Method for producing isolated lignin-containing material

Abstract

To provide a method for producing depolymerized isolated lignin having high solubility.SOLUTION: A method for producing isolated lignin-containing material is provided, comprising: (a) decreasing the pH of black liquor obtained by performing alkaline cooking on wood raw material, thereby forming a precipitate, and dewatering the precipitate to obtain dewatered cake of the precipitate; (b) adding alkaline water to the dewatered cake to form an alkaline solution including the dewatered cake; (c) heating the alkali solution at 120°C to 190°C to form a heated product; and (d) decreasing the pH of the heated product to generate isolated lignin-containing material, and thus depolymerized isolated lignin-containing material is obtained.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to a method for producing an isolated lignin-containing material and the isolated lignin-containing material produced by the method. [Background technology]

[0002] Lignin is an aromatic polymer that is found in abundance in nature and is contained in plant cell walls, etc. Lignin has been used primarily as fuel for boilers, etc., in the form of the main component of black liquor discharged from the paper pulp manufacturing process, but broader application development is currently underway, and expectations are growing for it as a renewable resource.

[0003] Lignin can be obtained by separating it from black liquor, which is discharged after the cooking process in the paper pulp manufacturing process, removing plant fibers. For example, in the sulfite cooking method, a mixture of acidic sulfite and sulfurous acid is added, and the wood is cooked at 130 to 145°C to elute the lignin in the wood as lignin sulfonate. In the kraft cooking method, which is a type of alkaline cooking method, chemicals mainly composed of caustic soda (NaOH) and sodium sulfide (Na2S) are added, and the wood is cooked at about 150 to 170°C to elute as kraft lignin. In the soda cooking method, which is also a type of alkaline cooking method, lignin is eluted by adding an alkaline aqueous solution such as caustic soda.

[0004] Lignin is expected to be used as a raw material for chemicals, resins, rubber, etc. For this reason, low molecular weight lignin is required. In order to reduce the average molecular weight of lignin, a method has been disclosed in which a black liquor flow is heat-treated at 150 to 200 ° C. and lignin is precipitated from the heat-treated black liquor (e.g., Patent Document 1). In addition, in order to obtain a highly reactive lignin product, a method has been disclosed in which black liquor is heat-treated at 200 to 300 ° C. in a state of pH 12 or more, and then the pH is lowered to recover the lignin as a precipitate (e.g., Patent Document 2). In addition, a method has been disclosed in which lignin can be separated using a small amount of acid so as to obtain a high-purity lignin product that can be used in the production of fuel or chemicals (e.g., Patent Document 3). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5894594 [Patent Document 2] WO2018 / 115592 [Patent Document 3] Special Publication No. 2008-513549 Summary of the Invention [Problem to be solved by the invention]

[0006] When a lignin product is provided as a raw material for the production of chemical products, it is desirable that the lignin product is low molecular weight. In addition, it is desirable that the lignin product provided as such a raw material for production has high solubility in a solvent. However, the isolated lignin-containing material separated from the black liquor does not necessarily have sufficient low molecular weight or solubility, and improvements have been required. In particular, no improvements focusing on solubility have been made so far, and in the conventional method of producing an isolated lignin-containing material from black liquor obtained by kraft cooking of wood chips, the solubility of the isolated lignin-containing material obtained, for example, when acetone is used as a solvent, is about 60% for the lignin-containing material derived from coniferous trees and about 70% for the lignin-containing material derived from broadleaf trees.

[0007] In view of the above circumstances, one of the problems to be solved is to provide a method for obtaining an isolated lignin-containing material with sufficiently low molecular weight. Another problem to be solved is to provide a method capable of improving the solubility of an isolated lignin-containing material. Another problem to be solved is to provide a method for obtaining an isolated lignin-containing material having a high solubility. [Means for solving the problem]

[0008] The invention presented in this disclosure can be understood from various aspects, and includes, for example, the following means for solving the problems. [1] A method for producing an isolated lignin-containing material, comprising the following steps (a) to (d): (a) reducing the pH of black liquor obtained by alkaline cooking of a wood raw material to generate a precipitate, and dehydrating the precipitate to obtain a dehydrated cake of the precipitate; (b) adding alkaline water to the dehydrated cake to generate an alkaline solution containing the dehydrated cake; (c) heating the alkaline liquid at 120° C. or more and 190° C. or less to generate a heated product; (d) reducing the pH of the heated product to produce an isolated lignin-containing product; A method comprising: [2] The method according to [1] above, wherein in (a), carbon dioxide is added to the black liquor to adjust the pH to 7 or more and 11 or less, and the precipitate is produced. [3] The method according to [1] or [2] above, wherein in (a), the dehydrated cake is dehydrated so that the solid content concentration of the dehydrated cake is 10 to 60% by weight. [4] In the step (a), carbon dioxide is added to the black liquor to adjust the pH to 7 or more and 11 or less, a first precipitate is produced, the first precipitate is dehydrated to obtain a first dehydrated cake, the first dehydrated cake is suspended in an aqueous solution containing an inorganic acid, the pH is adjusted to 1 or more and 7 or less, a second precipitate is produced, and the second precipitate is dehydrated to obtain the second dehydrated cake; The method according to [1] above, wherein in (b), the second dehydrated cake is used as the dehydrated cake. [5] The method according to [4] above, wherein in (a), the second dehydrated cake is dehydrated so that the solid content concentration of the second dehydrated cake is 10 to 60% by weight. [6] The method according to any one of the above [1] to [5], wherein the alkaline solution produced in (b) has a pH of 12 or higher. [7] The method according to any one of the above [1] to [6], wherein in (c), the heating time is 1 to 180 minutes. [8] The method according to any one of [1] to [7] above, wherein in (d), an inorganic acid is added to the heated material to lower the pH to 1 or more and 7 or less. [9] The method according to any one of [1] to [8] above, wherein the wood raw material is coniferous wood.

[10] The method according to any one of the above [1] to [8], wherein the wood raw material is hardwood wood.

