JP4958166B2 - Treatment of plant biomass with alcohol in the presence of oxygen - Google Patents

Description

  The present invention treats a plant raw material (plant-based biomass) containing cellulose, lignin, hemicellulose, etc., such as wood used as a pulp raw material, and separates components from the processed product, for example, recovers useful components or unnecessary components It is related with the processing method of plant biomass which removes.

  Traditionally, pulp is a typical useful material that has been used from plant-derived materials (plant-based biomass) such as wood and herbs. In recent years, focusing on the fact that each component separated from plant biomass can be converted chemically or biologically to produce useful substances such as ethanol and phenol, such as petroleum, which has problems such as global warming and resource depletion. As an alternative to fossil resources, there are active attempts to use useful materials derived from biomass. In general, component separation of plant-based biomass is aimed at utilization utilizing the chemical characteristics of the component, so it is necessary to avoid excessive chemical modification of the raw material in the separation process. Therefore, it is often performed under mild reaction conditions as compared with gasification and combustion treatment. In addition, since biomass is basically solid, a reaction in a liquid phase is preferably used, and a reaction in an aqueous solution is particularly preferably used particularly in consideration of the environment and economy.

  Separation of components in an aqueous solution of biomass has been performed so far, for example, a method in which lignocellulose is treated with steam to convert a part thereof into an organic solvent-soluble component (see Patent Document 1), and hydrothermal reaction with pulp sludge. And a method for forming water-soluble saccharides by applying water (see Patent Document 2), a method for producing water-soluble oligosaccharides by hydrolyzing cellulose powder with pressurized hot water (see Patent Document 3), and the like. ing.

  However, since water used in these methods has low decomposition activity, it is necessary to increase the treatment temperature in order to achieve sufficient component separation. However, when biomass is reacted under high temperature conditions, it is not preferable because it causes excessive decomposition, and it is necessary to perform the reaction in a short time. As the method, the raw material biomass is finely pulverized, made into a slurry, and sent into the apparatus to finish the reaction in a short time (see Patent Document 2), and using a percolator reactor, only the decomposition product is obtained. A method (see Patent Document 3 and Non-Patent Document 1) for quickly extracting the reaction system from the reaction system has been devised. Regarding the former, it is difficult to transport high-concentration slurry under high temperature and high pressure, so it becomes a low-concentration treatment, and the latter inevitably has to be a batch-type treatment. There is. In both cases, a large amount of water is required, resulting in excessive energy consumption.

  Therefore, many methods have been devised to chemically promote the decomposition of biomass by adding alkaline substances such as lime, sodium hydroxide, ammonia, or acidic substances such as sulfuric acid, phosphoric acid, hydrochloric acid, In these methods, a highly active substance is supplied from the outside, leading to an increase in cost. Also, corrosion of the device may be a problem. Furthermore, since these active substances inhibit the subsequent enzymatic saccharification, it is necessary to remove them in advance. However, the process of neutralization and salt separation for that purpose is complicated, and a substance with a high environmental load is generated. There is also.

  Thus, a method has been devised in which pretreatment is performed using an organic acid such as acetic acid or formic acid contained as a component such as hemicellulose that decomposes during hydrothermal treatment of biomass as a catalyst (see Non-Patent Document 2). However, in this method, since oxidative substances such as oxygen do not coexist, the decomposition of lignin is not sufficient, and the decomposition activity of organic acids is lower than that of mineral acids, so herbaceous biomass such as corn stover There is a problem that application is limited to biomass that is relatively easy to process, such as hardwood and broad-leaved trees.

  On the other hand, a method of promoting enzymatic saccharification of cellulose by partially oxidizing lignin is known. For this purpose, hydrogen peroxide and ozone are often used, but an increase in cost becomes a problem. Therefore, a method called wet oxidation has been devised that enhances the pretreatment effect by adding cheaper air or oxygen. Biomass pretreated by wet oxidation is saccharified with sulfuric acid (Non-patent Document 3) or enzyme (Non-patent Document 4). In the latter case, in order to enhance the pretreatment effect, a method of performing wet oxidation while adjusting the pH with an alkali (sodium carbonate) or an acid (sulfuric acid) (Non-Patent Document 4) has also been tried. The result is that treatment under neutral conditions without addition of alkali is most effective. In any case, the lignin removal rate by this method is 50% or less, and the sugar yield obtained by enzymatic saccharification of the pretreated product remains at a relatively low value of up to 257 mg / g based on the raw conifer wood chip. .

