Production method for (METH)acrylic acid

Abstract

To provide a production method that enables (meth)acrylic acid to be produced from 3-hydroxycarboxylic acid with high productivity while suppressing an increase in viscosity of a reaction liquid, in a stable manner for a long period of time.SOLUTION: The present invention provides a production method for (meth)acrylic acid, the method comprising the step of reacting a raw material containing 3-hydroxycarboxylic acid and / or a condensate thereof to obtain (meth)acrylic acid, wherein the production method comprises the step of performing the reaction under a condition in which a neutralization rate of carboxylic acids in a reaction liquid containing 3-hydroxycarboxylic acid and / or a condensate thereof is set to 1-50 mol%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing (meth)acrylic acid, and more particularly to a method for producing (meth)acrylic acid from a raw material containing a 3-hydroxycarboxylic acid or a condensate thereof. [Background technology]

[0002] (Meth)acrylic acid is widely used industrially as a raw material for acrylic resins and hydrophilic resins. A typical method for producing (meth)acrylic acid is a two-stage oxidation method in which fossil-derived raw materials, such as propylene or isobutylene, are converted into acrolein or methacrolein by catalytic gas-phase oxidation in the presence of an oxide catalyst using a fixed-bed multi-tubular continuous reactor, and this is then further catalytically oxidized (see Patent Documents 1 to 7). However, in light of growing awareness of environmental issues in recent years, it is desirable to produce (meth)acrylic acid from renewable resources rather than from fossil resources, and attempts have been made to economically produce (meth)acrylic acid on a commercial scale using renewable resources such as biomass.

[0003] Examples of methods for producing (meth)acrylic acid from biomass include methods in which sugars are obtained from natural products such as agricultural crops, or by decomposing cellulose, etc., and then the sugars are fermented to obtain 3-hydroxycarboxylic acids such as 3-hydroxypropionic acid (hereinafter also referred to as 3HP) and 3-hydroxyisobutyric acid, and then the 3-hydroxycarboxylic acids are reacted. Examples of methods for producing (meth)acrylic acid include a method comprising the steps of producing a composition containing a polymer of 3-hydroxycarboxylic acid and carrying out a liquid-phase reaction from the composition at a temperature exceeding 100°C (see Patent Document 8), a method for producing acrylic acid by reacting 3-hydroxycarboxylic acid in the liquid phase at 120 to 250°C to obtain acrylic acid, in which the ratio of 3-hydroxycarboxylic acid oligomers to 3-hydroxycarboxylic acid monomers is set within a specific range (see Patent Documents 9 and 10), and a method for producing acrylic acid by decomposing polypropiolactone using a catalyst such as sodium acrylate, potassium carbonate, or sodium carbonate (see Patent Documents 11 to 14). Also disclosed is a method for producing acrylic acid by reacting 3-hydroxypropionic acid or lactic acid with a liquid mixture containing a metal salt of 3-hydroxypropionic acid or lactic acid and water at a temperature higher than 150°C (see Patent Document 15). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2005 / 095320 [Patent Document 2] International Publication No. 2007 / 106100 [Patent Document 3] Special Publication No. 2006-518766 [Patent Document 4] Japanese Patent Application Laid-Open No. 2000-159724 [Patent Document 5] International Publication No. 2012 / 091114 [Patent Document 6] Special Publication No. 2004-532855 [Patent Document 7] International Publication No. 2011 / 002892 [Patent Document 8] Patent No. 6078447 [Patent Document 9] U.S. Patent No. 10,252,970 [Patent Document 10] U.S. Patent No. 9,809,526 [Patent Document 11] U.S. Patent No. 10,065,914 [Patent Document 12] U.S. Patent No. 10,703,707 [Patent Document 13] U.S. Patent No. 10,626,073 [Patent Document 14] U.S. Patent No. 1,099,989 [Patent Document 15] Patent No. 6290257 Summary of the Invention [Problem to be solved by the invention]

[0005] As mentioned above, one known method for producing (meth)acrylic acid from biomass is to obtain 3-hydroxycarboxylic acid from natural products and then react it to produce (meth)acrylic acid. However, the reaction rate from 3-hydroxycarboxylic acid to acrylic acid is slow, resulting in low productivity of acrylic acid. This makes the (meth)acrylic acid production process unnecessarily expensive and is not a desirable production method from the perspective of industrial productivity. If the reaction is carried out under high-temperature conditions to increase productivity, there is a high risk of polymerization of (meth)acrylic acid, which can cause operational problems in the production equipment. Furthermore, when producing (meth)acrylic acid from biomass, impurities specific to biomass can cause the reaction solution to become highly viscous, making it difficult to continue operating the reactor. As described above, there are various problems to be overcome in order to stably produce (meth)acrylic acid from biomass with high productivity for a long period of time.

[0006] The present invention has been made in view of the above-mentioned current situation, and aims to provide a production method that can produce (meth)acrylic acid from 3-hydroxycarboxylic acid with high productivity and stably for a long period of time while suppressing an increase in viscosity of the reaction solution. [Means for solving the problem]

[0007] The present inventors have investigated a production method for (meth)acrylic acid using 3-hydroxycarboxylic acid as a raw material with high productivity, which can be continued stably for a long period of time while preventing the reaction solution from becoming highly viscous. They have found that by neutralizing the carboxylic acid in a reaction solution containing 3-hydroxypropionic acid and / or a condensate thereof to a predetermined neutralization rate and then carrying out the reaction, (meth)acrylic acid can be produced with high productivity, and the reaction solution can be prevented from becoming highly viscous, allowing the production of (meth)acrylic acid to be continued stably for a long period of time. They have also found a suitable method for producing a hydrophilic resin using the (meth)acrylic acid thus obtained, and have arrived at the present invention.

[0008] That is, the present invention is as follows. [1] A method for producing (meth)acrylic acid, comprising a step of reacting a raw material containing a 3-hydroxycarboxylic acid and / or a condensate thereof to obtain (meth)acrylic acid, The production method includes a step of carrying out a reaction in a reaction liquid containing a 3-hydroxycarboxylic acid and / or a condensate thereof at a neutralization rate of 1 to 50 mol % of carboxylic acid. A method for producing (meth)acrylic acid.

[0009] [2] The method for producing (meth)acrylic acid according to [1], wherein the reaction step is carried out by adding an alkali metal compound.

[0010] [3] The method for producing (meth)acrylic acid according to [1] or [2], wherein the average degree of condensation of 3-hydroxycarboxylic acid in the reaction liquid is 3 or less.

[0011] [4] The method for producing (meth)acrylic acid according to any one of [1] to [3], wherein the temperature of the reaction liquid is 130 to 250°C.

[0012] [5] The method for producing (meth)acrylic acid according to any one of [1] to [4], wherein the pressure of the reaction solution is normal pressure or reduced pressure.

[0013] [6] A method for producing a hydrophilic resin using a raw material containing a 3-hydroxycarboxylic acid and / or a condensate thereof, comprising: The production method includes a reaction step of producing (meth)acrylic acid by adjusting the neutralization rate of carboxylic acid in a reaction liquid containing a 3-hydroxycarboxylic acid and / or a condensate thereof to 1 to 50 mol %; a polymerization step of polymerizing the monomer component containing (meth)acrylic acid obtained in the reaction step to produce a hydrophilic resin, A method for producing a hydrophilic resin, wherein the main product obtained in the reaction step is (meth)acrylic acid.

