JP2011213637A - Method for producing lactic acid by using indium compound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alternative method for efficiently producing lactic acids from a carbohydrate-containing raw material.SOLUTION: This method for producing the lactic acid and/or lactic acid esters includes heat-treating the carbohydrate-containing raw material in a solvent containing water and/or an alcohol and also containing at least one kind selected from the group consisting of an indium alkoxide and indium acetylacetonate.

Description

  The present invention relates to a method for producing lactic acids from a carbohydrate-containing raw material using an indium compound as a catalyst.

  At present, a method for producing lactic acid that is industrially used is based on lactic acid fermentation of saccharides (see Patent Document 1). However, in order to use cellulose as a raw material for lactic acid fermentation by this method, it is necessary to go through a saccharification step using an acid or an enzyme. In general, a method for producing lactic acid by fermentation has a slow reaction rate and requires a large fermenter, and also has a problem that energy consumption for purification is increased because the concentration of lactic acid produced is low. In addition, lactic acid fermentation is performed while neutralizing with a base because the fermentation efficiency of lactic acid bacteria decreases as the pH of the solution decreases as the fermentation progresses. Accordingly, lactate is produced by this lactic acid fermentation method, and treatment with acid is performed to liberate lactic acid from lactate, and treatment of neutralized salt resulting therefrom is a major problem in the process. Yes.

  As a method for producing lactic acid that does not depend on a biological method, a chemical method in which a carbohydrate is hydrothermally treated in the presence of an alkali is known. For example, when saccharides (see Non-Patent Documents 1 and 2), cellulose (see Patent Documents 2 and 3), or organic waste (see Non-Patent Document 4) are treated by this method, reaction conditions of high temperature and high pressure are performed. Lactic acid is produced by isomerization of some of the carbohydrates decomposed in However, in this method, lactic acid reacts with the alkali added as a catalyst to form a lactate, so that in order to separate lactic acid as an acid, it is necessary to add some inorganic acid to the reaction solution to make it acidic. There is a problem that the alkali and the inorganic acid are consumed stoichiometrically.

  As a chemical production method of lactic acid without using an alkali, there has been reported a method of converting starch, oligosaccharide or monosaccharide into a lactic acid ester by reacting with alcohol using a metal halide as a catalyst (Patent Literature). 3). However, as a result of investigations by the present inventors, the cellulose-based raw material could not be decomposed at a temperature lower than 200 ° C., and formation of lactic acid or lactic acid ester was not recognized.

  In addition, an example in which a cellulose-based raw material is directly converted to lactic acid by a chemical reaction without using an alkali has been reported, but this is very high temperature and high pressure (temperature 350 ° C. or more and less than 400 ° C., pressure 20 MPa or more and 35 MPa ), The energy consumption is large, and the yield of lactic acid is insufficient (see Patent Document 4).

  In addition, as a report of producing lactic acid from cellulose-based raw materials in one step, examples using Group 3 metal salts as catalysts (see Patent Documents 5 and 6) and examples using rare earth metal oxides as catalysts (Patent Document 7). Have been reported). Since these use relatively expensive Group 3 metals or rare earth metals, it is thought that this leads to an increase in costs during the production of lactic acid.

JP-A-6-31886 JP-A-2005-232116 JP 2004-359660 A JP 2004-323403 A JP 2008-120996 A JP 2009-263242 A JP 2009-263241 A

Byung Y.Y. and Montgomery R., Carbohydrate Research, Vol.280 (1996) p.27-45 Byung Y.Y. and Montgomery R., Carbohydrate Research, Vol.280 (1996) p.47-57 Niemelae K. and Sjoestroem E., Biomass, 11 (1986) p.215-221 Armando T.Q. et al., Journal of Hazardous Materials, B93 (2002)

  An object of the present invention is to provide an alternative method for efficiently producing lactic acids from a carbohydrate-containing raw material.

  As a result of intensive studies to solve the above problems, the present inventors have found that lactic acid (lactic acid and / or lactic acid ester) can be efficiently produced from a carbohydrate-containing raw material by using an indium compound as a catalyst. The present invention has been completed.

That is, the present invention includes the following.
Lactic acid and / or lactic acid characterized by heat-treating a carbohydrate-containing raw material in a solvent containing water and / or alcohol containing at least one selected from the group consisting of indium alkoxide and indium acetylacetonate Ester production method.

  In this method, it is also preferable that the solvent containing water and / or alcohol further contains a phenolic compound.

  In this method, the heat treatment is also preferably performed by heating at 100 ° C to 300 ° C.

  In the method of the present invention, lactic acids can be efficiently produced from carbohydrate-containing raw materials.

