalysts may be used.

[0134] (Reactor / Reaction Conditions)

[0135] The reaction in process (ii) can be carried out in either a batch or continuous manner; from a productivity point of view, a continuous manner is preferred. The reaction in process (ii) is preferably a gas-phase reaction. The reaction form of the gas-phase reaction is not particularly limited; examples include fixed bed and fluidized bed, with the simpler fixed bed form being preferred.

[0136] The reaction pressure in step (ii) can be any one of reduced pressure, normal pressure, or increased pressure, preferably 0.1 MPa to 2 MPa, more preferably 0.1 MPa to 1 MPa.

[0137] The reaction temperature in step (ii) is preferably 20°C to 200°C, more preferably 25°C to 150°C. Lower reaction temperatures are advantageous from an equilibrium perspective, but there is a tendency for hydrogenation to become difficult. On the other hand, when the reaction temperature is higher, the acetone hydrogenation conversion rate does not increase due to equilibrium limitations, and there is a tendency for the hydrogenolysis of acetone and isopropanol to occur simultaneously, resulting in a decrease in yield.

[0138] When the reaction in step (ii) is carried out in a gas phase reaction, the space velocity of the acetone-containing introduced material is preferably 200 to 50,000 (L / h), more preferably 1,000 to 20,000 (L / h), and even more preferably 2,000 to 10,000 (L / h).

[0139] (hydrogen)

[0140] The hydrogen used can be hydrogen extracted from a gas mainly composed of hydrogen or carbon dioxide obtained in step (i), or unreacted hydrogen from step (ii) can be reused, or hydrogen obtained separately. The hydrogen used only needs to be at least equimolar with acetone. From the perspective of separation and recovery, a suitable range is 1 to 10 times the molar ratio relative to acetone, preferably 1 to 5 times the molar ratio.

[0141] (Isolation of isopropanol)

[0142] If the obtained isopropanol is a gas-liquid mixture containing isopropanol and a gas, it can be separated into a gas mixture, for example, mainly composed of hydrogen, and a liquid mixture containing isopropanol using a known gas-liquid separation method, and then the isopropanol can be recovered. Here, the gas in this item refers to a substance that exists in gaseous form under pressurized and cooled conditions in the gas-liquid separation operation.

[0143] In the separation of isopropanol, the pressure during the gas-liquid separation operation is preferably 0.1 MPa to 2 MPa, more preferably 0.2 MPa to 1 MPa.

[0144] In the separation of isopropanol, the temperature during the gas-liquid separation operation is preferably 0℃~50℃, more preferably 5℃~40℃.

[0145] The isopropanol obtained through separation (gas-liquid separation) can be supplied to the next process as is (iii), or it can be further purified by distillation as needed before being supplied to the next process (iii).

[0146] (Purity of the obtained isopropanol)

[0147] From the viewpoint of improving the yield and purity of propylene in step (iii) described later, the purity of isopropanol obtained in step (ii) is preferably 85% by mass or more, more preferably 90% by mass or more, and even more preferably 93% by mass or more. Furthermore, the concentrations of water and acetone, which are impurities, in the isopropanol obtained in step (ii) are preferably 10,000 ppm or less, more preferably 5,000 ppm or less. Ethanol in isopropanol may become acetic acid after steps (iii) to (iv), therefore, the ethanol content in the isopropanol obtained in step (ii) is preferably 20,000 ppm or less, more preferably 10,000 ppm or less, and even more preferably 5,000 ppm or less. The ethanol content in isopropanol is preferably low, and considering the relationship between the yield of purified acetone and the purification cost, it is, for example, 100 ppm or more, or 500 ppm or more, and even more preferably 1,000 ppm or more. The ethanol content in isopropanol is, for example, 100 ppm or more and 20,000 ppm or less.

[0148] (Process (iii) for obtaining propylene from isopropanol)

[0149] In the method for manufacturing the absorbent resin of the present invention, step (iii) of obtaining propylene from isopropanol is necessary in order to obtain acrylic acid from bioethanol. Methods for producing propylene from isopropanol are known, and in order to obtain propylene from the isopropanol obtained in step (ii), known methods can be applied, for example, the methods described in Japanese Patent Nos. 2764058 and 2799004. The disclosures of these publications are referenced and incorporated herein by reference in their entirety.

[0150] It should be noted that while these patent documents describe the synthesis of propylene from isopropanol, they do not describe biological raw materials. Furthermore, propylene is commonly used as a raw material for polypropylene (PP), acrylonitrile (ACN), propylene oxide (PO), alcohols, and cumenes. None of the aforementioned documents on propylene preparation methods suggest the production of absorbent resins from bioethanol, nor do they imply the production of acrylic acid from bioethanol via steps (i) to (iv). The present invention is characterized by, among the numerous uses of propylene obtained from bioethanol, the production of absorbent resins via steps (v) to (vii) using bioacrylic acid obtained from ethanol as a raw material after steps (i) to (iv).

[0151] (catalyst)

[0152] Examples of catalysts used in step (iii) include: alumina catalysts, silica-alumina catalysts, magnesium oxide catalysts, zeolite catalysts, activated clay, etc. Catalysts that use these as supports and support metals such as titanium dioxide (TiO2), tungsten oxide, and zirconium oxide (ZrO2) are also examples. Among these, alumina catalysts are preferred, γ-alumina catalysts are more preferred, and more specifically, catalysts with tungsten oxide supported on γ-alumina are even more preferred. They can be used individually or in combination of two or more.

[0153] The catalyst can be obtained by subjecting the catalysts listed herein to acid treatment and / or calcination as needed. Acid treatment is performed to impregnate the catalyst (e.g., γ-alumina catalyst) in an acid and adjust the acid strength of the catalyst. Examples of acids used include, for example, aqueous solutions of hydrochloric acid, nitric acid, boric acid, etc.; and carboxylic acids such as acetic acid, formic acid, oxalic acid, etc.

[0154] The catalyst used can be any shape that can form a fixed catalyst layer; there are no particular limitations. Examples include plate-shaped, ring-shaped, spherical, cylindrical extrusion, trilobal extrusion, and granular types. Among these, spherical, plate-shaped, and extrusion types are preferred due to their high catalyst strength and ability to fill the reaction tube uniformly.

[0155] Furthermore, when the catalyst is a γ-alumina catalyst, it is preferable to use a catalyst with an average pore diameter of 3 to 15 nm and a standard deviation of 1 to 4 nm, which is obtained by statistical calculation based on the relationship between pore diameter and pore volume.

[0156] (Reactor / Reaction Conditions)

[0157] The reaction in step (iii) can be carried out in either a batch or continuous manner; from a productivity point of view, a continuous manner is preferred. The propylene synthesis reaction is preferably carried out via a gas-phase reaction. Examples of gas-phase reaction methods include fixed-bed, moving-bed, and fluidized-bed reactions; the simpler fixed-bed method is preferred.

[0158] The reaction temperature is typically 150–500℃, preferably 180–400℃. The reaction pressure can be any of reduced pressure, atmospheric pressure, or pressurized pressure, and the reaction system in the catalyst layer is preferably in a gas phase.

[0159] (Gasular substances other than isopropanol)

[0160] Furthermore, in order to rapidly remove the reaction product containing propylene generated by the dehydration reaction of isopropanol from the reaction system, the raw material mixture used in step (iii) may contain, in addition to isopropanol, a gaseous substance that is inactive in the dehydration reaction of isopropanol. Examples of such gaseous substances include nitrogen, helium, and argon. In addition, this gaseous substance may contain substances that are liquid before being supplied to the reactor but become gaseous under the reaction conditions within the reactor. Examples of such substances include pentane and hexane.

[0161] When this inert gaseous substance is mixed with isopropanol and supplied to the reactor, the amount used is typically preferably in the range of 0.01 to 15 mol or 0.05 to 10 mol relative to 1 mol of isopropanol. When too much gaseous substance is used, a large amount of inert gas needs to be separated from the mixture of propylene and water, which is a reaction product, and recycled back to the reactor, sometimes resulting in economic disadvantages such as increased separation costs and recycling costs.

[0162] (Impurities and purification of biopropylene)

[0163] The product obtained by the dehydration reaction of isopropanol (molecular weight 60.1) has approximately the following composition: Propylene (molecular weight 42.08): approximately 70 wt%; Water (molecular weight 18.0): approximately 30 wt%; Isopropanol: less than 1 wt%; Acetone: less than 1 wt%; Diisopropyl ether: less than 1 wt%; Others (impurities originally contained in the raw material isopropanol), wherein acetone and diisopropyl ether are byproducts of the isopropanol dehydration reaction. Here, approximately X (X is a numerical value) means that in addition to X itself, it may include X × ± 10%.

[0164] In this invention, propylene can be purified. Specifically, if the reaction mixture, which is mainly composed of propylene and water, is pressurized and / or cooled, oil-water separation is performed, forming two phases with a propylene layer on top and a water layer on the bottom. Through the oil-water separation process, a large amount of water generated by the dehydration reaction of isopropanol can be removed from the dehydration reaction product.

[0165] From the perspective of separation and purification cost, the pressure during pressurization is preferably 5–50 kg / cm². 2 G. Furthermore, the reaction product (in gaseous form) can be easily liquefied simply by cooling it to 20–50°C. The propylene obtained through separation (gas-liquid separation) can be supplied to the next process as is (iv), or it can be further purified by distillation as needed before being supplied to the next process (iv).

[0166] The water dissolved in the oil layer is typically in trace amounts, below 1000 ppm, and can therefore be easily separated from propylene in the subsequent distillation purification process. As a result, high-purity propylene free of water can be produced. Furthermore, if needed, the propylene fraction exiting the distillation column can be passed in liquid or gaseous form through a packed bed filled with commonly used desiccants such as molecular sieves to obtain substantially water-free propylene. In the oil layer after oil-water separation, in addition to propylene, small amounts of impurities can also be removed by distillation purification to obtain high-purity propylene.

[0167] (The process of obtaining acrylic acid from propylene (iv))

[0168] In the method for manufacturing the absorbent resin of the present invention, step (iv) of obtaining acrylic acid from propylene is necessary in order to obtain acrylic acid from bioethanol. Methods for manufacturing acrylic acid from propylene are known, and in order to obtain acrylic acid from the propylene obtained in step (iii), known methods can be applied, for example, by means of Japanese Patent Nos. 3948837, 4520637, 3938646, and 4765165, etc., whereby purification can be appropriately carried out by gas-phase oxidation of propylene to acrolein and acrylic acid, collection of oxidation products, distillation, and crystallization. The disclosures of these publications are referenced and are incorporated herein by reference in their entirety.

[0169] It should be noted that these patent documents do not record biological raw materials, do not provide any instructions for manufacturing water-absorbing resin from bioethanol, and do not provide any instructions for the manufacturing method of the water-absorbing resin of the present invention from bioethanol via steps (i) to (iv) and steps (v) to (vii).

[0170] In step (iv), to oxidize bio-propylene to obtain bio-acrylic acid, the method and production equipment used to produce acrylic acid by oxidizing propylene obtained from the cracking of naphtha, a conventional fossil feedstock, can be applied as is. That is, in the acrylic acid manufacturing method used in this invention, conventional acrylic acid manufacturing equipment operating worldwide (one or more stages of gas-phase oxidation of propylene derived from fossil feedstock) yields acrylic acid from bio-propylene via acrolein. The acrylic acid is then collected and further distilled and / or crystallized to obtain glacial acrylic acid (acrylic anhydride), which in turn yields the acrylic acid used in this invention for the hydrophobic resin.

[0171] In step (iv), propylene is oxidized by contacting it with a gas containing molecular oxygen, such as oxygen or air, in the presence of a known catalyst. Typically, the oxidation reaction proceeds in two stages. In the first stage, any catalyst capable of oxidizing propylene gas in the gas phase to acrolein is acceptable, and in the second stage, any catalyst capable of oxidizing acrolein gas in the gas phase to acrylic acid is acceptable; there are no particular restrictions.

[0172] (catalyst)

[0173] As a catalyst used in the first stage reaction, examples include solid catalysts containing at least one element selected from Fe, Co, Ni, Mo, Bi, Al, and Si, preferably containing at least one element selected from Fe, Mo, and Bi, more preferably containing a composite oxide containing at least one element selected from Fe, Mo, and Bi, more preferably containing at least one of Mo and Bi, and even more preferably containing Mo and Bi.

[0174] As a catalyst used in the second stage reaction, examples include solid catalysts containing at least one element selected from V, Mo, Cu, W, Sb, Al, and Si, preferably containing at least one element selected from Mo, V, and W, more preferably containing at least one of Mo and V, and even more preferably containing Mo and V.