[0014] [7] The method for producing a hydrophilic resin according to [6], wherein the hydrophilic resin is a water-absorbent resin. [Effects of the Invention]

[0015] The method for producing (meth)acrylic acid of the present invention is a useful method that can produce (meth)acrylic acid stably over a long period of time with high productivity and good yield, while effectively suppressing an increase in the viscosity of the reaction solution due to impurities specific to biomass-derived raw materials, while increasing the reactivity of the reaction from biomass-derived 3-hydroxycarboxylic acid to acrylic acid. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram of an apparatus used in the reaction of 3-hydroxypropionic acid in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be described in detail below. In addition, a combination of two or more of the individual preferred embodiments of the present invention described below is also a preferred embodiment of the present invention.

[0018] 1. Method for producing (meth)acrylic acid <Reaction process> The method for producing (meth)acrylic acid of the present invention is characterized by comprising a step of carrying out a reaction using a raw material containing 3-hydroxycarboxylic acid or a condensate thereof, with the neutralization rate of carboxylic acid in a reaction liquid containing 3-hydroxycarboxylic acid or a condensate thereof being 1 to 50 mol %. The reaction referred to here is a reaction that includes, as a reaction pathway, at least one of a dehydration reaction (intramolecular dehydration reaction and intermolecular dehydration reaction) of a 3-hydroxycarboxylic acid and / or its condensate and a reaction of thermally decomposing a condensate of a 3-hydroxycarboxylic acid. The reason why (meth)acrylic acid can be produced with high productivity and while preventing the reaction liquid from becoming highly viscous by setting the neutralization rate within this range is presumed to be as follows. In addition to 3-hydroxycarboxylic acid, condensates of 3-hydroxycarboxylic acid with various degrees of condensation are present in the reaction raw materials. (Meth)acrylic acid is produced by decomposing dimers and trimers of these condensates into 3-hydroxycarboxylic acid and (meth)acrylic acid. Therefore, by increasing the proportion of condensates with a low degree of condensation, such as dimers and trimers, in the reaction raw materials, more (meth)acrylic acid can be produced. Neutralizing the carboxylic acid in the reaction solution can suppress the formation of condensates with a high degree of condensation and increase the proportion of condensates with a low degree of condensation, such as dimers and trimers. However, adding too much base for neutralization inhibits the formation of the condensate of 3-hydroxycarboxylic acid, the precursor of (meth)acrylic acid. In contrast, adjusting the neutralization rate of the carboxylic acid in the reaction solution containing 3-hydroxycarboxylic acid or its condensate to 1 to 50 mol% can increase the proportion of condensates with a low degree of condensation without inhibiting the formation of the condensate of 3-hydroxycarboxylic acid, thereby enabling efficient production of (meth)acrylic acid. Furthermore, the generated (meth)acrylic acid may react again with 3-hydroxycarboxylic acid to oligomerize, which is also one of the factors that reduces the productivity of (meth)acrylic acid. However, partial neutralization of the carboxylic acid can suppress the re-reaction of (meth)acrylic acid with 3-hydroxycarboxylic acid, increasing the amount of (meth)acrylic acid produced and improving productivity. Furthermore, when a biomass-derived raw material is used, the viscosity of the reaction solution increases, hindering stable operation of the reactor. In the present invention, however, the neutralization rate of carboxylic acid in the reaction solution is set to 1 to 50 mol %, thereby effectively suppressing the increase in viscosity of the reaction solution. It is presumed that, due to these factors, the method for producing (meth)acrylic acid of the present invention achieves stable operation of the reaction apparatus while increasing the productivity of (meth)acrylic acid.

[0019] The method for producing (meth)acrylic acid of the present invention may include a step of reacting a reaction solution containing 3-hydroxycarboxylic acid and / or a condensate thereof under conditions where the neutralization rate of carboxylic acid in the reaction solution is less than 1 to 50 mol %, as long as it includes a step of reacting the reaction solution containing 3-hydroxycarboxylic acid and / or a condensate thereof under conditions where the neutralization rate of carboxylic acid in the reaction solution is less than 1 to 50 mol %, but the proportion of the time during which the neutralization rate is 1 to 50 mol % is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, particularly preferably 90% or more, and most preferably 100%.

[0020] In the method for producing (meth)acrylic acid of the present invention, the neutralization rate of the carboxylic acid in the reaction solution in the reaction step may be 1 to 50 mol %, but the neutralization rate is preferably 3 to 47 mol %, more preferably 5 to 45 mol %, and even more preferably 7 to 40 mol %. The neutralization rate of the carboxylic acid in the reaction solution in the reaction step can be confirmed by the method described in the examples below. The method for maintaining the neutralization rate of the carboxylic acid in the reaction solution in the reaction step is not particularly limited, and examples thereof include a method of extracting the carboxylic acid and / or the base described below from the reaction solution, and a method of adding the carboxylic acid and / or the base described below to the reaction solution.

[0021] In the reaction step of the method for producing (meth)acrylic acid of the present invention, the method for achieving a neutralization rate of 1 to 50 mol % of the carboxylic acid in the reaction liquid is not particularly limited, but a method of adding a base is preferred. The base to be added is not particularly limited, but examples thereof include metal compounds such as metal hydroxides and carbonates, and ammonia, and examples of metal compounds include compounds of metals in Groups 1 and 2 of the periodic table. Among these, the base to be added is preferably a metal compound of Group 1 of the periodic table, i.e., an alkali metal compound, more preferably a hydroxide or carbonate of an alkali metal.

[0022] As described above, when a dimer or trimer of 3-hydroxycarboxylic acid is decomposed into 3-hydroxycarboxylic acid, (meth)acrylic acid is produced by the reaction of 3-hydroxycarboxylic acid, and therefore, in order to increase the productivity of (meth)acrylic acid, it is preferable to increase the proportion of condensates with a low condensation degree, such as dimers or trimers, in the reaction raw materials, and the average condensation degree of the condensates of 3-hydroxypropionic acid in the reaction liquid is preferably 3 or less. The average condensation degree is more preferably 2.5 or less, and even more preferably 2.0 or less. The average degree of condensation of 3-hydroxypropionic acid in the reaction mixture can be determined by the following calculation formula using analytical values ​​obtained by liquid chromatography. The average degree of condensation of 3-hydroxypropionic acid = (number of moles of 3-hydroxycarboxylic acid units / number of moles of 3-hydroxycarboxylic acids). Number of moles of 3-hydroxycarboxylic acid units = (number of moles of 3-hydroxycarboxylic acid + number of moles of dimer × 2 + number of moles of trimer × 3 + number of moles of tetramer × 4 + number of moles of pentamer × 5 + number of moles of hexamer × 6 + number of moles of heptamer × 7 + number of moles of octamer × 8 + number of moles of nonamer × 9 + number of moles of 10amer × 10 + number of moles of 11amer × 11 + number of moles of 12amer × 12 + number of moles of 13amer × 13 + number of moles of 14amer × 14 + number of moles of 15amer × 15 + number of moles of 16amer × 16) Number of moles of 3-hydroxycarboxylic acids = (number of moles of 3-hydroxycarboxylic acid + number of moles of dimer + number of moles of trimer + number of moles of tetramer + number of moles of pentamer + number of moles of hexamer + number of moles of heptamer + number of moles of octamer + number of moles of nonamer + number of moles of 10amer + number of moles of 11amer + number of moles of 12amer + number of moles of 13amer + number of moles of 14amer + number of moles of 15amer + number of moles of 16amer)

[0023] The temperature of the reaction solution in the reaction step is not particularly limited as long as the reaction proceeds, but is preferably 130 to 250°C. By carrying out the reaction at such a temperature, the reaction can be promoted and the amount of (meth)acrylic acid produced can be increased. The temperature is more preferably 130 to 200°C, and even more preferably 130 to 180°C. The pressure in the reaction vessel in which the reaction step is carried out is not particularly limited as long as the reaction proceeds, but is preferably 5 to 101 kPa, and more preferably 10 to 50 kPa. When the reaction step is carried out under reduced pressure conditions of 50 kPa or less, it becomes easy to gasify and recover the (meth)acrylic acid produced in the reaction.