Hereinafter, the present invention will be described in detail.
In the present invention, by subjecting a carbohydrate-containing raw material to heat treatment in a solvent containing water and / or alcohol containing at least one selected from the group consisting of indium alkoxide and indium acetylacetonate, which functions as a catalyst. A reaction product containing lactic acid and / or lactic acid ester can be obtained.

  If the method of this invention is used, lactic acid and / or a lactic acid ester can be manufactured simply and very highly efficiently from the carbohydrate in a carbohydrate containing raw material.

  The carbohydrate-containing raw material that can be used as the raw material in the method of the present invention may be any raw material containing carbohydrate. Without limitation, the carbohydrate-containing material can be any carbohydrate such as a monosaccharide, oligosaccharide (2-9 linked monosaccharides), or polysaccharide (10 or more monosaccharides bonded), or It may be a biological material containing it. The monosaccharide can be glucose, fructose, galactose, mannose and the like. Although it does not limit as a polysaccharide, A cellulose is preferable. Carbohydrate-containing raw materials include, for example, carbohydrates containing hexoses such as cellulose, holocellulose, cellobiose, starch (eg, soluble starch), maltose, glucose, mannose, fructose, galactose, and growth, hemicellulose, xylose, arabinose, etc. It may be a hemicellulose-based material containing carbon sugar, or at least one of them, for example, a lignocellulosic material. Although a carbohydrate containing raw material is not specifically limited, For example, the biomass material containing the above carbohydrates (for example, glucose, fructose, cellulose, etc.) may be sufficient. The carbohydrate-containing raw material particularly preferably contains a monosaccharide. Examples of carbohydrate-containing raw materials include lignocellulosic biomass materials including agricultural waste such as waste paper, sawn timber, wheat straw, corn stover, corn cob, and corn ears, and food waste containing sugars such as starch and glucose Etc. The carbohydrate-containing raw material used in the method of the present invention preferably contains water in addition to a carbohydrate such as cellulose.

  In the method of the present invention, a catalyst for decomposition reaction and isomerization reaction of indium alkoxide or indium acetylacetonate to a carbohydrate compound and further isomerization reaction of a tricarbon sugar produced as an intermediate to lactic acid and / or lactic acid ester Used as In a preferred embodiment of this method, indium alkoxide is preferably used. In another embodiment of this method, it is preferred to use indium acetylacetonate. In yet another embodiment of this method, both indium acetylacetonate and indium alkoxide may be used. Examples of the indium alkoxide that can be used in the present invention include indium methoxide, indium ethoxide, indium isopropoxide, indium-n-butoxide, and indium-t-butoxide. Examples of indium acetylacetonate that can be used in the present invention include indium acetylacetone, tris (2,2,6,6-tetramethyl-3,5-heptanedionato) indium, indium trifluoroacetylacetonate, and the like. . One type of indium alkoxide and indium acetylacetonate may be used in one reaction system, or two or more types may be used.

  The solvent containing water and / or alcohol used in the method of the present invention is a solution containing water or alcohol, or both. This solvent may be water or alcohol alone, a mixed solution of water and alcohol, or a solution in which other components such as other organic solvents are mixed. As water, distilled water, ion exchange water, industrial water, or the like can be used. Although it does not specifically limit as alcohol, A C1-C8 aliphatic alcohol is preferable. For example, methanol, ethanol, propanol, isopropanol, 1-butanol, 2-butanol, ethylene glycol and the like can be mentioned. Hydrous alcohol can also be suitably used as a solvent in the present invention. One or two or more alcohols may be contained in the solvent. In the method of the present invention, when the carbohydrate raw material contains monosaccharide or oligosaccharide, lactic acid can be produced by using a solvent containing water (particularly preferably water), and lactic acid ester is produced by using a solvent containing alcohol. it can. The amount of water and / or alcohol-containing solvent used for the carbohydrate-containing raw material can be appropriately selected by those skilled in the art and is not particularly limited, but is usually raw material: solvent = 1: 1 in weight ratio. ˜1: 1000, preferably 1: 5 to 1: 100.

  The total amount (use amount) of indium alkoxide and / or indium acetylacetonate to be contained in a solvent containing water and / or alcohol is not limited, but relative to 1 mmol of glucose residue in the carbohydrate-containing raw material. Thus, an amount corresponding to 0.00001 to 1.0 mol, preferably 0.005 mol to 0.1 mol, for example, 0.01 to 0.05 mol in terms of mass ratio can be used.

  The method for producing lactic acids using indium alkoxide and / or indium acetylacetonate is particularly suitable for the production of lactic acids from monosaccharides, and is therefore particularly suitable when the carbohydrate-containing raw material contains monosaccharides.