[0175] (Reaction conditions)

[0176] Acrylic acid synthesis can be carried out in either batch or continuous mode; from a productivity standpoint, continuous mode is preferred. The reaction temperature in acrylic acid synthesis is typically in the range of 200–400°C. When acrylic acid synthesis is carried out in two stages, the temperatures in the first and second stages can be the same or different; the temperature in the second stage can be set lower than that in the first stage. If the temperatures in the first and second stages differ, the difference can be, for example, 40–60°C.

[0177] (Acrylic acid capture)

[0178] Typically, the mixed gas obtained from the reaction in step (iv) is contacted with a collecting liquid (typically water) for capturing acrylic acid from the mixed gas to obtain an aqueous solution containing acrylic acid. The mixed gas may contain acrylic acid, a gas containing molecular oxygen, unreacted components (propylene, acrolein), and byproducts (e.g., acetone, acrolein, furfural, formaldehyde, etc.). As described above, the liquid used for capturing acrylic acid from the mixed gas is typically water, but other liquids may also be used. In this case, the aqueous solution containing acrylic acid is replaced with a solution containing acrylic acid. As the collecting liquid for acrylic acid in the mixed gas, at least one of water and an organic solvent is used. As the organic solvent, at least one organic solvent selected from methyl isobutyl ketone, diisopropyl ketone, methyl propyl ketone, methyl isobutyl ketone, methyl tert-butyl ketone, n-propyl acetate, n-butyl acetate, diphenyl ether, and biphenyl is used. Water and diphenyl ether are preferred in the collecting liquid, and water is even more preferred.

[0179] There are no particular limitations on the water used as the capture solution for absorbing acrylic acid; tap water, industrial water, pure water (RO water, ion-exchange water, distilled water), etc., can be used. This water can be groundwater, river water, or water obtained through treatment. Furthermore, the water used can be purified from the acrylic acid capture water or water generated or used in other processes, or it can be used directly.

[0180] (Propylene purification)

[0181] Acrylic acid is typically obtained by purifying an aqueous solution containing acrylic acid. An aqueous solution of acrylic acid may contain acrylic acid, acetic acid, water, and other impurities (maleic acid, propionic acid, furfural, formaldehyde, etc.).

[0182] There are no particular limitations on the purification methods for acrylic acid; well-known methods such as distillation and crystallization can be appropriately employed. Purification can be performed solely by distillation, solely by crystallization, or a combination of both. Furthermore, distillation can be performed once or in combination multiple times. Similarly, crystallization can be performed once or in combination multiple times. Moreover, distillation and crystallization can be continuous or batch processes.

[0183] (Impurities in bioacrylic acid)

[0184] In step (iv), the content of propionic acid in the acrylic acid obtained by oxidation and purification of propylene is preferably 500 ppm or less, 400 ppm or less, or 300 ppm or less, and the content of acetic acid is preferably 1500 ppm or less, 1000 ppm or less, 500 ppm or less, 300 ppm or less, or 200 ppm or less. The content of propionic acid in the acrylic acid is, for example, 100 ppm or more, or 200 ppm or more. The content of propionic acid in the acrylic acid is, for example, 100 ppm or more and 500 ppm or less. The content of acetic acid in the acrylic acid is, for example, 100 ppm or more, or 200 ppm or more. The content of acetic acid in the acrylic acid is, for example, 100 ppm or more and 1500 ppm or less. By reducing the amount of propionic acid (more preferably acetic acid) in the acrylic acid, the odor (sour smell) of the obtained absorbent resin can be reduced. Furthermore, the yield of the absorbent resin (the ratio of the obtained absorbent resin to the acrylic acid used) is increased.

[0185] Of the six impurities in the acrylic acid—protoanemonin, allyl acrylate, allyl alcohol, aldehydes (particularly furfural), maleic acid, and benzoic acid—one or more are preferred, two or more are more preferred, three or more are even more preferred, four or more are particularly preferred, five or more are especially preferred, and all six are preferably 0 to 20 ppm (mass basis, the same below). Preferably, they are 0 to 10 ppm, more preferably 0 to 5 ppm, more preferably 0 to 3 ppm, particularly preferably 0 to 1 ppm, and most preferably ND (less than the detection limit). Among these impurities, aldehydes may sometimes increase in acrylic acid derived from biological raw materials, and it is preferable to control and reduce them. As a control method, aldehyde treatment agents (e.g., hydrazine) or crystallization can be used. Furthermore, the total amount (relative to the mass of acrylic acid) of protoanemonin, allyl acrylate, allyl alcohol, aldehydes, maleic acid, and benzoic acid is preferably 100 ppm or less, more preferably 0 to 20 ppm, more preferably 0 to 10 ppm, and particularly preferably 0 to 5 ppm. 0 ppm refers to ND. It should be noted that the content of these trace components can be determined, for example, by gas chromatography.

[0186] To prevent acrylic acid (melting point 14°C) from solidifying in winter, the resulting acrylic acid can be prepared as an aqueous solution (e.g., an 80% by weight aqueous solution of acrylic acid) for workability as a liquid. However, the moisture in the acrylic acid promotes the formation of acrylic acid dimers, and the increase in acrylic acid dimers increases the residual monomers in the superabsorbent resin. Therefore, the moisture content of the acrylic acid is preferably 2% by weight or less, 1% by weight or less, 0.5% by weight or less, 0.3% by weight or less, 0.1% by weight or less, and 0.05% by weight or less, in turn. A small amount of water has little adverse effect on the superabsorbent resin, and considering the balance with purification costs, the moisture content of the acrylic acid is, for example, 10 ppm or more, or 50 ppm or more. The moisture content of the acrylic acid is, for example, 10 ppm or more and 2% by weight or less. For the same reason, the amount of acrylic acid dimers in the acrylic acid is preferably 1000 ppm or less, 500 ppm or less, or 200 ppm or less. The amount of acrylic acid dimers in the acrylic acid supplied to the later-described step (v) is, for example, 1 ppm or more. The amount of acrylic acid dimer in acrylic acid is, for example, more than 1 ppm and less than 1000 ppm, further less than 500 ppm, less than 200 ppm, and particularly less than 100 ppm.

[0187] It should be noted that the impurities in these acrylic acids are ideally ND, but they are difficult to completely remove even through steps (i) to (iv). Therefore, acrylic acid containing a certain amount of impurities can be used in step (v), and at least a portion of the impurities (e.g., acetic acid and propionic acid in acrylic acid) can be removed in steps (v) and / or (vi) by heating during the manufacturing process of the water-absorbing resin. For example, at least a portion of one or more of acrylic acid, acetic acid, and propionic acid remaining in the reaction system can be removed by the heat of polymerization generated in step (v).

[0188] For acrylic acid obtained from the bioethanol of the present invention via steps (i) to (iv), the organic acids (further acetic acid / propionic acid, especially propionic acid) that are easily increased in conventional bioacrylic acid can be reduced as described above, thus making it preferably used as a water-absorbing resin. In addition, other impurities are also few, and as described below, it can provide a water-absorbing resin that is equivalent to or better than that of acrylic acid derived from fossil raw materials.

[0189] Therefore, one aspect of the present invention is a method for using bio-acrylic acid derived from biological raw materials obtained in steps (i) to (iv) below as a monomer of a water-absorbing resin, wherein the method includes the following steps:

[0190] Process (i) involves obtaining acetone from bioethanol;

[0191] Step (ii) involves obtaining isopropanol from the acetone;

[0192] Step (iii), obtaining propylene from the isopropanol; and

[0193] Step (iv) involves obtaining acrylic acid from the propylene.

[0194] (Polymerization inhibitor)

[0195] The resulting acrylic acid may contain polymerization inhibitors, such as 1–300 ppm, 10–200 ppm, or 20–80 ppm, and particularly p-methoxyphenol.

[0196] (Step (v) involves polymerizing an aqueous solution containing acrylic acid monomers to obtain polyacrylic acid (salt))

[0197] (Monomers and acrylic acid)

[0198] In this invention, the acrylic acid obtained in step (iv) described above must be used as the monomer of the absorbent resin. The absorbent resin of this invention is a cross-linked polymer obtained by cross-linking polymerization of monomers with acrylic acid and / or its salts (referred to as "acrylic acid (salt)") as the main component, for example, polyacrylic acid and / or its salts (referred to as "polyacrylic acid (salt)") containing grafted components as needed. From the perspective of the performance of the absorbent resin, the proportion of acrylic acid, based on all monomers, is preferably 50 to 100 mol%, more preferably 70 to 100 mol%, and particularly preferably 90 to 100 mol%.

[0199] In this invention, in addition to the acrylic acid obtained in step (iv), other acrylic acids may be used in combination. These can include acrylic acid derived from fossil fuels, bio-acrylic acids obtained from sources other than bioethanol (e.g., bio-acrylic acids from Patent Documents 1-14), and acrylic acid from conventional fossil fuels. The ratio of these combinations can be appropriately determined. When using acrylic acid obtained in step (iv) in combination with other acrylic acids, a higher percentage of acrylic acid obtained in step (iv) is preferred from the perspectives of performance, sustainability, and renewability. The acrylic acid obtained in steps (i) to (iv) is preferably 1 mol% or more, 5 mol% or more, 10 mol% or more, 20 mol% or more, 30 mol% or more, 40 mol% or more, 50 mol% or more, 60 mol% or more, and 70 mol% or more, respectively, relative to all acrylic acid. The acrylic acid obtained in steps (i) to (iv) may be 80 mol% or more, 90 mol% or more, or 95 mol% or more, relative to all acrylic acid. The upper limit also depends on the production capacity of the acrylic acid obtained in step (iv), and can be less than 100 mol%, less than 95 mol%, or less than 90 mol%. The usage ratio of the acrylic acid obtained in step (iv) is, for example, more than 1 mol% and less than 100 mol%. In this invention, as a method of using the acrylic acid obtained from step (iv) and other acrylic acids, one example is mixing the acrylic acid obtained in step (iv) with other acrylic acids (acrylic acid derived from fossil fuels).

[0200] Furthermore, to prevent the increase of residual monomers in the water-absorbing resin, the acrylic acid obtained in step (iv) is preferably used in step (v) within a short period of time after purification, preferably within 10 days between steps (iv) and (v), more preferably within 5 days, 2 days, or 1 day. In addition, the acrylic acid before use in step (v) is preferably stored below room temperature (preferably below 35°C, more preferably 30°C to above the melting point), and further stored and transported under an oxygen or air atmosphere.

[0201] From the perspective of water absorption performance, the neutralization rate of acid groups such as polyacrylic acid in the water-absorbing resin of the present invention is preferably 10 mol% or more, more preferably 40 mol% or more, further preferably 50 mol% or more, and particularly preferably 60 mol% or more. From the perspective of water absorption performance, the neutralization rate of acid groups such as polyacrylic acid in the water-absorbing resin of the present invention is preferably 90 mol% or less, more preferably 85 mol% or less, further preferably 80 mol% or less, and particularly preferably 75 mol% or less. From the perspective of water absorption performance, the neutralization rate of acid groups such as polyacrylic acid in the water-absorbing resin of the present invention is, for example, 10 mol% or more and 90 mol% or less. Neutralization can be performed on the monomer, on the polymerized hydrogel, or in combination. Examples of salts for neutralization include alkali metal salts such as sodium, potassium, and lithium, ammonium salts, and amine salts.

[0202] The monomer used to obtain the absorbent resin of the present invention can essentially be only acrylic acid (salt). Alternatively, other unsaturated monomers can be used in combination with acrylic acid (salt) (when all monomers are set to 100 mol%, the amount of other unsaturated monomers is, for example, 0-50 mol%, exceeding 0 mol% and below 48 mol%, further 5-45 mol%) to obtain the absorbent resin. There are no particular limitations on the monomers other than acrylic acid (salt) (other unsaturated monomers), but examples include methacrylic acid, maleic acid, itaconic acid, 2-(meth)acrylamide-2-methylpropanesulfonic acid, (meth)acrylamide, etc. These other unsaturated monomers can be used alone or in appropriate mixtures of two or more. Itaconic acid is obtained by fermentation, thus facilitating the use of biological raw materials, and is therefore preferred when used in combination with other monomers.

[0203] In addition, specific examples of internal crosslinking agents include: N,N'-methylenebis(meth)acrylamide, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, glycerol tri(meth)acrylate, glycerol acrylate methacrylate, ethylene oxide modified trimethylolpropane tri(meth)acrylate, pentaerythritol hexa(meth)acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly(meth)allyloxyalkane, (poly)ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol, propylene glycol, glycerol, pentaerythritol, ethylenediamine, ethylene carbonate, propylene carbonate, polyethyleneimine, glycidyl methacrylate, etc. According to a preferred embodiment, the average number of polyethylene glycol units in the (poly)ethylene glycol di(meth)acrylate is 7 to 11. From a physical property perspective, the amount of these internal crosslinking agents used relative to the monomer (excluding the crosslinking agent) is preferably 0.001 to 2 mol%, more preferably 0.005 to 0.5 mol%, even more preferably 0.01 to 0.2 mol%, and particularly preferably in the range of 0.03 to 0.15 mol%.

