JP3772238B2 - Method for producing α-hydroxycarboxylic acid - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing α-hydroxycarboxylic acid such as glycolic acid and glycolic acid.
[0002]
[Prior art]
α-Hydroxycarboxylic acid is an industrially important compound as a monomer for polymerization which is a raw material for various synthetic resins such as polyglycolic acid. Among these, glycolic acid is used as a metal cleaning agent for cleaning printed wiring boards and the like, and as a scale inhibitor for boilers and the like. In recent years, it is also used as an anti-wrinkle cosmetic liquid, basic cosmetics and the like. In particular, when it is used as a cosmetic product, it is necessary to consider safety and toxicity because it directly touches the human body. Glycolic acid itself does not have such problems, but impurities contained in the product may be problematic.
[0003]
Conventionally, glycolic acid is mainly produced by (1) a method of reacting carbon monoxide, formaldehyde and water under high pressure under an acid catalyst, or (2) a method of reacting chloroacetic acid and sodium hydroxide. Yes. The glycolic acid produced by these methods contains impurities such as organic acids other than glycolic acid such as formaldehyde, chlorine-containing compounds, and methoxyacetic acid.
[0004]
Accordingly, glycolic acid used in cosmetics and the like is required to have a high purity that does not contain these impurities.
[0005]
However, glycolic acid is difficult to isolate and purify by general-purpose purification methods such as distillation, and in particular, it is difficult to completely remove impurities as described above. In practice, high-purity products in which impurities are removed as much as possible from industrial grade glycolic acid containing a large amount of impurities are used.
[0006]
Commercially available industrial grade glycolic acid is mainly produced by the following two methods. One is a production method in which formaldehyde and carbon monoxide are subjected to a carbonylation reaction in the presence of an acid catalyst under high temperature and high pressure. The industrial grade product by this manufacturing method is in the form of a 70% aqueous solution. As organic acids other than glycolic acid, glyric acid dimer, diglycolic acid, methoxyacetic acid, formic acid, etc. total 10 weights with respect to glycolic acid. More than% is included. These impurities cannot be separated by a method such as distillation. Therefore, it is necessary to go through a complicated purification process, and there is a problem that the yield is low.
[0007]
High-purity products manufactured by this method are also available on the market, but their purity is as high as 99% or more, but their price is more than 10 times that of industrial products, and their general-purpose applications are limited.
[0008]
Another method for producing glycolic acid is a method in which monochloroacetic acid is hydrolyzed with sodium hydroxide and then neutralized. In this method, sodium hydroxide twice as much as the stoichiometric amount is consumed as an auxiliary material, so that sodium chloride contaminated with organic substances is generated in large quantities as waste.
[0009]
Thus, development of a method capable of producing high-purity glycolic acid free of impurities such as formaldehyde and chlorine-containing compounds with high economic efficiency is strongly demanded.
[0010]
[Problems to be solved by the invention]
Accordingly, a main object of the present invention is to provide a method for producing a high-purity α-hydroxycarboxylic acid that does not contain formaldehyde, chlorine-containing compounds and the like as impurities.
[0011]
[Means for Solving the Problems]
As a result of intensive studies to solve the problems of the prior art, the present inventor has found that (i) only 1,2-diol, or (ii) in the presence of a catalyst supporting metal and oxygen. The inventors have found that the above object can be achieved by hydrolyzing an α-hydroxycarboxylic acid ester obtained by reacting 1,2-diol with a primary alcohol, and have completed the present invention.
[0012]
That is, the present invention relates to a method for producing α-hydroxycarboxylic acid such as glycolic acid described below and glycolic acid.
1. α-hydroxycarboxylic acid ester obtained by reacting (i) 1,2-diol or (ii) 1,2-diol and a primary alcohol with oxygen in the presence of a metal-supported catalyst Is a method for producing an α-hydroxycarboxylic acid by hydrolysis.
2. Hydrolyzing a glycolic acid ester obtained by oxygen oxidation using ethylene glycol and a primary alcohol (preferably a primary alcohol having 1 to 4 carbon atoms) as raw materials in the presence of a metal-supported catalyst. A process for producing glycolic acid by
3. 3. The production method according to 1 or 2 above, wherein the average particle size of the metal supported on the carrier is 10 nm or less.
4). 4. The production method according to any one of 1 to 3, wherein the carrier is an inorganic oxide.
5). 5. The production method according to 4 above, wherein the inorganic oxide support is an oxide containing at least one selected from the group consisting of Si, Al, Ti and Zr.
6. The production method according to 1 above, wherein the molar ratio of primary alcohol to 1,2-diol is about 1: 3 to 20.
7. The method according to any one of 1 to 6 above, which comprises any one of the steps of removing oxalic acid or oxalic acid ester of (A) to (C) shown below before or after hydrolysis:
(A) A step of adding a metal salt and / or an ammonium salt and separating a metal oxalate salt and / or an ammonium oxalate salt to be produced
(B) adding ammonia and separating the oxamic acid ester and oxamide produced; and
(C) A step of adsorbing the oxalate ester to the resin using an anion exchange resin.
8). Glycolic acid substantially free of formaldehyde and chlorine as impurities.
9. 2. Glycolic acid comprising 10 wt. Ppb or more of ethylene glycol and obtained by the method described in 1 above.
10. Glycolic acid containing 10 wt ppb or more of ethylene glycol.
11. It can be produced by hydrolyzing a glycolic acid ester obtained by oxygen oxidation in the presence of a metal-supported catalyst using ethylene glycol and a primary alcohol as raw materials. Glycolic acid not included.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The production method of α-hydroxycarboxylic acid of the present invention comprises (i) 1,2-diol or (ii) 1,2-diol and a primary alcohol supported on a catalyst (hereinafter referred to as “supported metal”). The α-hydroxycarboxylic acid ester is produced by hydrolyzing an α-hydroxycarboxylic acid ester obtained by reacting with oxygen in the presence of a catalyst.
[0014]
I. Production of glycolic acid
1. Supported metal catalyst
(1) Catalytic active ingredients
The catalyst used in the present invention is a catalyst in which a metal as an active component is supported on a carrier, that is, a supported metal catalyst.
[0015]
The metal as the active component is not particularly limited, but is preferably a noble metal, and examples thereof include noble metals such as gold, palladium, ruthenium, rhodium, iridium, and platinum, and gold, palladium, ruthenium, and the like are more preferable. .
[0016]
The catalyst used in the present invention contains the above-mentioned noble metal as an essential component, and further, as an active component, the 2B group, the 3B group, the 4B group, the 5B group, the 6B group, the 6B group, and the 8th cycle of the 4th period to the 6th period. It can contain at least one element selected from the group consisting of groups. Hereinafter, these elements may be referred to as second elements. Specific examples of the second element include 2B group such as Zn, Cd and Hg; 3B group such as Ga, In and Tl; 4B group such as Ge, Sn and Pb; 5B group such as As, Sb and Bi; Se , Te, Po etc. 6B group; Fe, Co, Ni etc. 8 group etc. can be illustrated. The catalyst used in the present invention is preferably a catalyst containing at least Pb as the second element. For example, a catalyst in which metal fine particles containing at least one active component selected from the group consisting of Au, Pd and Ru and Pb are supported on a support can be suitably used.
[0017]
The metal which is an active ingredient may contain the said noble metal independently, and may contain 2 or more types. When two or more kinds of noble metals are included, part or all of them may form an alloy, an intermetallic compound, or the like as long as the effects of the present invention are obtained.
[0018]
Moreover, when the metal which is an active component contains a noble metal and a second element, as long as the effect of the present invention is obtained, a part or all of them may form an alloy, an intermetallic compound, or the like. The catalyst used in the present invention, in which the noble metal and the second element are usually supported on the carrier as fine particles, contains other elements or impurities other than the noble metal and the second element within a range not impeding the effects of the present invention. Also good.
