JP2014208803A - Lignin recovery method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an easy lignin recovery method.SOLUTION: A lignin recovery method comprises precipitating, in an acidic condition, lignin in an extract obtained by bringing a lignocellulose-containing material into contact with an aqueous alkaline solution, not containing a sulfur compound, of 0.25 M concentration or less. A lignin production method in a pulp manufacturing process uses the lignin recovery method.

Description

  The present invention relates to a simple lignin recovery method.

  In recent years, the use of recyclable resources has been called out from the viewpoint of depletion of petroleum resources and global warming, and the use of plant resources has attracted attention. Cellulose is the most abundant resource among plant-derived materials, and has been used as a raw material for pulp. Currently, cellulose is an energy resource that does not compete with food, and is a raw material for producing bioethanol by hydrolysis and fermentation. It is also attracting attention.

  Lignin, which is abundantly contained as a natural aromatic polymer next to cellulose as a wood component, has just begun to be developed as a resource, except that it is used for the production of vanillin. The reason why the lignin industry has not developed yet is that lignin that can be stably obtained at low cost cannot be secured. In the production of bioethanol targeting wood, lignin removal and lignin utilization are urgently needed.

  The use of lignin is currently attracting attention as an adhesive used in shaping reclaimed wood, and by adding it to phenolic resins, the use of expensive phenolic resins can be reduced. Helps to reduce the weight of materials. In addition, lignin is decomposed and converted to aromatic compounds, and attempts have been made to use it for pharmaceuticals, raw materials for organic synthesis, plastics, and the like. Other applications include functional foods, soil conditioners, concrete additives, and heavy metal adsorption using ion exchange functions.

  Wastes containing cellulose and lignin, such as hay, straw, and tea husks, are difficult to process and are bulky and difficult to use as a heat source for incineration. Began to be considered. The use of lignin has begun to spread because it can be used as an easy-to-handle fuel when it is hardened by adding lignin to cotton or paper waste. Attempts to produce carbon fibers from lignin have begun as high value-added applications.

Natural lignin is a polymer compound having a skeleton in which phenylpropane units (C6-C3 units) are oxidized into an indefinite form by an enzyme. Its basic skeleton has OCH ₃ groups and OH groups, and is divided into guanosyl type (G type), syringyl type (G type), and p-hydroxyphenyl type (H type). Lignin often undergoes denaturation by reacting with cooking reagents during pulp production. Sulfur (S) atoms bind to kraft method (kraft pulp method), which is the mainstream of pulp production, and lignin produced by sulfite pulp method. On the other hand, soda lignin produced by the soda method maintains a lignin skeleton without denaturation. When considering the use of lignin, soda lignin is desirable because it allows various chemical reactions.

  As a current method for isolating lignin, there is a “phase separation system conversion system” that uses an acid catalyst and reacts at normal temperature and pressure to separate lignin without modifying the chemical structure (Patent Document 1). A method using an acid (acid decomposition method) has also been proposed (Patent Document 2). A method of extracting in a subcritical water and methyl ethyl ketone solvent without using acid or alkali (Patent Document 3) and an attempt to extract lignin using an ionic liquid have also been proposed (Patent Document 4).

  However, the acid decomposition method has a problem that the amount of acid used is enormous and its recovery is difficult, resulting in enormous industrial waste. Other methods also require expensive or harmful compounds, there are problems with the yield of the reaction, severe reaction conditions, special equipment is required and the energy cost is enormous, etc. Has problems in practical application. Moreover, it is necessary to consider simultaneously the use of the cellulose produced | generated with manufacture of lignin. As a means for solving such a problem, a technique capable of simultaneously recovering lignin in the pulp manufacturing process and applying no load to conventional pulp manufacturing is required.

  The lignin content in wood is 20-30%. The structural component of wood, lignin, is a mixture of compounds with many different molecular weights, many present in wood in the form of lignocellulose combined with cellulose. About 20% of lignin in wood is said to be water-soluble lignin. The mainstream of conventional pulp production is the kraft pulp method, which aims to dissolve all lignin and is characterized by cooking at a high temperature and high pressure in an aqueous solvent using a high concentration NaOH solution and a sulfur compound as a cooking accelerator. is there. In this pulp manufacturing method, there is a problem that a bad odor and pollution due to sulfur compounds are accompanied. In addition, most of the lignin produced in the pulp production is used as a heat source and thus does not lead to the production of lignin.

  Regarding lignin production performed together with pulp production, Patent Document 5 proposes a method of producing pulp without using sodium sulfide and high-temperature / high-pressure conditions and recovering lignin. In this method, 1-10% by weight dilute caustic soda aqueous solution is used to treat wood chips at room temperature, followed by washing with water, followed by selective partial oxidation of lignin in wood chips in dilute nitric acid. In this method, pulp is produced by digesting under an atmospheric pressure using a 1 to 20% by weight dilute caustic soda aqueous solution, and lignin is agglomerated and separated from the separated black liquor. However, this method involves complicated processes and is difficult to combine with conventional pulp manufacturing processes.