[11] An isolated lignin-containing material obtained by the method according to any one of [1] to [8] above.

[12] The wood raw material is coniferous wood, The weight average molecular weight of the isolated lignin-containing material is 1500 to 6000, and The isolated lignin-containing material has an acetone solubilization rate of 75% or more. The isolated lignin-containing material described in

[11] above.

[13] The black liquor obtained by alkali cooking of the wood raw material is black liquor obtained by kraft cooking of hardwood wood, The weight average molecular weight of the isolated lignin-containing material is 1500 to 3500, and The acetone solubilization rate of the isolated lignin-containing material is 80% or more. The isolated lignin-containing material described in

[11] above.

[14] The black liquor obtained by alkali cooking the wood raw material is black liquor obtained by soda cooking hardwood wood, The weight average molecular weight of the isolated lignin-containing material is 1500 to 2700, and The acetone solubilization rate of the isolated lignin-containing material is 93% or more. The isolated lignin-containing material described in

[11] above. Effect of the Invention

[0009] According to one aspect of the present invention, an isolated lignin-containing material with highly reduced molecular weight can be obtained. According to one aspect of the present invention, a method for improving the solubility of an isolated lignin-containing material can be provided. According to one aspect of the present invention, an isolated lignin-containing material having high solubility can be obtained. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described. In this disclosure, unless otherwise specified, the expression "AA to BB" in relation to a numerical range means "AA or more and BB or less" (here, "AA" and "BB" indicate arbitrary numerical values). In addition, the units of the lower and upper limits are the same as the units immediately following the latter (i.e., "BB" here) unless otherwise specified. In addition, in this disclosure, the expression "X and / or Y" means both X and Y, or either one of them.

[0011] In the present disclosure, the term "isolated lignin" is a term that is distinguished from natural lignin. Natural lignin exists in a plant cell wall in a tightly complexed state with polysaccharides such as cellulose and hemicellulose, and it is still difficult to isolate it without some kind of chemical structure modification. That is, in the present disclosure, "isolated lignin" refers to lignin that has been isolated through physical or chemical treatment, as distinguished from natural lignin. Isolated lignin is also called industrial lignin.

[0012] In the present disclosure, the term "isolated lignin-containing material" refers to a material containing isolated lignin. The isolated lignin-containing material may be a mixture containing various organic compounds obtained by decomposing a plant material containing lignin and isolating natural lignin. The components of the isolated lignin-containing material may be, for example, a material containing one or more of aromatic compounds derived from natural lignin, organic compounds that are precursors of lignin and are generally called monolignols, organic compounds present in the biosynthetic pathway of lignin, compounds that have been chemically modified or functional group converted during the decomposition of a plant material containing lignin, condensates thereof, and complex compounds formed by the bonding of a plurality of these compounds.

[0013] Examples of monolignols and their analogs include p-coumaric alcohol, coniferyl alcohol, sinapyl alcohol, p-coumaric aldehyde, coniferyl aldehyde, sinapyl aldehyde, p-coumaric acid, ferulic acid, sinapic acid, caffeyl alcohol, caffeyl aldehyde, caffeic acid, cinnamic acid, vanillyl alcohol, 5-formyl vanillic acid, 5-formyl vanillin, 5-hydroxymethyl vanillin, 5-carboxyvanillin, p-hydroxybenzaldehyde, p-hydroxybenzoic acid, acetovanillone, vanillin, vanillic acid, syringaldehyde, syringic acid, and guaiacol.

[0014] In one embodiment of the method for producing isolated lignin of the present invention, the following processes (a), (b), (c), and (d) are carried out. (a) Lowering the pH of black liquor obtained by alkaline cooking of a wood raw material to generate a precipitate, and dehydrating the precipitate to obtain a dehydrated cake of the precipitate. (b) adding alkaline water to the dehydrated cake to generate an alkaline solution containing the dehydrated cake. (c) heating the alkaline liquid at 120°C or more and 190°C or less to produce a heated product. (d) reducing the pH of the heated product to produce an isolated lignin-containing product. Hereinafter, the above-mentioned embodiments of each of the treatments (a) to (d) will be described as steps in the manufacturing process.

[0015] <Step (a): Producing (first) precipitate and dehydrated cake> The black liquor used in step (a) is obtained by alkaline digestion of a wood raw material.

[0016] As the wood raw material, preferably, wood chips etc. are used. The wood chips may be in a form that is usually used in paper pulp production etc. For example, the above-mentioned wood may be subjected to a process of physically reducing the wood into small pieces such as cutting, shredding, breaking, crushing, etc., and then may be prepared as it is or by forming into a desired shape.

[0017] As the raw material wood, either broad-leaved or coniferous trees can be used. Examples of broad-leaved trees include beech, chinaberry, white birch, poplar, eucalyptus, acacia, oak, sugar maple, angelica tree, elm, paulownia, magnolia, willow, ash, phillyraeoides, oak, sawtooth oak, horse chestnut, zelkova, beech, dogwood, and green ash. Examples of coniferous trees include cedar, spruce, larch, black pine, Japanese larches, Japanese larches, Himekomatsu, yew, Japanese jew's yew, fir, Japanese spruce, Japanese bead, fir, Japanese yew, Japanese spruce, Asunaro, Japanese cypress, Japanese hemlock, Japanese cypress, Japanese yew, Japanese yew, spruce, yellow cedar, Lawson cypress, Douglas fir, Sitka spruce, Radiata pine, Eastern spruce, Eastern white pine, Western larch, Western fir, Western hemlock, and tamarack.

[0018] The molecular weight of lignin contained in black liquor obtained from coniferous trees tends to be higher than that contained in black liquor obtained from broadleaf trees. According to one embodiment of the present invention, even when black liquor obtained from coniferous trees is used, the molecular weight of isolated lignin can be significantly reduced. Therefore, using wood chips derived from coniferous trees can be an advantageous embodiment of the present invention.