On the other hand, as a method for separating lignin and hemicellulose in biomass, a treatment called organosolv by a mixed system of water and an organic solvent has been performed for a long time. Examples of the organic solvent used so far include alcohols, ketones, and glycols (Non-Patent Document 5). In addition to these organic compounds, catalysts such as mineral acids, organic acids, inorganic salts, and alkalis may be used to promote delignification. However, in these methods, since there is no oxidizing agent, lignin is not sufficiently decomposed, and in order to obtain a high-quality pulp and a processed product suitable for enzymatic saccharification, applicable biomass species are herbaceous biomass and There is a problem that it is limited to biomass that is relatively easy to process such as hardwood. On the other hand, a method of oxidatively removing lignin in the presence of oxygen using a mixed solvent of water and acetic acid is known (Non-Patent Document 6). However, in this method, hydrolysis of cellulose by water and an organic acid proceeds excessively, so that there is a problem that the molecular weight of cellulose is lowered and a good quality pulp cannot be obtained. In addition, when this method is used as a pretreatment for enzymatic saccharification, the ratio of the solubilized saccharide increases and a relatively large amount of saccharide is present in the liquid substance. This will decrease the amount of sugar available for enzymatic saccharification. If the amount of sugar that can be used for enzymatic saccharification decreases, the amount of sugar that can be used for alcohol fermentation, which is the next step, will decrease, and the alcohol yield will decrease. On the other hand, when trying to use solubilized sugar to make up for this, since the solubilized sugar and organic compounds such as solvents exist in the liquid processed product, an operation to separate them is necessary, and the process is complicated. Become.
JP-A-2004-243541 (Claims and others) JP 2001-79595 A (Claims and others) JP-A-10-327900 (Claims and others) Ind. Eng. Chem. Res., 31, 1157 (1992) Bioresource Tech., 96, 1986 (2005) Ind. Eng. Chem. Prod. Res. Dev., 22, 352 (1983) Appl. Biochem. Biotech., 117, 1 (2004) Biotechnol. Bioeng., 31, 643 (1988) Holzforschung, 46 (3), 233 (1992)

  Therefore, an object of the present invention is to provide a plant raw material treatment method that is advantageous in recovering useful components such as ethanol, lignin, and pulp from plant raw materials. More specifically, taking advantage of the fact that the lignin component contained in plant raw materials is more easily oxidized than carbohydrate components such as cellulose and hemicellulose, oxygen is oxidized under relatively mild conditions, so that conifers, etc. It is an object of the present invention to provide a method for efficiently obtaining a pulp for papermaking and a pretreated product for enzymatic saccharification even from plant biomass that is difficult to be delignified.

  As a result of intensive studies in view of the above-mentioned problems of the prior art, the inventor heat-treats plant biomass in an alcohol solvent in the presence of oxygen, so that most of the lignin in the plant biomass is oxidized. It was decomposed | disassembled and melt | dissolved in a processing solvent, and it discovered that most cellulose and hemicellulose in plant-type biomass became a solid content residue insoluble in a processing solvent, and completed this invention. This is because oxygen acts on plant biomass to produce organic acids, organic acids react with alcohols to produce organic acid esters, and oxygen and organic acids act on lignin to promote oxidative degradation of lignin. It is presumed that most of cellulose and hemicellulose do not dissolve in the processing solvent while the lignin degradation product soluble in the solvent is generated. Since the insoluble residue obtained by this treatment has a low lignin content, it is suitable for use as an enzyme saccharification raw material, a papermaking raw material and the like.