[0024] The reaction time is not particularly limited, but when the raw material composition is not continuously supplied to the reactor, the reaction time is preferably 0.5 to 200 hours, more preferably 1 to 150 hours, and even more preferably 3 to 100 hours, in consideration of the production efficiency and yield of (meth)acrylic acid.

[0025] The time for the reaction step is not particularly limited, but when the raw material composition is continuously supplied to the reactor, the residence time is preferably 1 to 700 hours, more preferably 8 to 600 hours, and even more preferably 15 to 500 hours. The residence time can be determined by the following calculation formula. Residence time = (amount of liquid phase in reactor) / (amount of liquid phase withdrawn from reactor per unit time)

[0026] The reactor used in the reaction step does not require complicated equipment as long as it can be heated. Thus, one of the advantageous effects of the method for producing (meth)acrylic acid of the present invention is that the reaction can be carried out using a relatively simple device. The reactor preferably has a structure that efficiently transfers heat to the raw material composition supplied in a liquid state. Examples of such reactors include horizontal or vertical pipe natural circulation heaters, forced circulation heaters, multi-tube heat exchangers, thin film heat exchangers, etc. Alternatively, a heating system using a jacket on the outside of the reactor or a coil installed inside the reactor may be used in combination.

[0027] In the method for producing (meth)acrylic acid of the present invention, the method for recovering (meth)acrylic acid produced in the reaction step from the reaction liquid is not particularly limited, but it is preferable to carry out the recovery by a method in which a certain amount of liquid phase is held in a heater, a reaction for producing (meth)acrylic acid is carried out in the liquid phase while supplying the raw material composition thereto in liquid form, and the produced (meth)acrylic acid is evaporated and distilled out of the reactor. By extracting the (meth)acrylic acid, which is a low-boiling component, in the form of a gas by distillation, the unreacted oligomers that have not been decomposed sufficiently remain in the reaction liquid, and the yield of (meth)acrylic acid can be improved. The residence time required for the production of (meth)acrylic acid can be controlled by the temperature, pressure, amount of heat, feed rate of the raw material composition, and amount of liquid raw material present in the reactor. Furthermore, in order to suppress the distillation of 3-hydroxycarboxylic acid and / or its condensation product or (meth)acrylic acid polymer, a distillation column may be installed in the reactor to apply reflux. When distillation is performed, (meth)acrylic acid and water are recovered from the reaction liquid.

[0028] The reaction process may be carried out under air or inert gas atmosphere, but is preferably carried out under air when a distillation column is installed in the reactor. Oxygen can be additionally used to suppress polymerization in the distillation column. For example, it is particularly preferred to introduce an oxygen-containing gas mixture into the reactor, the oxygen content of which in the gas phase is 18% by volume or less, preferably 5% by volume or less, which is below the explosion limit. Inert gas-oxygen mixtures, such as nitrogen-oxygen, argon-oxygen, or carbon dioxide-oxygen mixtures, can also be used.

[0029] In the above reaction step, it is preferable to add a polymerization inhibitor to prevent polymerization of the produced (meth)acrylic acid. Examples of the polymerization inhibitor include methoquinone, manganese acetate, nitrosophenol, cupferron, N-oxyl compounds, copper dibutylthiocarbamate, phenothiazine, hydroquinone, and iron-based compounds such as iron oxide, iron sulfate, iron acetate, and iron chloride. One or more of these can be used. Among these, iron-based compounds are preferred. While iron-based compounds do not exhibit a polymerization inhibitory effect in the presence of (meth)acrylic acid alone, they exhibit a polymerization inhibitory effect on (meth)acrylic acid in an environment in which 3-hydroxycarboxylic acid and / or a condensate thereof coexists with (meth)acrylic acid, and can effectively suppress the polymerization reaction of (meth)acrylic acid in a reactor even at a high reaction temperature exceeding 100°C.

[0030] The amount of the polymerization inhibitor used is preferably an amount that results in a concentration of the polymerization inhibitor in the reaction liquid of 1 to 30,000 ppm, more preferably an amount that results in a concentration of 10 to 10,000 ppm, and even more preferably an amount that results in a concentration of 50 to 5,000 ppm.

[0031] The reaction step may be carried out using a catalyst, such as the acid catalysts and base catalysts described below, with solid acid catalysts and solid base catalysts being particularly preferred. Crystalline metallosilicates such as zeolites; crystalline metallosilicates supported by methods such as ion exchange with alkali metals, alkaline earth metals, transition metals, etc.; natural or synthetic clay compounds such as kaolinite, bentonite, and montmorillonite; sulfuric acid, heteropolyacid, phosphoric acid, or phosphates (alkali metal salts of phosphoric acid, alkaline earth metal salts, manganese phosphate, zirconium phosphate, etc.), alkali metals, alkaline earth metals supported on supports such as alumina or silica. inorganic oxides or inorganic composite oxides such as Al2O3, SiO2, TiO2, ZrO2, SnO2, V2O5, SiO2-Al2O3, SiO2-TiO2, SiO2-ZrO2, TiO2-WO3, and TiO2-ZrO2; solid acidic substances such as metal sulfates and phosphates such as MgSO4, Al2(SO4)3, K2SO4, AlPO4, and Zr(SO4)2; and solid basic substances such as calcium oxide, magnesium oxide, and hydrotalcite. Suitable catalysts include Al2O3, SiO2, SiO2-Al2O3, TiO2, zeolite, and zeolite supported with an alkali metal or alkaline earth metal, and catalysts in which phosphoric acid, phosphates, alkali metals, or alkaline earth metals are supported on a support such as silica.

[0032] <3-Hydroxycarboxylic acid and method for producing same> The 3-hydroxycarboxylic acid used in the present invention includes 3-hydroxypropionic acid, 3-hydroxyisobutyric acid, etc., and any of these may be used, but since acrylic acid obtained by reacting 3-hydroxypropionic acid is particularly highly reactive and easily polymerized, the technical significance of using the production method of the present invention is more fully realized when 3-hydroxypropionic acid is used as the 3-hydroxycarboxylic acid. Therefore, using 3-hydroxypropionic acid as the 3-hydroxycarboxylic acid is one of the preferred embodiments of the present invention.