[0019] The black liquor used in one embodiment of the present invention is obtained by alkaline cooking of wood chips. There are no particular limitations on the alkaline cooking as long as it is a cooking method that uses an alkaline chemical as the cooking liquor, and representative examples include kraft cooking and soda cooking. Generally, in kraft cooking, caustic soda (NaOH) and sodium sulfide (Na2S) are used as the cooking liquor. In soda cooking, caustic soda is basically used as the cooking liquor, and sulfur components such as sodium sulfide are not mixed. A cooking aid such as a quinone compound may be added to the cooking liquor.

[0020] In step (a), the pH of the black liquor obtained after alkaline cooking is lowered to obtain a precipitate. The pH of the black liquor obtained by alkaline cooking is usually about pH 12 to 14, depending on the specific conditions of the alkaline cooking. In step (a), the pH of the black liquor can be preferably adjusted to 11 or less. By setting the pH of the black liquor to the upper limit as described above, for example, 11 or less, insoluble matter of lignin can be sufficiently generated. On the other hand, if the pH of the black liquor is excessively low, for example, less than 1, the amount of acid used increases, which increases the amount of alkali used in step (b) and the amount of salt generated during neutralization. Therefore, it is preferable to avoid such an excessively low pH from the viewpoint of a practical production method.

[0021] The pH of the black liquor can be lowered by adding an acid and / or carbon dioxide to form a suspension. The acid used may be an inorganic acid or an organic acid. Examples of inorganic acids include sulfuric acid, sulfurous acid, hydrochloric acid, nitric acid, nitrous acid, phosphoric acid, and carbonic acid, and among these, sulfuric acid is preferred. Residual acid discharged from a chlorine dioxide generator may also be used. Examples of organic acids include acetic acid, lactic acid, oxalic acid, citric acid, and formic acid.

[0022] Before adjusting the pH, the black liquor may be concentrated using an evaporator, etc. The solid content in the black liquor may be preferably 10% by mass or more, more preferably 20% by mass or more.

[0023] The temperature when adjusting the black liquor to lower its pH (for example, to pH 11 or less) as described above may be preferably from room temperature to 100° C., more preferably from 40 to 80° C. By adjusting the upper limit of the temperature in this manner, it is possible to suppress lignin condensation and to suppress an increase in the molecular weight of the lignin contained in the black liquor.

[0024] When carbon dioxide is added to the black liquor, the method of adding carbon dioxide is not particularly limited, but examples include a method of blowing carbon dioxide under atmospheric pressure, or a method of blowing carbon dioxide into a sealed container and pressurizing (0.1 to 1 MPa), etc. As carbon dioxide, pure carbon dioxide gas may be used, but combustion exhaust gas discharged from an incinerator, boiler, etc., or gas containing carbon dioxide generated from a lime burning process, etc. may also be used.

[0025] If necessary, a flocculant may be added to promote precipitation of lignin. Examples of the flocculant include aluminum sulfate, aluminum chloride, polyaluminum chloride, polyamine, DADMAC, melamine colloid, and zinc anhydride.

[0026] A precipitate containing isolated lignin is obtained by adding acid and / or carbon dioxide to the black liquor to lower the pH of the black liquor, for example by adjusting the pH to 11 or less. The precipitate can be separated in the form of a dehydrated cake by dehydrating the precipitate in the liquor. By dehydrating and separating the precipitate in the liquor, it is possible to remove impurities and increase the concentration of the lignin-derived components contained in the raw material. After dehydration, the product may be washed to further remove impurities.

[0027] As a device for dehydrating and washing the precipitate, a filter press, a drum press, a centrifugal dehydrator, a suction filter, etc. can be used. When dehydrating with a filter press, the air permeability of the filter cloth used is 0.5 cm 3 / cm 2 / sec, 60cm 3 / cm 2 It is preferable that the air permeability of the filter cloth is less than 0.5 cm 3 / cm 2 If the air permeability exceeds 60 cm / sec, clogging during dehydration is unlikely to occur. 3 / cm 2By setting the washing time to less than 10 min / sec, lignin is easily retained on the filter cloth. The water used for washing is not particularly limited, but industrial water, tap water, carbonated water, dilute acid, etc. can be used, and it is preferable that the pH is 1 to 9, the temperature is 20 to 80° C., and the electrical conductivity is 0.2 S / m or less.

[0028] The upper limit of the solid content of the dehydrated cake is preferably 60% by weight or less, more preferably 50% by weight or less, and even more preferably 40% by weight or less. By dehydrating the cake to at least this extent, the amount of alkaline water added in the subsequent step can be reduced. On the other hand, the preferred lower limit of the solid content of the dehydrated cake is not particularly limited, but is preferably 10% by weight or more, more preferably 20% by weight or more, and even more preferably 30% by weight or more. Such a lower limit can be easily achieved by the dehydration method exemplified above.

[0029] A preferred embodiment of the step (a) of preparing the precipitate may be a mode in which carbon dioxide is added to the black liquor to adjust the pH to 7 or more and 11 or less to produce the precipitate. The precipitate obtained by adding carbon dioxide to the black liquor is also called "carbonate-neutralized lignin" in industrial practice.

[0030] When an embodiment of the present disclosure is implemented in conjunction with a facility that can supply carbon dioxide as combustion exhaust gas discharged from an incinerator, boiler, etc., it is possible to suppress the emission of carbon dioxide outside the facility. In addition, using carbon dioxide generated within the facility can be beneficial in terms of improving the operational efficiency of the facility.

[0031] In a preferred embodiment, the dehydrated cake of the carbonation neutralized lignin may be subjected to the alkali treatment in step (b) as it is. Such an embodiment in which the dehydrated cake of the carbonation neutralized lignin is subjected to the alkali treatment in step (b) is advantageous in that the number of steps can be reduced.