JP 2008-266266 A JP 2011-091990 A JP 2010-227673 A JP 2011-042806 A JP 2009-167554 A

  An object of the present invention is to provide a simple lignin recovery method.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the alkaline solution used as the extraction solvent can be extracted and recovered with higher efficiency in a lower concentration range than before. The headline and the present invention were completed.
That is, the present invention includes the following.

[1] A method for recovering lignin, comprising bringing a lignocellulose-containing material into contact with an alkaline aqueous solution containing no sulfur compound and having a concentration of 0.25 M or less, and precipitating lignin in the resulting extract under acidic conditions.
In this method, it is also preferable that the alkaline aqueous solution has a concentration of 0.05 to 0.15M.
In a preferred embodiment of this method, the lignocellulose-containing material can be contacted with the alkaline aqueous solution at a temperature of 110 ° C. or lower.
The alkaline aqueous solution used in this method may contain hydrogen peroxide.
In this method, the aqueous alkaline solution is preferably at least one aqueous solution selected from the group consisting of sodium hydroxide, potassium hydroxide, and sodium carbonate.
In a preferred embodiment of this method, the lignocellulose-containing material may be contacted with the alkaline aqueous solution while applying vibration.
In a preferred embodiment of this method, the solution after recovering lignin from the extract may be reused as the alkaline aqueous solution and brought into contact with the lignocellulose-containing material.

[2] A method for producing lignin in a pulp production process, comprising collecting lignin from a lignocellulose-containing material by the method of [1] and using the residue for pulp production.

  According to the method of the present invention, lignin can be extracted and recovered with high efficiency using a lower concentration alkaline solution.

FIG. 1 is a graph showing the amount of lignin extracted using NaOH solutions having different concentrations. FIG. 2 is a diagram showing the amount of lignin extracted using different temperature conditions. FIG. 3 is a graph showing the amount of lignin extracted using different temperature conditions around 85 ° C. FIG. 4 is a diagram showing the influence on the amount of lignin for each extracted fraction obtained under different conditions such as temperature. FIG. 5 is a diagram showing the amount of lignin extracted using different dilute alkaline solutions. FIG. 6 is a diagram showing the amount of lignin extracted by sonication in 0.1M NaOH solution. FIG. 7 is a diagram showing the amount of lignin extracted using a shaking treatment in a 0.1M NaOH solution. FIG. 8 is a diagram showing the results of lignin extraction from mechanical pulp. FIG. 9 is a diagram showing the results of extraction of lignin from the seeds of the brown crab seed using different concentrations of NaOH solution. FIG. 10 is a graph showing the amount of lignin (mg) extracted at 100 ° C. (gray bar) and 150 ° C. (black bar) under different extraction conditions including the conditions using the collected NaOH solution. FIG. 11 is a graph showing the degree of coloration (absorbance at 595 nm) of the extract obtained at 100 ° C. (gray bar) and 150 ° C. (black bar) under different extraction conditions including conditions using the collected NaOH solution. It is.

Hereinafter, the present invention will be described in detail.
In the method according to the present invention, the lignocellulose-containing material is brought into contact with a low-concentration alkaline aqueous solution not containing a sulfur compound to extract lignin from the lignocellulose-containing material.

  In the present invention, the “lignocellulose-containing material” is a plant-derived material containing lignocellulose, which is a substance in which lignin and cellulose are combined, and is, for example, lignocellulosic biomass. The plant from which the lignocellulose-containing material is derived may be a dicotyledonous plant or a monocotyledonous plant, may be a gymnosperm or an angiosperm, may be a hardwood or a conifer. Good. In the present invention, the lignocellulose-containing material may be a wood material or a non-wood material (grass or bamboo-derived material). The plant from which the lignocellulose-containing material is derived may be an oil plant or a cereal plant that can be used for biofuel production. Preferable examples of the plant from which the lignocellulose-containing material is derived include, but are not limited to, for example, pine, rapeseed (also called jatropha), bamboo, corn, sugar cane, sugar beet (sugar beet), rice , Wheat, barley, cassava, palm, soybean, coconut, rapeseed, sunflower, flax, primrose and the like. Specific examples of the “lignocellulose-containing material” used in the present invention include wood, bamboo, grass, moss, seaweed, bark, leaves, stems, branches, vines, straw (such as rice straw and wheat straw), and rice husks. Seed husk, bagasse (residue after squeezing; squeezed residue), or processed products (tea leaves, woodwork products, etc.), or cut or crushed materials (cutting materials, chips, explosives, chips, powder, etc.) ) And the like, but is not limited thereto. The lignocellulose-containing material in the present invention typically contains, for example, 10% or more, preferably 20% or more, more preferably 40% or more, more preferably 70% or more by weight ratio relative to the whole material. . The lignocellulose-containing material in the present invention also contains, for example, 5% or more, preferably 10% or more, more preferably 20% or more, more preferably 30% or more lignin in a weight ratio with respect to the whole material.