[0019]
The particle size of the metal particles as the active component is not limited as long as a predetermined catalytic activity is obtained, but the average particle size is usually about 10 nm or less, preferably about 6 nm or less, more preferably about 5 nm or less, particularly preferably. Is about 1 to 5 nm. If it is set within this range, excellent catalytic activity can be obtained more reliably. The lower limit of the average particle diameter is not particularly limited, but may be about 1 nm from the viewpoint of physical stability.
[0020]
The average particle diameter of the metal particles in the present invention is as follows: (1) 10 particles from the top in the descending order and (2) among 120 particles arbitrarily selected by observation with a transmission electron microscope (TEM). ) Shows the arithmetic average value of 100 particle diameters, excluding a total of 10 particles from the bottom 10 in order from the smallest. Moreover, in this invention, it is preferable that the maximum value of the particle diameter distribution of a metal particle exists in the range of about 1-6 nm, especially about 1-5 nm. The particle size distribution is preferably narrow, and the standard deviation of the 120 particle diameters is preferably about 2 or less, particularly about 1.5 or less.
[0021]
The supported amount of the metal active component in the catalyst may be appropriately determined according to the use of the final product, the type of the carrier, etc. It is preferable to set it as 1-10 weight part.
[0022]
(2) Carrier
As the carrier, those conventionally used as catalyst carriers can be used, and are not particularly limited. For example, a commercial item can be used. Moreover, what is obtained by a well-known manufacturing method can also be used. For example, metal oxides (silica, alumina, titania, zirconia, magnesia, etc.), composite metal oxides (silica / alumina, titania / silica, silica / magnesia, etc.), zeolite (ZSM-5, etc.), mesoporous silicate (MCM- Inorganic oxides such as 41; natural minerals (clay, diatomaceous earth, pumice, etc.); various supports of carbon materials (activated carbon, graphite, etc.), among which inorganic oxides are preferred.
[0023]
In the present invention, at least one of Mg, Ca, Sr, Ba, Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Sn, Pb, La, and Ce is used. An inorganic oxide carrier made of an oxide containing an element can be preferably used. The oxide may be a mixed oxide in which two or more elemental element oxides are mixed, or may be a double oxide (or composite oxide). As the inorganic oxide carrier, an oxide containing at least one element selected from the group consisting of Si, Al, Ti and Zr is preferable.
[0024]
The production method of the carrier is not limited, and a known production method can be used. For example, an impregnation method, a coprecipitation method, an ion exchange method, a vapor deposition method, a kneading method, a hydrothermal synthesis method, and the like can be given.
[0025]
For example, the above inorganic oxide support includes Mg, Ca, Sr, Ba, Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Sn, Pb, La, and Ce. It is obtained by impregnating silica with an aqueous solution of a water-soluble compound containing at least one kind and then firing the resulting impregnated body. Such an inorganic oxide carrier can more reliably support fine particles as a catalytically active component, and can obtain higher catalytic activity due to a synergistic action with the fine particles.
[0026]
The compound used in the above carrier production method is not limited. Examples thereof include inorganic compounds such as nitrates, sulfates and hydroxides, and organic compounds such as carboxylates, alkoxides and acetylacetonates.
[0027]
The water-soluble compound is not limited as long as it is water-soluble. For example, inorganic acid salts such as titanyl sulfate, zirconyl nitrate, zinc nitrate, lanthanum nitrate, iron nitrate, nickel nitrate, aluminum nitrate; titanium n-butoxide, titanium acetylacetonate, zirconium acetylacetonate, lead acetate, magnesium acetate, etc. Mention may be made of organic acid salts. These salts may be either anhydrides or hydrates. The concentration of the aqueous solution can be appropriately set according to the type of water-soluble compound used.
[0028]
The amount of the aqueous solution impregnated into the silica is not limited, but usually it may be about 1 to 20 parts by weight with respect to 100 parts by weight of silica.
[0029]
In the present invention, the inorganic oxide support is preferably porous, and particularly has a specific surface area (BET method) of 50 m.²/ G or more is preferable, 100m²/ G or more is preferable, 100 to 800 m²Particularly preferred is about / g. The shape and size of the carrier are not limited and may be appropriately determined according to the use of the final product.
[0030]
2. Method for producing catalyst used in the present invention
The method for producing the catalyst used in the present invention is not limited as long as the above support is obtained. For example, it can be obtained by heat-treating a support containing at least one of a desired metal and its compound. The metal compound may be any of hydroxide, chloride, carboxylate, nitrate, alkoxide, acetylate toner salt and the like.
[0031]
Moreover, when carrying | supporting 2 or more types of metals on a support | carrier, the order to carry | support is not limited, either may be first and may be simultaneous. In the case where the noble metal and the second element are supported on the support, the order in which the precious metal and the second element are supported is not limited, and any of them may be first or simultaneously. Hereinafter, a case where gold and a second element are used in combination as active ingredients will be described as an example. That is, (A) a method in which gold is supported on a carrier and then a second element, (B) a method in which gold is supported after the second element is supported on a carrier, and (C) gold and the second element. Any method of simultaneously supporting the carrier may be used. Hereinafter, each method will be described. The method for producing a gold carrier described in the method (A) is an example of a method for producing a catalyst that supports a metal and does not contain a second element.
[0032]
Method (A)
The method (A) is a method of supporting a second element after supporting gold on a carrier. First, a gold carrier on which gold is carried is manufactured. The method for producing the gold carrier is not limited, and conventional methods such as a coprecipitation method, a precipitation method, an impregnation method, and a vapor deposition method can be applied. In the present invention, the coprecipitation method, the precipitation method, and the like are preferable, and the precipitation method is more preferable.
[0033]
In the case of using the precipitation method, for example, the carrier is allowed to coexist in an aqueous solution containing a gold compound, the gold-containing precipitate is precipitated on the surface of the carrier, and then the carrier on which the gold-containing precipitate is deposited is fired. A carrier can be obtained. When the gold-containing precipitate is precipitated on the support surface, various conditions such as the gold concentration, temperature, pH, etc. of the aqueous solution may be appropriately controlled. Further, the carrier on which the gold-containing precipitate is deposited may be washed with water, dried, or the like prior to firing.
[0034]
The gold compound is not particularly limited as long as it is water-soluble. For example, tetrachloroauric (III) acid “H [AuCl_Four], Sodium tetrachloroaurate (III) "Na [AuCl_Four], Potassium dicyanoaurate (I) "K [Au (CN)₂], Diethylamine gold (III) trichloride "(C₂H_Five)₂NH [AuCl_Three]; And gold compounds such as gold (C) cyanide. At least one of these compounds can be used.
[0035]
The gold concentration of the aqueous solution varies depending on the type of compound used, but is usually about 0.1 to 100 mmol / L. Moreover, what is necessary is just to set pH of the said aqueous solution to about 5-10 normally, Preferably it is about 6-9. The pH can be adjusted with an alkali such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, or ammonia. If necessary, an acid such as hydrochloric acid can be used. These alkalis or acids may be used in the form of an aqueous solution if necessary.
[0036]
If necessary, a surfactant can be added to the aqueous solution. The surfactant may be appropriately selected from known or commercially available products according to the aqueous solution. For example, anionic surfactants such as long-chain alkyl sulfonic acids and salts thereof, long-chain alkyl benzene sulfonic acids and salts thereof, long-chain alkyl carboxylic acids and salts thereof, aryl carboxylic acids and salts thereof; long-chain alkyl quaternary ammonium salts And the like; and nonionic surfactants such as polyalkylene glycol and polyoxyethylene nonylphenol. At least one of these surfactants can be used. In the present invention, anionic surfactants and nonionic surfactants are preferred, and anionic surfactants are particularly preferred. Among anionic surfactants, in particular, long-chain alkyl sulfonic acids having 8 or more carbon atoms and salts thereof, long-chain alkyl benzene sulfonic acids and salts thereof having 8 or more carbon atoms, long-chain alkyl carboxylic acids having 8 or more carbon atoms and their salts More preferred are salts, arylcarboxylic acids and salts thereof.