[0204] During the above polymerization, 0-50% by weight (relative to monomer) of hydrophilic polymers such as starch / cellulose, starch / cellulose derivatives, polyvinyl alcohol, linear polyacrylic acid (salt), and polyacrylic acid (salt) crosslinkers (especially micronized powders of water-absorbing resins), and 0-10% by weight, further 0-1% by weight (relative to monomers) of various foaming agents such as carbonates (bicarbonates), carbon dioxide, azo compounds, and inactive organic solvents; various surfactants; chelating agents; and chain transfer agents such as hypophosphite (salt). It should be noted that, as mentioned above, natural polymers can adversely affect the heat resistance and performance of water-absorbing resins; therefore, even under arbitrary use, it is preferable to use them in small amounts (e.g., less than 10% by weight) or not at all.

[0205] According to a preferred embodiment, the chelating agent is an aminopolycarboxylic acid or an aminopolyphosphate. As an aminopolycarboxylic acid, compounds having 2 to 100, more preferably 3 to 20, 4 to 10, or 5 to 8 carboxyl groups are preferred. Specifically, examples include: iminodiacetic acid, hydroxyethyliminodiacetic acid, hypozinotriacetic acid, hypozinotripropionic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraaminehexaacetic acid, trans-1,2-diaminocyclohexanetetraacetic acid, N,N-bis(2-hydroxyethyl)glycine, diaminopropanoltetraacetic acid, ethylenediaminedipropionic acid, N-hydroxyethylethylenediaminetriacetic acid, ethylene glycol ether diaminetetraacetic acid, diaminopropanetetraacetic acid, N,N'-bis(2-hydroxybenzyl)ethylenediamine-N,N'-diacetic acid, 1,6-hexamethylenediamine-N,N,N',N'-tetraacetic acid, and their salts. As a salt, a sodium salt is preferred. Examples of amino polyphosphoric acids include: ethylenediamine-N,N'-di(methylenephosphonic acid), ethylenediaminetetra(methylenephosphonic acid), hypoazinoacetic acid-di(methylenephosphonic acid), hypoazinodiaacetic acid-(methylenephosphonic acid), hypoazinoacetic acid-β-propionic acid-methylenephosphonic acid, hypoazinotri(methylenephosphonic acid), cyclohexanediaminetetra(methylenephosphonic acid), ethylenediamine-N,N'-diaacetic acid-N,N'-di(methylenephosphonic acid), ethylenediamine-N,N'-di(methylenephosphonic acid), ethylenediaminetetra(methylenephosphonic acid), poly(methylenediaminetetra(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), 1-hydroxyethylenediphosphonic acid, and their salts. By using a chelating agent (preferably at a concentration of 1 ppm or more relative to the monomer, further at 10 ppm or more, with an upper limit of, for example, 1% by weight or less, further at 0.5% by weight or less), the polymerization of the above-mentioned acrylic acid is further stabilized, resulting in a water-absorbing resin with superior performance, which is therefore preferred. This chelating agent can be added in step (v) or later, as described later, to improve performance.

[0206] The monomers described above can be produced by bulk polymerization (solvent-free polymerization), but from the perspective of water absorption performance, it is preferable to prepare an aqueous solution for polymerization. From the viewpoint of the physical properties of the water-absorbing resin, the total concentration of the monomer components in the monomer aqueous solution is preferably 10% by weight or more, more preferably 20% by weight or more, and even more preferably 30% by weight or more. The concentration is preferably 80% by weight or less, more preferably 75% by weight or less, and even more preferably 70% by weight or less. For example, the total concentration of the monomer components in the monomer aqueous solution is 10% by weight or more and 80% by weight or less. Furthermore, to promote polymerization, the dissolved oxygen in the monomer aqueous solution during polymerization can be reduced (preferably 5 ppm or less, even more preferably 2 ppm or less) by heating or introducing an inert gas.

[0207] (Aggregation method)

[0208] The polymerization method used in the embodiments of the present invention is not particularly limited. From the viewpoint of water absorption characteristics and ease of polymerization control, spray droplet polymerization, aqueous solution polymerization, reverse suspension polymerization, droplet polymerization, bulk polymerization, precipitation polymerization, etc., are preferred. Aqueous solution polymerization or reverse suspension polymerization is more preferred, aqueous solution polymerization is even more preferred, and continuous aqueous solution polymerization is even more preferred. Continuous aqueous solution polymerization is particularly preferred, and any of continuous belt polymerization or continuous kneader polymerization can also be used. The polymerization can be a neutralization polymerization of monomers, or it can be a post-neutralization reaction after the polymerization of monomers via acid polymerization.

[0209] Representative examples of acid polymerization followed by neutralization include: Japanese Patent Application Laid-Open No. 10-101735, Japanese Patent Application Laid-Open No. 01-103606, Japanese Patent Application Laid-Open No. 62-054751, Japanese Patent Application Laid-Open No. 2002-527547, Japanese Patent Application Laid-Open No. 03-174414, etc., but are not limited to these. Representative examples of reverse-phase suspension polymerization include: Japanese Patent Application Laid-Open No. 57-158209, Japanese Patent Application Laid-Open No. 61-087702, Japanese Patent Application Laid-Open No. 03-227301, Japanese Patent Application Laid-Open No. 11-005808, WO2004 / 083284, WO2009 / 025235, WO13 / 018571, WO2022 / 265459, WO2022 / 265459, etc., but are not limited to these. It should be noted that the publicly available content of these communiqués was referenced and incorporated as a whole.

[0210] The polymerization initiator used in the embodiments of the present invention can be appropriately selected according to the type of monomer to be polymerized, the polymerization morphology, etc., and can be selected from one or more polymerization initiators used in the manufacture of commonly used water-absorbing resins, so there is no particular limitation.

[0211] Examples of polymerization initiators include, for example, pyrolytic polymerization initiators, photolytic polymerization initiators, or redox polymerization initiators that combine a reducing agent to promote the decomposition of these polymerization initiators. Specifically, one or more of the polymerization initiators disclosed in U.S. Patent No. 7,265,190 can be used. It should be noted that, from the viewpoint of operability of the polymerization initiator and the physical properties of the water-absorbing resin, peroxides or azo compounds are preferred, peroxides are more preferred, and persulfates are even more preferred. As a peroxide, potassium persulfate, ammonium persulfate, sodium persulfate, tert-butyl hydroperoxide, and hydrogen peroxide are preferred. The polymerization initiation temperature is preferably, for example, around 50 to 100°C.

[0212] The amount of polymerization initiator used relative to the total molar number of the monomers excluding the internal crosslinking agent is preferably 0.001 mol% or more, more preferably 0.01 mol% or more, preferably 1 mol% or less, more preferably 0.5 mol% or less, and even more preferably 0.1 mol% or less. Furthermore, the amount of reducing agent used relative to the total molar number of the monomers excluding the internal crosslinking agent is preferably 0.0001 to 0.02 mol%.

[0213] The polymerization reaction can be carried out by irradiating with active energy rays such as radiation, electron beams, and ultraviolet rays instead of the above-mentioned polymerization initiators, or by using these active energy rays and polymerization initiators together.

[0214] The reaction temperature in the above polymerization reaction is not particularly limited, but the temperature range from the lowest to the highest temperature (peak temperature) is preferably in the range of 15 to 130°C, more preferably in the range of 20 to 120°C. Furthermore, the reaction time and polymerization pressure are not particularly limited, and can be appropriately set according to the type of monomer, polymerization initiator, and reaction temperature. The polymerization rate is typically 95% or higher, further 98% or higher, and particularly 99% or higher. The upper limit of the polymerization rate is 100%. To balance productivity and avoid prolonged polymerization, the upper limit of residual monomer can be 0.05% by weight, further approximately 0.1% by weight or 0.5% by weight.

[0215] Furthermore, the polymerization temperature and pressure can be appropriately selected, with the minimum and maximum temperatures ranging from 20°C to boiling point, further from 50°C to boiling point, and from 70°C to boiling point.

[0216] In this invention, high-purity acrylic acid suitable for use as a water-absorbing resin is obtained from bioethanol through steps (i) to (iv). Preferably, in step (v), the maximum polymerization temperature is set to a temperature at which water readily evaporates from the reaction system, for example, 105°C or higher, or 110°C or higher. The upper limit of the maximum polymerization temperature in step (v) is, for example, 130°C or 120°C. In step (v), the maximum polymerization temperature is set to, for example, 105°C or higher and 130°C or lower. In this way, during polymerization (step (v)), as water evaporates, at least a portion of the impurities in the acrylic acid (e.g., acetic acid, propionic acid) can be further volatilized and removed. Here, "at least a portion" refers to, for example, 1% by weight or more, 5% by weight or more, or 10% by weight or more of the impurities. By setting the maximum polymerization temperature in step (v) to a temperature at which water readily evaporates from the reaction system, it is not necessary to excessively purify the impurities in the acrylic acid in step (iv). From the perspective of performance and impurity removal, the rate of moisture reduction due to water evaporation during polymerization (the rate of reduction in the water content (by weight) of the resulting hydrogel relative to the water content (by weight) of the monomer) is preferably 1 to 20% by weight, more preferably 2 to 15% by weight, and even more preferably 3 to 10% by weight. Furthermore, in this invention, compared to conventional acrylic acid, acrylic acid of equal or higher purity than that derived from fossil fuels can be obtained. Therefore, excessive purification of the obtained acrylic acid is unnecessary, and the amount of further impurity removal in at least one of steps (iv), (v), and (vi) can be reduced. For example, in at least one of steps (iv), (v), and (vi), when removing impurities from the acrylic acid, the amount removed is, for example, 0.1% by weight or less, or 0.01% by weight or less relative to the mass of the acrylic acid. As a result, the yield of acrylic acid and the water-absorbing resin is also improved. The water content of the resulting hydrogel can be adjusted by evaporating a portion of the water during polymerization. From a performance perspective, the preferred moisture content at this time is within the range of the moisture content of the aforementioned monomers, for example, 20-80% by weight, and further approximately 30-75% by weight.

[0217] (Any ripening process)

[0218] As an arbitrary step following the polymerization step, a curing step can be performed. In the curing step, the polymerized hydrogel can be removed from the polymerizer, and the hydrogel with the above-mentioned polymerization rate can be stored under heating, preferably at a temperature of 40 to 100°C or 50 to 90°C (for example, for 1 minute to 5 hours), thereby increasing the polymerization rate and molecular weight.

[0219] (Any gel crushing process)

[0220] The gel pulverization process involves kneading or pulverizing the hydrogel (hydrogel-like cross-linked polymer) obtained in the polymerization process described above, to obtain a finely granulated hydrogel of a specified size. For example, this process involves pulverizing the hydrogel using a kneader, a screw extruder such as a meat grinder, or a gel pulverizer such as a shredder (also referred to as gel pulverization) to obtain a granular hydrogel (hereinafter referred to as "granular hydrogel"). It should be noted that when the polymerization process described above is kneader polymerization, the polymerization process and the gel pulverization process are performed simultaneously. Furthermore, in cases such as gas-phase polymerization or reverse suspension polymerization, where granular hydrogel is directly obtained during polymerization, this gel pulverization process may sometimes be omitted. It should be noted that a process for cutting the hydrogel into appropriate sizes can be arbitrarily included before the gel pulverization process. Furthermore, by mixing the additives used in the polymerization process described above, and various additives described later, into the hydrogel during the gel pulverization process, the performance of the superabsorbent resin can be improved.

[0221] To ensure uniform and efficient drying (and removal of impurities from the acrylic acid during drying), the average particle size of the particulate hydrogel can be 5 mm or less, more preferably 2 mm or less, and particularly 1 mm or less. Furthermore, the water content of the particulate hydrogel is preferably 30% by weight or more, more preferably 45% by weight or more. Additionally, the water content of the particulate hydrogel is preferably 70% by weight or less, more preferably 55% by weight or less. For example, the water content of the particulate hydrogel can be 30% by weight or more and 70% by weight or less, 30% by weight or more and 55% by weight or less, or 45% by weight or more and 55% by weight or less.