[0033] The 3-hydroxycarboxylic acid used in the present invention can be obtained from various sources, but from the viewpoint of suppressing global warming and protecting the environment, it is preferable to obtain it from a biological resource that can be recycled as a carbon source. Specifically, it can be prepared by further fermenting sugars obtained from agricultural crops or sugars obtained by decomposing cellulose or the like. In the present invention, it is preferable that at least a part or all of the 3-hydroxycarboxylic acids contained in the raw material composition are 3-hydroxycarboxylic acids obtained by fermentation. That is, the method for producing (meth)acrylic acid of the present invention preferably includes a fermentation step, and is a production method in which a 3-hydroxycarboxylic acid is produced as a raw material by the fermentation step. Furthermore, the raw material for 3-hydroxycarboxylic acid is preferably a biological resource such as biomass.

[0034] Known methods can be used to obtain 3-hydroxycarboxylic acids from biological resources. For example, a method described in WO 2008 / 027742 can be used, in which Escherichia coli introduced with the beta-alanine aminotransferase gene derived from Streptomyces griseus ATCC21897 is subjected to fermentation using glucose as a carbon source. Alternatively, a method described in WO 2001 / 016346 can be used, in which Escherichia coli introduced with glycerol dehydratase derived from Klebsiella pneumoniae and aldehyde oxidase derived from Escherichia coli is subjected to fermentation using glycerol as a carbon source.

[0035] Although the above-mentioned known literature has been described as an example of a method for obtaining 3-hydroxycarboxylic acid, the microorganism or genetically modified microorganism used for fermentation is not particularly limited, and any 3-hydroxycarboxylic acid obtained by fermentation using an organism capable of producing 3-hydroxycarboxylic acid can be used in the production method of the present invention. Furthermore, 3-hydroxycarboxylic acid produced by contacting a raw material sugar with an organism other than fermentation can also be converted to (meth)acrylic acid by the production method of the present invention.

[0036] When a raw material composition containing a 3-hydroxycarboxylic acid and / or a condensate thereof obtained from a biological resource is used as a raw material for the production method of the present invention, the raw material composition is preferably obtained through a fermentation process and contains fewer impurities. Examples of impurities in the raw material composition obtained through a fermentation process include bacterial cells, proteins, amino acids, glucose, salts, etc. that are typically contained in a fermentation broth, and by-products that may be produced together with the 3-hydroxycarboxylic acid during fermentation, such as formic acid, acetic acid, propionic acid, butyric acid, succinic acid, fumaric acid, pyruvic acid, glycolic acid, lactic acid, ethanol, amino acids, 1,3-propanediol, glycerin, hydroxypropionaldehyde, and alanine.

[0037] A method for obtaining a raw material composition containing 3-hydroxycarboxylic acid and / or a condensate thereof with few impurities includes a method for preparing the raw material composition using 3-hydroxycarboxylic acid that has been purified from a fermentation broth. Known methods can be used for the purification step from the fermentation broth. Specifically, a method in which crude 3-hydroxycarboxylic acid obtained by fermentation is precipitated using a calcium salt, and the calcium salt of 3-hydroxycarboxylic acid is recovered and then reacted with an acid such as sulfuric acid to purify the 3-hydroxycarboxylic acid; a method in which ammonium-type 3-hydroxycarboxylic acid obtained by fermentation is chemically converted to 3-hydroxycarboxylic acid by electrodialysis or cation exchange, followed by purification; etc. can be used. Furthermore, membrane separation operations can be used, such as removing impurities using ordinary filter cloth, MF membranes (microfiltration membranes), or UF membranes (ultrafiltration membranes), or concentrating 3-hydroxycarboxylic acids using RO membranes (reverse osmosis membranes). Alternatively, an amine solution of 3-hydroxycarboxylic acid can be extracted by adding a water-immiscible amine solvent to an aqueous solution of 3-hydroxycarboxylic acid or its ammonium salt obtained by fermentation and heating as necessary. Water can then be added to the solution and back-extracted by heating to obtain an aqueous solution of 3-hydroxycarboxylic acid. Alternatively, the 3-hydroxycarboxylic acid can be purified by evaporation or distillation, taking advantage of its vapor pressure. However, because the vapor pressure of 3-hydroxycarboxylic acid is low, operations under high vacuum are preferred. Furthermore, purified 3-hydroxycarboxylic acids can also be obtained by esterifying 3-hydroxycarboxylic acids with alcohols, purifying and concentrating the resulting 3-hydroxycarboxylic acid esters by distillation, and then hydrolyzing the 3-hydroxycarboxylic acid esters. Alternatively, the aqueous solution of 3-hydroxycarboxylic acid can be concentrated by removing water by evaporation or distillation, for example, by using a multi-effect reactor.

[0038] A condensation product of 3-hydroxycarboxylic acid is a polymer in which 3-hydroxycarboxylic acids are linked together via intermolecular ester bonds, and a condensation product of 3-hydroxypropionic acid can be represented by the following formula (1).

[0039] [ka]

[0040] (In formula (1), n ​​represents a number of 1 or more.) In the above formula (1), n ​​is preferably 1 to 20, and more preferably 1 to 10.

[0041] The raw material for the reaction step used in the present invention may be a composition containing a 3-hydroxycarboxylic acid and / or a condensate thereof and a solvent. Examples of the solvent include water, alcohols, hydrocarbons, ethers, ketones, esters, amines, amides, etc., and these can be used alone or in combination of two or more. Among these, solvents having a boiling point lower than that of 3-hydroxycarboxylic acid are preferred in that the solvent can be easily evaporated, and for example, water is preferred.

[0042] When the raw material for the reaction step is a composition containing a 3-hydroxycarboxylic acid and / or a condensate thereof and a solvent, the concentration of the 3-hydroxycarboxylic acid and / or a condensate thereof in the composition is preferably 20 to 100% by mass, more preferably 30 to 99% by mass, and even more preferably 40 to 98% by mass, based on 100% by mass of the composition.

[0043] The raw materials for the reaction step used in the present invention may contain components other than the 3-hydroxycarboxylic acid and / or its condensate and the solvent, such as by-products produced when synthesizing the 3-hydroxycarboxylic acid by fermentation or the like.

[0044] The content of components other than 3-hydroxycarboxylic acid and / or its condensate and solvent contained in the raw materials for the reaction step used in the present invention is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less, based on 100% by mass of the raw materials.

[0045] <Other processes> The method for producing (meth)acrylic acid of the present invention may include other steps as long as it includes a reaction step for obtaining (meth)acrylic acid from a raw material containing a 3-hydroxycarboxylic acid and / or a condensate thereof. Examples of such other steps include a step of recovering a reaction liquid containing the (meth)acrylic acid obtained in the reaction step, and a step of purifying the (meth)acrylic acid obtained in the reaction step. The purification step can be carried out by a method such as membrane separation, distillation, extraction, or crystallization.

[0046] The method for recovering the reaction solution containing (meth)acrylic acid obtained in the above reaction step is not particularly limited, but recovery by distillation is preferred. The distillation recovery solution contains (meth)acrylic acid, which is the main reaction product, and may also contain by-products, the solvent in the raw material composition, and impurities. When the solvent is water, the (meth)acrylic acid can be used as a raw material for polymer production in the form of an aqueous solution. Furthermore, by adding a purification step, high-purity (meth)acrylic acid can be obtained. The purification step can be carried out by known techniques such as membrane separation, distillation, extraction, crystallization, etc., or a combination of these. Among these, the purification step is preferably a step of purifying (meth)acrylic acid by distillation or crystallization.