[0037]
The amount of the surfactant used can be appropriately determined depending on the desired dispersibility, the type of the surfactant to be used, and the like. Usually, the surfactant concentration may be about 0.1 to 10 mmol / L.
[0038]
As the carrier to be mixed with the aqueous solution, various carriers as described above can be used. The carrier may be used in any form such as a granular form or a granulated body. What is necessary is just to set the usage-amount of a support | carrier suitably according to the density | concentration of the said aqueous solution, the kind of support | carrier used, etc. When mixing the aqueous solution and the carrier, the aqueous solution may be heated as necessary. The temperature in this case is usually about 10 to 100 ° C. The mixing time of the aqueous solution and the simple substance can be changed depending on the type of carrier, constituent elements, etc., but is usually within a range of about 1 minute to 24 hours, preferably 10 minutes to 3 hours. May be set so as to be supported on the carrier as much as possible. What is necessary is just to set suitably the usage-amount of a support | carrier so that it may become a predetermined carrying amount.
[0039]
After mixing and stirring the aqueous solution and the carrier, the solid content is recovered. The solid content can be recovered by recovering the supernatant or according to a known solid-liquid separation method. The recovered solid content is preferably washed with ion-exchanged water or the like until residual ions are substantially eliminated.
[0040]
Next, the solid content is fired. If necessary, it may be dried by heating in advance to a predetermined temperature prior to firing. The drying temperature is usually about less than 150 ° C. The firing temperature is usually about 150 to 800 ° C, preferably about 200 to 700 ° C, more preferably about 250 to 600 ° C. The firing atmosphere may be in air (air) or an oxidizing atmosphere, or in an inert gas atmosphere such as nitrogen, argon gas, or helium, or in a reducing atmosphere such as hydrogen gas or carbon monoxide. . Moreover, what is necessary is just to determine a baking time suitably according to a baking temperature, the magnitude | size of solid content, etc. By such firing, a predetermined gold carrier in which gold is firmly fixed to the surface of the carrier can be obtained. The gold carrier obtained by such a method can be used as a catalyst in the method of the present invention.
[0041]
Next, after supporting at least one of the second element and its compound on a gold support, gold and the second element are combined by heat treatment.
[0042]
The above loading method is not limited and can be carried out according to a conventional method. For example, an impregnation method, an ion exchange method, a vapor deposition method, and the like can be given. Of these, the impregnation method can be suitably used. For example, after preparing a mixture of a solution in which a compound containing the second element is dissolved and the gold carrier, the second element can be suitably supported by heat-treating the solid content recovered from the mixture.
[0043]
Although it does not specifically limit as a compound containing a 2nd element, For example, organic compounds, such as inorganic compounds, such as nitrate, a sulfate, a hydroxide, a chloride, formate, acetate, a beta-diketone compound, and an alkoxide, are illustrated. can do. More specifically, lead acetate, zinc acetate, zinc nitrate, bismuth nitrate, germanium (III) butoxide, nickel bismuth acetylacetonate, iron acetate and the like can be mentioned.
[0044]
The solution in which the compound containing the second element is dissolved can be prepared by using a combination of the compound containing the second element and the solvent in which it dissolves. Although there is no limitation in particular as a solvent, Water, an organic solvent, etc. can be used. Examples of the organic solvent include alcohols, ketones, aromatic hydrocarbons, carboxylic acid esters, and nitriles. In particular, it is preferable to use at least one of water and alcohol (particularly methanol and ethanol). Therefore, the above combination preferably uses the above compound that is soluble in water or alcohol. For example, when Pb is used as the second element, a solution in which lead acetate (which may be a hydrate) is dissolved in methanol can be preferably used.
[0045]
The concentration of the second element in the solution in which the compound containing the second element is dissolved can be appropriately determined according to the type of the compound, the type of the solvent, and the like, but it may be usually about 0.01 to 10 mmol / L.
[0046]
Moreover, the mixing ratio of the gold carrier and the solution in which the compound containing the second element is dissolved can be appropriately determined according to the concentration of the solution, the desired loading amount of gold or the second element, and the like.
[0047]
After preparing a mixture of the gold carrier and a solution in which the compound containing the second element is dissolved, the solid content is recovered from the mixture. The solid content recovery method is not limited. For example, a compound containing the second element may be supported on the gold support. For example, it is preferable to distill off the solvent with an evaporator or the like.
[0048]
Next, heat treatment of the solid content is performed. The heat treatment temperature may be a temperature at which each obtained metal particle is composed of gold and the second element. That is, when the finally obtained metal particle carrier is used as a catalyst, heat treatment may be performed so that the catalytic activity due to the combination of gold and the second element is expressed.
[0049]
The heat treatment temperature varies depending on the type of the second element and the like, but is generally about 50 to 800 ° C., preferably about 100 to 600 ° C.
[0050]
The heat treatment atmosphere is not particularly limited, and may be any of a reducing atmosphere, an oxidizing atmosphere, an inert atmosphere, and the like. In order to obtain a reducing atmosphere, for example, in addition to reducing gases such as hydrogen, carbon monoxide and alcohol, a mixed gas obtained by diluting these reducing gases with an inert gas such as nitrogen, helium, and argon may be used. good. In order to obtain an oxidizing atmosphere, a gas containing oxygen, air, or the like may be used. In order to obtain an inert atmosphere, an inert gas such as nitrogen, helium, or argon may be used. In the present invention, a reducing atmosphere is particularly desirable. Further, after heat treatment in an oxidizing atmosphere, heat treatment can also be performed in a reducing atmosphere.
[0051]
The heat treatment time can be appropriately changed depending on the temperature of the heat treatment or the like, but it is usually about 10 minutes to 24 hours.
[0052]
Depending on the type of the second element, the solid content may be reduced using a reducing agent such as formalin, hydrazine, sodium borohydride, formic acid or the like prior to the heat treatment in order to further promote the complexation with gold. good.
[0053]
Method (B)
The method (B) is a method of supporting gold after the second element is supported on the carrier. The method for supporting the second element is not limited. For example, the same method as in the above (A) can be used. That is, the second element may be supported on the carrier by the same method as in the above (A). The raw material of the second element, the loading conditions, etc. may be the same as those listed in (A) above.
[0054]
However, in some cases, as a preferable additional treatment in the subsequent gold loading operation, the second element is firmly attached to the carrier by firing at about 300 to 900 ° C. in an oxidizing atmosphere (in the presence of a gas containing air or oxygen). Can be immobilized.
[0055]
Gold support on the second element carrier thus manufactured can be carried out by the same method as in the above (A). That is, after supporting gold by a precipitation method or the like, drying and firing may be performed in the same manner as in the above (A). Further, similarly to the above (A), it is desirable to perform a heat treatment in a reducing atmosphere similar to the above (A) in order to make the composite of gold and the second element more satisfactory. Moreover, the reduction process using a reducing agent can also be combined as needed.
[0056]
Method (C)
The method (C) is a method in which gold and the second element are simultaneously supported on a carrier. The method is not limited as long as both can be supported simultaneously. For example, conventional methods such as a coprecipitation method, a precipitation method, an impregnation method, and a vapor deposition method can be used. In either case, when gold is supported on the carrier, both can be simultaneously supported by allowing the compound containing the second element to coexist in the system. Further, a catalyst in which ultrafine metal particles containing gold and a second element are supported on a carrier by subjecting both of them to heat treatment and / or reduction treatment in the same manner as in the above method (A) or (B). Can be obtained.
[0057]
In the present invention, a precipitation method or an impregnation method can be preferably used. In the precipitation method, it is deposited as a compound containing gold (for example, a hydroxide), and conditions under which the precipitate is easily formed (for example, when the compound is a hydroxide, the temperature is about 30 to 100 ° C., the pH is about 5 to 10, It is desirable to control so that the compound containing the second element precipitates and forms a precipitate at a gold concentration of about 0.1 to 100 mmol / L. In this case, it is desirable to use a water-soluble compound containing the second element as a starting material and form a precipitate as a hydroxide containing the second element from the aqueous solution. In addition, it is desirable to form a hydroxide containing both gold and the second element by simultaneously forming the precipitates of the gold and the second element during precipitation. These precipitates can be further subjected to heat treatment and / or reduction treatment to obtain a catalyst.