[0222] (Any acrylic acid recycling process)

[0223] In the polymerization step (step (v)) and the drying step (step (vi)) described later, acrylic acid (boiling point 141°C) may sometimes volatilize. While the volatilized acrylic acid can be discarded, from an environmental perspective and from the viewpoint of CO2 reduction and carbon neutrality, it is preferable that the volatilized acrylic acid be recycled, for example, by means of capture. Acrylic acid can be captured, for example, by using water, alkaline solution, or by cooling methods. As a method of recycling acrylic acid in this invention, one example is using the captured bio-acrylic acid or its aqueous solution (or alkaline solution) in step (v) for polymerization. The amount of acrylic acid recycled can be appropriately determined, for example, 0 to 20% relative to the acrylic acid used in the polymerization, and more further, 0.01 to 10%.

[0224] (The process of drying polyacrylic acid (salt) (vi))

[0225] The hydrogel-like crosslinked polymer obtained in step (v) above can achieve the target moisture content through a drying process. It should be noted that polymerization and drying can be continuously carried out by evaporating a portion of the moisture in the hydrogel-like crosslinked polymer using the polymerization heat of step (v), thus performing both steps (v) and (vi). However, from a performance perspective, it is preferable to perform a separate drying step (vi) after step (v) is completed. The preferred moisture content (%) at the start of drying in step (vi) is within the range described above. That is, the moisture content of the particulate hydrogel at the start of drying can be 30–70% by weight, or 45–55% by weight, etc. Considering the reduction of coloring, the reduction of residual monomers, and the removal of impurities from acrylic acid, drying should preferably begin within 2 hours, more preferably within 1 hour (after discharge from the gel pulverizer in the case of discharge from the polymerizer and subsequent gel pulverization process), or it can begin within 0.5 hours or 0.2 hours (after discharge from the dryer) after polymerization. Drying is typically carried out at temperatures ranging from 60 to 250°C, preferably from 100 to 220°C, more preferably from 120 to 200°C, and even more preferably from 150 to 190°C. The drying time is preferably around 0.1 to 5 hours. The temperature, airflow, and dew point during drying can be constant or varied in stages. Preferred drying methods include azeotropic dehydration in aqueous organic solvents, hot air drying (especially ventilated belt drying), agitated drying in a rotary stirred vessel (e.g., steam tube dryer, rotary kiln), agitated drying in a heat transfer dryer with stirring blades (e.g., paddle dryer), and flow drying in a fluidized bed, or a combination of both. Furthermore, when multiple drying methods are used in combination, a pulverization step of the dried material (semi-dried material) can be incorporated in the middle to promote drying and to remove a portion of the undried material.

[0226] According to one embodiment, the drying time depends on the surface area of ​​the polymer, its moisture content, the type of dryer, etc., and is selected in a way that achieves the target moisture content. Considering the physical properties such as reducing residual monomers and removing impurities from acrylic acid, it is preferable to use hot air containing water vapor and having a dew point of 50 to 100°C, more preferably hot air containing water vapor and having a dew point of 60 to 90°C, and preferably hot air drying for 0.1 to 5 hours. The moisture content of the water-absorbing resin in this invention (defined as the amount of water contained in the water-absorbing resin / measured as the loss on drying at 180°C for 3 hours) is not particularly limited. Considering the physical properties of the obtained water-absorbing resin product, it is preferable to be a powder that exhibits fluidity even at room temperature, more preferably 0.2 to 30% by weight, more preferably 0.3 to 15% by weight, and particularly preferably 0.5 to 10% by weight in powder form. Furthermore, the surface crosslinking step (vii) described later can be performed after drying, or it can be performed simultaneously with surface crosslinking at the beginning of the drying step (vi) or during the drying step (vi) (e.g., when the moisture content is 10-40% by weight, or more preferably 15-30% by weight). Alternatively, moisture can be removed by heat of polymerization during the polymerization step (v) as part or all of the drying step (vi), but it is preferable to perform the drying step (vi) separately after the polymerization step (v), and even more preferably, the surface crosslinking step (vii) separately after the drying step (vi).

[0227] The heat used to heat the hot air and heat transfer components in the drying process is preferably the oxidative heat from the process (iv) of obtaining acrylic acid from propylene. Preferably, the heat medium heated by the oxidative heat, typically steam, is supplied to the dryer to heat the hot air and heat transfer components. If the heat medium used in the drying process is still hot, it can be reheated as needed and reused as the drying heat medium, or used for heating or maintaining the temperature of equipment after process (v). Alternatively, the heat medium can be distributed for use in the drying process and other processes after process (v).

[0228] (Removal of the aforementioned acrylic acid impurities during the drying process)

[0229] In this invention, through steps (i) to (iv), high-purity acrylic acid suitable for use in absorbent resins is obtained from bioethanol. Furthermore, it is preferable that step (vi) involves the aforementioned high-temperature, high-dew-point drying (e.g., 120–200°C, 150–190°C with a dew point of 50–100°C). This allows at least a portion (1% or more by weight, further 5% or more by weight) of impurities in the acrylic acid (e.g., acetic acid (boiling point 118°C), propionic acid (boiling point 141°C)) to be volatilized and removed during drying. Therefore, excessive purification of impurities in the bioacrylic acid in step (iv) is unnecessary.

[0230] Furthermore, in this invention, compared to conventional bio-acrylic acid, bio-acrylic acid with a purity equal to or higher than that of acrylic acid derived from fossil raw materials can be obtained, thus eliminating the need for excessive purification of the bio-acrylic acid. Moreover, the amount of further impurity removal in steps (iv) to (vi) can be minimal. For example, the amount of impurities removed relative to the bio-acrylic acid is 0.1% by weight or less, 0.05% by weight or less, or 0.01% by weight or less. As a result, CO2 can be reduced, the yield of acrylic acid and the obtained water-absorbing resin can be increased.

[0231] In some applications of absorbent resins, the final product can be prepared without the later-described step (vii), i.e., without the surface crosslinking step of the polyacrylic acid (salt), and before the drying step (vi) of the polyacrylic acid and / or its salt. In this case, one aspect of the invention is a method for manufacturing an absorbent resin derived from biological raw materials, comprising the following steps (i) to (vi):

[0232] Process (i) involves obtaining acetone from bioethanol;

[0233] Step (ii) involves obtaining isopropanol from the acetone;

[0234] Step (iii) involves obtaining propylene from the isopropanol;

[0235] Step (iv) involves obtaining acrylic acid from the propylene;

[0236] Step (v) involves polymerizing an aqueous monomer solution containing said acrylic acid to obtain polyacrylic acid and / or its salts; and

[0237] Step (vi) involves drying the polyacrylic acid and / or its salts.

[0238] (Any crushing process)

[0239] In the manufacturing method of the present invention, after drying the hydrogel-like crosslinked polymer obtained by the polymerization step in the above-described drying step, a pulverizing step may be included as needed to pulverize it with a pulverizer to produce particulate water-absorbing resin. In particular, when aqueous solution polymerization is carried out in the polymerization step, a pulverizing step is preferred.

[0240] (Any grading process before or after surface cross-linking)

[0241] In this invention, it is preferable to further classify the powder through a classification process, thereby adjusting the powder particle size to correspond to the target. The classification process is preferably performed after the drying process, and more preferably after the pulverizing process. Furthermore, in cases including a surface crosslinking process, the classification process is preferably performed before the surface crosslinking process, and more preferably a second classification process is performed after the surface crosslinking process.

[0242] The particle size of the absorbent resin obtained in this invention varies depending on the application. For example, in the case of disposable diapers, which are used primarily as absorbent resins, the weight-average particle size (as defined by sieve grading) is preferably in the range of 200 to 700 μm after grading or as the final product, more preferably in the range of 250 to 600 μm, and particularly preferably in the range of 300 to 500 μm.

[0243] The absorbent resin obtained in this invention varies depending on its intended use. For example, in the case of disposable diapers, where the absorbent resin is the primary component, it is preferable, as a graded or final product, to contain 95-100% by weight of an absorbent resin powder of 850-150 μm (passing through an 850 μm standard sieve and the 150 μm standard sieve being non-passing material / standard sieve being JIS or its equivalent). The absorbent resin obtained in this invention preferably contains a small proportion of micro-powder (e.g., preferably less than 100 μm, more preferably less than 150 μm), specifically less than 5.0% by weight, further less than 3.0% by weight, and particularly less than 1.0% by weight. For example, the proportion of polyacrylic acid and / or its salts in the micro-powder supplied to step (iv) is less than 5.0% by weight, less than 3.0% by weight, or less than 1.0% by weight. Furthermore, the water-absorbing resin obtained in this invention preferably contains a low proportion of coarse particles (e.g., preferably substantially 1000 μm or more, more preferably 850 μm or more), specifically, preferably 5.0% by weight or less, more preferably 1.0% by weight or less. For example, the proportion of coarse-particle polyacrylic acid and / or its salts in the polyacrylic acid and / or its salts supplied in step (iv) is 5.0% by weight or less, or 1.0% by weight or less.

[0244] (Suitable micron powder recovery process)

[0245] In this invention, a manufacturing process not described in Patent Document 1, etc., may include a micronized powder recovery process for the superabsorbent resin. Micronized powder recovery allows for a more carbon-neutral manufacturing method. In the micronized powder recovery process, micronized powder is removed from the superabsorbent resin before and / or after surface cross-linking, and recycled in the superabsorbent resin manufacturing process. That is, after step (v), a portion of the superabsorbent resin is separated and recycled in step (v) and / or step (vi). Micronized powder recovery is preferably performed before the drying process, and is recycled in at least one of the following steps: polymerization (step (v)), gel pulverization, and drying (step (vi)). The recycled micronized powder can be recycled in the superabsorbent resin manufacturing process in the form of dried powder or hydrated water-swellable gel.

[0246] Micropowder recovery from the polymerization process is documented in WO92 / 01008, WO92 / 020723, WO10 / 046267, WO11 / 101188, etc., where micropowder is mixed with monomers for polymerization. Micropowder recovery from the post-polymerization hydrogel is documented in Japanese Patent Application Laid-Open No. 03-152104, Japanese Patent Application Laid-Open No. 04-227934, Japanese Patent Application Laid-Open No. 04-041532, etc., where micropowder or its hydrate is mixed with the hydrogel obtained in the polymerization process and then dried. Micropowder recovery from the granulation process is documented in EP0885917A2, WO2015 / 088242A1, WO2017 / 010660A1, WO2019 / 194399A, etc., where the granulated micropowder is further dried (generally recycled in the drying process). In these micropowder recovery processes, the micropowder is generally recycled before the drying process. It should be noted that the publicly available content of these communiqués was referenced and incorporated as a whole.

[0247] The recovered micropowder is the micropowder removed in the above-described grading process, preferably micropowder smaller than 150 μm (as defined by a standard sieve), and less than 150 μm means micropowder comprising 50% or more, further 70% or more, and particularly 90% or more by weight. The amount of micropowder is appropriately determined within the range of 1 to 40% by weight, further 2 to 35% by weight, and even further 5 to 30% by weight in the manufactured water-absorbing resin.

[0248] (Vii) Step for surface crosslinking of polyacrylic acid (salt)

[0249] In this invention, it is preferable to further perform surface crosslinking through a surface crosslinking process (vii). As described above, the surface crosslinking process (vii) can be performed after the drying process (vi), or it can be performed simultaneously at the beginning of the drying process (vi) or during the drying process (vi).

[0250] Surface crosslinking is an operation that improves various physical properties by increasing the crosslinking density near the surface of the absorbent resin to be higher than that inside the particles. Unlike internal crosslinking, various surface crosslinking agents (which are secondary crosslinking agents relative to internal crosslinking agents) are added to the absorbent resin, and only the surface or surface layer is crosslinked. Through this process, the absorbency under pressure required, especially for disposable diapers where absorbent resin is the primary application, is improved. There are no particular limitations on the surface crosslinking agent, but crosslinking agents that react with carboxyl groups are preferred, and dehydration-reactive crosslinking agents are particularly preferred.

[0251] When the dehydration reactive crosslinking agent is described more specifically, examples include: polyol compounds such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, glycerol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol; amino alcohol compounds such as ethanolamine, diethanolamine, and triethanolamine; alkyl carbonate compounds such as 1,3-dioxolane-2-one (ethylene carbonate) and 4-methyl-1,3-dioxolane-2-one; oxetane compounds such as 3-methyl-3-oxetane methanol; and polyoxetane compounds, etc. In order to maximize the effect of the present invention, it is preferable to select one or more dehydration reactive crosslinking agents selected from polyols, alkyl carbonates, oxazolidinone compounds, and (poly)oxetane compounds, and polyols or alkyl carbonates are particularly preferred.