That is, this invention includes the processing method of the following plant-type raw materials.
Item 1. It includes a step of heat-treating a plant-based raw material in an alcohol solvent under an oxygen atmosphere to obtain a heat-treated product containing the first liquid component and the first solid component, and separating both components into solid and liquid. A method for treating plant-based raw materials.
Item 2. Item 2. The treatment method according to Item 1, wherein the alcohol solvent contains at least one selected from the group consisting of water, an organic acid, and an organic acid ester.
Item 3. Item 3. The treatment method according to Item 1 or 2, wherein the alcohol is ethanol.
Item 4. Item 4. The processing method according to any one of Items 1 to 3, wherein the oxygen atmosphere is an oxygen or air atmosphere.
Item 5. Item 5. The treatment method according to any one of Items 1 to 4, comprising a step of subjecting the first solid component obtained by solid-liquid separation to a saccharification enzyme treatment to obtain an enzyme saccharification saccharide.
Item 6. Item 6. The treatment method according to Item 5, comprising a step of solid-liquid separation of an ethanol fermented product obtained by subjecting an enzyme saccharified sugar to ethanol fermentation, and recovering ethanol from the obtained liquid product.
Item 7. Item 6. The treatment method according to Item 5, comprising a step of solid-liquid separation of an ethanol fermented product obtained by subjecting an enzyme saccharified sugar to ethanol fermentation to obtain lignin as a solid.
Item 8. Item 5. The processing method according to any one of Items 1 to 4, wherein the first solid component obtained by solid-liquid separation is used as papermaking pulp.
Item 9. The first liquid component obtained by solid-liquid separation is distilled, the alcohol is recovered from the gaseous product obtained by distillation, and / or the liquid product obtained by distillation is selected from the group consisting of organic acids and organic acid esters The processing method in any one of claim | item 1 -4 including the process of collect | recovering at least 1 sort (s).

  In the present invention, the plant-based raw material used as the raw material is plant-based biomass and is not particularly limited, and examples thereof include woody or herbaceous plant raw materials (fibrous raw materials). Examples of this wood-based raw material include thinned wood, sawn timber, scraps of scrapped house, wood processing waste, and furniture waste. , Pineapple and banana leaves, coconut coconut shells, sugar cane stalks, rice bran, agricultural waste. These are merely examples, and plant-based raw materials are not limited to these in the present invention, and can be widely used as long as they are substances composed of plants containing carbohydrates and lignin.

  These biomasses are preferably preliminarily pulverized to a size of 30 mm or less in order to facilitate component separation. This coarse pulverization can be carried out using a pulverizer commonly used for normal coarse pulverization such as a hammer mill, a rotary mill, or a crusher.

  In the present invention, the “gas containing oxygen” may be a gas having an oxygen concentration of 10% by weight or more, and includes, for example, air.

  Although it does not restrict | limit especially as reaction container used for this invention, For example, as shown in FIG. 1, it can endure high temperature and high pressure, the supply apparatus of plant-type raw materials, such as gas containing oxygen, wood flour, and a chip, and after reaction A container equipped with a device for extracting the residue and solution out of the system is used. This container is composed of a processing tank, a biomass supply device (biomass inlet and biomass supply screw), an oxygen supply valve, a pressure holding valve, a stirring device (stirring blade), and a portion for extracting a processed product.

  Examples of the alcohol applied to the plant material in the present invention include monohydric alcohols such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, sec-butanol, and t-butanol; ethylene glycol, 1,2-propane Dihydric alcohols such as diols; trihydric alcohols such as glycerin can be mentioned, preferably monovalent lower alcohols having 1 to 4 carbon atoms, more preferably ethanol.

  In the present invention, the alcohol used as the processing solvent can contain water, an organic acid, an organic acid ester, or the like. When the treatment solvent contains at least one selected from the group consisting of water, organic acid and organic acid ester, preferable content (volume) of at least one selected from the group consisting of water, organic acid and organic acid ester ) Is 1/2 or less, more preferably 1/5 or less, and still more preferably 1/10 or less of the volume of alcohol in the treatment solvent. The preferable content (volume) of alcohol in the processing solvent is 50 to 100%, more preferably 80 to 100%, still more preferably 90 to 100%, and still more preferably 95 to 100%. In addition to water, organic acids, and organic acid esters, it is also possible to add other various additives used for the treatment of plant raw materials to the extent that the effects of the present invention are not significantly impaired. .

  In the present invention, an alcohol-insoluble residue suitable for papermaking pulp and enzyme saccharification raw material can be obtained by heat-treating plant biomass in an alcohol solvent in the presence of oxygen. As processing temperature in this case, it is 100-250 degreeC normally, Preferably it is 120-190 degreeC. The reaction time is not particularly limited, but is usually 0.1 to 72 hours, preferably 1 to 24 hours, more preferably 5 to 20 hours. The reaction pressure is usually 0.1 to 2 MPa, preferably 0.5 to 1 MPa in the case of oxygen, and is usually 0.5 to 10 MPa, preferably 2.5 to 5 MPa in the case of air. In the case of producing pulp for papermaking, it is preferable to use a plant raw material having a particle diameter as large as possible in order to obtain long-fiber cellulose. It is preferable to do. When used as a pretreatment for enzymatic saccharification, it is preferable to use a plant material having a particle size as small as possible. In this case, treatment at a relatively high temperature for a short time is possible.