[0058]
In the impregnation method, a gold compound and a compound containing a second element are added simultaneously to a solution in which a compound containing a gold compound and a second element is dissolved in an organic solvent, and if necessary, the organic solvent is distilled off and the like. The catalyst can be obtained by being deposited on a support and then subjected to heat treatment and / or reduction treatment. As a typical example, a carrier is impregnated with a methanol solution containing a gold acetylacetonate compound (eg, dimethylgold acetylacetonate) and a second element acetylacetonate compound (eg, nickel acetylacetonate), and methanol is added. After the solvent is distilled off, a catalyst in which gold alloy ultrafine particles (for example, Au—Ni alloy ultrafine particles) containing gold and a second element are supported on a carrier can be obtained by drying and reducing treatment.
[0059]
The raw material compounds used in the above precipitation method or impregnation method, the operating conditions, etc. can be those shown in the above method (A).
[0060]
3. Method for producing α-hydroxycarboxylic acid ester
In the method for producing an α-hydroxycarboxylic acid ester of the present invention, (i) 1,2-diol or (ii) 1,2-diol and a primary alcohol are reacted in the presence of a supported metal catalyst and oxygen. It is characterized by that. That is, (i) oxygen is reacted with 1,2-diol, or (ii) oxygen is reacted with 1,2-diol and a primary alcohol.
[0061]
The 1,2-diol is not particularly limited as long as it has a hydroxyl group at the 1-position and the 2-position, and may be, for example, a trihydric or higher polyhydric alcohol. Specific examples of the 1,2-diol include aliphatic 1,2 carbon atoms having 2 to 10 carbon atoms such as ethylene glycol, 1,2-propylene glycol, 1,2-butanediol, and 1,2-hexanediol. -Diols: C3-C10 aliphatic polyhydric alcohols having a hydroxyl group at the 1- and 2-positions such as glycerin, erythritol, xylitol, sorbitol, etc., and derivatives of these 1,2-diols. Examples of 1,2-diol derivatives include aliphatic 1,2-diols having 2 to 10 carbon atoms containing halogen such as 3-chloro-1,2-propanediol; 2-phenyl-1,2- C2-C10 aliphatic 1,2-diol having an aromatic ring such as ethanediol. As the 1,2-diol, an aliphatic diol having about 2 to 6 carbon atoms such as ethylene glycol can be suitably used. These 1,2-diols can be used alone or in combination of two or more.
[0062]
The primary alcohol is not particularly limited as long as it has a primary hydroxyl group, and may be, for example, a dihydric or higher polyhydric alcohol. Specific examples of the primary alcohol include aliphatic primary alcohols having 1 to 10 carbon atoms such as methanol, ethanol, 1-propanol, 1-butanol, 1-hexanol and 1-octanol; 1,3-butanediol, 1 C2-C10 aliphatic polyhydric alcohols having primary hydroxyl groups such as 1,4-butanediol; C3-C10 aliphatic unsaturated alcohols having primary hydroxyl groups such as allyl alcohol and methallyl alcohol; benzyl Examples include alcohols having an aromatic ring such as alcohol. As the alcohol, aliphatic primary alcohols having 1 to 4 carbon atoms such as methanol, ethanol, 1-propanol and 1-butanol can be suitably used, and monohydric alcohols such as methanol, ethanol, 1-propanol and 1-butanol. Is particularly preferred. These primary alcohols can be used alone or in combination of two or more.
[0063]
In the production method of the present invention, the 1,2-diol and primary alcohol may be appropriately selected depending on the type of the desired α-hydroxycarboxylic acid ester. For example, when a glycolic acid ester is synthesized, ethylene glycol as 1,2-diol and primary alcohol such as methanol, ethanol, 1-propanol, 1-butanol and the like may be used as primary alcohol. Alternatively, when only ethylene glycol is used as the 1,2-diol, glycolic acid 2-hydroxyethyl ester can be produced.
[0064]
The reaction ratio of 1,2-diol and primary alcohol is not particularly limited, but the molar ratio of primary alcohol to 1,2-diol is usually about 1: 2 to 50, and about 1: 3 to 20 More preferred. By setting it within the above range, it becomes possible to synthesize α-hydroxycarboxylic acid ester more efficiently.
[0065]
In the present invention, (i) 1,2-diol alone or (ii) 1,2-diol and primary alcohol are reacted in the presence of a supported metal catalyst and oxygen (molecular oxygen).
[0066]
The reaction may be any of a liquid phase reaction and a gas phase reaction. Oxygen (oxygen gas) may be diluted with an inert gas such as nitrogen gas, argon gas, helium gas or carbon dioxide gas. An oxygen-containing gas such as air can also be used. The method for supplying the oxygen-containing gas to the reaction system is not particularly limited, and a known method can be adopted. In particular, bubbling into the liquid can be suitably used.
[0067]
The form of the reaction may be any of continuous type, batch type, semi-batch type, etc., and is not particularly limited. In the case of adopting a batch system as a reaction form, the catalyst may be charged into the reaction apparatus together with the raw materials. Further, when a continuous type is adopted as the reaction form, the catalyst may be charged in advance in the reaction device, or the catalyst may be continuously charged together with the raw material in the reaction device. The catalyst may be in any form such as a fixed bed, a fluidized bed, and a suspended bed.
[0068]
The amount of the catalyst used may be appropriately determined according to the type of raw material 1,2-diol or primary alcohol, the type of catalyst, reaction conditions, and the like. The reaction time is not particularly limited and varies depending on the set conditions. Usually, the reaction time or residence time (retention liquid amount in the reactor / liquid supply amount) is about 0.5 to 20 hours, preferably 1 to 10 hours. It should be a degree.
[0069]
Various conditions such as reaction temperature and reaction pressure may be appropriately determined according to the type of raw material 1,2-diol or primary alcohol, the type of catalyst, and the like. The reaction temperature is usually about 0 to 180 ° C, preferably about 20 to 150 ° C, more preferably about 50 to 120 ° C. By setting the temperature within this range, the reaction can proceed more efficiently. The reaction pressure may be any of reduced pressure, normal pressure or increased pressure, but is usually in the range of about 0.05 to 5 MPa (gauge pressure), particularly about 0.1 to 2 MPa. The total pressure may be set so that the oxygen concentration of the reactor effluent gas does not exceed the explosion range (8%). Further, the pH of the reaction system is preferably about 2 to 9 from the standpoint of by-product suppression. In order to adjust the pH, for example, an alkali metal compound or an alkaline earth metal compound (carboxylate) can be used as an additive to the reaction system.
[0070]
The above reaction can be carried out in the presence of a solvent. By using a solvent, the target carboxylic acid ester may be produced efficiently. The solvent that can be used is not limited as long as it dissolves the raw material 1,2-diol or primary alcohol and is difficult to react by itself under the reaction conditions, depending on the type of raw material alcohol, reaction conditions, etc. What is necessary is just to select suitably. For example, water, ethers such as diethyl ether, diisopropyl ether, and dioxane; aromatic hydrocarbons such as toluene, xylene, and benzene; halogen-containing compounds such as methylene chloride, chloroform, and ethylene dichloride . What is necessary is just to set the usage-amount of a solvent suitably according to the kind of solvent, the kind of alcohol, the kind of catalyst, etc.
[0071]
4). Purification of α-hydroxycarboxylic acid ester or α-hydroxycarboxylic acid
After the oxygen oxidation reaction, the catalyst is separated from the reaction system, and the produced α-hydroxy acid ester may be recovered using a known separation and purification means. The separation method of the catalyst may follow a known method. For example, when the reaction system comprises a catalyst (solid content) and a reaction product (liquid component), the catalyst and the reaction product can be separated using a known solid-liquid separation method such as filtration or centrifugation.