[0032] Another preferred embodiment of the step (a) of preparing a precipitate before the alkali treatment may include adding carbon dioxide to the black liquor to adjust the pH to 7 or more and 11 or less, producing a first precipitate, dehydrating the first precipitate to obtain a first dehydrated cake, suspending the first dehydrated cake in an aqueous solution containing an inorganic acid, adjusting the pH to 1 or more and 7 or less, producing a second precipitate, dehydrating the second precipitate to obtain a second dehydrated cake, and using the second dehydrated cake as the dehydrated cake to be provided to the alkali treatment in the step (b) performed following the step (a). The preferred solids concentration of the second dehydrated cake is the same as described above.

[0033] When the second precipitate is produced, the upper limit of the pH may be preferably 6, 5, 4, or 3 or less. By performing washing in the step of producing the second precipitate, the purity of lignin is improved, and the amount of acid (e.g., sulfuric acid) used in the subsequent step (d) can be reduced. In addition, since the yield is reduced by about half in the step of obtaining the second precipitate from the first precipitate, the amount of the target product (isolated lignin-containing product) obtained is greater when the second precipitate is used compared to when the same amount of the first precipitate or second precipitate is used in the alkali treatment.

[0034] <Step (b): Step of preparing alkaline solution> In step (b), alkaline water is added to the dehydrated cake prepared by the treatment in the above-mentioned step (a) to produce an alkaline liquid containing the dehydrated cake obtained in step (a).

[0035] Examples of the alkaline water to be added to the dehydrated cake include one or more aqueous solutions selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, alkali metal hydrogencarbonates, alkali metal phosphates, alkali metal carboxylates, alkaline earth metal hydroxides, alkaline earth metal carbonates, alkaline earth metal hydrogencarbonates, alkaline earth metal hydrogencarbonates, alkaline earth metal carboxylates, ammonia, amine compounds, and alkali metal alkoxides. Among these, from the viewpoints of reactivity and cost, preferred are aqueous alkali metal hydroxide solutions, and particularly preferred is an aqueous sodium hydroxide solution.

[0036] The dehydrated cake is added with alkaline water and suspended to prepare an alkaline solution containing the dehydrated cake obtained in step (a). The pH of the alkaline solution can be adjusted to preferably greater than 11, more preferably 12 or more. The preferred upper limit of the solution concentration of the alkaline solution is preferably 60% by weight or less, more preferably 40% by weight or less, and even more preferably 20% by weight or less. On the other hand, the preferred lower limit of the solution concentration of the alkaline solution is not particularly limited, but is preferably 1% by weight or more, more preferably 3% by weight or more, and even more preferably 5% by weight or more.

[0037] <Step (c): Alkali heating step> In step (c), the alkaline solution prepared by the treatment in step (b) is heated to a temperature range of 120° C. or more and 190° C. or less to produce a heated product. The heated product obtained in step (c) contains isolated lignin that has a lower molecular weight than the lignin present in the wood raw material.

[0038] The lower limit of the heating temperature depends on conditions such as the pH level and heating time, but is preferably 120° C. or higher, more preferably 140° C. or higher, and even more preferably 150° C. or higher. The upper limit of the heating temperature depends on conditions such as the pH level and the heating time, but can be 190° C. or lower, preferably 180° C. or lower, and more preferably 170° C. or lower. In order to obtain an isolated lignin-containing material having a lower molecular weight and a highly soluble isolated lignin-containing material, it is preferable to adjust the heating temperature to the above-mentioned range.

[0039] The lower limit of the heating time depends on conditions such as the pH level and the heating temperature, but is preferably 1 minute or more, more preferably 30 minutes or more, and even more preferably 60 minutes or more. The upper limit of the heating time depends on conditions such as the pH level and the heating temperature, but is preferably 300 minutes or less, more preferably 240 minutes or less, and even more preferably 210, 180, or 150 minutes or less. In order to obtain an isolated lignin-containing product with a lower molecular weight and a highly soluble isolated lignin-containing product, it is preferable to adjust the heating time to the above range.

[0040] As shown in the above processes (a) to (c), it is presumed that the pH of the black liquor is lowered, the precipitate formed is then raised in pH again, and the precipitate is exposed to highly alkaline conditions and subjected to heat treatment, thereby promoting the decomposition of isolated lignin into smaller molecules. It is also presumed that the above processes (a) to (c) can promote the solubilization of the isolated lignin-containing material.

[0041] <Step (d): Solid-liquid separation step> In step (d), the pH of the heated product (liquid or slurry containing isolated lignin) prepared by the treatment in step (c) is lowered to generate a precipitate again, thereby obtaining an isolated lignin-containing material. The isolated lignin-containing material as a precipitate is dehydrated and washed with water, whereby the isolated lignin-containing material can be separated in the form of a dehydrated cake. The treatments such as dehydration and washing of the precipitate can be carried out using the apparatus described in step (a).

[0042] To lower the pH, an acid may be added to the heated product obtained in step (c). The acid may be an inorganic acid or an organic acid, and is the same as that exemplified in step (a) above. Preferably, sulfuric acid is used. The pH may be lowered to preferably 6 or less, more preferably 5 or less, and even more preferably 4 or 3 or less. By lowering the pH in this way, a precipitate rich in isolated lignin can be obtained. Although the mechanism of action is not necessarily clear, it is believed that the solubility of the finally obtained isolated lignin-containing product can be increased by adjusting the pH to a low level in this way.

[0043] The precipitate produced in step (d) may be further dehydrated and washed. The washing is desirably carried out until the electrical conductivity of the washing filtrate is 0.2 S / m or less. As in step (a), a filter press, a drum press, a centrifugal dehydrator, a suction filtration device, or the like may be used as an apparatus for dehydrating and washing the precipitate of the isolated lignin-containing material. The water used for washing the precipitate of the isolated lignin-containing material may be the same as the water used for washing in step (a). The pH of the washing water may be preferably pH 6 to 8.