  In the method of the present invention, the lignocellulose-containing material may be brought into contact with a low-concentration alkaline aqueous solution and, for example, immersed in the aqueous solution. This alkaline aqueous solution does not contain a sulfur compound (for example, a compound having a sulfur element such as sulfuric acid, sodium sulfate, or sodium sulfide). The alkaline aqueous solution used here is an aqueous solution having an alkali concentration (hydroxide ion concentration) of 0.25M or less, preferably 0.01 to 0.15M, more preferably 0.05 to 0.15M, and still more preferably 0.05 to 0.1M (for example, 0.1M). It is. The alkaline aqueous solution is not limited to the following, but is an aqueous solution containing at least one selected from, for example, sodium hydroxide, potassium hydroxide, and sodium carbonate. The alkaline aqueous solution may be, for example, at least one aqueous solution selected from the group consisting of sodium hydroxide, potassium hydroxide, and sodium carbonate, for example, 0.25M or less, preferably 0.01 to 0.15M, more preferably 0.05 to It may be 0.15M, more preferably 0.05-0.1M sodium hydroxide aqueous solution, potassium hydroxide aqueous solution or sodium carbonate aqueous solution. The alkaline aqueous solution used in the present invention is more preferably a sodium hydroxide aqueous solution. In the method according to the present invention, although not limited to 1 part by weight of the lignocellulose-containing material, the alkaline aqueous solution can be added, for example, 5 to 50 parts by weight, preferably 10 to 20 parts by weight.

  The alkaline aqueous solution used in the present invention may contain hydrogen peroxide. In the present invention, the browning of the residue obtained from the lignocellulose-containing material can be suppressed by using an alkaline aqueous solution containing hydrogen peroxide. The concentration of hydrogen peroxide is preferably 0.1 to 1.0% by weight, for example 0.1 to 0.5% by weight, based on the total amount of the alkaline aqueous solution, as an amount that does not greatly affect the lignin recovery rate.

  In the method according to the present invention, lignin can be eluted from the lignocellulose-containing material into the aqueous solution by bringing the lignocellulose-containing material into contact with the low-concentration alkaline aqueous solution. The temperature at which the lignocellulose-containing material is brought into contact with the alkaline aqueous solution (treated with the alkaline aqueous solution) is not limited, but a temperature within the range of 10 to 200 ° C., for example, 30 to 180 ° C. can be used. . When water-insoluble lignin is mainly extracted, it is preferable to use a temperature higher than 110 ° C. On the other hand, when water-soluble lignin is mainly extracted, it is preferable to use a temperature of 110 ° C. or lower. The temperature of 110 ° C. or lower can be, for example, more than 0 ° C. to 110 ° C., but for example, 60 to 110 ° C. is preferable when heating. For extraction of water-soluble lignin, a temperature around 85 ° C. (80 to 110 ° C .; for example, around 85 to 100 ° C.) is more preferable. The treatment of the lignocellulose-containing material with an alkaline aqueous solution can be performed under no pressure (atmospheric pressure) or under pressure.

  In the method according to the present invention, it is also preferable to apply vibration when the lignocellulose-containing material is brought into contact with the alkaline aqueous solution. Specifically, vibration can be applied by shaking (by hand or shaking machine), ultrasonic treatment, microwave irradiation (by microwave oven, etc.), rotation, or the like. The vibration may be applied for an appropriate time, for example, 1 minute to 90 minutes, and those skilled in the art can appropriately adjust the time. Extraction of lignin can be promoted by applying vibration. When the lignocellulose-containing material and the alkaline solution are brought into contact with each other, vibration can be applied as described above regardless of the temperature (that is, regardless of whether or not heating is performed).

  In the method according to the present invention, the lignocellulose-containing material may be treated with the alkaline aqueous solution after being subjected to the physical pretreatment such as ultrasonic treatment and microwave irradiation as described above.

  In the present invention, it is preferable that the “lignocellulose-containing material” is not subjected to modification by chemical treatment other than alkali treatment and hydrogen peroxide treatment at the time of lignin extraction with the alkaline aqueous solution or before. For example, the “lignocellulose-containing material” is preferably not treated with dilute nitric acid, dilute sulfuric acid, sodium chlorite or the like.