[0072]
In the production method of the present invention, for example, when ethylene glycol is used as a 1,2-diol and a primary alcohol (preferably a primary alcohol having 1 to 4 carbon atoms) is used as a primary alcohol, a glycolic acid ester is produced. Can do. The solution obtained after the reaction contains glycolic acid ester as a main product, and in some cases, primary alcohol and ethylene glycol which are unreacted raw materials. Furthermore, the reaction solution contains water as a by-product, and in some cases, a carboxylic acid ester derived from a primary alcohol (for example, methyl formate when methanol is used as the primary alcohol), oxalic acid Examples include esters, hydrolysis products such as glycolic acid, oxalic acid, and oxalic acid monoester.
[0073]
As a method for isolating the target glycolic acid ester from such a reaction solution, a method of first distilling off the primary alcohol and water and then separating the glycolic acid ester by distillation is illustrated as an easily feasible method. it can. When the glycolic acid ester is distilled, unreacted ethylene glycol is contained in the distillation bottom. The distillation bottom containing the primary alcohol and glycolic acid ester recovered at this time can be reused as a raw material when producing the glycolic acid ester.
[0074]
However, since glycolate ester and oxalate ester have close boiling points, it is not easy to separate them by distillation. For example, methyl glycolate has a boiling point of 151 ° C. and dimethyl oxalate has a boiling point of 164 ° C. Oxalic acid ester produced when ethylene glycol and primary alcohol are reacted is as low as about 10 mol% or less based on glycolic acid ester. However, when used as a polymer raw material for polyglycolic acid or the like, a high molecular weight polyglycolic acid may not be obtained if a small amount of oxalic acid is contained. In such a case, it is necessary to remove the oxalate ester by some method.
[0075]
Therefore, the oxalate ester may be removed as necessary. As a purification method of an oxalic acid ester and / or a glycolic acid ester containing oxalic acid, for example, (A) a method of adding a metal salt and / or an ammonium salt and separating the resulting metal oxalate salt and / or ammonium oxalate salt And (B) a method of adding ammonia and separating the produced oxamic acid ester and / or oxamide, and (C) a method of adsorbing oxalic acid to the resin using an anion exchange resin. Hereinafter, the purification methods (A) and (B) will be described. The above purification methods (A) to (C) may be used in combination. The following purification methods (A) to (C) may be performed either before or after the hydrolysis step.
[0076]
Purification method ( A )
The purification method (A) is a method in which a metal salt and / or an ammonium salt is added and a metal oxalate salt and / or an ammonium oxalate salt to be produced is separated. Hereinafter, the reaction mixture after oxygen oxidation or hydrolysis may be referred to as “crude product”.
[0077]
The metal salt and ammonium salt used in the purification method (A) are not particularly limited as long as they are soluble in water, lower alcohols (eg, methanol, ethanol, etc.), and mixed solvents thereof. A metal salt can be preferably used rather than an ammonium salt. The metal salt may be a complex salt.
[0078]
Examples of metal salts include hydroxides, carboxylates, carbonates, alkoxides, halides, 1,3-diketone salts, and the like. Examples of the carboxylate include 1 to 1 carbon atoms such as formic acid, acetic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, 2-ethylhexanoic acid, lauric acid, and 2-hexyldodecanoic acid. Examples thereof include salts of about 16 fatty acids; salts of hydroxycarboxylic acids such as glycolic acid and lactic acid. Examples of the alkoxide include aliphatic alkoxides having about 1 to 4 carbon atoms such as methoxide, ethoxide, isopropoxide and n-butoxide; aromatic alkoxides such as phenoxide. Examples of the halide include fluoride, chloride, bromide, iodide and the like. Examples of 1,3-diketone salts include acetylacetonate salts. As the metal salt, carboxylate such as glycolate, acetate, 2-ethylhexanoate; hydroxide; acetylacetonate salt and the like are preferable, and glycolate is particularly preferable.
[0079]
The metal ion contained in the metal salt is preferably an ion that has a low solubility in water, lower alcohols (for example, methanol, ethanol), and a mixed solvent thereof when the salt is formed with oxalic acid and easily precipitates. Examples of metal ions contained in the metal salt include Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺Alkali metal ions such as Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Br²⁺, Ra²⁺Alkaline earth metal ions such as Ti⁴⁺, V⁵⁺, Cr³⁺, Mn²⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu⁺, Cu²⁺, Zn²⁺Transition metal ions such as La;³⁺, Ce³⁺, Ce⁴⁺, Pr³⁺, Pr⁴⁺, Nd²⁺, Nd³⁺, Nd⁴⁺, Pm³⁺, Sm²⁺, Sm³⁺, EU²⁺, EU³⁺, Gd²⁺, Gd³⁺, Tb³⁺, Tb⁴⁺, Dy²⁺, Dy³⁺, Dy⁴⁺, Ho³⁺, Er³⁺, Tm²⁺, Tm³⁺, Yb²⁺, Yb³⁺, Lu³⁺And lanthanoid ions. As the metal ions, alkaline earth metal ions and lanthanoid ions are preferred.
[0080]
As the metal salt, magnesium glycolate, zinc acetate, calcium acetate, calcium hydroxide, sodium hydroxide, nickel 2-ethylhexanoic acid, tris (acetylacetonato) lanthanum and the like can be preferably used.
[0081]
Examples of ammonium salts include ammonium acetate and ammonium carbonate, with ammonium carbonate being preferred.
[0082]
The addition amount of the metal salt and ammonium salt is not particularly limited, but the lower limit of the addition amount is usually about 0.1 equivalent or more, preferably about 0.5 equivalent or more, with respect to the total amount of oxalate ester and oxalic acid, More preferably, it is about 1 equivalent or more. The upper limit of the addition amount of the metal salt and ammonium salt is usually about 50 equivalents or less, preferably about 10 equivalents or less, more preferably about 5 equivalents or less with respect to the total amount of oxalate ester and oxalic acid.
[0083]
Metal salts and ammonium salts are added to crude products as solutions in lower alcohols such as water, methanol and ethanol; ketones such as acetone; aromatic organic solvents such as toluene and xylene; mixed solvents thereof. May be. When the crude product already contains water, lower alcohol, etc., the metal salt and ammonium salt can be added as a solid, but it is preferable to add them as a solution.
[0084]
Examples of the lower alcohol used as the solvent include primary alcohols having about 1 to 8 carbon atoms, preferably about 1 to 4 carbon atoms. Specifically, methanol, ethanol, propanol, isopropanol, butanol and the like can be exemplified.
[0085]
When adding and mixing the metal salt and / or oxalate, heating is usually performed so that a metal salt / ammonium salt of oxalic acid is easily formed. The mixing temperature is not particularly limited as long as oxalate is produced, but is usually about 20 to 120 ° C, preferably about 40 to 90 ° C.
[0086]
The mixing time is not particularly limited as long as oxalate is sufficiently generated and the effects of the present invention are exhibited, and can be appropriately set according to the amount of the crude product, the composition of the crude product, and the like. The mixing time is usually about 0.1 to 5 hours, preferably about 0.5 to 3 hours.
[0087]
The mixing may be performed in an oxidizing atmosphere such as air, but is preferably performed in an inert atmosphere such as nitrogen or a rare gas (such as helium or argon).
[0088]
When a metal salt or ammonium salt is added to the crude product, since oxalic acid is stronger than glycolic acid, the oxalate ester selectively forms a metal salt or an acid ammonium salt via oxalic acid. Moreover, when the addition amount of the metal salt and ammonium salt is about 1 equivalent or more with respect to the oxalate ester and oxalic acid contained in the crude product, the oxalate ester and oxalic acid are almost quantitatively converted to the metal salt or ammonium salt thereof. Can be converted to In particular, when metal salts such as alkaline earths and lanthanoids are added, the resulting oxalate has low solubility and precipitates as a precipitate, so it can be easily separated by known solid-liquid separation means such as filtration and centrifugation. Can be separated.