[0044] The isolated lignin-containing material obtained in step (d) may be further purified by adding an organic solvent to dissolve the lignin and separating the insoluble matter as an impurity. As the organic solvent to be added, a non-solvent or poor solvent for sugars is suitable, and for example, one or more of the following may be used: alcohols including methanol, ethanol, isopropyl alcohol, 2-methoxylethanol, butanol, etc.; ethers including 1,4-dioxane, tetrahydrofuran, etc.; ketones including acetone and methyl ethyl ketone, etc.; nitriles including acetonitrile, etc.; amines including pyridine, etc.; amides including formamide, etc.; esters including ethyl acetate, methyl acetate, etc.; aliphatic hydrocarbons including hexane, etc.; aromatic hydrocarbons including benzene, toluene, etc.; or a mixture of one or more of the following and adding water. Among the above, acetone may be suitable. As a method for solid-liquid separation of insoluble matter in the suspension, a filter press, a drum press, a centrifugal dehydrator, a suction filter, etc. may be used.

[0045] According to some embodiments of the present disclosure, it is possible to obtain an isolated lignin-containing material that is low molecular weight and highly soluble in solvents such as organic solvents. Such isolated lignin-containing material is expected to be easily used as a material or raw material for thermosetting resins, dispersants, adhesives, and the like.

[0046] A preferred embodiment of the isolated lignin-containing material obtained by the method disclosed above may be, for example, an isolated lignin-containing material having a weight average molecular weight of 1500 to 6000 and a solubility in acetone of 75% or more.

[0047] The upper limit of the weight average molecular weight of the isolated lignin content is, in general, preferably 6000 or less, more preferably 5000 or less, and even more preferably 4000, 3500, 3000, 2700, or 2500 or less. In addition, it can be said that the weight average molecular weight of the isolated lignin-containing product is generally preferably smaller. According to the method disclosed above, the lower limit of the weight average molecular weight of the isolated lignin-containing product obtained can be, in general, preferably 2100, 1800, or 1500 or more.

[0048] Generally, lignin contained in black liquor obtained from coniferous trees tends to have a larger weight average molecular weight than that of hardwoods. According to some embodiments of the present disclosure, even from black liquor made from coniferous trees as wood raw materials, the weight average molecular weight of the isolated lignin-containing material can be significantly reduced as described above. In the case of hardwoods, the weight average molecular weight of lignin in black liquor obtained from hardwoods may originally be smaller than that of hardwoods, but even in the case of hardwoods, it can be sufficiently reduced to the weight average molecular weight as described above.

[0049] As described above, the weight average molecular weight of the isolated lignin-containing material obtained may vary depending on the type of wood raw material. The weight average molecular weight of the isolated lignin-containing material obtained may also vary depending on the type of cooking method. The weight average molecular weight of the isolated lignin-containing material may be as follows, depending on the type of wood raw material and the type of cooking method.

[0050] When coniferous wood is used as the raw material, the upper limit of the weight average molecular weight of the isolated lignin-containing product obtained is preferably 6,000 or less, more preferably 5,000 or less, and even more preferably 4,000 or less. When coniferous wood is used as the raw material, the lower limit of the weight average molecular weight of the isolated lignin-containing product obtained can be preferably 2500, 2100, 1800, or 1500 or more. In the case of softwood, whether it is the kraft cooking method or the soda cooking method, the above-mentioned upper and lower limits of the weight average molecular weight are generally the same.

[0051] In contrast, when hardwood lumber is used as the raw material, the upper and lower limits may differ depending on whether the kraft cooking method or the soda cooking method is used. When hardwood wood is used as a raw material and black liquor is obtained by the kraft cooking method, the upper limit of the weight average molecular weight of the isolated lignin-containing material obtained is preferably 3,500 or less, more preferably 3,200 or less, and even more preferably 3,000 or 2,800 or less. When hardwood wood is used as a raw material and black liquor is obtained by the kraft cooking method, the lower limit of the weight average molecular weight of the isolated lignin-containing product obtained can be preferably 2200, 2100, 1800, or 1500 or more.

[0052] When hardwood wood is used as a raw material and black liquor is obtained by soda cooking of the isolated lignin-containing material obtained, the upper limit of the weight average molecular weight is preferably 2700 or less, more preferably 2600 or less, and even more preferably 2500, 2400, or 2300 or less. When hardwood wood is used as a raw material and black liquor is obtained by soda cooking of the isolated lignin-containing material obtained, the lower limit of the weight average molecular weight can be preferably 2000, 1800, or 1500 or more.

[0053] As an index showing the solubility of the isolated lignin-containing material, the solubility in acetone as an organic solvent can be used. The solubility of the isolated lignin-containing material in acetone is preferably 75% or more, more preferably 80% or more, and even more preferably 85, 86, 87, 89, 90, 91, 92, or 93% or more, in general.

[0054] It has not been easy to increase the acetone solubility of an isolated lignin-containing material obtained from black liquor obtained from coniferous trees as described above by conventional methods. However, according to some embodiments of the present disclosure, an isolated lignin-containing material having a high acetone solubility can be obtained even from wood raw materials derived from coniferous trees.

[0055] When coniferous wood is used as the raw material, the acetone soluble rate is preferably 75% or more, more preferably 80% or more, and even more preferably 85, 86, 87, 88 or 89% or more.

[0056] On the other hand, the present inventors have found that in the case of hardwood, even without alkali treatment, it may be possible to increase the acetone solubilization rate compared to that of softwood, but it is still difficult to improve it to the extent of some embodiments of the present disclosure. According to some embodiments of the present disclosure, even in the case of hardwood, it is possible to improve the acetone solubilization rate to the following level.

[0057] When hardwood wood is used as a raw material and black liquor is obtained by the kraft cooking method, the acetone soluble rate is preferably 80% or more, more preferably 83% or more, and even more preferably 85, 87, or 90% or more.

[0058] When hardwood wood is used as the raw material and black liquor is obtained by the soda cooking method, the acetone soluble rate is preferably 85% or more, more preferably 90% or more, and even more preferably 92 or 93% or more.