[0047] 2. Manufacturing method of hydrophilic resin and uses of hydrophilic resin (Meth)acrylic acid can be produced by the above-mentioned method. The (meth)acrylic acid thus produced can be used as a raw material for hydrophilic resins such as water-absorbent resins or water-soluble resins. In other words, one aspect of the present invention is to use the (meth)acrylic acid obtained by the production method of the present invention as a raw material for producing a hydrophilic resin. The method for producing a hydrophilic resin of the present invention includes the above-mentioned reaction step and a polymerization step of polymerizing a monomer component containing (meth)acrylic acid to produce a hydrophilic resin, and is characterized in that the main product among the products obtained in the reaction step is (meth)acrylic acid. The (meth)acrylic acid obtained by the method for producing (meth)acrylic acid of the present invention has high quality with few impurities and the polymerization reaction is easy to control. Furthermore, using this (meth)acrylic acid as a raw material stabilizes the quality of the hydrophilic resin and improves various properties such as water absorption capacity and inorganic material dispersion capacity. The method for carrying out the polymerization step to produce the hydrophilic resin is not particularly limited, and a method in which an initiator and other components are added to a monomer component containing (meth)acrylic acid and the polymerization reaction is allowed to proceed by heating or other methods can be used.

[0048] Furthermore, the (meth)acrylic acid obtained by the production method of the present invention can be suitably used for producing various (meth)acrylic acid derivatives, and the (meth)acrylic acid derivatives can be produced by carrying out a step for producing various (meth)acrylic acid derivatives after the above reaction step.

[0049] Examples of the (meth)acrylic acid derivatives include (meth)acrylic acid esters and polymers thereof, (meth)acrylic acid salts and polymers thereof, and the like. Specific examples of (meth)acrylic acid esters include esters of (meth)acrylic acid with methyl, ethyl, propyl, n-butyl, isobutyl, 2-ethylhexyl, 1-octyl, 2-octyl, isononyl, isobornyl, lauryl, stearyl, 2-hydroxyethyl, 2-hydroxypropyl, 4-hydroxybutyl, 2-methoxyethyl, trimethylpropanyl, tetrahydrofurfuryl, pentaerythritol, glycerin, 1,4-butanediol, and 1,6-hexanediol. Specific examples of (meth)acrylate salts include sodium, potassium, calcium, magnesium, ammonium, and zinc salts.

[0050] The above (meth)acrylic acid esters and (meth)acrylic acid salts can be (co)polymerized alone or in combination to produce various polymers. Examples of the polymers include poly(meth)acrylic acid esters, poly(sodium meth)acrylic acid, and crosslinked products thereof. Examples of the crosslinked products include water-absorbent resins and slightly crosslinked resins (commonly called carbomers). The (meth)acrylic acid obtained by the method for producing (meth)acrylic acid of the present invention is useful as a raw material for synthesizing (meth)acrylic acid derivatives such as (meth)acrylic acid esters; water-absorbing resins such as poly(meth)acrylic acid and sodium poly(meth)acrylate; etc.

[0051] The (meth)acrylic acid and hydrophilic resin produced by the present invention, as well as the various (meth)acrylic acid derivatives described above, are of high quality and can be suitably used in a wide range of applications, including building materials, optical applications, automobiles, detergents, disposable diapers, sanitary materials, food applications, and pharmaceuticals, and can be used as adhesives, pressure-sensitive adhesives, paints, coating agents, inks, superabsorbent resins, thickeners, water-retaining materials, vibration-damping materials, acrylic rubbers, acrylic fibers, acrylic resins, molding resins, electronics materials, reactive diluents, and pharmaceutical raw materials. (Meth)acrylic acid derivatives such as (meth)acrylic acid esters are used in a wide range of applications, including building materials and optical applications. Other applications include printing ink solvents, printing ink compositions and ink cleaners for printing machines, plastic additives, antistatic agents, biodiesel, fuels and their additives, electrical insulating oils, lubricating oils, spilled oil recovery agents, industrial cleaners, paint solvents, urethane viscosity reducers, adhesive solvents, solvents for reactions, separation, purification, and extraction, and solvents for the textile industry.

[0052] The above-mentioned water-absorbent resins are water-swellable, water-insoluble polymer gelling agents, and are used for a variety of purposes, including absorbent articles such as disposable diapers and sanitary napkins, soil water retention agents for agricultural and horticultural use, and industrial water-stopping agents. Although many types of monomers and water-absorbent polymers are used as raw materials for the water-absorbent resins, polyacrylic acid (salt)-based water-absorbent resins using acrylic acid and / or its salts (hereinafter referred to as "acrylic acid (salt)") as a monomer are most commonly used from the viewpoint of the water-absorbing performance and production costs of the water-absorbent resins. The use of the water-absorbent resin is not particularly limited, but preferred examples include absorbent materials for absorbent articles such as disposable diapers (for infants and adults), sanitary napkins, and incontinence pads. In particular, the water-absorbent resin can be used as an absorbent material for high-concentration disposable diapers. The absorbent body may contain an absorbent material such as pulp fiber in addition to the water-absorbent resin of the present invention. In this case, the amount of the water-absorbent resin in the absorbent body (hereinafter referred to as "core concentration") is preferably 30% by weight to 100% by weight, more preferably 40% by weight to 100% by weight, even more preferably 50% by weight to 100% by weight, still more preferably 60% by weight to 100% by weight, particularly preferably 70% by weight to 100% by weight, and most preferably 75% by weight to 95% by weight.

[0053] Examples of other absorbent articles include drip absorbers, freshness-preserving materials, portable toilets for disasters, pet sheets, cat litter, etc. Other uses of water-absorbent resins include soil water retention agents, seedling raising sheets, seed coating materials, anti-condensation sheets, disposable warmers, cooling bandanas, ice packs, medical waste liquid solidifying agents, surplus soil solidifying materials, water-damage preventing waste liquid gelling agents, water-absorbing sandbags, compresses, thickeners for cosmetics, water-stopping materials for communication cables of electric and electronic materials, gasket packing, sustained-release agents for fertilizers, various sustained-release agents (space disinfectants, air fresheners, etc.), wound protection dressings, anti-condensation building materials, oil moisture removers, paints, adhesives, anti-blocking agents, light diffusing agents, matting agents, additives for resins such as additives for decorative panels, additives for artificial marble, and additives for toner.

[0054] The method for producing (meth)acrylic acid according to the present invention can naturally be incorporated into the production of (meth)acrylic acid derivatives and water-absorbent resins, and such methods for producing water-absorbent resins also constitute the present invention. That is, the present invention also provides a method for producing a water-absorbent resin using 3-hydroxycarboxylic acid as a raw material, the method comprising: a reaction step of reacting a raw material containing 3-hydroxycarboxylic acid and / or a condensate thereof to obtain (meth)acrylic acid; and a polymerization step of polymerizing a monomer component containing the (meth)acrylic acid to produce a water-absorbent resin, wherein the main product among the products obtained in the reaction step is (meth)acrylic acid. Here, "the main product in the product obtained in the reaction step is (meth)acrylic acid" means that the proportion of (meth)acrylic acid produced is 50% by mass or more relative to the total mass of the product obtained in the reaction step. The proportion of (meth)acrylic acid in the product obtained in the reaction step is more preferably 65% ​​by mass or more, and even more preferably 80% by mass or more.