[0252] In addition to these dehydration-reactive crosslinking agents, examples of non-dehydration-reactive crosslinking agents include: epoxy compounds such as ethylene glycol diglycidyl ether and γ-epoxypropoxypropyltrimethoxysilane; polyisocyanate compounds such as 2,4-toluene diisocyanate; polyoxazoline compounds such as 1,2-ethylene bisoxazoline; silane coupling agents such as γ-aminopropyltrimethoxysilane; polyaziridine compounds such as 2,2-dihydroxymethylbutanol-tris[3-(1-aziridinyl)propionate]; and polyvalent metals such as beryllium, magnesium, calcium, strontium, zinc, aluminum, iron, chromium, manganese, titanium, and zirconium.

[0253] When considering physical properties, the amount of surface crosslinking agent used (the total amount when using two or more) is preferably in the range of 0.001 to 10 parts by mass relative to 100 parts by mass of water-absorbing resin (preferably, 100 parts by mass of water-absorbing resin as a dry body), more preferably in the range of 0.01 to 8 parts by mass, further preferably in the range of 0.05 to 5 parts by mass, and most preferably in the range of 0.1 to 2 parts by mass.

[0254] When mixing a surface crosslinking agent into a water-absorbing resin, water and / or a hydrophilic organic solvent can be used. The amount of water used relative to 100 parts by weight of the water-absorbing resin (preferably, 100 parts by weight of the water-absorbing resin as a dry product) is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 8 parts by weight, and even more preferably 1 to 5 parts by weight. Furthermore, examples of hydrophilic organic solvents include alcohols such as ethanol and isopropanol; ketones such as acetone; and ethers such as dioxane, alkoxy(poly)ethylene glycol, and tetrahydrofuran. The amount used relative to 100 parts by weight of the water-absorbing resin is preferably 0 to 10 parts by weight, more preferably 0 to 5 parts by weight, and even more preferably 0 to 3 parts by weight.

[0255] When heat treatment is performed, the treatment time is preferably 1 to 180 minutes, more preferably 3 to 120 minutes, and particularly preferably 5 to 100 minutes. The heat treatment temperature (defined by the temperature of the heat medium or the material temperature) is preferably in the range of 100 to 250°C, more preferably in the range of 140 to 220°C, further preferably in the range of 150 to 220°C, and particularly preferably in the range of 160 to 220°C. In order to stop the reaction after heat treatment, it is preferable to forcibly cool the surface-crosslinked water-absorbing resin, particularly to 40 to 100°C or 50 to 90°C.

[0256] (The process of adding any additives)

[0257] In the manufacturing method of the present invention, additives such as inactive surfactants, inactive deodorants, and inactive inorganic particulate powders that do not cause surface crosslinking and mean that they do not substantially react with the water-absorbing resin can be added to the surface of the water-absorbing resin before, during, or after the surface crosslinking process.

[0258] In the manufacturing method of the present invention, in any step after step (v), various additives may be further added to the monomer aqueous solution and / or the polyacrylic acid (salt). That is, it may include steps to add deodorants, antibacterial agents, fragrances, foaming agents, pigments, dyes, hydrophilic short fibers, plasticizers, adhesives, surfactants, fertilizers, oxidants, reducing agents, water, salts, chelating agents, bactericides, hydrophilic polymers such as polyethylene glycol, paraffin wax, hydrophobic polymers, thermoplastic resins such as polyethylene or polypropylene, thermosetting resins such as polyester resins, urea-formaldehyde resins, etc., to impart various functions to the water-absorbing resin, preferably including addition steps to the surface of the water-absorbing resin. For example, the chelating agent added in or after the polymerization step (v) can further improve the performance of the polymerized bioacrylic acid and water-absorbing resin obtained in steps (i) to (iv).

[0259] The amount of these additives used relative to 100 parts by weight of the water-absorbing resin is preferably in the range of 0 to 30 parts by weight, more preferably in the range of 0 to 10 parts by weight, and even more preferably in the range of 0 to 1 part by weight. It should be noted that, in this invention, the water-absorbing resin is also referred to as such when the water-absorbing resin is surface cross-linked and / or when additives are added, provided that the water-absorbing resin is the main component and the resin is substantially integrated.

[0260] (Any granulation process)

[0261] Water or an aqueous adhesive solution can be added to the surface of the absorbent resin simultaneously with or separately from the surface crosslinking process to granulate the absorbent resin, which can also reduce dust. As an adhesive for the absorbent resin, approximately 0.1 to 5 parts by weight of water or water-soluble polymer, polyol or aqueous solution thereof is used.

[0262] (Transportation or storage of any intermediate goods)

[0263] The method for preparing the water-absorbing resin of the present invention includes a polymerization step, a drying step, and a surface crosslinking step, and further includes any curing step, any gel pulverization step, any pulverization step, any classification step, any micron powder recovery step, any classification step after surface crosslinking, and any additive addition step. However, these steps can be carried out in the same apparatus (e.g., gel pulverization and drying are carried out in a polymerization apparatus, and drying and surface crosslinking are carried out in a drying apparatus) or in different apparatuses. When the above steps are carried out in different apparatuses, a conveying step for the hydrogel and its dried product can be set between the steps to connect the steps. In this case, a storage step for the hydrogel and its dried product of the intermediate product (e.g., an intermediate hopper) can be arbitrarily set between the steps.

[0264] (Any foreign object removal process)

[0265] The superabsorbent resin that has undergone the above manufacturing process is then subjected to a foreign matter removal process. Examples of foreign matter from the superabsorbent resin manufacturing process include metallic foreign matter such as metal fragments from the grading mesh, and colored particles (black or brown particles) that have been partially charred due to overheating during the manufacturing process. Metallic foreign matter can be removed using a magnet, while colored foreign matter (colored particles of the superabsorbent resin) can be removed using color sorting.

[0266] The magnetic flux density of the magnetic lines of force in the iron separator is preferably 0.05 Wb / m. 2 (500 Gauss) or higher, more preferably 0.5 Wb / m 2 The above is particularly preferred to be 1.0 Wb / m 2In the above, permanent magnets and / or electromagnets are preferably used, and more preferably, the magnets are arranged in a grid pattern and the water-absorbing resin passes through the grid.

[0267] (Final storage process)

[0268] The manufacturing method of the present invention may include a storage step of storing the aforementioned dried absorbent resin in a storage tank. Examples of storage tanks used in this storage step include silos and hoppers, with tanks equipped with a unit for heating their inner walls being preferred. Considering the abrasiveness and electrical conductivity of the absorbent resin, tanks with metallic inner surfaces, such as those made of iron or stainless steel, are preferred. Furthermore, in addition to storing the final product, a separate storage step (intermediate hopper) may be provided between each step. For continuous manufacturing, buffer hoppers and metering hoppers may be used to connect the various steps.

[0269] (A combination of acetone, isopropanol, and propylene derived from fossil fuels)

[0270] As for the acrylic acid used in step (v) above, in order to be compatible with other bio-acrylic acids derived from fossil raw materials or from bioethanol other than bioethanol, as long as at least a portion of the monomers constituting the main chain of the superabsorbent resin contains monomers derived from bioethanol, at least one of acetone, isopropanol, and propylene derived from fossil raw materials or from bio-raw materials other than bioethanol can be included in a portion of the acetone in step (ii), the isopropanol in step (iii), and the propylene in step (iv). For example, in cases of crop failure as a raw material for bioethanol, or in cases of treating residues or byproducts of compounds derived from fossil raw materials generated in the production of other compounds, at least one of acetone, isopropanol, and propylene derived from fossil raw materials or from bio-raw materials other than bioethanol can be used. Furthermore, depending on the type of plant used as a raw material, or the difference between fossil raw materials and non-fossil raw materials, carbon isotopes can be used... 13 C quantity and 14 By varying the carbon content and using different ratios and raw materials, it is possible to manufacture materials with various carbon isotopes. 13 C quantity and 14 C-grade water-absorbing resin. Through 13 C quantity and 14The determination of C content reflects the traceability (identifiability) of the produced absorbent resin. When using at least one of acetone, isopropanol, propylene, and acrylic acid selected from fossil raw materials and / or biological raw materials other than bioethanol, the proportion of acrylic acid derived from bioethanol in the monomers constituting the main chain of the final absorbent resin is preferably 1 mol% or more, 5 mol% or more, 10 mol% or more, 20 mol% or more, 30 mol% or more, 40 mol% or more, 50 mol% or more, 60 mol% or more, or 70 mol% or more. This proportion can be 80 mol% or more, 85 mol% or more, 90 mol% or more, or 95 mol% or more.

[0271] (Method for connecting process (i) to process (vii))

[0272] The above-described steps (i) to (vii) can be performed consecutively or individually. Furthermore, the individual purification of at least one of acetone, isopropanol, propylene, and acrylic acid described in steps (i) to (iv) can be omitted. In addition, steps (i) to (vii) can be performed by the same producer or partially or entirely by different producers. For example, they can be shared in the following manner.

[0273] Company A: Process (i) for obtaining acetone from bioethanol.

[0274] Company B: Process (ii) for obtaining isopropanol from bioacetone.

[0275] Company C: Process (iii) for obtaining propylene from bioisopropanol.

[0276] Company D: Process (iv) for obtaining acrylic acid from biopropylene.

[0277] Company E: The process of polymerizing an aqueous solution of a monomer containing bioacrylic acid to obtain polyacrylic acid and / or its salts (v).

[0278] Company F: The process of drying polyacrylic acid and / or its salts (vi).

[0279] Company G: The process of surface crosslinking polyacrylic acid and / or its salts (vii).

[0280] The aforementioned processes (i) to (vii) can be carried out at the same location or at different locations. It should be noted that "same location" refers to the degree to which they can be connected by pipelines within the industrial land. If they are carried out at different locations, it involves long-distance transportation using methods other than pipelines, such as tankers, trucks, and railways.

[0281] In addition, as mentioned above, bioethanol can be anhydrous ethanol, aqueous ethanol, or ethanol containing acetone and isopropanol (crude ethanol, especially crude aqueous ethanol).

[0282] Prior to step (i), the step of obtaining bioethanol (referred to as step (0)) involves fermentation and distillation, as well as any other purifications, as described above, thereby adjusting the water content and trace components (acetone, isopropanol, etc.) of the ethanol to be used. Step (i) of obtaining acetone from bioethanol and step (0) of obtaining ethanol (adjusted as needed for water content and trace component amounts) can be carried out at the same location or at different locations, and steps (0) and steps (i) can be connected by pipelines described later.

[0283] Considering the performance of the absorbent resin, it is preferable that process (v) and process (vi) are carried out in the same location, further preferably process (v) to process (vii) are carried out in the same location, and the locations of each process (i) to (vii) are preferably at most four locations, further preferably at most three locations, two locations, and especially preferably all processes are carried out in one location.

[0284] Furthermore, since step (iv) is an exothermic reaction involving oxidation, by performing steps (iv) and (v) and (vi) at the same location, the heat generated in step (iv) can be used for heating the polymerization in step (v), the drying in step (vi), and / or the surface crosslinking in step (vii), allowing for the use of a method to manufacture water-absorbing resins that further reduces CO2 and is environmentally friendly. For example, the heat can be supplied as high-pressure steam via pipeline to at least one of steps (v), (vi), and (vii). In addition, since the dehydration in step (iii) and the oxidation in step (iv) are both gas-phase reactions, and the yield of biopropylene from the isopropanol dehydration reaction in step (iii) is also high, the purification of biopropylene in step (iii) can be omitted, allowing for the continuous operation of steps (iii) and (iv). From the perspective of CO2 reduction, it is preferable to make steps (iii) and (iv), as well as steps (iii) through (vii), continuous operations at the same location.

[0285] On the other hand, acetone is lighter than ethanol, making it easier to transport, and isopropanol is easy to handle, making it easy to transport as well.

[0286] The ethanol (boiling point 78°C), acetone (boiling point 56°C), isopropanol (boiling point 82°C), propylene (boiling point -47°C), and acrylic acid (boiling point 141°C) used or produced in the above processes (i) to (v) are processed as liquids or gases. Propylene can be liquefied by cooling, or processed as a gas, and liquid or gas transportation (e.g., pipeline transportation) and storage (e.g., liquid cooling or storage in tanks with circulation mechanisms) can be appropriately carried out between processes. It should be noted that when propylene is liquefied and transported, and the liquefied propylene is used in process (iv), a hot or cold medium can be produced by recovering the latent heat from the propylene for cooling in processes after (iv). Furthermore, the polyacrylic acid obtained from liquid acrylic acid in process (v) is a gel-like substance; therefore, the transportation and storage of the gel-like substance are selected between processes (v) and (vi). That is, in processes (v) to (vii), since the product is a gel or solid (especially a powder), it is appropriately transported by various conveyors, air conveyors, etc.