[0059] Preferred embodiments of the isolated lignin-containing material according to the present disclosure include, for example, the following:

[0060] An isolated lignin-containing material obtained by using coniferous wood as a wood raw material, the isolated lignin-containing material having a weight average molecular weight of 1500 to 6000 and an acetone solubilization rate of 75% or more.

[0061] An isolated lignin-containing material obtained by using black liquor obtained by kraft cooking of hardwood lumber, the isolated lignin-containing material having a weight average molecular weight of 1500 to 3500 and an acetone solubilization rate of 80% or more.

[0062] An isolated lignin-containing material obtained by using black liquor obtained by soda cooking hardwood lumber, the isolated lignin-containing material having a weight average molecular weight of 1500 to 2700 and an acetone solubilization rate of 93% or more. EXAMPLES

[0063] The present invention will be described in detail below with reference to examples, but the technical scope of the present invention is not limited to the following examples.

[0064] <Molecular weight analysis> Weight average molecular weight (Mw) was measured by aqueous GPC. The eluent was 0.5 mol / l aqueous sodium hydroxide, the column carrier was Tosoh HT-55, the detection method was RI and UV, and the flow rate was 1.0 ml / min. The samples used for the measurement were dissolved in 0.5 mol / l aqueous sodium hydroxide to a concentration of 0.1%, and each sample was measured. After the measurement, the calibration curve obtained from the results of five points of molecular weights of polyethylene glycol: 106, 410, 1480, 3,870, 10, and 370 was used to calculate Mw from the GPC chart of each sample.

[0065] <Acetone solubility rate> 4.0 g of each sample was taken in a 100 ml beaker, dried to a solid content of 90% or more, and then 40 ml of acetone was poured into it. The sample was stirred at room temperature (approximately 25°C) for 5 hours at 300-400 rpm, and then separated into acetone-soluble and insoluble parts using No. 2 qualitative filter paper. After separation, each sample was dried in a vacuum dryer at 50°C for 2 days, and the acetone-soluble rate was calculated from the weights of the soluble and insoluble parts after drying.

[0066] Example 1 <Step (a): Step of Producing Precipitate and Dehydrated Cake> Kraft cooking was performed using coniferous wood chips, and 500 ml of the resulting black liquor (pH 13.6) was cooled to 60°C, and while keeping the temperature, carbon dioxide gas was injected into it to lower the pH to approximately 10, producing a (first) precipitate.

[0067] The liquid containing the (first) precipitate was filtered using a Buchner funnel to obtain an isolated lignin filter cake (carbonate-neutralized lignin) having a solids concentration of 30.2% as a (first) dehydrated cake.

[0068] <Step (b): Step of Producing Alkaline Solution> To 30 g of the bone-dry carbonated lignin obtained in step (a), 19.7 ml of a 50% sodium hydroxide solution was added, and then pure water was added so that the solution concentration of the carbonated lignin became 10.0%, to produce an alkaline solution.

[0069] <Step (c): Heating step> The alkaline liquid obtained in step (b) was heated at 170°C for 2 hours using a 6-unit multi-digester to produce a heated product (slurry).

[0070] <Step (d): Step of obtaining a liquid containing an isolated lignin-containing material> The heated product (slurry) obtained in step (c) was cooled to 50° C., and while keeping the temperature, 8N sulfuric acid was added with stirring until the pH of the slurry became 2. Thereafter, stirring was continued at 50° C. for 1 hour to obtain a liquid containing an isolated lignin-containing material.

[0071] <Step (e): Step of dehydrating and washing and recovering the isolated lignin-containing material> The liquid containing the lignin-containing material obtained in step (d) was filtered using a Buchner funnel, and 150 ml of hot water at 50° C. was added to the isolated lignin cake obtained, followed by filtration. Filtration and washing were repeated until the electrical conductivity of the filtrate reached 0.2 S / m or less, and an isolated lignin-containing material was obtained.

[0072] <Drying of isolated lignin cake> The isolated lignin-containing material obtained in step (e) was dried for about 2 days in a blower dryer at 50° C. to obtain a powder with a solid content of about 95%.

[0073] <Weight average molecular weight (Mw) and acetone solubility measurement> The weight-average molecular weight and acetone solubility of the isolated lignin-containing material were measured, and the weight-average molecular weight was 3,350 g / mol and the acetone solubility was 92.2%.

[0074] Example 2 In Example 1, pure water was added to 60 g of the carbonated lignin (first dehydrated cake) obtained in step (a) so that the solution concentration of the carbonated lignin was 10.0%, and the mixture was heated to 50°C, and 8N sulfuric acid was added while stirring until the pH became 2. Stirring was then continued at 50°C for 1 hour. The liquid containing the second precipitate generated by the sulfuric acid treatment was filtered with a Buchner funnel, and 300 ml of hot water at 50°C was added to the obtained filter cake and filtered. Filtration and washing were repeated until the electrical conductivity of the filtrate was 0.2 S / m or less, and a second dehydrated cake was obtained.

[0075] For the second dehydrated cake, the solution concentration in step (b) in Example 1 was changed to 15%, and the heating time in step (c) was changed to 1 hour, and an isolated lignin-containing material was obtained in the same manner as in Example 1. The weight-average molecular weight and acetone solubility of the lignin-containing material after drying were measured, and the weight-average molecular weight was 3,600 g / mol, and the acetone solubility was 91.7%.

[0076] Example 3 <Step (a): Step of Producing Precipitate and Dehydrated Cake> A (first) precipitate was produced in the same manner as in step (a) of Example 1, except that hardwood chips were used instead of softwood chips in step (a) of Example 1. Filtration was carried out in the same manner as in step (a) of Example 1, and a lignin filter cake (carbonate-neutralized lignin) with a solid content of 27.7% was obtained as a (first) dehydrated cake.

[0077] <Step (b): Step of Producing Alkaline Solution> To 30 g of the carbonate-neutralized lignin obtained in the above step (a), 19.7 ml of a 50% sodium hydroxide solution was added, and then pure water was added so that the solution concentration of the carbonate-neutralized lignin became 15.0%, to generate an alkaline solution.