  The liquorcellulose-containing material is brought into contact with the alkaline aqueous solution as described above, and the extract obtained by eluting lignin into the aqueous solution is acidic (pH 5 or less, preferably pH 4 or less, more preferably pH 3 or less, for example, By adjusting to pH 3), the extracted lignin can be precipitated. The pH of the extract can be adjusted according to a conventional method, but it can usually be appropriately adjusted by repeatedly adding and mixing an appropriate concentration of dilute hydrochloric acid or glacial acetic acid while confirming the pH. The lignin thus precipitated under acidic conditions can be separated from the extract by any precipitation separation method such as centrifugation, filtration or a combination thereof. Centrifugation is not limited, but may be performed at 4,000 rpm for about 10 minutes, for example. Although filtration is not limited to the following, for example, filter paper filtration, vacuum filtration and the like can be used. In the method according to the present invention, lignin can be extracted and recovered from the lignocellulose-containing material as described above.

  The lignin recovery method of the present invention is preferably carried out, for example, by flowing the alkaline aqueous solution as an extraction solvent onto the lignocellulose-containing material in the column. It is also preferable that the alkaline aqueous solution flow is performed at a stage where the lignocellulose-containing material is under a temperature condition in the range of 10 to 200 ° C, preferably 85 to 110 ° C. It is also preferable that the alkaline aqueous solution flow down while applying vibration such as ultrasonic treatment.

  In an example of the lignin recovery method of the present invention, an alkaline solution of 0.01M to 0.25M (in a preferred example, 0.05 to 0.15M NaOH solution, for example, 0.1M NaOH solution) is applied to wood chips packed in a column at around 100 ° C. Flow down 5 to 50 times the wood chip weight, preferably 10 to 20 times, adjust the pH of the resulting extract to 3 or lower, collect the resulting precipitate by centrifugation or filtration and dry Thus, lignin can be recovered from the wood chips. By this method, lignin with less denaturation can be obtained. When sodium hydroxide aqueous solution is used as the alkaline solution, the drainage solution after separating the precipitate (lignin) becomes a lower concentration saline solution (0.1M NaCl = 0.59% NaCl) than the physiological saline solution (0.9%). , Can minimize the load on the natural environment.

  In a preferred embodiment of the present invention, the lignocellulose-containing material (residue) such as wood chips after extraction of lignin using a low-concentration alkaline aqueous solution as described above is separated from the extract by filtration or the like. The residue is reacted at a higher temperature (for example, 140 to 170 ° C., preferably 150 to 160 ° C.) by adding a high-concentration aqueous alkaline solution (but not limited to, for example, 1M to 5M, preferably 2M to 4M). Lignin may be further extracted from the residue. In this method, lignin can be recovered more efficiently from the residue, and the degree of coloration is higher than in the case where only high-temperature extraction using a high-concentration alkaline aqueous solution is performed from a lignocellulose-containing material such as wood chips. A low lignin can be recovered. Pulp can also be produced by utilizing the residue generated here after extraction of lignin with a highly concentrated aqueous alkaline solution in a pulp production method.

  In the method of the present invention, the aqueous alkaline solution (extraction solvent waste liquid) after extracting lignin by the method of the present invention, precipitating and recovering from the extract is brought into contact with a new lignocellulose-containing material according to the method of the present invention. Thus, it can be reused as an extraction solvent (the alkaline aqueous solution) for extracting lignin from a new lignocellulose-containing material.

  By the method of the present invention, a lignin fraction can be extracted and collected from a lignocellulose-containing material with high efficiency. In the lignin recovery method of the present invention, lignin with less denaturation can be produced.

The lignin recovery method of the present invention does not require any special equipment or reagents, and the drainage is a dilute salt solution. Therefore, the lignin recovery method is easy as a pretreatment step for conventional pulp production without excessive load on pulp production. Can be incorporated into. In the conventional kraft pulp method as a conventional method for producing chemical pulp, lignin is dissolved (alkaline by heating wood chips together with a high-concentration alkaline solution called white liquor at 150 to 160 ° C. and normal pressure or pressurization. Cooking to remove cellulose pulp, and after washing, proceed to the next step such as bleaching or drug recovery. Examples of the high-concentration alkaline solution used in the kraft pulping, NaOH 86.1g, Na2S 36.2g, and Na ₂ CO ₃ 19.0 g is obtained by dissolving in water 1L, include aqueous solutions of NaOH concentration 2.15. In the present invention, for example, in the kraft pulp method, at the time of a temperature of 110 ° C. or less (preferably around 100 ° C.) in the middle of heating the wood chips packed in the column and raising the temperature to the cooking temperature, The lignin in the wood chip can be extracted by adding the alkaline aqueous solution to be used to the wood chip and passing it through the column. If lignin contained in the column effluent is precipitated under acidic conditions, lignin can be easily recovered. The drainage liquid after separating lignin is a dilute salt solution, and can be reused as a cleaning liquid in pulp production. The wood chips (residue) after the alkaline aqueous solution has passed are added with a sulfur accelerator (such as sodium sulfide) as a cooking accelerator according to the pulp production method, followed by heating to raise the temperature to the cooking temperature and pressurizing. Cooking at high temperature and pressure. After cooking, the digested pulp and black liquor are separated and the pulp is washed. Lignin may be further recovered from the black liquor by aggregation or the like, but it is not necessary. The washed pulp may be further delignified by enzyme treatment or alkali treatment as necessary, and then foreign matters such as dust may be removed and bleached using a bleaching agent such as chlorine. Thereby, a pulp can be manufactured.