[0055] The method for producing a water absorbent resin of the present invention includes a step of polymerizing a monomer component containing (meth)acrylic acid obtained from 3-hydroxycarboxylic acid and / or a condensate thereof, and when the non-petroleum-based acrylic acid alone does not meet the required production amount of the water absorbent resin due to the production amount (supply amount) or trace amount of components, petroleum-based (meth)acrylic acid may be used in combination as necessary. When non-petroleum-based (meth)acrylic acid and petroleum-based (meth)acrylic acid are used in combination, the mass ratio is determined within a range of 0 / 100 to 100 / 0, preferably 5 / 95 to 100 / 0, and more preferably 10 / 90 to 100 / 0.

[0056] 3. Definitions [1] Water absorbent resin, water absorbent resin powder, water absorbent resin particles, In the present invention, the term "water-absorbent resin" refers to a water-swellable, water-insoluble polymer gelling agent. "Water-swellable" means that the CRC defined by ERT441.2-02 is 5 g / g or more, and "water-insoluble" means that the Ext defined by ERT470.2-02 is 50 wt% or less. The above-mentioned "water-absorbent resin" is preferably a hydrophilic cross-linked polymer obtained by cross-linking polymerizing an unsaturated monomer having a carboxyl group, but the entire amount (100% by weight) does not need to be a cross-linked polymer, and additives and the like can be contained within a range that satisfies the above-mentioned performance (CRC, Ext). Furthermore, the above-mentioned "water-absorbent resin" may refer to "a polymer crosslinked only inside (i.e., a polymer in which the crosslink density inside and on the surface are substantially the same)" or "a polymer crosslinked both inside and on the surface (i.e., a polymer in which the crosslink density on the surface is relatively high compared to the crosslink density inside)". In this specification, for convenience, a polymer crosslinked only inside may be referred to as "water-absorbent resin powder", and a polymer crosslinked both inside and on the surface may be referred to as "water-absorbent resin particles".

[0057] [2] Polyacrylic acid (salt)-based water-absorbing resin The water-absorbent resin obtained by the method for producing a water-absorbent resin of the present invention is a polyacrylic acid (salt)-based water-absorbent resin. In the present invention, the "polyacrylic acid (salt)-based water-absorbent resin" means a water-absorbent resin made from acrylic acid and / or its salt (hereinafter referred to as "acrylic acid (salt)"). In other words, the polyacrylic acid (salt)-based water-absorbent resin is a water-absorbent resin having structural units derived from acrylic acid (salt) in the polymer and having a graft component as an optional component. Specifically, the polyacrylic acid (salt)-based water-absorbing resin is a water-absorbing resin that contains preferably 50 mol % to 100 mol %, more preferably 70 mol % to 100 mol %, even more preferably 90 mol % to 100 mol %, and particularly preferably substantially 100 mol % of acrylic acid (salt) relative to the total monomers involved in the polymerization reaction (excluding the internal crosslinking agent).

[0058] [3] EDANA and ERT "EDANA" is an abbreviation for European Disposables and Nonwovens Associations, and "ERT" is an abbreviation for EDANA Recommended Test Methods. ERT is a European standard (almost a global standard) for methods of measuring physical properties of water-absorbent resins. In the present invention, unless otherwise specified, the physical properties of the water-absorbent resin are measured in accordance with the original ERT (revised in 2002 / publicly known document).

[0059] [3-1] CRC (ERT441.2-02) "CRC" (Centrifuge Retention Capacity) is an abbreviation for Centrifuge Retention Capacity, and means the water absorption capacity of a water-absorbent resin under no pressure. Specifically, 0.2 g of the water-absorbent resin is placed in a nonwoven bag, and then immersed in a large excess of 0.9 wt % sodium chloride aqueous solution for 30 minutes to allow the water-absorbent resin to freely swell, and then the water-absorbent resin is reacted using a centrifuge (250 G), and the water absorption capacity (unit: g / g) is measured.

[0060] [3-2] Absorption under pressure (AAP) (ERT442.2-02) "AAP" is an abbreviation for Absorption Against Pressure, and refers to the water absorption capacity of a water-absorbent resin under pressure. Specifically, it is the water absorption capacity (unit: g / g) after 0.9 g of water-absorbent resin is swelled in a large excess of 0.9 wt % sodium chloride aqueous solution for 1 hour under a load of 2.06 kPa (21 g / cm2, 0.3 psi). ERT442.2-02 uses the term "Asorption Under Pressure," but the meaning is essentially the same. In the present invention, the load condition is changed to 4.83 kPa (49 g / cm2, 0.7 psi) for measurement. Although "AAP" is used in this specification, it is always the water absorption capacity measured under a load of 4.83 kPa.

[0061] [3-3] Soluble content (ERT470.2-02) The term "soluble content" refers to the water-soluble content (amount of water-soluble components) of a water-absorbent resin. Specifically, it refers to the amount of dissolved polymer (unit: wt%) after 1.0 g of water-absorbent resin is placed in 200 ml of a 0.9 wt % sodium chloride aqueous solution and stirred at 500 rpm for 16 hours. The amount of dissolved polymer is measured by pH titration.

[0062] [3-4] Residual Monomer (ERT430.2-02) The residual monomer means an unreacted monomer component remaining in a water absorbent resin. Specifically, the residual monomer is the amount of the residual monomer component extracted after adding 1.0 g of a water absorbent resin to 200 ml of a 0.9 wt % aqueous sodium chloride solution and stirring at 500 rpm for 1 hour, and is measured using high performance liquid chromatography.

[0063] [3-5] Vortex (JIS K7224 (1996)) Vortex is a method for evaluating the absorption rate of a water-absorbent resin. Specifically, 2.0 g of a water-absorbent resin is added to 50 g of a 0.9 mass % sodium chloride aqueous solution stirred at 600 rpm with a stirrer tip, and the time (unit: seconds) until the stirrer tip is covered with the liquid is measured.

[0064] [3-6] Particle size distribution (ERT480.2-02) The particle size distribution means the particle size distribution of a water absorbent resin measured by sieve classification. Specifically, using a set of sieves with a diameter of 200 mm, sieve openings of 850 μm, 600 μm, 300 μm, 150 μm, and 45 μm, and a tray, 100.0 g of a water absorbent resin is classified for 10 minutes with a sieve shaker, and the amount of the water absorbent resin remaining on each sieve mesh and in the tray is measured, and the particle size distribution is calculated (unit: weight %).

[0065] [4] Other In this specification, "X to Y" indicating a range means "greater than or equal to X and less than or equal to Y." Furthermore, the unit of weight, "t (ton)," means "metric ton." Unless otherwise noted, "ppm" means "ppm by weight," and "weight" and "mass," "weight %" and "mass %, "parts by weight" and "parts by mass" are treated as synonyms. Furthermore, "acid (salt)" means "acid and / or its salt," and "(meth)acrylic" means "acrylic and / or methacrylic." [Example]

[0066] The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention should not be construed as being limited to these examples and comparative examples. Examples obtained by appropriately combining the technical means disclosed in each example are also included within the scope of the present invention. Unless otherwise noted, electrical equipment used in the examples and comparative examples, as well as for measuring the physical properties of the water-absorbing agent, uses a 200V or 100V power supply. Unless otherwise noted, the physical properties of the water-absorbing agent were measured under conditions of room temperature (20°C to 25°C) and a relative humidity of 50±5% RH. For convenience, "liter" may be expressed as "l" or "L," and "weight %" as "wt%" or "%."