  Next, an example of a process suitable for producing ethanol and lignin degradation products by the method of the present invention will be described with reference to the accompanying drawings. FIG. 2 shows a schematic diagram of a process for producing ethanol and lignin degradation products (for example, malonic acid and succinic acid) from wood flour. By treating the pulverized biomass with alcohol under pressure of oxygen (or air) (first treatment), a first liquid component and a first solid component (insoluble residue) are generated. The lignin in the biomass is oxidized and decomposed to react with an organic acid, and further with an alcohol as a solvent, to become an organic acid ester, become soluble in the solvent and contained in the first liquid component. On the other hand, the first solid component is mainly a cellulose and hemicellulose, and is a solvent-insoluble residue having a low lignin content. Therefore, the first solid component has a high carbohydrate content and is very useful as a raw material for enzymatic saccharification, and is also very useful as a raw material for papermaking pulp because of its low lignin content. Furthermore, if silage processing is carried out, it can be used also as livestock feed.

  The first solid component and the first liquid component are subjected to solid-liquid separation (for example, filtration, centrifugation, etc.), and the first solid component is subjected to enzymatic saccharification treatment. In the enzymatic saccharification treatment, the first solid component is treated with a cellulose saccharifying enzyme (for example, Acremomo) in the presence of a solvent suitable for the enzyme such as water. Saccharides (mainly glucose) generated by enzymatic action are added to yeast (Saccharomyces cerevisiae, etc.), bacteria (Zymomonas genus, etc.), etc. and subjected to ethanol fermentation treatment. Ethanol, unreacted cellulose and lignin produced by the ethanol fermentation treatment are subjected to solid-liquid separation (for example, centrifugation, filtration, etc.), and liquid components containing ethanol are concentrated by distillation or the like and recovered as high-purity ethanol. Solid components composed of unreacted cellulose and lignin are burned in a boiler or the like and can be used as thermal energy.

  The first liquid component is separated into ethanol and an organic acid (or organic acid ester) by distillation or the like, and the recovered ethanol can be reused as a solvent for the first treatment. Moreover, the ethanol collect | recovered from the above-mentioned ethanol fermentation processed material can be utilized as a solvent for 1st processes as needed.

  Although a preferred example of the present invention has been described above, the present invention is not limited to this process, and those skilled in the art can appropriately modify this process, and such modified processes are also included in the present invention. Is done.

Conventionally, pulp (crude pulp) produced by cooking plant-based raw materials remains colored with a certain amount of lignin. ₂ O ₄ ) and other bleaching agents. When the crude pulp is treated by the method according to the present invention, it is possible to obtain a color-suppressed pulp as the first solid component (insoluble residue). This is because oxygen in the first treatment exerts an oxidative bleaching action on colored substances such as lignin as in the case of the oxidative bleach, but the solubility of oxygen in alcohol is about 7 times that of water. From this, it is considered that the oxygen oxidation reaction proceeds very efficiently. Moreover, according to this process, since it is preferentially oxidized and removed from the lignin component on the pulp surface, bleaching can be performed while suppressing a decrease in the weight of the raw material pulp.

  As described above, the treatment method of the present invention can remove most of lignin from plant-based biomass while suppressing the decomposition of cellulose and hemicellulose without using mineral acid, alkali or the like. This method enables various applications. For example, since the treatment method of the present invention can efficiently remove lignin in plant biomass, the solid component obtained by the treatment method can be used as a lignin-free cellulose and hemicellulose-containing material. The liquid component obtained by the treatment method of the present invention contains alcohol, an organic acid generated by oxidizing the alcohol, and an organic acid ester generated by the alcohol acting on the organic acid. By doing so, an alcohol, an organic acid, and an organic acid ester can be produced. For example, when ethanol is used as the alcohol, acetic acid is produced as the organic acid, and ethyl acetate is produced as the organic acid ester.