[0089]
Moreover, even when the produced metal oxalate salt and ammonium oxalate salt exhibit a certain degree of solubility in organic solvents such as water and alcohol and mixed solvents thereof, the metal oxalate salt and ammonium oxalate Since the salt is non-volatile, it can be easily separated by distillation.
[0090]
Purification method ( B )
The purification method (B) is a method of separating oxamic acid ester and oxamide produced by adding ammonia to the crude product. In the said refinement | purification method (B), when ammonia is added to a crude product, an oxalate ester or an oxamide will produce | generate by azolysis of an oxalate ester.
[0091]
The amount of ammonia added is not particularly limited, but the molar ratio (ammonia / oxalic acid diester) to the oxalic acid diester contained in the crude product is about 1 to 10, preferably about 1 to 5, and more preferably. It is about 1.2 to 3. By setting it as the said range, an oxalic acid diester can be removed more reliably. Alternatively, the glycolic acid ester can be purified with a high yield.
[0092]
The reaction temperature for the amylolysis is not particularly limited as long as the oxamic acid ester or oxamide is formed, but is usually about 0 to 100 ° C, preferably about 30 to 60 ° C.
[0093]
There are no particular restrictions on the pressure or rate of addition of ammonia to the crude product. The pressure may be normal pressure or pressurization, and the addition rate may be a rate at which the reaction temperature is maintained in the above range. Ammonia is added to the mixture by, for example, dropping a liquid ammonia or an ammonia solution (a solution in which ammonia is dissolved in a solvent inert to a reaction such as alcohol) dropwise into the mixture in a normal reactor equipped with a stirrer. , Ammonia gas or diluted ammonia gas (ammonia gas diluted with a gas inert to the reaction such as nitrogen gas) is directly blown into the mixture.
[0094]
Since the oxamide produced by the above-mentioned amylolysis is non-volatile and hardly soluble, it can be easily separated from the glycolic acid ester by a known solid-liquid separation method such as distillation, filtration or centrifugation. Oxamic acid esters can also be easily separated from glycolic acid esters by distillation.
[0095]
After removing the oxalate ester by the above method or the like, the glycolate ester can be separated and purified at a high yield by distilling the glycolate ester. As described above, it is usually preferable to distill off the primary alcohol and water prior to the distillation of the glycolic acid ester. A known method can be used for distillation of the glycolic acid ester. For example, as a batch-type distillation apparatus, a normal apparatus capable of refluxing equipped with a charging tank, a rectifying section, a condenser section, and the like can be used. The total content of oxalic acids (oxalic acid, oxalic acid ester, oxalic acid metal salt, ammonium oxalate, oxamide, etc.) in glycolic acid ester obtained by distillation can be reduced to about 10 ppm or less.
[0096]
Even if it is a glycolic acid ester obtained by removing oxalic acid ester and oxalic acid by the above method, distilling off water and alcohol, and further distilling, primary alcohol and ethylene glycol as unreacted raw materials, Further, it may contain produced water. The primary alcohol contained in the glycolic acid is usually about 1% by weight or less, and can be about 0.2% by weight or less depending on the purification conditions. Further, the content of ethylene glycol is usually about 1% by weight or less, and can be made about 1000 ppm by weight or less depending on the purification conditions. The water content is usually about 1% by weight or less, and can be about 0.2% by weight or less depending on the purification conditions. In addition, the content of the oxalic acid ester in the glycolic acid ester purified by distillation without removing the oxalic acid ester is usually 0.1% by weight or more, more precisely about 0.1 to 2% by weight.
[0097]
5). Hydrolysis of α-hydroxycarboxylic acid esters
Next, the α-hydroxycarboxylic acid ester obtained by oxygen oxidation is hydrolyzed to obtain α-hydroxycarboxylic acid. The hydrolysis step may be performed after the above purification. By hydrolysis, dimethyl oxalate and ethylene glycol contained as impurities in the α-hydroxycarboxylic acid ester become oxalic acid, methanol, and ethylene glycol. Oxalic acid and methanol can be easily removed by a known purification method such as distillation.
[0098]
Hydrolysis of the α-hydroxycarboxylic acid ester involves reacting (i) 1,2-diol or (ii) 1,2-diol and a primary alcohol as raw materials with oxygen in the presence of a supported metal catalyst. As long as the α-hydroxycarboxylic acid ester obtained by the above is used, it is not particularly limited, and known conditions can be applied.
[0099]
The hydrolysis in the present invention means a reaction in which an α-hydroxycarboxylic acid and an alcohol are generated by a reaction between the α-hydroxycarboxylic acid ester and water. The method for carrying out the hydrolysis reaction is not particularly limited, and conventionally known methods can be applied.
[0100]
The reaction temperature is usually about 30 to 150 ° C, preferably about 50 to 120 ° C. The molar ratio of water to α-hydroxycarboxylic acid ester (water / α-hydroxycarboxylic acid ester) is usually about 1/1 to 1/5, more preferably about 3/1 to 20/1. Moreover, a catalyst can be used if necessary, and usually an acid catalyst can be preferably used.
[0101]
Since the hydrolysis reaction of the α-hydroxycarboxylic acid ester is an equilibrium reaction, by removing the by-product alcohol out of the system, the equilibrium tends to be biased toward the production system side and the hydrolysis tends to proceed. Accordingly, a reaction method such as reactive distillation is suitable. For example, a method of reactive distillation in the presence of water can be exemplified. When the reactive distillation method is used, the α-hydroxycarboxylic acid ester is hydrolyzed by gas-liquid contact to obtain α-hydroxycarboxylic acid, and by-product alcohol (hereinafter sometimes referred to as byproduct alcohol) is obtained. It can be distilled out of the system. Therefore, the hydrolysis reaction can be carried out efficiently.
[0102]
The molar ratio of water and α-hydroxycarboxylic acid ester (water / α-hydroxycarboxylic acid ester) in the reactive distillation may be determined according to the reaction conditions of the reactive distillation and is not particularly limited. However, it is usually about 1/1 to 50/1, more preferably about 3/1 to 20/1.
[0103]
In order to further promote the reaction, the hydrolysis can be reactively distilled in the presence of an acid, if necessary. Such an acid is not particularly limited, and a conventionally known homogeneous acid catalyst or heterogeneous acid catalyst can be used. Specific examples include inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid; organic acids such as acetic acid; and solid acids such as activated alumina, silica-alumina, and zeolite. These acids may be used alone or in combination of two or more. The method for adding an acid to the α-hydroxycarboxylic acid ester is not particularly limited. Further, as the acid, α-hydroxycarboxylic acid, particularly α-hydroxycarboxylic acid as a target product (for example, glycolic acid in the case of methyl glycolate) can also be used. When the target α-hydroxycarboxylic acid is used as the acid, a high-purity α-hydroxycarboxylic acid can be produced more easily and inexpensively.
[0104]
After performing the above-mentioned reactive distillation, in order to distill off water, it can be distilled in the presence of an organic solvent (azeotropic agent) that forms an azeotropic composition with water, if necessary. The organic solvent is not particularly limited, and examples thereof include cyclohexane and n-propyl acetate. After performing reactive distillation in the presence of an organic solvent, by forming an azeotropic composition and distilling off water, that is, by performing an azeotropic dehydration operation, α- of higher purity and higher concentration can be obtained. Hydroxycarboxylic acids can be produced.
[0105]
The reactive distillation apparatus is not particularly limited. For example, the reactive distillation apparatus has a structure in which a gas phase portion exists in the apparatus, and the produced by-product alcohol (low boiling point component) can be continuously separated and removed to the gas phase portion. Just do it. As the reactive distillation apparatus, for example, various commonly used distillation apparatuses, and more specifically, batch (batch type) distillation apparatuses such as a multistage distillation column or continuous distillation apparatuses are suitable. That is, the reactive distillation of α-hydroxycarboxylic acid ester can be carried out continuously as necessary.