[0078] <Step (c): Heating step> The alkaline liquid obtained in step (b) was heated at 160°C for 2 hours using a 6-unit multi-digester to produce a heated product (slurry).

[0079] <Step (d): Step of obtaining a liquid containing an isolated lignin-containing material> The heated product (slurry) obtained in step (c) was cooled to 50° C., and while keeping the temperature, 8N sulfuric acid was added with stirring until the pH of the slurry became 2. Thereafter, stirring was continued at 50° C. for 1 hour to obtain a liquid containing an isolated lignin-containing material.

[0080] <Step (e): Step of dehydrating and washing and recovering lignin-containing material> The liquid containing the isolated lignin-containing material obtained in step (d) was filtered using a Buchner funnel, and 150 ml of hot water at 50° C. was added to the isolated lignin cake obtained, followed by filtration. Filtration and washing were repeated until the electrical conductivity of the filtrate reached 0.2 S / m or less, and an isolated lignin-containing material was obtained.

[0081] <Drying of isolated lignin cake> The isolated lignin-containing material was dried for about 2 days in a blower dryer at 50°C to obtain a powder with a solid content of about 95%.

[0082] <Weight average molecular weight (Mw) and acetone solubility measurement> The weight-average molecular weight and acetone solubility of the isolated lignin-containing material were measured, and the weight-average molecular weight was 2,730 g / mol and the acetone solubility was 93.5%.

[0083] Example 4 In Example 3, pure water was added to the carbonated lignin (first dehydrated cake) obtained in step (a) (absolute dry 60 g) so that the solution concentration of the carbonated lignin was 10.0%, and the mixture was heated to 50°C, and 8N sulfuric acid was added while stirring until the pH became 2. Stirring was then continued at 50°C for 1 hour. The liquid containing the second precipitate generated by the sulfuric acid treatment was filtered with a Buchner funnel, and 300 ml of hot water at 50°C was added to the obtained filter cake and filtered. Filtration and washing were repeated until the electrical conductivity of the filtrate was 0.2 S / m or less, and a second dehydrated cake was obtained (step (a) of Example 4).

[0084] For the second dehydrated cake obtained in step (a) of this Example 4, the solution concentration in step (b) in Example 1 was changed to 20%, and the heating time in step (c) was changed to 1 hour, and an isolated lignin-containing material was obtained in the same manner as in Example 1. The weight average molecular weight and acetone solubility of the isolated lignin-containing material after drying were measured, and the weight average molecular weight was 2,550 g / mol and the acetone solubility was 93.8%.

[0085] Example 5 <Step (a): Step of Producing Precipitate and Dehydrated Cake> Soda cooking was performed using coniferous wood chips, and 500 ml of the resulting black liquor was cooled to 70°C. Carbon dioxide gas was then injected while keeping the temperature high to lower the pH to approximately 8, producing a (first) precipitate.

[0086] The liquid containing the (first) precipitate was filtered using a Buchner funnel to obtain an isolated lignin filter cake (carbonate-neutralized lignin) having a solids concentration of 34.4% as a (first) dehydrated cake.

[0087] <Step (b): Step of Producing Alkaline Solution> To 30 g of the bone-dry carbonated lignin obtained in step (a), 19.7 ml of a 50% sodium hydroxide solution was added, and then pure water was added so that the solution concentration of the carbonated lignin became 10.0%, to produce an alkaline solution.

[0088] <Step (c): Heating step> The alkaline liquid obtained in step (b) was heated at 170°C for 2 hours using a 6-unit multi-digester to produce a heated product (slurry).

[0089] <Step (d): Step of obtaining a liquid containing an isolated lignin-containing material> The heated product (slurry) obtained in step (c) was cooled to 50° C., and while keeping the temperature, 8N sulfuric acid was added with stirring until the pH of the slurry became 2. Thereafter, stirring was continued at 50° C. for 1 hour to obtain a liquid containing an isolated lignin-containing material.

[0090] <Step (e): Step of dehydrating and washing and recovering the isolated lignin-containing material> The liquid containing the lignin-containing material obtained in step (d) was filtered using a Buchner funnel, and 150 ml of hot water at 50° C. was added to the isolated lignin cake obtained, followed by filtration. Filtration and washing were repeated until the electrical conductivity of the filtrate reached 0.2 S / m or less, and an isolated lignin-containing material was obtained.

[0091] <Drying of isolated lignin cake> The isolated lignin-containing material was dried for about 2 days in a blower dryer at 50°C to obtain a powder with a solid content of about 95%.

[0092] <Weight average molecular weight (Mw) and acetone solubility measurement> The weight-average molecular weight and acetone solubility of the isolated lignin-containing material were measured, and the weight-average molecular weight was 4,490 g / mol and the acetone solubility was 87.3%.

[0093] Example 6 <Step (a): Step of Producing Precipitate and Dehydrated Cake> In Example 4, a second dewatered cake was obtained in the same manner as in step (a) of Example 4, except that the black liquor obtained by soda cooking using hardwood chips in Example 3 was used.

[0094] In the above step (a), the second dehydrated cake was subjected to the subsequent steps in the same manner as in Example 1 to obtain an isolated lignin-containing material. The weight-average molecular weight and acetone solubility of the isolated lignin-containing material after drying were measured, and the weight-average molecular weight was 2,220 g / mol and the acetone solubility was 94.8%.

[0095] Comparative Example 1 In Example 1, the weight average molecular weight and acetone solubility of the carbonic acid neutralized lignin obtained in step (a) without carrying out steps (b) and after were measured. The weight average molecular weight was 6,420 g / mol, and the acetone solubility was 2.2%.

[0096] Comparative Example 2 The weight average molecular weight and the acetone soluble rate of the second dehydrated cake obtained in Example 2 were measured, and the weight average molecular weight was 5,380 g / mol and the acetone soluble rate was 64.1%.