  In the method of the present invention, in addition to indium alkoxide and / or indium acetylacetonate, it is also preferable to add a phenolic compound to the solvent. Examples of the phenolic compound include, but are not limited to, phenol, cresol, alkylphenol, catechol, pyrogallol, alkoxyphenol, salicylic acid, salicylic acid ester, 2,2'-biphenol, quinolinol, and the like. The amount of the phenolic compound used can be appropriately adjusted by those skilled in the art, but it is 0.1 to 10.0 mol with respect to 1.0 mol of indium alkoxide and / or indium acetylacetonate. It is preferable that it is in the range of 1.0 mol to 4.0 mol. By adding a phenolic compound, the yield of lactic acids can be greatly improved.

  In the method of the present invention, a carbohydrate-containing raw material is heat-treated in a solvent containing water and / or alcohol containing indium alkoxide and / or indium acetylacetonate. In the method of the present invention, it is preferable to add indium alkoxide and / or indium acetylacetonate and a carbohydrate-containing raw material into a solvent containing water and / or alcohol before the heat treatment. A phenolic compound may be added to a solvent containing water and / or alcohol together with indium alkoxide and / or indium acetylacetonate. The conditions for the heat treatment can be appropriately adjusted by those skilled in the art depending on the type of saccharide or alcohol contained in the raw material, but are preferably 100 ° C to 300 ° C, more preferably 100 ° C to 250 ° C, for example, 140 ° C. -195 degreeC can be used conveniently. Thus, the method of the present invention can be carried out at a relatively low heating temperature.

  In the method of the present invention, the heat treatment is preferably performed in the absence of oxygen. In order to make the oxygen non-existing condition, it is preferable to fill the reaction vessel with an inert gas before the heat treatment and purge (exclude) the air. Although the kind of inert gas is not specifically limited, For example, nitrogen gas, argon gas, carbon dioxide gas etc. are mentioned as an example.

  The heat treatment of the present invention is also preferably performed under pressure. The reaction pressure is preferably at least atmospheric pressure, preferably 0.2 MPa to 20 MPa, and more preferably 0.4 MPa to 10 MPa.

  Although the reaction in the solvent containing water and / or alcohol in the method of the present invention is not limited, it is preferably carried out in a pressure reaction apparatus such as an autoclave. Another preferred reaction form is a continuous flow reaction method (continuous method). The reaction liquid in which the raw material / solvent / catalyst is mixed can be continuously supplied to a reactor controlled at a predetermined temperature and pressure, and allowed to stay in the reactor for a predetermined time for reaction.

  In the method of the present invention, for example, a magnetic stir autoclave is charged with a solvent containing indium alkoxide and / or indium acetylacetonate (catalyst), a carbohydrate-containing raw material, a phenolic compound as necessary, and water and / or alcohol. Then, after purging air with an inert gas, heating to the above heating temperature may be performed for a predetermined time. The heating time can be appropriately adjusted by those skilled in the art and is not particularly limited, but may be 3 to 24 hours after reaching the heating temperature, and preferably 5 to 12 hours. After a predetermined heating time has elapsed, heating may be stopped and allowed to cool to room temperature. After cooling to room temperature, the reaction product is removed from the autoclave.

  In the method of the present invention using a continuous flow system reaction method, a carbohydrate-containing raw material, a solvent containing water and / or alcohol, indium alkoxide and / or indium acetylacetonate (catalyst), and optionally a phenolic compound are added. The mixed reaction solution may be continuously supplied to a reactor controlled at a predetermined heating temperature and pressure, and allowed to stay in the reactor for a predetermined heating time for reaction. After the heating time has elapsed, heating may be stopped and allowed to cool to room temperature. After cooling to room temperature, the reaction product is removed from the reactor.

  By the above method, lactic acid and / or lactic acid ester can be produced in high yield. When the carbohydrate-containing material contains monosaccharides or oligosaccharides, when indium alkoxide and / or indium acetylacetonate is used as a catalyst, lactic acid or lactic acid ester can be efficiently produced from those sugars. For example, by this method, lactic acid and / or lactic acid ester is obtained in a yield of 5% to 60%, for example 30 to 50%, based on the number of moles produced per glucose residue in the carbohydrate-containing raw material. Can do. In addition to indium alkoxide and / or indium acetylacetonate, when a phenolic compound is used in combination, lactic acid and / or lactate ester is used compared to when indium alkoxide and / or indium acetylacetonate is used alone. The yield of can be increased, for example, by 5 to 15%. In addition to indium alkoxide and / or indium acetylacetonate, when a phenolic compound is used in combination, lactic acid and / or lactate ester is used compared to when indium alkoxide and / or indium acetylacetonate is used alone. The yield of can be increased, for example, by 5 to 15%.