[0287] Furthermore, the transportation between adjacent processes in steps (i) to (vii) depends on the location of each process and the manufacturing company. However, to solve the aforementioned technical problems, the transportation of biological raw materials between at least one process in steps (i) to (vii) (preferably between at least one process in steps (i) to (v)) is carried out by long-distance transportation of more than 10 km using tankers, trucks, or railways. In addition, other transportation methods are also used in at least another process (preferably between steps (i) to (iv) and between steps (v) and (vii)). With this configuration, more suitable water-absorbing resins can be produced.

[0288] Furthermore, to address the aforementioned technical problems, the transport of biological raw materials between at least one of steps (i) to (vii) is carried out via pipelines connecting the steps, and transport can be arbitrarily carried out between other steps other than via pipelines. This configuration enables the production of more suitable absorbent resins. Specifically, in steps (i) to (iv), since the product is a liquid or gas, when each step is carried out by one or more companies, it is preferable that the steps are connected via pipelines; moreover, between one or more steps, and especially between all steps, pipelines are used for connection. The length of the pipelines for all steps is appropriately adjusted to be less than 100 km, moreover less than 10 km, and particularly less than 1 km.

[0289] Furthermore, the aforementioned process (0) for manufacturing bioethanol and the process for obtaining bioacetone from bioethanol can also be carried out by one or more companies. The process (0) and process (i) are also connected by the same method as the aforementioned processes (i) to (vii), or by pipelines.

[0290] Furthermore, from the viewpoint of reducing residual monomers in the absorbent resin, as described in step (v) above, steps (iv) and (v) are preferably carried out within a certain time (especially including transportation and storage) and within 10 days, and more preferably within 5 days, 2 days, or 1 day. Here, the temperature and conditions for storing and transporting acrylic acid are as described above.

[0291] Some or all of the above-described steps (i) to (vi) may be performed at multiple locations by multiple manufacturing companies, or, within the scope of this invention, under different conditions. It should be noted that, within the scope of this invention, different conditions correspond to, for example, the use of purified raw materials with or without differences in their presence in subsequent steps, or the use of raw materials obtained using different catalysts in subsequent steps.

[0292] (Differences from existing technologies)

[0293] In the above-described method for manufacturing the absorbent resin of the present invention, the method for manufacturing the absorbent resin derived from biological raw materials replaces the method of using natural polymers with poor performance and heat resistance in the raw materials of the absorbent resin, and replaces the existing representative manufacturing method of acrylic acid derived from biological raw materials (the raw materials are glycerol, bio-naphtha, lactic acid, 3-hydroxypropionic acid, and bio-naphtha based on natural oils and / or fats). As the starting material for the absorbent resin, the absorbent resin is obtained for the first time from inexpensive bioethanol, thereby obtaining an absorbent resin with the same or better performance than conventional absorbent resins derived from fossil raw materials and with the same or further reduced amount of impurities at low cost.

[0294] Regarding absorbent resins, the aforementioned Patent Documents 1-20 and Non-Patent Document 1 do not provide any guidance on manufacturing absorbent resins from bioethanol via steps (i) to (vii) of this invention. Furthermore, the prior art in the patent documents described in steps (i) to (iv) does not provide any guidance on manufacturing absorbent resins from bioethanol, nor does it provide any guidance on manufacturing acrylic acid from bioethanol via steps (i) to (iv). In the conventional methods for manufacturing absorbent resins derived from biological raw materials, such as those in Patent Documents 1-20, not only is the bioacrylic acid required to produce expensive biological raw materials (and biological raw materials with limited production), but even with the aforementioned purification processes, the resulting absorbent resin is insufficient due to the increase in impurities in the acrylic acid, particularly organic acids (especially propionic acid). The aforementioned patent documents and non-patent documents provide no guidance on the method for manufacturing absorbent resins from bioethanol via steps (i) to (vii) of this invention, which is a solution to the technical problem of this invention.

[0295] [The water-absorbing resin of the present invention]

[0296] In this invention, a water-absorbing resin obtained by the above-described manufacturing method is provided.

[0297] The water-absorbing resin obtained through the above manufacturing method (manufacturing process) has the following target properties.

[0298] The target properties vary depending on the water-absorbing resin, and in particular, the following can be listed: water absorption ratio under no pressure, water absorption ratio under pressure, particle size distribution, water absorption rate, liquid permeability, flowability, color, dust content, deodorization performance, and antibacterial properties. Representative properties of superabsorbent polymers can be found in the WSP (Worldwide Strategic Partners) standard of the EDANA Recommended Test Methods, which includes: pH (WSP200.2), residual monomer (WSP210.2), particle size distribution (WSP220.2), loss on drying (WSP230.2), FSC (WSP240.2), CRC (WSP241.2), AAP (WSP242.2), PDAUP (WSP243.1), flow rate (WSP250.2), bulk density (WSP260.2), water-soluble components (WSP270.2), attracted particles (WSP280.2), and dust (WSP290.2). In addition to WSP, other properties such as liquid permeability (SFC, GBP), coloring (YI / WB), and water absorption rate (Vortex / FSR / DW) can also be listed, but these are not the only ones.

[0299] As an example, the water-absorbing resin of the present invention has the following properties.

[0300] ( 14 C quantity)

[0301] The ratio of bio-based raw materials can be determined by the amount of polyacrylic acid obtained. 14 C (radiocarbon) / 12 C (carbon) is used to determine this. In acrylic (salt)-based absorbent resins obtained from previous fossil raw materials (especially petroleum and propylene), 14 C / 12 C is less than 1.0 × 10 -14 In contrast, the water-absorbing resin of the present invention is preferably... 14 C / 12 C is 1.0 × 10 -14 The above is further preferred to be 1.0×10 -13 The above is further preferred to be 5.0×10 -13 The above is particularly preferred, with 1.0 × 10⁻⁶ being the optimal value. -12That's all. Assuming almost 100% by weight is non-fossil material, the upper limit is 1.25 × 10⁻⁶. -12 . 14 C / 12 C can be determined using isotope mass spectrometry, as shown in U.S. Patent Nos. 3,885,155, 4,427,884, 5,438,194, and 5,661,299. The specific determination process is described below.

[0302] 1. It causes the acrylic (salt)-based water-absorbing resin to burn and convert into carbon dioxide.

[0303] 2. Carbon dioxide is separated and purified using a vacuum pipeline.

[0304] 3. Using iron as a catalyst, carbon dioxide generated from acrylic (salt)-based water-absorbing resin is reduced with hydrogen to produce graphite.

[0305] 4. Use 14 C-AMS assay apparatus for determining graphite derived from acrylic (salt) based water-absorbing resins. 14 C concentration and 12 The ratio of C concentration ( 14 C / 12 C).

[0306] 14 C (radioactive carbon) can be adjusted by the ratio of biological feedstocks (especially bioethanol) used.

[0307] ( 13 C quantity)

[0308] Carbon stable isotope ratios (δ¹²) determined by accelerator mass spectrometry 13 C) The ratio can be appropriately adjusted within the range of 0 to -40‰ (per mille). Carbon stable isotope ratio (δ¹⁰) 13 C) Adjustments can be made based on the type of plant used as raw material, and this can be achieved by adjusting δ. 13 C3 plants (wheat, potato, rice, etc.) with C ≤ -20‰ and δ 13 The raw materials were appropriately adjusted using C4 plants (such as corn) with a C content of -20‰. The determination method is based on patent documents 13 and 14.

[0309] (CRC (WSP241.2))

[0310] The CRC (water absorption ratio without pressure) of the water-absorbing resin obtained in this invention is preferably 10 g / g or more, more preferably 20 g / g or more, further preferably 25 g / g or more, and particularly preferably 27 g / g or more. The upper limit of the CRC is not particularly limited, but considering the balance of other physical properties, it is preferably 50 g / g or less, more preferably 45 g / g or less, further preferably 42 g / g or less, and most preferably 35 g / g or less. The CRC can be appropriately controlled by the crosslinking dosage during polymerization and subsequent surface crosslinking (secondary crosslinking). For example, the CRC (water absorption ratio without pressure) of the water-absorbing resin obtained in this invention is 10 g / g or more and 50 g / g or less.

[0311] (AAP (WSP242.2))

[0312] Because the purity of the acrylic acid used in this invention is equal to or higher than that of conventional fossil raw materials, the AAP (absorbency ratio under pressure) of the absorbent resin obtained in this invention is not reduced. Regarding AAP, to prevent leakage in diapers, as an example of the means of achieving the above polymerization, the AAP under pressure of 2.1 kPa or 4.8 kPa is preferably 17 g / g or more, more preferably 20 g / g or more, further preferably 22 g / g or more, even more preferably 23 g / g or more, and most preferably 24 g / g or more. There is no particular upper limit to the AAP value, but considering the balance with other physical properties, it is preferably 35 g / g or less, more preferably 30 g / g or less, and even more preferably 28 g / g or less. After the drying step (iv), preferably after particle size control, the AAP can be increased (adjusted) by surface crosslinking. It should be noted that the AAP value may sometimes change depending on the step performed after the surface crosslinking step. The AAP (water absorption ratio under pressure) of the water-absorbing resin obtained in this invention is, for example, 17 [g / g] or more and 35 [g / g] or less under pressure of 2.1 kPa or 4.8 kPa.

[0313] (Water-soluble components (WSP270.2))

[0314] Regarding the water-soluble component of the absorbent resin obtained in this invention, the purity of the bioacrylic acid is equal to or higher than that of conventional fossil raw materials, thus the soluble component is not increased. To prevent stickiness or other issues during use in diapers due to the influence of the liquid-soluble component, the content is preferably 35% by weight or less, more preferably 25% by weight or less, further preferably 15% by weight or less, even more preferably 10% by weight or less, even more preferably less than 10% by weight, and particularly preferably less than 8.3% by weight. The water-soluble component can be appropriately controlled by controlling the crosslinking dosage during polymerization and, preferably, by the breaking of chemical bonds caused by the mechanical action during subsequent gel pulverization. The lower limit of the water-soluble component of the absorbent resin obtained in this invention is, for example, 4.0% by weight or more.

[0315] (SFC (Saline Fluid Conductivity))

[0316] To prevent leakage in diapers, the SFC (saline solution conductivity) of the absorbent resin obtained in this invention can be improved by surface crosslinking after the above-described preparation method, particularly after gel pulverization according to this invention, preferably after the above-described particle size control. As an example of a method for achieving the above-described AAP range for surface crosslinking, the preferred SFC for pressurized liquid flow characteristics, i.e., 0.69% sodium chloride aqueous solution conductivity (SFC), is 10 × 10⁻⁶. -7 ·cm 3 ·s·g -1 More preferably, it is 20 [×10] or higher. -7 ·cm 3 ·s·g -1 The above is further preferred to be 30 [×10] -7 ·cm 3 ·s·g -1 The above, and more preferably 50 [×10] -7 ·cm 3 ·s·g -1 The above, especially preferred, is 70 [×10] -7 ·cm 3 ·s·g -1 The optimal value is 100 [×10] or higher. -7 ·cm 3 ·s·g -1 ]above.

[0317] (Residual monomer (WSP210.2))

[0318] Regarding the residual monomers of the absorbent resin obtained in this invention, bio-acrylic acid can be obtained with high purity, thus having the advantage of very low residual monomer levels. From a safety point of view, as an example of the method for achieving the above polymerization, the residual monomer level is typically controlled to be less than 500 ppm, preferably less than 500 ppm, more preferably 0 to 450 ppm, further preferably 0 to 400 ppm, particularly preferably 0 to 300 ppm, and especially preferably 0 to 200 ppm. The residual monomer level can be appropriately controlled by the polymerization initiator used during polymerization and the subsequent drying conditions, etc.

[0319] (Impurities other than residual monomers)

[0320] Regarding the absorbent resin obtained in this invention, since the purity of the acrylic acid used in this invention is equal to or higher than that of conventional fossil raw materials, the impurity content is not increased. Furthermore, there are no issues with coloring or odor. Representative impurities in absorbent resins other than residual monomers include acetic acid and propionic acid, with a preferred total content of 1000 ppm or less, 800 ppm or less, 600 ppm or less, 500 ppm or less, 400 ppm or less, 300 ppm or less, or 250 ppm or less. The total content of acetic acid and propionic acid in the absorbent resin obtained in this invention is preferably low, but sometimes excessive reduction in balance with cost reduction can lead to performance degradation; for example, it can be 100 ppm or more, or 200 ppm or more. The total content of acetic acid and propionic acid in the absorbent resin obtained in this invention is, for example, 100 ppm or more and 1000 ppm or less, or 100 ppm or more and 250 ppm or less.