[0097] Comparative Example 3 In Example 3, the weight average molecular weight and acetone solubility of the carbonate-neutralized lignin obtained in step (a) without carrying out steps (b) and after were measured. The weight average molecular weight was 4,860 g / mol, and the acetone solubility was 2.4%.

[0098] Comparative Example 4 The weight average molecular weight and the acetone soluble rate of the second dehydrated cake obtained in Example 4 were measured, and the weight average molecular weight was 3,730 g / mol and the acetone soluble rate was 70.3%.

[0099] Comparative Example 5 In Example 5, the weight average molecular weight and acetone solubility of the carbonate-neutralized lignin obtained in step (a) without carrying out steps (b) and after were measured. The weight average molecular weight was 10,310 g / mol, and the acetone solubility was 2.3%.

[0100] Comparative Example 6 500 ml of the black liquor used in step (a) of Example 1 was heated at 170° C. for 2 hours using a 6-unit multi-digester to produce a heated product (slurry).

[0101] The resulting heated product (slurry) was cooled to 50° C., and while keeping the temperature, 8N sulfuric acid was added with stirring until the pH of the slurry became 2. Thereafter, stirring was continued at 50° C. for 1 hour to obtain a liquid containing an isolated lignin-containing material.

[0102] The liquid containing the lignin-containing material was filtered using a Buchner funnel, and 300 ml of 50°C hot water was added to the resulting lignin cake and filtered. Filtration and washing were repeated until the electrical conductivity of the filtrate was 0.2 S / m or less, and an isolated lignin-containing material was obtained.

[0103] The isolated lignin-containing material 2 obtained was dried for about 2 days in a blower dryer at 50° C. to obtain a powder having a solid content of about 95%.

[0104] <Weight average molecular weight (Mw) and acetone solubility measurement> The weight-average molecular weight and acetone solubility of the isolated lignin-containing material were measured, and the weight-average molecular weight was 6,140 g / mol and the acetone solubility was 69.7%.

[0105] The results of Comparative Example 6 show that even if black liquor is directly subjected to alkali heating treatment without neutralizing it with carbon dioxide, the black liquor is not sufficiently depolymerized and the acetone solubility is not improved.

[0106] Comparative Example 7 500 ml of the black liquor obtained in step (a) of Example 1 was heated at 170°C for 2 hours using a 6-unit multi-digester to produce a heated product (slurry).

[0107] The resulting heated material (slurry) was cooled to 60°C, and while keeping the temperature, carbon dioxide gas was blown in to lower the pH to about 10, producing a liquid containing a precipitate.

[0108] The liquid containing the precipitate was filtered using a Buchner funnel to obtain a lignin filter cake (carbonate-neutralized lignin) with a solid content of 28.5%.

[0109] <Drying of isolated lignin cake> The obtained carbon dioxide-neutralized lignin was dried in a blast dryer at 50°C for about 2 days to obtain a powder with a solid content of about 95%.

[0110] <Weight average molecular weight (Mw) and acetone solubility measurement> The weight-average molecular weight and acetone solubility of the resulting carbonic acid neutralized lignin were measured, and the weight-average molecular weight was 4,760 g / mol and the acetone solubility was 2.4%.

[0111] The results of Comparative Example 7 showed that even if the black liquor was subjected to an alkali heat treatment without carbonation neutralization and then carbonation neutralization was performed, the carbonation neutralized cake obtained by this procedure had low solubility in acetone.

[0112] Comparative Example 8 The weight average molecular weight and the acetone solubility of the second dehydrated cake obtained in Example 6 were measured, and the weight average molecular weight was 2,810 g / mol and the acetone solubility was 91.5%.

[0113] The results of Examples 1 to 6 and Comparative Examples 1 to 8 are shown in Table 1.

[0114] [Table 1]

Claims

1. A method for producing an isolated lignin-containing material, comprising the steps of: (a) reducing the pH of black liquor obtained by alkaline cooking of a wood raw material to 11 or less to generate a precipitate, and dehydrating the precipitate to obtain a dehydrated cake of the precipitate; (b) adding alkaline water to the dehydrated cake to produce an alkaline solution containing the dehydrated cake and having a pH greater than 11; (c) heating the alkaline liquid at 120° C. or more and 190° C. or less to generate a heated product; (d) reducing the pH of the heated product to produce an isolated lignin-containing product; Including, In the above (a), the black liquor obtained by alkali cooking the wood raw material is black liquor obtained by kraft cooking the wood raw material, or black liquor obtained by soda cooking a wood raw material containing a coniferous wood raw material. , the method.

2. The method according to claim 1, wherein in (a), carbon dioxide is added to the black liquor to adjust the pH to 7 or more and 11 or less to produce the precipitate.

3. The method according to claim 1 or 2, wherein in (a), the dewatering is performed so that the solid content concentration of the dewatered cake is 10 to 60% by weight.

4. In the step (a), carbon dioxide is added to the black liquor to adjust the pH to 7 or more and 11 or less, a first precipitate is produced, the first precipitate is dehydrated to obtain a first dehydrated cake, the first dehydrated cake is suspended in an aqueous solution containing an inorganic acid, the pH is adjusted to 1 or more and 7 or less, a second precipitate is produced, and the second precipitate is dehydrated to obtain a second dehydrated cake; The method according to claim 1 , wherein in (b), the second dewatered cake is used as the dewatered cake.

5. The method according to claim 4, wherein in (a), the second dehydrated cake is dehydrated so that the solid content concentration of the second dehydrated cake is 10 to 60% by weight.

6. The method according to any one of claims 1 to 5, wherein in the step (b), alkaline water containing an alkali metal hydroxide and / or an alkaline earth metal hydroxide is added to the dehydrated cake to produce an alkaline liquid containing the dehydrated cake and having a pH of 12 or more.

7. The method according to any one of claims 1 to 6, wherein in (c), the heating time is 1 to 180 minutes.

8. The method according to any one of claims 1 to 7, wherein in (d), an inorganic acid is added to the heated material to lower the pH to 1 or more and 7 or less.

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