  It is also preferable to separate lactic acid or lactic acid ester from the reaction solution obtained as described above. This separation can be performed by an organic acid separation method known to those skilled in the art, such as liquid chromatography.

The following examples illustrate the invention but do not limit its scope.
(Example 1) Lactic acid ester synthesis from fructose using indium compound In a 50-ml stainless steel pressure reactor (manufactured by Nitto Koatsu), 15 mg (0.05 mmol) of indium isopropoxide as an indium compound and raw material carbohydrate After adding 0.450 g (2.5 mmol) of fructose and 10 mL of methanol as a solvent at room temperature, 0.5 MPa of nitrogen gas was injected into the reactor of the apparatus, and the inside of the reactor became 150 ° C. using a mantle heater. Until heated. After holding at 150 ° C. for 10 hours, heating was stopped and the mixture was allowed to cool. After cooling the reaction apparatus to room temperature, the pressure was released and the remaining organic phase was extracted, and the resulting solution was quantitatively analyzed by liquid chromatography. As a result, 2.4 mmol of methyl lactate was produced. The yield of methyl lactate was 48% when expressed in terms of fructose, that is, as a percentage (%) of the number of moles produced per mole of fructose of the raw material.

(Example 2) Lactic acid synthesis from fructose using an indium compound In a 50-ml stainless steel pressure reactor (manufactured by Nitto High Pressure), 15 mg (0.05 mmol) of indium isopropoxide as an indium compound and a raw material carbohydrate After 0.450 g (2.5 mmol) of fructose and 10 mL of pure water as a solvent were added at room temperature, 0.5 MPa of nitrogen gas was injected into the reactor of the apparatus, and the inside of the reactor was 160 ° C. using a mantle heater. Heated until. After holding at 160 ° C. for 5 hours, heating was stopped and the mixture was allowed to cool. After cooling the reaction apparatus to room temperature, the pressure was released and the remaining organic phase was extracted, and the resulting solution was quantitatively analyzed by liquid chromatography. As a result, 0.24 mmol of lactic acid was produced. The yield of this lactic acid was 5% when expressed in terms of fructose, that is, as a percentage (%) of the number of moles produced per mole of fructose of the raw material.

(Example 3) Synthesis of lactate ester from glucose using indium compound Same as Example 1 except that 0.450 g (2.5 mmol) of glucose was used instead of fructose as a raw material carbohydrate and the reaction temperature was 180 ° C. The reaction was conducted under conditions. As a result, 2.0 mmol (40% yield based on glucose) of methyl lactate was produced, and 0.08 mmol of methyl levulinate (3% yield based on glucose) was produced as a by-product. The glucose standard is the percentage (%) of the number of moles produced per mole of glucose of the raw material.

(Example 4) Lactate ester synthesis from glucose using indium acetylacetonate The same conditions as in Example 1 except that 20.8 mg (0.05 mmol) of acetylacetone indium (In (acac) ₃ ) was used as the indium compound. The reaction was carried out. As a result, 1.55 mmol of methyl lactate (yield 31% based on fructose) was produced, and no methyl levulinate was produced.

(Example 5) Effect of adding phenolic compound In addition to indium isopropoxide, fructose and methanol, the reaction was conducted under the same conditions as in Example 1 except that 0.1 mmol of catechol was added as a phenolic compound to the reactor. It was. As a result, 2.6 mmol of methyl lactate (52% yield based on fructose) was produced, and 0.15 mmol of methyl levulinate (6% yield based on glucose) was produced as a by-product.

(Example 6) Effect of addition of phenolic compound The same conditions as in Example 1 except that 0.1 mmol of 2,2-biphenol was added to the reactor as a phenolic compound in addition to indium isopropoxide, fructose and methanol. The reaction was carried out. As a result, 2.5 mmol of methyl lactate (yield 50% based on fructose) was produced.

  The method of the present invention provides a novel catalytic reaction system that efficiently converts biomass containing saccharides such as monosaccharides and polysaccharides into lactic acid and lactic acid esters. By using the method of the present invention, it becomes possible to efficiently produce lactic acid and / or lactic acid ester using biomass containing carbohydrates. By using the method of the present invention, for example, lactic acid and lactic acid esters can be efficiently produced in one step by a chemical reaction from a saccharide (for example, a monosaccharide) in a carbohydrate-containing raw material.

Claims (3)

  Lactic acid and / or lactic acid characterized by heat-treating a carbohydrate-containing raw material in a solvent containing water and / or alcohol containing at least one selected from the group consisting of indium alkoxide and indium acetylacetonate Ester production method.   The method according to claim 1, wherein the solvent containing water and / or alcohol further comprises a phenolic compound.   The method according to claim 1 or 2, wherein the heat treatment is performed by heating at 100C to 300C.