[0067] <Liquid chromatography analysis conditions> Liquid chromatography analyses in the following Preparation Examples, Examples, and Comparative Examples were carried out under the following conditions. Columns used: Inertsil ODS-4 (GL Sciences Inc.) x 2 Eluent: acetonitrile / water / phosphoric acid / potassium dihydrogen phosphate = 35 / 64 / 0.7 / 0.3 (weight ratio) Detector: UV 205nm and 220nm Column temperature: 50℃

[0068] The yield of acrylic acid in the following examples was determined according to the following definition. Yield of acrylic acid (mol %)=100×(moles of acrylic acid produced) / (moles of 3-hydroxycarboxylic acid units fed) Number of moles of 3-hydroxycarboxylic acid units = (number of moles of 3-hydroxycarboxylic acid + number of moles of dimer × 2 + number of moles of trimer × 3 + number of moles of tetramer × 4 + number of moles of pentamer × 5 + number of moles of hexamer × 6 + number of moles of heptamer × 7 + number of moles of octamer × 8 + number of moles of nonamer × 9 + number of moles of 10amer × 10 + number of moles of 11amer × 11 + number of moles of 12amer × 12 + number of moles of 13amer × 13 + number of moles of 14amer × 14 + number of moles of 15amer × 15 + number of moles of 16amer × 16)

[0069] <Physical properties of water-absorbent resin> Hereinafter, methods for measuring various physical properties of the water-absorbent resin according to the present invention will be described. (a) CRC The CRC (centrifuge retention capacity) of the water-absorbent resin according to the present invention was measured in accordance with the EDANA method (ERT441.2-02). (b) Absorption under pressure (AAP) The absorbency under load (AAP) of the water-absorbent resin according to the present invention was measured in accordance with the EDANA method (ERT442.2-02). In the present invention, the load condition was changed to 4.83 kPa (49 g / cm, 0.7 psi) for the measurement. Although "AAP" is used in this specification, it is always the absorbency measured under a load of 4.83 kPa. (c) Soluble content The extractable content of the water-absorbent resin according to the present invention was measured in accordance with the EDANA method (ERT470.2-02). (d) Residual Monomer The residual monomer amount of the water absorbent resin according to the present invention was measured in accordance with the EDANA method (ERT430.2-02). Specifically, 1.0 g of the water absorbent resin was added to 200 ml of a 0.9 mass % sodium chloride aqueous solution, stirred at 500 rpm for 1 hour using a 35 mm long stirrer tip, and then filtered, and the amount of the monomer eluted in the filtrate was measured by high performance liquid chromatography. The residual monomer amount is expressed as a mass ratio relative to the water absorbent resin (unit: ppm). (e) Vortex The vortex of the water-absorbent resin according to the present invention was measured according to the following procedure. First, 0.02 parts by mass of a food additive, edible blue No. 1 (brilliant blue), was added to 1,000 parts by mass of a 0.9% by mass aqueous solution of sodium chloride prepared in advance, and the liquid temperature was then adjusted to 30°C. Subsequently, 50 ml of the 0.9% by mass aqueous solution of sodium chloride was measured and placed in a 100 ml beaker, and 2.0 g of the water-absorbent resin was added all at once while stirring at 600 rpm using a cylindrical stirrer tip 40 mm long and 8 mm in diameter at a cross section perpendicular to the length direction and a magnetic stirrer. The time until the water-absorbent resin absorbed the saline solution and covered the stirrer tip was measured as vortex (unit: seconds). (f) Particle size distribution The particle size distribution of the water absorbent resin according to the present invention was measured in accordance with the EDANA method (ERT480.2-02). Specifically, using a set of sieves with a diameter of 200 mm, sieve openings of 850 μm, 600 μm, 300 μm, 150 μm, and 45 μm, and a tray, 100.0 g of the water absorbent resin is classified for 10 minutes with a sieve shaker, and the amount of the water absorbent resin remaining on each sieve mesh and in the tray is measured, and the particle size distribution is calculated (unit: weight %).

[0070] Examples 1 to 15, Comparative Examples 1 to 4 The apparatus shown in Figure 1 was assembled, and the specified amount of 95 wt% 3-hydroxypropionic acid (3HP) aqueous solution and the specified amount of base shown in Table 1 were added to the reactor. The amount of base was (moles of potassium added to the reactor / moles of 3-hydroxycarboxylic acids added to the reactor). After reducing the pressure in the system to the specified pressure shown in Table 1, the temperature was raised, and the 3-hydroxypropionic acid aqueous solution was fed at the specified rate at the specified reaction temperature shown in Table 1. Air was also fed into the gas phase of the reactor at a rate of 3 L per hour. A mixed gas of the product and air was extracted from the reactor through a gas extraction tube, and the gas was condensed and collected using a condenser. The reaction was continued until a certain amount of liquid remained in the reactor and the balance between the raw materials and the product stabilized. The collected liquid obtained at the stable state was analyzed by liquid chromatography to confirm the amount of acrylic acid produced. Furthermore, a portion of the reaction liquid in the reactor was extracted and analyzed by liquid chromatography to confirm the average degree of condensation and neutralization of the 3-hydroxypropionic acid condensate in the reaction liquid. In Table 1, the space-time yield is the value obtained by dividing the amount of acrylic acid extracted as a gas per hour by the amount of liquid in the reactor, and the neutralization rate is (number of moles of potassium in the reactor during the reaction / number of moles of carboxylic acid in the reactor during the reaction). The average degree of condensation of 3HP is (the number of moles of 3-hydroxycarboxylic acid units in the reactor during the reaction / the number of moles of 3-hydroxycarboxylic acids in the reactor during the reaction). Number of moles of 3-hydroxycarboxylic acid units = (number of moles of 3-hydroxycarboxylic acid + number of moles of dimer × 2 + number of moles of trimer × 3 + number of moles of tetramer × 4 + number of moles of pentamer × 5 + number of moles of hexamer × 6 + number of moles of heptamer × 7 + number of moles of octamer × 8 + number of moles of nonamer × 9 + number of moles of 10amer × 10 + number of moles of 11amer × 11 + number of moles of 12amer × 12 + number of moles of 13amer × 13 + number of moles of 14amer × 14 + number of moles of 15amer × 15 + number of moles of 16amer × 16) Number of moles of 3-hydroxycarboxylic acids = (number of moles of 3-hydroxycarboxylic acid + number of moles of dimer + number of moles of trimer + number of moles of tetramer + number of moles of pentamer + number of moles of hexamer + number of moles of heptamer + number of moles of octamer + number of moles of nonamer + number of moles of 10amer + number of moles of 11amer + number of moles of 12amer + number of moles of 13amer + number of moles of 14amer + number of moles of 15amer + number of moles of 16amer) The reaction continuity was evaluated as "good" when continuous operation was possible, and as "-" when gel-like acrylic acid polymer was produced and the reaction liquid solidified, making it impossible to continue operation.

[0071] [Table 1]

[0072] Examples 16 to 19, Comparative Example 5 The reaction was carried out in the same manner as in Example 1, except that the amount of base, etc. was changed as shown in Table 2. The viscosity of the reaction solution was also measured. The results are shown in Table 2.