[0321] The total content of acetic acid, propionic acid, and residual monomers (especially acrylic acid), which are the cause of the sour odor in absorbent resins, is preferably 1500 ppm or less, 1200 ppm or less, 1000 ppm or less, 900 ppm or less, 800 ppm or less, 700 ppm or less, or 685 ppm or less. The total content of acetic acid, propionic acid, and residual monomers (especially acrylic acid) in the absorbent resin is preferably low, but sometimes excessive reduction in order to balance cost can lead to a decrease in performance; for example, it can be 100 ppm or more, or 200 ppm or more.

[0322] (FSR (Water Absorption Rate))

[0323] To prevent leakage in diapers, as an example of the polymerization method described above, the absorbent resin obtained in this invention typically has an FSR (free speed of absorption) of 0.20 g / (g·s) or higher, preferably 0.25 g / (g·s) or higher, more preferably 0.30 g / (g·s) or higher, even more preferably 0.35 g / (g·s) or higher, particularly preferably 0.40 g / (g·s) or higher, and most preferably 0.45 g / (g·s) or higher. Furthermore, the upper limit for the FSR is 1.00 g / (g·s) or lower. The method for determining the FSR is specified in International Publication No. 2009 / 016055. The FSR can be adjusted using the manufacturing method of this invention and the aforementioned particle size control after drying.

[0324] (Particle size distribution)

[0325] The water-absorbing resin of the present invention can be in the form of flakes or fibers, and is preferably adjusted to the particle size described above (preferably 850 to 150 μm, etc.) in the grading process before or after surface crosslinking.

[0326] (coloring)

[0327] YI (Yellow Index) represents white values ​​below 20, 15, and 10.

[0328] (Properties of representative water-absorbing resins)

[0329] As an example, the present invention provides a bio-based absorbent resin that satisfies the following properties, further satisfies the above properties, has the same properties as absorbent resins derived from 100% fossil raw materials, and has the same or further reduced amount of impurities.

[0330] CRC = 10~50g / g.

[0331] AAP2.1kPa≥17g / g.

[0332] AAP 4.81kPa ≥ 17g / g.

[0333] Water-soluble components ≤35%.

[0334] Residual monomer ≤500ppm.

[0335] FSR≥0.20g / g / sec.

[0336] Preferably, it has the following properties.

[0337] CRC = greater than 27.5 g / g and less than 50 g / g, AAP 2.1 kPa = greater than 20.5 g / g, or AAP 4.81 kPa = greater than 20.5 g / g, water soluble components = less than 10%, residual monomers = less than 500 ppm.

[0338] CRC = greater than 30.0 g / g and less than 50 g / g, AAP 4.81 kPa = greater than 20.5 g / g and less than 4050 g / g, water soluble components = greater than 4.0% and less than 8.3%, residual monomers = greater than 50 ppm and less than 500 ppm.

[0339] [Uses of the water-absorbing resin of the present invention]

[0340] The application of absorbent resin is not particularly limited; it is directed towards hygiene materials. That is, in this invention, a hygiene material comprising absorbent resin is provided. Preferred applications as a hygiene material include its use as an absorbent element in absorbent articles such as disposable diapers (for infants and adults), sanitary napkins, and incontinence pads. In particular, it can be used as an absorbent element in high-concentration disposable diapers. Examples of other absorbent articles include leak-absorbing materials, food preservation materials, makeshift toilets for disaster relief, pet pee pads, and cat litter. Other uses for water-absorbing resins include: soil moisture retention agents, seedling sheets, seed coating materials, anti-condensation sheets, disposable hand warmers, cooling headbands, cold insulators, medical waste liquid solidifying agents, residual soil solidifying materials, dehydrating agents for water-containing bulk materials, waterproof waste liquid gelling agents, absorbent sandbags, wet cloth materials, cosmetic tackifiers, water-stopping materials for electrical / electronic materials and communication cables, sealing packaging, fertilizer slow-release agents, various slow-release agents (space sterilizers, fragrances, etc.), wound dressings, anti-condensation building materials, oil moisture removal agents, coatings, adhesives, anti-blocking agents, light diffusing agents, matting agents, additives for decorative panels, additives for artificial marble, additives for colorants, and other resin additives.

[0341] Example

[0342] [Manufacturing Example 1]

[0343] As bioethanol, it is produced using JAPAN ALCOHOL TRADING COMPANY LIMITED as “Specific Alcohol Traceability Grade 95 1” (quality specification; ethanol content 95.2–95.4% by volume (equivalent to approximately 92.6–92.8% by weight (calculated from specific gravity at 20°C)), with the remainder being mostly water. Evaporation residue is less than 0.5 mg / 100 ml. 2-Propanol is less than 30 mg / L, methanol, 1-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 2-methylbutanol, and acetone are each less than 1 mg / L, other organic impurities are less than 2 mg / L, acetaldehyde is less than 1 mg / L, and 1,4-dioxane is less than 0.01 mg / L).

[0344] As step (i) of this invention, in the presence of a composite metal oxide catalyst with a molar ratio of Fe / Zn / Zr = 1 / 0.5 / 0.5, a gas mixture of bioethanol / water vapor / nitrogen in a molar ratio of 2 / 8 / 1 is reacted at 400°C to synthesize acetone. The acetone is then purified to obtain acetone with a purity of 95% by mass or higher. As impurities, it contains a total of 4000 ppm of ethanol and acetaldehyde. The remainder is mostly water.

[0345] Next, as step (ii), in the presence of a catalyst containing 5% by weight nickel and 5% by weight ruthenium supported on spherical silica (particle size 1.7–4 mm), a gas with a hydrogen / acetone purity of 95% or higher = 2.7 / 1 (molar ratio) is reacted at 0.5 MPa and 100 °C to synthesize isopropanol, obtaining isopropanol with a purity of 98% by weight. The ethanol content in the isopropanol is 2200 ppm. The remainder is mostly water and acetone.

[0346] Furthermore, as step (iii), in the presence of a catalyst containing 10% by weight of tungsten oxide supported on spherical γ-alumina with a particle size of 2 to 4 mm, the gas with a purity of 98% by weight of isopropanol / oxygen / nitrogen = 6.8 / 12.5 / 80.7% by volume is reacted at 325°C to obtain propylene.

[0347] Next, as step (iv), the propylene is oxidized at 325°C in the presence of a bismuth-molybdenum-based catalyst (catalyst for acrolein) with a particle size of 5-7 mm to obtain acrolein. Then, the acrolein is reacted at 275°C in the presence of a molybdenum-vanadium-based catalyst with a particle size of 5-7 mm to obtain acrylic acid. By purification, acrylic acid (bioacrylic acid) with a purity of 99% by mass or higher is obtained. The bioacrylic acid contains 140 ppm acetic acid and 200 ppm propionic acid. Furthermore, the water content is 1500 ppm. Additionally, the acrylic acid dimer content is 80 ppm.

[0348] [Comparative Manufacturing Example 1] Manufacturing of Acrylic Acid Derived from Fossil Raw Materials

[0349] As a conventional method, acrylic acid is produced by contacting gas phase oxidation of propylene derived from fossil raw materials in step (iv), instead of obtaining biopropylene from bioethanol in steps (i) to (iii) of the above-mentioned manufacturing example 1.

[0350] When the obtained reaction gas is absorbed into water in an absorption tower, it is added to the absorbent at a concentration of 300 ppm relative to the aqueous acrylic acid solution in which hydroquinone was generated, to obtain an aqueous acrylic acid solution. Then, using the azeotropic solvent toluene, low-boiling-point components such as acetic acid and propionic acid are removed from the aqueous acrylic acid solution by distillation, and high-boiling-point components such as maleic acid and acrylic acid dimer are removed, yielding crude acrylic acid. This crude acrylic acid is purified using a simple distillation apparatus to obtain acrylic acid (2). The acrylic acid contains 170 ppm acetic acid and 210 ppm propionic acid.

[0351] [Comparative Manufacturing Example 2] Manufacturing Acrylic Acid from Glycerin

[0352] Acrolein, containing byproducts such as propionaldehyde, was obtained by dehydrating glycerol derived from natural sources under a strong acid solid catalyst. The acrolein containing propionaldehyde was then subjected to gas-phase oxidation to produce gaseous acrylic acid, which was then captured with water to form an aqueous solution of acrylic acid. This solution was then distilled to obtain acrylic acid containing 3% by weight of propionic acid. To further purify this acrylic acid, simple distillation and crystallization were performed to obtain acrylic acid derived from non-fossil materials containing 2000 ppm propionic acid and 300 ppm acetic acid (3).

[0353] [Example 1] Preparation of a water-absorbing resin from acrylic acid derived from bioethanol

[0354] Step (v) involves polymerizing an aqueous solution of monomers containing acrylic acid and its salts to obtain polyacrylates.

[0355] An aqueous solution was prepared by mixing 439.4 parts by weight of bio-acrylic acid (containing 80 ppm of acrylic acid dimer and 70 ppm of p-methoxyphenol) obtained in steps (i) to (iv) of Manufacturing Example 1, 181.1 parts by weight of a 48.5% sodium hydroxide aqueous solution, 1.9 parts by weight of polyethylene glycol diacrylate (average number of polyethylene glycol units (average n): 9), 1.35 parts by weight of a 2.0% trisodium diethylenetriaminepentaacetate aqueous solution, and 351.7 parts by weight of deionized water. It should be noted that the deionized water was preheated to 40°C.

[0356] Next, while stirring the above aqueous solution, 196.1 parts by weight of a 48.5% sodium hydroxide aqueous solution was added to the aqueous solution over approximately 30 seconds under open atmospheric conditions to mix, thereby preparing the monomer aqueous solution. It should be noted that the temperature of the monomer aqueous solution rises to approximately 80°C due to the heat of neutralization and heat of solution generated during the above mixing process.

[0357] Then, at the point when the temperature of the above monomer aqueous solution reaches 78°C, 28.45 parts by weight of 3% sodium persulfate aqueous solution as a polymerization initiator are added, and the mixture is stirred for about 5 seconds to prepare a reaction solution.

[0358] Next, the reaction solution is allowed to flow into a stainless steel trough-shaped container under open atmospheric conditions. The trough-shaped container has a bottom dimension of 200mm × 260mm, an upper dimension of 460mm × 560mm, a height of 140mm, a trapezoidal cross-section in the center, and silicone sheets are adhered to its inner surface. Furthermore, the trough-shaped container is preheated by being placed on a heating plate heated to 50°C before the reaction solution flows in.

[0359] After the above-mentioned reaction solution is poured into the aforementioned trough-shaped container, the polymerization reaction begins within 1 minute. During the polymerization reaction, the reaction solution expands upwards in all directions while generating water vapor, and after the polymerization reaction occurs simultaneously with foaming, it contracts to a size slightly larger than the bottom of the trough-shaped container. The polymerization reaction (expansion and contraction) ends within approximately 1 minute. It should be noted that the highest polymerization temperature shown in the polymerization thermogram is 112°C. During polymerization, some of the residual acrylic acid, acetic acid, and propionic acid in the reaction system evaporates and is removed along with the generated water vapor. Through this polymerization reaction, a hydrogel-like crosslinked polymer (hereinafter referred to as "hydrogel") is obtained.

[0360] Next, the hydrogel is cut into appropriate sizes and fed into a screw extruder for gel pulverization (gel pulverization process) to produce particulate hydrogels with a particle size of 0.1–2 mm. The water content of the particulate hydrogels is 52% by weight.

[0361] (The process of drying the polymerized hydrogel (vi), followed by the process of surface cross-linking (vii))

[0362] Next, as step (vi), the above-mentioned particulate hydrogel is spread on a metal mesh with a mesh size of 300 μm (50 mesh) and placed in a hot air dryer. Then, the particulate hydrogel is dried by passing hot air at 190°C for 30 minutes to obtain a dried polymer. The water content of the dried polymer is 2% by weight. It should be noted that the particulate hydrogel discharged from the screw extruder is supplied to the drying step (vi) within 1 hour. Next, the dried polymer is fed into a roller mill for pulverization, and then classified using two JIS standard sieves with mesh sizes of 850 μm and 150 μm, thereby obtaining randomly fragmented water-absorbing resin powder (1). The weight-average particle size (D50) of the water-absorbing resin powder (1) is 390 μm.