  Moreover, in the conventional method for producing mechanical pulp, wood and the like are ground together with water by mechanical force to loosen the cellulose contained in the wood and the like to make it into a pulp. In the conventional mechanical pulp manufacturing method, lignin is not removed, so the yield of pulp is 90% of wood, but browning occurs with the remaining lignin. In the present invention, for example, in the process of producing mechanical pulp, by using the alkaline aqueous solution instead of water in the step of grinding wood or the like, the lignin contained in the wood or the like is eluted into the aqueous solution, and the pH of the solution is adjusted. By adjusting to acidity, lignin can be precipitated and recovered. From the wood (residue) after lignin extraction, pulp may be produced by grinding and then by a normal production procedure for mechanical pulp. Thereby, it is possible to produce a pulp that is difficult to discolor between chemical pulp and mechanical pulp in combination with the production of lignin.

  Thus, in the present invention, in the pretreatment step of pulp production, lignin is extracted and collected from the lignocellulose-containing material using the lignin collection method of the present invention, and the generated residue is used for pulp production. Pulp can be produced in parallel. The present invention also provides a method for producing lignin in the pulp production process.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the technical scope of the present invention is not limited to these examples.

[Example 1] Examination of optimum NaOH concentration
In a 20 mL test tube, 1.500 g of crushed pine, various concentrations of 0.05M (0.2 wt%), 0.1M (0.4 wt%), 0.25M (1.0 wt%), 0.5M (2.0 wt%), and 2M (8.0 (15% by weight) of sodium hydroxide aqueous solution (NaOH solution) was added, and the mixture was heated at 100 ° C. for 20 minutes with an aluminum block heater. The extract was separated from the pine wood by decantation and filtered with filter paper. The obtained filtrate was adjusted to pH 3 or less with 6M HCl under ice cooling. As a control, the same lignin extraction was performed using pure water instead of the sodium hydroxide solution.

  The resulting grey-brown precipitate (crude lignin) was centrifuged (4000 rpm, 10 minutes), the supernatant was discarded, the collected precipitate was dried under reduced pressure, and the weight was measured. The result is shown in FIG.

  As shown in FIG. 1, more lignin could be extracted using NaOH concentrations lower than 2M, especially 0.05-0.25M NaOH concentrations. From this result, it was shown that a concentration 10 times or more lower than the NaOH concentration (2M) generally used in conventional pulp production is optimal for lignin extraction. From 0.1M to 2M, the amount of lignin extracted decreased as the NaOH concentration increased. On the other hand, no lignin precipitation was obtained in the control experiment using pure water.

[Example 2] Examination of optimum temperature 1.700 g of crushed pine wood was packed in a 7.6 x 150 mm stainless steel column, 0.1 M NaOH solution was fed to the column at a flow rate of 2 mL / min, and the extract was collected. During extraction, the column was heated to 30 ° C, 85 ° C, 130 ° C, 150 ° C, or 180 ° C using a hot plate and sea sand. The resulting extract was naturally cooled to room temperature and then adjusted to pH 3 with 6M HCl, resulting in a whitish precipitate. The precipitate was collected by centrifugation, the supernatant was discarded by decantation, the precipitate was dried, and the weight was measured. The result is shown in FIG.

  As shown in FIG. 2, a large amount of lignin was extracted around 85 ° C. and around 150 ° C. to 180 ° C. Water-soluble lignin was mainly extracted at around 85 ° C, and water-insoluble lignin was mainly extracted at 150 ° C to 180 ° C.

  Further experiments were conducted to further investigate the influence of the extraction concentration around 85 ° C. Place 2 g of crushed pine wood in a 50 mL Falcon tube, add 30 mL of 0.1M NaOH solution, heat to 45 ° C, 65 ° C, 85 ° C, or 105 ° C for 30 minutes using an aluminum block heater, then 10 minutes at 4000 rpm The supernatant was obtained by centrifugation and decantation. The residue was further washed twice with 10 mL of pure water and centrifuged at 4000 rpm for 10 minutes to obtain a supernatant twice. The supernatants were combined and ice-cooled, adjusted to pH 3 with 6M HCl, and the resulting precipitate was collected as a lignin fraction by centrifugation at 4000 rpm for 10 minutes. The weight of the precipitate was measured after drying under reduced pressure. The result is shown in FIG. The amount of lignin extracted was large around 65 ° C to 105 ° C, and the amount of lignin extracted around 85 ° C was the largest.