[0073] [Table 2]

[0074] From the results in Table 1, by using the manufacturing method of the present invention, it is possible to achieve a reaction temperature of 100 kg / h m even at a relatively low temperature of 130 to 150°C. 3 It was confirmed that the above space-time yield could be achieved. The results in Table 2 confirm that by adjusting the amount of base added, it is possible to significantly reduce the viscosity of the reaction solution while minimizing the decrease in space-time yield. From these results, it was confirmed that the production method of the present invention enables the production of (meth)acrylic acid with high productivity and stably for a long period of time while suppressing the increase in viscosity of the reaction solution.

[0075] Example 20 A 3-L jacketed glass vessel equipped with a distillation column with three perforated trays and no downcomer was used. 1240 g of 95 wt% 3-hydroxypropionic acid aqueous solution and 90 g of potassium hydroxide were added to the reactor. 2 g of iron acetate was added as a polymerization inhibitor. The system was depressurized to 20 kPa and heated to 150 °C. An 85 wt% 3-hydroxypropionic acid aqueous solution was added at a rate of 600 g / h. The jacket was heated with heat transfer oil. Air was also supplied to the vapor phase of the reactor at a rate of 3 L / h. The distillate was condensed in its entirety in a condenser. 300 g / h was recycled to the distillation column as reflux, and 600 g / h was collected as product. The reaction proceeded for a total of 16 hours, yielding 8.7 kg of aqueous acrylic acid. The collected solution was analyzed by liquid chromatography to determine the amount of acrylic acid produced and the space-time yield. The reaction solution was extracted from the reactor at a rate of 24 g / h and analyzed by liquid chromatography to determine the neutralization rate (moles of potassium in the reaction solution / moles of carboxylic acid in the reaction solution). The viscosity of the reaction solution was also measured. The results are shown in Table 3.

[0076] [Table 3]

[0077] Preparation Example 1 The aqueous acrylic acid solution obtained in Example 20 was supplied to an azeotropic dehydration column, and water and low-boiling impurities were distilled off using toluene as the azeotropic solvent, yielding crude acrylic acid. This crude acrylic acid was supplied to the bottom of a high-boiling impurity separation column having 27 perforated trays with weirs, and distilled at a reflux ratio of 1 to remove high-boiling impurities such as a dimer of acrylic acid (acrylic acid dimer), yielding crude acrylic acid. Hydrazine hydrate was added to the crude acrylic acid as an aldehyde treating agent, and the mixture was distilled in a simple distillation apparatus to obtain purified acrylic acid.

[0078] Example 21 An aqueous solution was prepared by adding 439.4 parts by weight of the purified acrylic acid obtained in Preparation Example 1, 181.1 parts by weight of a 48.5 wt% aqueous sodium hydroxide solution, 1.9 parts by weight of polyethylene glycol diacrylate (average number of polyethylene glycol units (average n number): 9), 1.35 parts by weight of a 2.0 wt% aqueous solution of trisodium diethylenetriaminepentaacetate, and 351.7 parts by weight of deionized water to a 2 L polypropylene container and mixing them. The deionized water had been preheated to 40°C. Next, while stirring the aqueous solution, 196.1 parts by weight of a 48.5 wt % aqueous sodium hydroxide solution was added to the aqueous solution over a period of about 30 seconds in an open-to-air state, and mixed to prepare an aqueous monomer solution. Note that the temperature of the aqueous monomer solution rose to about 80°C due to the heat of neutralization and heat of dissolution generated during the mixing process. Thereafter, when the temperature of the aqueous monomer solution reached 78°C, 28.45 parts by weight of a 3.0 wt % aqueous solution of sodium persulfate was added as a polymerization initiator, and the mixture was stirred for about 5 seconds to form a reaction liquid. Next, the reaction solution was poured into a stainless steel bat-shaped container in an open-air state. The bat-shaped container had a bottom size of 200 mm × 260 mm, an upper size of 460 mm × 560 mm, and a height of 140 mm, and the cross section of the central part was trapezoidal. A silicone sheet was attached to the inner surface. Before pouring the reaction solution into the bat-shaped container, it was placed on a hot plate heated to 50°C to preheat it. After the reaction liquid was poured into the bat-shaped container, the polymerization reaction started within 1 minute. The reaction liquid expanded and foamed upward in all directions while generating steam, and then shrunk to a size slightly larger than the bottom of the bat-shaped container. The polymerization reaction (expansion and contraction) was completed within about 1 minute. A hydrogel-like cross-linked polymer (hereinafter referred to as "hydrogel") was obtained through the polymerization reaction. Next, the hydrogel was cut into pieces of an appropriate size, and then fed into a screw extruder to crush the gel, thereby obtaining a particulate hydrogel having a particle size of 0.1 to 2 mm. Next, the particulate hydrogel was spread on a wire mesh with an opening of 300 μm (50 mesh) and placed in a hot air dryer. Thereafter, the particulate hydrogel was dried by passing hot air at 190° C. for 30 minutes to obtain a dried polymer. Subsequently, the dried polymer was put into a roll mill and pulverized, and then classified using two types of JIS standard sieves with openings of 850 μm and 150 μm to obtain an irregularly pulverized water absorbent resin powder (1). Next, 3.5 parts by weight of a surface cross-linking 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 was added to 100 parts by weight of the water absorbent resin powder (1) and mixed until uniform, thereby obtaining a humidified mixture (1). Subsequently, the humidified mixture (1) was heat-treated at 200°C for 40 minutes, cooled to 60°C, and passed through a sieve with a mesh size of 850 μm. Particles that did not pass through the 850 μm mesh size were crushed by lightly pressing them on a mesh with a spatula and passed through, and particles that were not completely crushed were removed. In this way, surface cross-linked water absorbent resin particles (1) in an irregular crushed shape were obtained. Tables 4 and 5 show the physical properties of the water absorbent resin powder (1) and the water absorbent resin particles (1).

[0079] [Table 4]

[0080] [Table 5]

Claims

1. A method for producing (meth)acrylic acid, comprising a step of reacting a raw material containing a 3-hydroxycarboxylic acid and / or a condensate thereof to obtain (meth)acrylic acid, The production method includes a step of carrying out a reaction in a reaction solution containing a 3-hydroxycarboxylic acid and / or a condensate thereof at a neutralization rate of 1 to 50 mol % of carboxylic acid. A method for producing (meth)acrylic acid, comprising:

2. 2. The method for producing (meth)acrylic acid according to claim 1, wherein the reaction step is carried out by adding an alkali metal compound.

3. 3. The method for producing (meth)acrylic acid according to claim 1, wherein the average condensation degree of 3-hydroxycarboxylic acid in the reaction liquid is 3 or less.

4. 4. The method for producing (meth)acrylic acid according to claim 1, wherein the temperature of the reaction solution is 130 to 250°C.

5. 5. The method for producing (meth)acrylic acid according to claim 1, wherein the pressure of the reaction solution is normal pressure or reduced pressure.

6. A method for producing a hydrophilic resin using a raw material containing a 3-hydroxycarboxylic acid and / or a condensate thereof, comprising: The production method includes a reaction step of producing (meth)acrylic acid by adjusting the neutralization rate of carboxylic acid in a reaction liquid containing a 3-hydroxycarboxylic acid and / or a condensate thereof to 1 to 50 mol %; a polymerization step of polymerizing the monomer component containing (meth)acrylic acid obtained in the reaction step to produce a hydrophilic resin, A method for producing a hydrophilic resin, wherein the main product obtained in the reaction step is (meth)acrylic acid.

7. 7. The method for producing a hydrophilic resin according to claim 6, wherein the hydrophilic resin is a water-absorbent resin.

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