[0363] Next, as step (vii), 3.5 parts by weight of a surface crosslinking agent solution (1) consisting of 0.4 parts by weight of ethylene carbonate, 0.6 parts by weight of propylene glycol, and 2.5 parts by weight of deionized water were added to 100 parts by weight of the above-mentioned water-absorbing resin powder (1) and mixed until homogeneous, thereby obtaining a humidifying mixture (1). Next, the humidifying mixture (1) was heated at 200°C for 40 minutes and then cooled to 60°C, allowing it to pass through a mesh of 850 μm. Particles that did not pass through the 850 μm mesh were gently pressed and broken up on the mesh using a scraper, allowing them to pass through, and incompletely broken particles were removed. Thus, a randomly fragmented, surface-crosslinked water-absorbing resin (1) was obtained. Table 1 shows various physical properties of the water-absorbing resin powder (1) and the water-absorbing resin (1).

[0364] [Comparative Example 1] Manufacturing using water-absorbing resin of acrylic acid derived from fossil raw materials

[0365] In step (v) of Example 1, the acrylic acid produced from propylene derived from fossil raw materials in Comparative Manufacturing Example 1 was changed. Otherwise, the same operation as in Example 1 was performed to obtain randomly fragmented comparative water-absorbing resin powder (1) and surface-crosslinked comparative water-absorbing resin (1).

[0366] [Comparative Example 2] Manufacturing of a water-absorbing resin of acrylic acid derived from glycerin

[0367] In step (v) of Example 1, the acrylic acid manufactured in Comparative Manufacturing Example 2 was changed, and the same operation as in Example 1 was performed to obtain randomly broken comparative water-absorbing resin powder (2) and surface-crosslinked comparative water-absorbing resin (2).

[0368] [Comparative Example 3] Manufacturing using natural polymer water-absorbing resin

[0369] In Comparative Example 1 (manufacturing of acrylic acid derived from fossil raw materials), in order to produce a portion of a water-absorbing resin derived from biological raw materials, in step (vi) of Comparative Example 1, soluble starch (25% by weight relative to the monomer solid content) was mixed into the polymerized hydrogel. Otherwise, the operation was carried out in the same manner as in Comparative Example 1 to obtain comparative water-absorbing resin (3) (starch content 20% by weight). The water-absorbing resins of Example 1 and Comparative Examples 1 and 2 were white. In contrast, as shown in Comparative Example 1, the comparative water-absorbing resin (3) containing 20% ​​by weight of starch had a lower water absorption ratio and was colored as tan during drying (hot air at 190°C for 30 minutes) due to the low heat resistance of starch. After drying, the surface crosslinking (heat treatment at 200°C for 40 minutes) further colored the water-absorbing resin as brown.

[0370] [Comparative Example 4]

[0371] In Comparative Example 3 (coloring at 20% starch), in order to suppress the coloring and the decrease in water absorption ratio during drying and surface crosslinking, the drying conditions (hot air at 190°C for 30 minutes) were changed to hot air at 100°C for 4 hours in step (vi) of Comparative Example 3. It was confirmed that coloring during drying was suppressed, but the drying time was extended, and the productivity was significantly reduced.

[0372] Furthermore, in order to suppress coloration during surface crosslinking (heat treatment at 200°C for 40 minutes) after drying, the surface crosslinking temperature was changed to 100°C. However, even with a heating time of 1 hour, surface crosslinking did not occur, and the AAP was low. It should be noted that "Comparative Example 4" shown in Table 1 illustrates the results of surface crosslinking performed at 100°C for 1 hour.

[0373] [Comparative Example 5]

[0374] In Comparative Example 3, in order to suppress coloring during surface crosslinking (heat treatment at 200°C for 40 minutes) after drying, 0.1 parts of ethylene glycol diglycidyl ether with high low-temperature reactivity was added as a surface crosslinking agent to 0.4 parts by weight of ethylene carbonate and 0.6 parts by weight of propylene glycol, and surface crosslinking was carried out at 100°C for 1 hour.

[0375] [Table 1]

[0376]

[0377] [Example 2] Recycling of water-absorbing resin

[0378] In Example 1, the dried polymer obtained in the drying step (vi) of Example 1 was graded using two JIS standard sieves with mesh sizes of 850 μm and 150 μm. The 150 μm passing material, i.e., the micro powder, was then mixed into the gel pulverization step of Example 1 at 1% by weight (relative to the monomer used in step (v), thereby recycling the water-absorbing resin micro powder derived from biological raw materials. A water-absorbing resin substantially the same as that of Example 1 was obtained.

[0379] [Example 3] Recycling of acrylic acid

[0380] In the polymerization step (v) of Example 1 (where the highest polymerization temperature is 112°C due to the heat of polymerization, and some of the residual acrylic acid, acetic acid, and propionic acid in the reaction system evaporates along with the generated water vapor), the evaporated acrylic acid is collected by cooling. The collected acrylic acid is purified and used in the polymerization of Example 1 at 1% by weight (relative to the monomer used in step (v)), thereby recycling the bio-acrylic acid. A water-absorbing resin substantially the same as that of Example 1 is obtained.

[0381] [Summarize]

[0382] When comparing Example 1 (using the absorbent resin (1) of acrylic acid obtained from bioethanol of the present invention) with Comparative Example 1 (using the comparative absorbent resin (1) of acrylic acid obtained from conventional fossil raw materials), it can be seen that in the manufacturing method of the present invention, the performance is equivalent to that of the conventional absorbent resin derived from fossil raw materials and the impurities (acetic acid and propionic acid, which are the cause of odor) are equal to or further reduced.

[0383] When comparing Example 1 (using the absorbent resin (1) of acrylic acid obtained from bioethanol of the present invention) with Comparative Example 2 (using the comparative absorbent resin (2) of acrylic acid obtained from bioglycerol), it can be seen that in the manufacturing method of the present invention, the water absorption performance (the relationship between water absorption ratio and soluble components) is excellent and the impurities (acetic acid and propionic acid) are further reduced. In the absorbent resin of Comparative Example 2 (the residual acetic acid / propionic acid ratio is 1400 ppm), even if acrylic acid is highly purified in Comparative Example 2 at the expense of yield and cost, it is difficult to sufficiently purify and remove impurities such as propionic acid (boiling point 141°C) from acrylic acid (boiling point 141°C). Therefore, in addition to the problems of acrylic acid purification cost and yield, it was also confirmed that the obtained absorbent resin will produce a sour odor when stored.

[0384] Furthermore, when comparing Example 1 (the total residual acetic acid / propionic acid in acrylic acid was 340 ppm) with Comparative Example 2 (the total residual acetic acid and propionic acid in acrylic acid was 2300 ppm), it can be seen that in Comparative Example 2, which had more impurities in acrylic acid, acetic acid and propionic acid further volatilized. Therefore, Example 1 was also superior in terms of the yield of the water-absorbing resin (the ratio of acrylic acid used to the water-absorbing resin obtained).

[0385] When comparing Example 1 (the absorbent resin (1) of acrylic acid obtained from bioethanol according to the present invention), Comparative Example 1 (the comparative absorbent resin (1) of acrylic acid obtained from conventional fossil raw materials), and Comparative Examples 3 to 5 (the comparative absorbent resin (3) of acrylic acid grafted with starch (25% by weight relative to the monomer solid content) obtained from fossil raw materials (20% by weight of biological raw materials), it can be seen that further use of starch in polyacrylate will reduce the water absorption ratio (CRC) of the absorbent resin, increase the residual monomer, and cause the absorbent resin to be colored yellow to brown. Since the main use of absorbent resin is in sanitary materials such as diapers, in addition to the decrease in water absorption ratio (CRC), the coloring and increase of residual monomer of the absorbent resin as in Comparative Examples 3 to 5 are also undesirable.

[0386] As shown in Examples 2 and 3, by recycling bio-acrylic acid and bio-derived absorbent resins, carbon-neutral high-performance absorbent resins can also be provided.

[0387] Furthermore, as demonstrated by the absorbent resin of Example 1, which uses acrylic acid obtained from aqueous ethanol containing a specified trace amount of the manufacturing example 1, it is evident that the residual water and isopropanol in the ethanol used do not adversely affect the acrylic acid used in the absorbent resin. As the ethanol used in this invention, relatively inexpensive aqueous ethanol that is not mixed with hydrophobic solvents, particularly aqueous ethanol containing fermentation byproducts (isopropanol, acetone) and water (further crude ethanol), can be appropriately used instead of highly purified anhydrous ethanol that requires hydrophobic solvents, and the same results as in Example 1 can be confirmed.

[0388] That is, it can be seen that in the manufacturing method of the embodiment of the present invention, the main chain is essentially 100% by weight derived from biological raw materials, but compared with the comparative absorbent resins (3) to (5) derived from 20% starch, the water absorption performance (CRC / AAP) and residual monomers are also excellent. Furthermore, even when manufactured at high temperature, it is a white absorbent resin.

[0389] Industrial availability

[0390] By using bioethanol as a raw material to manufacture absorbent resins, carbon-neutral, high-performance absorbent resins can be provided. Bioethanol is also an inexpensive and mass-producible biological raw material. Therefore, absorbent resins manufactured from bioethanol using the method of this invention can replace the large quantities of conventional absorbent resins derived from fossil raw materials and be widely used in the application fields of absorbent resins.

[0391] This invention is based on Japanese Patent Application No. 2023-198629 filed on November 22, 2023 and Japanese Patent Application No. 2023-223208 filed on December 28, 2023, the disclosures of which are incorporated herein by reference in their entirety.

Claims

1. A method for manufacturing a water-absorbing resin derived from biological raw materials, comprising the following steps (i) to (vii): Process (i) involves obtaining acetone from bioethanol; Step (ii) involves obtaining isopropanol from the acetone; Step (iii) involves obtaining propylene from the isopropanol; Step (iv) involves obtaining acrylic acid from the propylene; Step (v) involves polymerizing an aqueous monomer containing the acrylic acid to obtain polyacrylic acid and / or its salts; Step (vi) involves drying the polyacrylic acid and / or its salts; and Step (vii) involves surface crosslinking of the polyacrylic acid and / or its salts.

2. The manufacturing method according to claim 1, wherein, The total content of ethanol and acetaldehyde in the acetone is less than 20,000 ppm.

3. The manufacturing method according to claim 1 or 2, wherein, The ethanol content in the isopropanol is below 20,000 ppm.

4. The manufacturing method according to any one of claims 1 to 3, wherein, The bioethanol is aqueous ethanol with a water content of 3% by weight or more.

5. The manufacturing method according to any one of claims 1 to 4, wherein, The bioethanol contains less than 1% by weight of lower alcohols with 1, 3 to 5 carbon atoms, acetaldehyde, and acetone.

6. The manufacturing method according to any one of claims 1 to 5, wherein, The bioethanol is ethanol containing isopropanol and / or acetone.

7. The manufacturing method according to any one of claims 1 to 6, wherein, The bioethanol is obtained by fermentation of one or more genetically recombinant or non-genetically recombinant plant materials selected from sugarcane, corn, and sugar beet.

8. The manufacturing method according to any one of claims 1 to 7, wherein, The acrylic acid contains less than 500 ppm of propionic acid.

9. The manufacturing method according to any one of claims 1 to 8, wherein, The acetic acid content in the acrylic acid is below 1500 ppm.

10. The manufacturing method according to any one of claims 1 to 9, wherein, At least a portion of the impurities in the acrylic acid are removed in step (v) and / or step (vi).

11. The manufacturing method according to any one of claims 1 to 10, wherein, The acrylic acid that volatilizes in step (v) and / or step (vi) will be recycled in step (v).

12. The manufacturing method according to any one of claims 1 to 11, wherein, After step (v), a portion of the absorbent resin is separated and recycled in step (v) or step (vi).

13. The manufacturing method according to any one of claims 1 to 12, wherein, In step (v), acrylic acid obtained in step (iv) is added to the monomer, and other acrylic acid is used, wherein the acrylic acid obtained in step (iv) is more than 1 mol% relative to the total acrylic acid.

14. The manufacturing method according to any one of claims 1 to 13, wherein, The combined content of acetic acid and propionic acid in the water-absorbing resin is less than 1000 ppm.

15. The manufacturing method according to any one of claims 1 to 14, wherein, The total content of acetic acid, propionic acid, and acrylic acid in the water-absorbing resin is less than 1500 ppm.

16. The manufacturing method according to any one of claims 1 to 15, wherein, The water-absorbing properties of resins were determined by radiocarbon dating. 14 C / 12 C is 1.0 × 10 -14 above.

17. The manufacturing method according to any one of claims 1 to 16, wherein, After step (v), a chelating agent is added to the monomer aqueous solution and / or the polyacrylic acid and / or its salt.

18. The manufacturing method according to claim 6, wherein, The combined content of acetone and isopropanol in the bioethanol is above 1 ppm.

19. A water-absorbing resin obtained by the manufacturing method according to any one of claims 1 to 18.

20. A sanitary material comprising the absorbent resin according to claim 19.

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