[Example 3] Effect of heating temperature and hydrogen peroxide 1.700 g of crushed pine wood was packed in a column (7.5 x 150 mm), and 0.1 M NaOH (containing 0.3% H ₂ O ₂ ) or 0.1 M NaOH (H ₂ O ₂ free) and heated at different temperature conditions (95 ° C. and 125 ° C.) for 10 minutes. Subsequently, 0.1 M NaOH solution was fed at a flow rate of 1 mL / min, and 8 fractions were collected in 10 mL portions. The obtained extract was adjusted to pH 3 with 6M HCl, cooled on ice, and then centrifuged at 4000 rpm for 10 minutes, and the precipitate was recovered as a lignin fraction. The precipitate was dried under reduced pressure and weighed. The results are shown in FIG.
As a result of the test, there was almost no effect due to the difference in heating temperature in this temperature range.

  The first 2 fractions (total 20 mL) contained most of the lignin extracted by this method. Therefore, in this lignin extraction method, sufficient extraction was possible with a 0.1M NaOH solution in an amount 10 times the weight of the crushed pine (wood chips) as the raw material.

When hydrogen peroxide (H ₂ O ₂ ) was added, the amount of lignin extracted was slightly reduced, but a sufficient amount of lignin could still be extracted.

[Example 4] Production of plastic sheet It is known that a biodegradable plastic (lignin plastic) can be produced by heating and compressing a mixture of lignin and cellulose. Therefore, a plastic was produced using the lignin extracted in the above example.

  First, 1 g of cellulose prepared by crushing filter paper with a coffee mill to form cotton and 200 mg of the dried lignin fraction obtained in Examples 1 to 3 under a temperature condition of 110 ° C. or less were mixed in a mortar. In addition, 1 g of the same cellulose and 300 mg of the dried lignin fraction obtained under the temperature conditions of more than 110 ° C. in Examples 2 to 3 were mixed in a mortar.

  Add 5 mL of distilled water and knead until it becomes as clay as possible, roll it into dumplings, sandwich it in a Teflon sheet, heat it to 110 ° C with an aluminum block heater, and then use a jack for a light vehicle to 10 Heat compression was performed by pressurizing for a minute.

  The lignin fraction extracted under a temperature condition higher than 110 ° C. was blackish brown, and when mixed with cellulose, a brownish mixture was formed. The lignin fraction extracted at 110 ° C. or lower was light yellow. When heated and compressed, the overlapped portion of the pressed lignin turned brown, but most of the dough was white. Lignin extracted below 110 ° C is mainly water-soluble, so it dissolved in water and mixed with cellulose relatively uniformly, whereas lignin extracted above 110 ° C was mainly insoluble and particles were solidified. It is considered that the lignin particles were relatively darkly colored and browned. Any lignin fraction could form a hard sheet.

  In addition, 2.5 g of cellulose prepared by crushing filter paper with a coffee mill to form cotton, and a dried product of a lignin fraction extracted from the crushed pine wood in Example 1 with a 0.1 M NaOH solution (dilute alkaline solution) 1.0 g was added, stirred in a coffee mill, mixed almost uniformly, and then transferred to a 100 mL beaker. 20 mL of water was added and kneaded, rolled into a dumpling, sandwiched between Teflon sheets, heated to 120 ° C. using an aluminum block heater, and then pressurized with a jack for a light vehicle. The heating was stopped and the product was left as it was, and after 10 minutes, when the temperature of the aluminum block heater had cooled to 90 ° C, the pressure was released and the sheet was taken out. The sheet became a hard plastic at a temperature below the melting point of lignin (near 90 ° C).

  Thus, a hard bioplastic sheet could be produced using the obtained lignin fraction, and the properties specific to lignin were confirmed.

[Example 5] Lignin extraction with various dilute alkaline solutions
In addition to the 0.1 M NaOH solution, lignin extraction was performed using a dilute alkaline solution 0.1 M KOH or 0.1 M Na ₂ CO ₃ solution. Take 1.700 g of crushed pine wood in a 50 mL falcon tube, add 20 mL of diluted alkaline solution (0.1 M NaOH, 0.1 M KOH, or 0.1 M Na ₂ CO ₃ solution), and sonicate for 60 minutes using an ultrasonic cleaner. The mixture was centrifuged at 4000 rpm for 10 minutes, and an extract was obtained by decantation. The extract was adjusted to pH 3 and lignin was precipitated and collected. After drying under reduced pressure, the weight was measured. The result is shown in FIG.

When 0.1M NaOH solution was used, lignin could be extracted most efficiently. However, lignin was also extracted efficiently when 0.1M KOH solution or 0.1M Na ₂ CO ₃ solution was used.

[Example 6] Extraction of lignin from rice straw After litter was softened with a hammer and cut into 10 mm length, 20 g of 0.1 M NaOH solution was added using 2 g of the sample as a sample, and the mixture was kept in a boiling bath for 10 minutes. Extracted lignin.
As a result, 50 mg of lignin was obtained. According to the method of the present invention, it was shown that lignin can be efficiently extracted from rice straw.