Therefore, the present invention
A method for producing a sugar by adding an enzyme that generates sugar using cellulose as a substrate to the first solid component generated by the first treatment,
A method for producing alcohol (particularly ethanol) by adding alcohol-fermenting microorganisms (particularly ethanol-fermenting microorganisms) to the sugar obtained by the method for producing sugars;
-A method for producing bleached pulp by the first treatment using lignin-containing pulp raw material as plant biomass,
A method for producing an organic acid and / or an organic acid ester by distilling the first liquid component produced by the first treatment;
Etc. may be included.

  According to the present invention, lignin can be efficiently separated from plant biomass. Therefore, the present invention is also useful for recovering lignin and lignin degradation products, producing bleached pulp, producing sugar, producing alcohol such as ethanol. For example, enzymatic saccharified sugars such as mannose, arabinose, xylose, glucose and the like can be obtained in high yield, and further, bioalcohol can be produced by subjecting these sugars to alcohol fermentation. Moreover, since this invention does not require a mineral acid or an alkali, there is also little environmental impact.

  EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited at all by these examples.

<Example 1>
In a 50 mL autoclave, 1000 mg of rice pinewood powder (particle size 0.25 to 0.42 mm) and 10 mL of ethanol were charged, the lid of the autoclave was closed, and air was press-fitted (5 MPa at room temperature), and then heating was started. When the temperature of the reaction solution reached 160 ° C., the temperature was maintained at that temperature for 3 hours, and then the heating was stopped and the autoclave was cooled. The residue was separated from the reaction solution with a centrifuge, washed several times with ethanol, dried under reduced pressure, and the weight was measured. The pale yellow residue was a fine fibrous substance as shown in the electron micrograph (FIG. 3). This is considered to indicate a microfibril structure in which lignin is removed from the wood fiber. About 10 mg from the residue (581 mg) after drying was precisely weighed, suspended in water, and saccharified with cellulase 40 FPU. The total amount of enzyme saccharified sugar (glucose and mannose) produced after the reaction for 48 hours was 468 mg / g on the basis of the raw material rice pine.

  On the other hand, when the ethanol solution obtained by removing the residue from the reaction solution was analyzed with a gas chromatograph mass spectrometer, esters such as ethyl acetate, ethyl formate, diethyl malonate, and diethyl succinate were detected. Furthermore, when the ethanol solution was diluted with water and analyzed by liquid chromatography, acetic acid (5 mg) and formic acid (8 mg) were produced. These products are thought to be produced by oxidation of ethanol or rice pine components.

<Comparative Example 1>
When rice pine wood powder (particle diameter 0.25 to 0.42 mm) was treated in the same manner as in Example 1 except that 10 mL of water was used instead of ethanol, a black residue was obtained. This was an amorphous substance as shown in an electron micrograph (FIG. 4). About 10 mg of the dried black powder (507 mg) was precisely weighed and saccharified with cellulase 40 FPU. The total amount of enzyme saccharified saccharide (glucose and mannose) produced after the reaction for 48 hours was 76 mg / g based on the raw material rice pine. Moreover, when the aqueous solution obtained by removing a residue from the reaction solution was analyzed by liquid chromatography, 130 mg / g of glucose and mannose were produced in total. In addition, acetic acid (27 mg), formic acid (56 mg), glycolic acid (38 mg), and levulinic acid (2 mg), which were thought to be produced by oxidation of ethanol or rice pine components, were detected.

<Comparative example 2>
Argon was injected in place of air (5 MPa at room temperature), and the reaction was performed in the same manner as in Example 1 except that the reaction was performed at 210 ° C. for 1 hour. The resulting pretreatment residue (991 mg) was added to cellulase 40FPU. Saccharified. The total amount of enzyme saccharified saccharide (glucose and mannose) produced after the reaction for 48 hours was 16 mg / g based on the raw material rice pine.

<Example 2>
In a 50 mL autoclave, 1000 mg of rice pinewood powder (particle size 0.42-1 mm) with 25.3% lignin content and 10 mL of ethanol were charged, the autoclave lid was closed, and air was injected (5 MPa at room temperature). The heating was started. When the temperature of the reaction solution reached 150 ° C., the temperature was maintained at that temperature for 18 hours, and then the heating was stopped and the autoclave was cooled. The pale yellow fibrous residue was separated from the reaction solution with a centrifuge, washed several times with ethanol, dried under reduced pressure, and the weight was measured. About 10 mg from the pretreated residue (665 mg) after drying was precisely weighed, suspended in water, and saccharified with cellulase 40 FPU. The total amount of the enzymatic saccharified sugars (glucose and mannose) produced after the reaction for 48 hours was 457 mg / g based on the raw material rice pine. Moreover, when 300 mg was precisely weighed from the said residue and the lignin content was measured by the method based on JIS-P8211, the lignin content was 3.5%.