[0106]
When the reactive distillation apparatus is a multistage distillation column, the number of stages of the distillation column, and reaction conditions (operating conditions) such as reaction temperature, reaction pressure, liquid residence time, reflux ratio, and liquid hold-up amount are as follows: Experimentally or theoretically, for example, the number of stages and reaction conditions may be such that the amount of water distilled off with the by-product alcohol does not become excessive (so that water is not excessively distilled off) and the reaction conditions. is not. However, if the number of stages and the reflux ratio are extremely small, the reaction efficiency is lowered, and it may be difficult to efficiently produce α-hydroxycarboxylic acid. Further, if the number of stages and the reflux ratio are extremely increased, the apparatus (equipment) becomes excessively large for industrially implementing the production method according to the present invention, which is economically disadvantageous.
[0107]
As the multistage distillation column, a distillation column having three or more stages excluding the top (uppermost stage) and the bottom (lowermost stage) is preferable. Examples of such distillation columns include packed columns filled with packing materials such as Raschig rings, pole rings, interlock saddles, Dixon packing, McMahon packing, and sulzer packing; trays such as bubble bell trays, sieve trays, and valve trays A generally used distillation column such as a plate column using (plate) is suitable. A composite distillation tower having both a shelf and a packed bed can also be employed. The number of plates indicates the number of plates in a plate column, and the number of theoretical plates in a packed column.
[0108]
When performing the above reactive distillation using a batch distillation apparatus as a reactive distillation apparatus, α-hydroxycarboxylic acid ester, water, and, if necessary, an acid and / or an organic solvent are added to the evaporator of the apparatus. Then, the mixture is heated to the reaction temperature (distillation temperature), and hydrolysis proceeds while distilling off the by-product alcohol from the top of the apparatus. Thereby, the aqueous solution containing α-hydroxycarboxylic acid remains in the evaporator.
[0109]
When performing the above reactive distillation using a continuous distillation apparatus as a reactive distillation apparatus, for example, a mixture containing an α-hydroxycarboxylic acid ester, water, and, if necessary, an acid and / or an organic solvent. The mixed solution was subjected to reactive distillation while continuously supplying the liquid to the middle stage of the apparatus (the middle stage excluding the tower bottom and the tower top), and by-product alcohol was continuously fed from the tower top of the apparatus. While distilling off, an aqueous solution containing α-hydroxycarboxylic acid is continuously withdrawn from the bottom of the apparatus. The method for supplying the α-hydroxycarboxylic acid ester, water, acid and organic solvent to the continuous distillation apparatus is not particularly limited, and these components may be separately supplied to the apparatus. In other words, the supply stages of these components in the apparatus may be different stages.
[0110]
However, it is desirable to set the supply stage of the component having a lower boiling point in these components to be lower than the supply stage of the component having a higher boiling point so that the reactive distillation is efficiently performed. In the case of using an acid, the more the region (stage) where the acid is present, the greater the contact frequency between the α-hydroxycarboxylic acid ester and the acid, and the better the reaction efficiency. For this reason, it is preferable to supply an acid to the uppermost stage as possible in a continuous distillation apparatus. Furthermore, each of the above components may be supplied in a liquid state, may be supplied in a gaseous state, or may be supplied in a gas-liquid mixed state. When the acid is a solid acid (heterogeneous acid catalyst), the acid may be held (filled) in advance in a continuous distillation apparatus in place of, for example, part or all of the packing. In addition, in order to easily remove by-product alcohol out of the system, gas (nitrogen gas, etc.) inert to α-hydroxycarboxylic acid ester and α-hydroxycarboxylic acid is introduced from the bottom of the continuous distillation unit. You can also
[0111]
The reaction conditions in the reactive distillation may be set according to the type of α-hydroxycarboxylic acid ester and the like, and are not particularly limited, but the reaction temperature is not less than the boiling point of the by-product alcohol and not more than the boiling point of water. It is desirable that When the reaction temperature is lower than the boiling point of the byproduct alcohol, the byproduct alcohol cannot be distilled off efficiently. On the other hand, when the reaction temperature exceeds the boiling point of water, water is distilled off excessively, so that reactive distillation cannot be carried out efficiently. Moreover, there exists a possibility of causing side reactions, such as a decomposition reaction of (alpha) -hydroxycarboxylic acid ester and (alpha) -hydroxycarboxylic acid. When the acid is an inorganic acid or an organic acid (homogeneous acid catalyst), the acid may be separated and recovered from the α-hydroxycarboxylic acid by using a known method such as distillation.
[0112]
When the α-hydroxycarboxylic acid ester is hydrolyzed by the reactive distillation to obtain α-hydroxycarboxylic acid, the by-product is substantially only a by-product alcohol. Since the by-product alcohol is distilled off, the α-hydroxycarboxylic acid can be easily separated and purified. According to said method, highly purified alpha-hydroxycarboxylic acid is obtained in the state of aqueous solution.
[0113]
The obtained α-hydroxycarboxylic acid aqueous solution may be further processed according to a desired form. For example, (1) a method of concentrating to an aqueous solution having a high concentration (eg, about 70% by weight or more of glycolic acid), (2) an α-hydroxycarboxylic acid crystal solid through steps such as crystallization, filtration and drying A method etc. can be illustrated.
[0114]
Examples of the method for concentrating the α-hydroxycarboxylic acid aqueous solution include a method in which the α-hydroxycarboxylic acid aqueous solution after the hydrolysis step is heated as it is to distill off water. At the time of concentration, the pressure may be reduced as necessary.
[0115]
Examples of the crystallization method of α-hydroxycarboxylic acid include, for example, a method of crystallization by distilling water while heating until α-hydroxycarboxylic acid solid starts to precipitate and then cooling to near room temperature. Can do. The obtained crystals can be easily separated by a known solid-liquid separation method such as filtration.
[0116]
Further, when water is distilled off by performing an azeotropic dehydration operation using an organic solvent, α-hydroxycarboxylic acid with higher purity and higher concentration can be obtained.
[0117]
The α-hydroxycarboxylic acid thus obtained is substantially free of formaldehyde and chlorine. This is because in the present invention, neither formaldehyde nor chlorine is used as a raw material, and is hardly produced by reaction. According to the present invention, it is possible to provide an α-hydroxycarboxylic acid such as glycolic acid having a formaldehyde and chlorine content of about 1 ppm by weight or less, preferably about 100 ppm by weight or less, more preferably about 10 ppm by weight or less. .
[0118]
The α-hydroxycarboxylic acid obtained by the production method of the present invention can be suitably used for known uses such as polymerization monomers that are raw materials for various synthetic resins such as polyα-hydroxycarboxylic acid. Among these, glycolic acid is, for example, a cleaning agent, a tanning agent, a chelating agent, a metal cleaning agent for cleaning printed wiring boards, a scale inhibitor such as a boiler, or a pharmaceutical, an agricultural chemical, a cosmetic, an organic chemical, etc. As an intermediate raw material for various products, it can be suitably used as a synthetic raw material for polyesters, polymer surfactants and the like. Since glycolic acid obtained by the production method of the present invention does not contain impurities such as formaldehyde, chlorine-containing compounds, and methoxyacetic acid, it can be particularly suitably used for applications that directly touch the human body such as cosmetics.
[0119]
【The invention's effect】
According to the production method of the present invention, glycolic acid substantially free of formaldehyde and chlorine can be obtained.
[0120]
Also, glycolic acid substantially free of methoxyacetic acid can be obtained.
[0121]
Conventional high-purity glycolic acid is expensive because it is purified by a complicated method such as crystallization. According to the production method of the present invention, α-hydroxycarboxylic acid such as high purity glycolic acid can be obtained at low cost.
[0122]
Therefore, according to the method of the present invention, a glycolic acid oligomer, a low-cost and high molecular weight polyglycolic acid, and glycolide can be obtained.