[Example 7] Extraction of lignin under non-heated conditions 1.700 g of pulverized pine wood was put into a 50 mL falcon tube, 20 mL of extraction solvent was added, and sonication was performed for 60 minutes without heating, and the resulting extract was adjusted to pH 3. Prepared and lignin precipitated and collected. As extraction solvents, 1: H ₂ O, 2: 0.1M NaOH solution, 3: 0.1M NaOH + 0.1% H ₂ O ₂ , 4: 0.1M NaOH + 0.3% H ₂ O ₂ , 5: 0.1M NaOH + 0.5% H ₂ O ₂ or 6: 0.1 M NaOH + 1.0% H ₂ O ₂ was used. The results are shown in FIG.

The results shown in FIG. 6 indicate that heating is not necessarily required to extract lignin when sonication is performed in the method of the present invention. When H ₂ O was used as the extraction solvent, no lignin was recovered. Lignin was efficiently extracted by using 0.1M NaOH solution. The addition of H ₂ O ₂ slightly reduced the yield of lignin, which is probably because the extracted lignin was reduced in molecular weight by H ₂ O ₂ treatment. On the other hand, browning of lignin and residue (pulp) could be prevented by adding H ₂ O ₂ .

[Example 8] Extraction of lignin by shaking under non-heated condition In Example 7, sonication was performed for 60 minutes under non-heated conditions, but it was examined whether this sonication could be changed to a milder condition. did.

  Take 1.700 g of crushed pinewood in a 50 mL falcon tube, add 20 mL of 0.1 M NaOH solution as an extraction solvent, and heat for 60 minutes, sonicate for 5 minutes, or shake for 5 minutes without heating. The obtained extract was adjusted to pH 3 for lignin precipitation and collected. The results are shown in FIG.

  As shown in FIG. 7, almost the same amount of lignin was extracted by the ultrasonic treatment for 5 minutes as compared with the case of ultrasonic treatment for 60 minutes. Moreover, even when shaken for 5 minutes, lignin extraction comparable to ultrasonic treatment was observed.

[Example 9] Effect of hydrogen peroxide on lignin extraction 2.000 g of crushed pine wood is taken into a 50 mL falcon tube, suspended by adding 30 mL of 0.1 M NaOH solution, and then various concentrations of hydrogen peroxide (0.0, 0.1 , 0.5, 1.0, 3.0%) and mixed until uniform, heated at 95 ° C. for 30 minutes, centrifuged at 4000 rpm for 5 minutes, and the supernatant was collected. The residue was suspended by adding 20 mL of pure water, centrifuged at 4000 rpm for 5 minutes, and the supernatant was collected twice. The obtained supernatant was ice-cooled and adjusted to pH 3 with 6M HCl to precipitate lignin. This reaction solution was further centrifuged at 4000 rpm for 10 minutes to precipitate lignin, and the supernatant was discarded, dried under reduced pressure, and weighed. The results are shown in Table 1. The judgment of the color tone was made visually.

The color of the recovered lignin was decolorized from brown to light brown depending on the H ₂ O ₂ concentration. The color of the residue of the crushed pine wood also changed from brown to almost white depending on the H ₂ O ₂ concentration. The amount of lignin recovered decreased slightly with the addition of H ₂ O ₂ , but a sufficient amount of lignin extract could be obtained up to an H ₂ O ₂ concentration of 1%. When performing lignin extraction in one step of pulp production, the color of lignin can be decolored in one step by adding H ₂ O ₂ , and the residual pulp is also obtained in white, The addition of H ₂ O ₂ up to about 1% is particularly useful.

[Example 10] Extraction of lignin from mechanical pulp Mechanical pulp (laboratory Kim towel) was fluffed with a coffee mill to prepare a sample, and 1.000 g was put in a falcon tube. 20 mL of water (H ₂ O), 0.1M NaOH solution, or 0.1M NaOH + 0.3% H ₂ O ₂ solution was added as an extraction solvent, and sonication was performed at room temperature for 60 minutes to extract lignin.

As a result, as shown in FIG. 8, lignin could also be extracted from mechanical pulp (Kim towel). In addition, the extraction efficiency of lignin increased by adding 0.3% hydrogen peroxide (H ₂ O ₂ ) to 0.1 M NaOH solution. This is probably because insoluble lignin was cleaved by hydrogen peroxide. Moreover, when hydrogen peroxide was added and extracted, a residue was decolored more than the raw material sample. Lignin was not extracted with water.

[Example 11]
Extraction of lignin was carried out from the seed husks of african oil (dicotyledonous plants) using various alkaline solutions. More specifically, the seed husk of nanyo aburagiri was ground with a coffee mill to prepare a sample, and 1.00 g of the powder was placed in 100 mL of a Teflon container, and 10 mL of extraction solvent was added. As the extraction solvent, water, 0.05M NaOH solution, 0.1M NaOH solution, 0.5M NaOH solution, or 1.0M NaOH solution was used. Next, after microwave irradiation for 20 seconds in a microwave oven, HCl was added to 5 mL of the obtained extract to adjust to pH3. The mixture was centrifuged at 4000 rpm for 10 minutes, the supernatant was discarded, the precipitate was dried under reduced pressure, and the weight was measured.