<Example 3>
Except that oxygen was injected in place of air (1 MPa at room temperature), rice pine wood powder (particle size 0.42 to 1 mm) having a lignin content of 25.3% was treated in the same manner as in Example 3 to obtain a pale yellow fiber. A residue (703 mg) was obtained. About 10 mg of the residue after drying was precisely weighed, suspended in water, and saccharified with cellulase 40 FPU. The total amount of enzyme saccharified saccharide (glucose and mannose) produced after the reaction for 48 hours was 463 mg / g based on the raw material rice pine. Moreover, when 300 mg was precisely weighed from the said residue and lignin content was measured by the method based on JIS-P8211, lignin content was 5.0%.

<Example 4>
In a 20 mL autoclave with a glass inner tube, 200 mg of rice pine wood powder (particle size under 0.25 mm), 1 mL of ethanol, and 3 mL of water were charged, the autoclave lid was closed, and air was injected (5 MPa at room temperature). The heating was started. When the temperature of the reaction solution reached 200 ° C. after about 1 hour and 25 minutes, the heating was stopped and the autoclave was cooled. The reaction solution was filtered, the residue was washed several times with water, dried under reduced pressure, and the weight was measured. As a result of analyzing the combined solution of the reaction solution and the water washing solution by liquid chromatography, 131 mg / g of saccharide was produced based on the raw material Yonematsu. The pretreatment residue after drying (106 mg) was suspended in water, subjected to ultrasonic waves for 30 minutes, and then saccharified with cellulase 20FPU. The amount of glucose produced after the reaction for 24 hours was 184 mg / g based on the raw material Yonematsu.

  The method of the present invention is useful for separating components of cellulose, hemicellulose, and lignin from lignocellulosic biomass and producing various useful substances such as ethanol and lignin degradation products from the separated components.

It is a figure which shows the example of a reaction apparatus. It is explanatory drawing of the biomass component separation process for enforcing this invention method. 2 is an electron micrograph of the residue obtained in Example 1. 2 is an electron micrograph of the residue obtained in Comparative Example 1.

Claims (11)

Including a step of heat-treating a plant-based raw material in an alcohol solvent under an oxygen- only atmosphere to obtain a heat-treated product containing the first liquid component and the first solid component, and solid-liquid separation of both components. The processing method of the plant-type raw material characterized by these. The treatment method according to claim 1, wherein the alcohol solvent contains at least one selected from the group consisting of water, an organic acid, and an organic acid ester. The treatment method according to claim 1 or 2, wherein the alcohol is ethanol. The processing method in any one of Claims 1-3 including the process of saccharifying-enzyme processing the 1st solid component obtained by solid-liquid separation, and obtaining an enzyme saccharifying saccharide. The processing method of Claim 4 including the process of solid-liquid-separating the ethanol fermented material obtained by ethanol-fermenting enzyme saccharified saccharide, and collect | recovering ethanol from the liquid material obtained. The processing method of Claim 4 including the process of solid-liquid-separating the ethanol fermented material obtained by ethanol-fermenting an enzyme saccharified saccharide, and obtaining a lignin as a solid substance. The processing method in any one of Claims 1-3 which utilizes the 1st solid component obtained by solid-liquid separation as pulp for papermaking. The first liquid component obtained by solid-liquid separation is distilled, the alcohol is recovered from the gaseous product obtained by distillation, and / or the liquid product obtained by distillation is selected from the group consisting of organic acids and organic acid esters the method according to any one of claims 1 to 7 comprising the step of recovering at least one member. The processing method according to any one of claims 1 to 8, wherein a reaction pressure in the heat treatment is 0.1 to 2 MPa. The processing method according to claim 1, wherein a reaction pressure in the heat treatment is 0.5 to 1 MPa. The processing method in any one of Claims 1-10 which does not use a mineral acid and an alkali.

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