[0123]
In the method of the present invention, when ethylene glycol is used as the 1,2-diol, glycolic acid containing a small amount of ethylene glycol can be obtained.
[0124]
【Example】
Examples are given below to further clarify the features of the present invention. However, the scope of the present invention is not limited to the scope of the examples.
[0125]
In addition, the measurement of the physical property in an Example was implemented with the following method.
(1) Amount of metal fine particles supported
Measured by fluorescent X-ray analysis.
(2) Average particle diameter of metal fine particles
The particle size was observed with a transmission electron microscope (TEM) (device name “HF-2000”, Hitachi, Ltd., acceleration voltage 200 kV), and the component analysis of the particles was performed with the attached X-ray analyzer.
(3) Determination of reaction products
The components of the reaction product in the reaction solution were quantitatively analyzed by gas chromatography and / or liquid chromatography.
[0126]
[Example 1] (Example of reaction of Pb-Au alloy catalyst, EG + MeOH)
(1) Catalyst preparation
TiO prepared by coprecipitation method₂-SiO₂(Molar ratio Ti / Si = 8: 2, firing temperature 600 ° C., 50 to 250 mesh) was used as a carrier.
[0127]
0.5 L of an aqueous tetrachloroauric acid solution having a concentration of 20 mmol / l was adjusted to pH 7 using a 0.5 N aqueous sodium hydroxide solution in a range of 65 to 70 ° C. In this aqueous solution, the TiO₂-SiO₂20 g of the carrier was added under stirring, and stirring was continued for 1 hour while maintaining the temperature at 65 to 70 ° C. Thereafter, the supernatant was removed by allowing to stand, 0.5 L of ion exchanged water was added to the remaining gold immobilization product, the mixture was stirred at room temperature for 5 minutes, and then the supernatant was removed three times. . The gold-immobilized product obtained by filtration was dried at 100 ° C. for 10 hours, and further calcined in air at 400 ° C. for 3 hours.₂-SiO₂Catalyst with gold supported on support (Au / TiO₂-SiO₂)
[0128]
Next, 50 ml of a methanol solution containing 1.835 g of lead acetate trihydrate was added to the gold support Au / TiO.₂-SiO₂20 g was added, and methanol was removed at 80 ° C. and normal pressure using an evaporator to impregnate and carry lead acetate. Thereafter, 20 g of a gold carrier carrying lead was filled in a glass tube and heated at 400 ° C. for 3 hours while flowing a mixed gas of hydrogen and nitrogen (volume ratio 10/90). In this way, metal particles containing gold and lead become TiO.₂-SiO₂A gold alloy carrier supported on a carrier was obtained. The amounts of gold and lead supported on this carrier were 5.4 wt% and 4.9 wt%, respectively, with respect to the carrier. Moreover, when the particle diameter of the metal particles was observed, almost all of them were highly dispersed with a particle diameter of 6 nm or less, showed a narrow particle diameter distribution having a maximum in the vicinity of 2 to 3 nm, and the average particle diameter was 6 nm or less. .
[0129]
(2) Oxidative esterification reaction (α-hydroxycarboxylic acid ester production)
Pb—Au alloy / TiO obtained in (1) above₂-SiO₂Α-hydroxycarboxylic acid ester was synthesized using a catalyst.
[0130]
Ethylene glycol (62 g, 1.0 mol), methanol (320 g, 10 mol) and the catalyst (20 g) were charged into a rotary stirring type 1 L autoclave with a cooling tube and sealed. Subsequently, a mixed gas of oxygen and nitrogen (volume ratio: 10/90) is blown into the liquid at a flow rate of 1 L / min for 5 hours at 90 ° C. while adjusting with a back pressure valve to maintain the system at 0.5 MPa. Reaction was performed.
[0131]
Thereafter, the product was cooled and opened, and the contents were analyzed by gas chromatography. As a result, 0.180 mol of raw material ethylene glycol was contained, and the product methyl glycolate, 2-hydroxyethyl glycolate, glycolide, The contents of dimethyl oxalate and other oxalic acids were 0.656 mol, 0.068 mol, 0.012 mol, 0.008 mol and 0.001 mol, respectively. The molar ratios of methyl formate and 2-hydroxyethyl formate to methyl glycolate were 0.12 and 0.03, respectively.
[0132]
(3) After removing oxalate, purify glycolate
In the reaction filtrate (404.9 g) obtained by separating the catalyst from the reaction solution obtained in the oxidative esterification reaction of (2) above, ethylene glycol and methanol as the remaining raw materials, the product of the above reaction, and the reaction were produced. Water was included. Of these, the oxalate ester was a total of 0.011 mol of 0.008 mol (0.92 g) of dimethyl oxalate and 0.001 mol of other oxalic acids (such as oxalic acid).
[0133]
After adding 3 ml of a methanol solution containing 0.013 mol of a magnesium salt of glycolic acid to this reaction solution, the whole amount was charged into a 1 L autoclave, and after nitrogen substitution, heated to 80 ° C. and stirred for 2 hours. After cooling and opening, it was confirmed that a white precipitate of magnesium oxalate was generated. Furthermore, when the reaction solution after filtration was analyzed by gas chromatography, signals corresponding to dimethyl oxalate and other oxalic acids almost disappeared.
[0134]
After filtering off magnesium oxalate, methanol and water were distilled off from the obtained filtrate under reduced pressure using a thin layer distillation apparatus. Thereafter, methyl glycolate was distilled off at a bottom temperature of 70 to 80 ° C. and a pressure of 5 to 10 torr using a glass distillation column having three stages. The purity of methyl glycolate in the distillate was 98% by weight or more, and methanol and water were contained in a total of about 1.5% by weight, but other impurities were 0.1% by weight or less. It was. The total content of dimethyl oxalate and other oxalic acids (such as oxalic acid) was 100 ppm by weight or less.
[0135]
(4) Hydrolysis reaction (hydrolysis by reactive distillation)
As the reactive distillation apparatus, an apparatus in which a packed tower having 3 stages was connected to a flask and a reflux apparatus was provided at the top of the packed tower was used. The above-mentioned flask was charged with a mixed solution obtained by mixing 150 g of water with 50 g of 98% by weight or more of methyl glycolate distillate obtained in (3). Subsequently, the column bottom temperature (liquid temperature) of the reactive distillation apparatus was maintained at 95 to 97 ° C., and reactive distillation was performed over 2 hours at normal pressure. At this time, a distillate containing methanol was distilled off. The column top temperature was 65 ° C. at the start of reactive distillation, but reached 100 ° C. at the end.
[0136]
After the reaction distillation was completed, 114 g of an aqueous solution containing 36.1% by weight of glycolic acid was taken out from the flask. The glycolic acid yield based on methyl glycolate was 100%. As impurities, formaldehyde and chlorine compounds were not detected, and oxalic acid and ethylene glycol were detected at 20 ppm and 76 ppm, respectively.

Claims (5)

Α-hydroxycarboxylic acid ester obtained by reacting (i) 1,2-diol or (ii) 1,2-diol with a primary alcohol with oxygen in the presence of a metal-supported catalyst Is a method for producing an α-hydroxycarboxylic acid , wherein the metal contains at least one selected from the group consisting of gold and palladium . The α-hydroxycarboxylic acid according to claim 1, wherein the ester is obtained by reacting 1,2-diol and a primary alcohol with oxygen in the presence of a catalyst supporting a metal. How to manufacture. The method for producing an α-hydroxycarboxylic acid according to claim 1 or 2, wherein the average particle diameter of the metal is 1 to 6 nm. A process for producing glycolic acid by hydrolyzing a glycolic acid ester obtained by oxygen oxidation in the presence of a catalyst comprising a metal supported on ethylene glycol and a primary alcohol , wherein the metal Is a method for producing an α-hydroxycarboxylic acid, which comprises at least one selected from the group consisting of gold and palladium . The method for producing an α-hydroxycarboxylic acid according to claim 4, wherein the average particle diameter of the metal is 1 to 6 nm.