  As a result, as shown in FIG. 9, the concentration of the alkaline solution serving as the extraction solvent was optimally about 0.1M even when using the seeds of the brown seeds of the seeds. A precipitate was obtained at pH 3, indicating that this precipitate was also lignin.

[Example 12]
Attempts were made to continuously extract lignin under different extraction conditions and to reuse the extraction solvent after lignin recovery. 2.5 g of wood flour was placed in a 100 mL pressure vessel and 50 mL of 0.1 M NaOH solution was added. The vessel was sealed and extracted by heating at 100 ° C. for 30 minutes, the extract was filtered, and the filtrate was collected. The residue was put in a pressure vessel again, 50 mL of 3M NaOH solution was added, extraction was performed by heating at 150 ° C. for 30 minutes, filtration, and the filtrate was recovered. After measuring the absorbance at 595 nm for each filtrate, the pH was adjusted to 3 or lower to precipitate and recover lignin.

Furthermore, 0.1M NaOH solution and 3M NaOH solution were prepared using the waste liquid after precipitation and recovery of lignin from the extract using 0.1M NaOH solution (referred to as recovered 0.1M NaOH solution and recovered 3M NaOH solution, respectively) ). This was used (reused) instead of 0.1M NaOH solution or 3M NaOH solution, and the same lignin extraction test was performed. For comparison, only extraction at 100 ° C using 0.1M NaOH solution as extraction solvent, only extraction at 150 ° C using 3M NaOH solution as extraction solvent, extraction at 150 ° C using recovered 0.1M NaOH solution An experiment was also conducted.
The results are shown in Table 2 and FIGS.

  As shown in Table 2 and FIGS. 10 and 11, when the residue after extraction at 100 ° C. with 0.1M NaOH solution was further extracted at 150 ° C. with 3M NaOH solution, a sufficient amount of lignin was extracted into the filtrate. In addition, the residue after extraction with 0.1M NaOH solution at 100 ° C is further extracted with 3M NaOH solution at 150 ° C, and compared with the case where only extraction with 3M NaOH solution at 150 ° C is performed. Was significantly less colored (decrease in absorbance at 595 nm). By performing such continuous extraction, it was shown that coloring of lignin extracted at a higher temperature using a higher concentration alkaline solution can be suppressed.

  Furthermore, it was shown that 0.1M and 3M NaOH solutions prepared using waste liquid after recovering lignin from the extract with 0.1M NaOH did not affect the lignin extraction even when used for extraction (Table 2). Therefore, it was shown that the extraction solvent after lignin recovery can be reused.

  Lignin produced as a by-product in conventional pulp manufacturing is not purified from pulp black liquor because its size and skeleton are denatured by the cooking reagent, and it is simply incinerated in the pulp manufacturing process and used for heat energy. It is not used as lignin. However, its fuel efficiency is as low as 1/3 that of heavy oil, which is not an effective usage. Use of lignin as lignin is an effective use of resources. By using the method according to the present invention, lignin can be efficiently produced in the current pulp production process. Currently, 7 million tonnes of lignin are produced annually in the pulp production field, so that the method according to the present invention, in a preferred embodiment, is theoretically more than 1 million tonnes of unmodified water Lignin is obtained. Water-soluble lignin is also useful because it is easy to handle when it is used as a resource for reducing the molecular weight or for various reactions.

Claims (8)

  A method for recovering lignin, comprising bringing a lignocellulose-containing material into contact with an alkaline aqueous solution containing no sulfur compound and having a concentration of 0.25 M or less, and precipitating lignin in the resulting extract under acidic conditions.   The method according to claim 1, wherein the aqueous alkaline solution has a concentration of 0.05 to 0.15M.   The method of Claim 1 or 2 which makes a lignocellulose containing material contact the said alkaline aqueous solution at the temperature of 110 degrees C or less.   The method according to claim 1, wherein the aqueous alkaline solution contains hydrogen peroxide.   The method according to any one of claims 1 to 4, wherein the aqueous alkaline solution is at least one aqueous solution selected from the group consisting of sodium hydroxide, potassium hydroxide, and sodium carbonate.   The method according to any one of claims 1 to 5, wherein the lignocellulose-containing material is brought into contact with the aqueous alkaline solution while applying vibration.   The method of any one of Claims 1-6 including reusing the solution after collect | recovering lignin from the said extract as said alkaline aqueous solution, and making it contact with a lignocellulose containing material.   The method of manufacturing a lignin in a pulp manufacturing process including collect | recovering lignin from a lignocellulose containing material by the method of any one of Claims 1-7, and using the residue for pulp manufacture.

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