Method for producing α-hydroxycarboxylic acid composition

Abstract

Provided is a means for producing an α-hydroxy carboxylic acid composition purified at high yield and high purity. This method for producing an α-hydroxy carboxylic acid composition involves distilling a mixed solution containing α-hydroxy carboxylic acid, water, and organic impurities, wherein the distillation is performed under a condition in which the upper limit temperature of a bottom liquid is at most 140ºC.

Description

[Technical Field]

[0001] The present invention relates to a method for producing an α-hydroxycarboxylic acid composition. [Background technology]

[0002] α-Hydroxycarboxylic acids are used as such in foods, cosmetics, fragrances, preservatives, pH adjusters, etc. They are also important chemical raw materials and intermediates, and are used in the manufacture of a wide variety of products. With growing awareness of environmental issues in recent years, α-hydroxycarboxylic acids are also attracting attention as raw materials for biodegradable polymer materials.

[0003] α-Hydroxycarboxylic acids are generally produced by oxidizing diols, introducing a cyano group, and hydrolyzing the resulting cyano group. The α-hydroxycarboxylic acids thus obtained contain impurities such as water, which must be removed by purification.

[0004] For example, Patent Document 1 describes an invention relating to a method for purifying a hydroxycarboxylic acid such as glycolic acid. Specifically, Patent Document 1 describes a method for purifying a hydroxycarboxylic acid, which comprises purifying an aqueous solution of hydroxycarboxylic acid by crystallization, separating the resulting hydroxycarboxylic acid crystals from a mother liquor, and then further purifying them by washing, using an aqueous solution of hydroxycarboxylic acid as a washing liquid.

[0005] According to the purification method described in Patent Document 1, it is described that the purification (production) of hydroxycarboxylic acid can be achieved in an industrially appropriate high yield by crystallization that places a small thermal load on the hydroxycarboxylic acid.

[0006] Incidentally, Patent Document 1 describes that hydroxycarboxylic acids contain, as impurities, dimers or oligomers formed by ester-forming dehydration condensation, and dimers formed by ether-forming dehydration condensation.

[0007] It is also described that hydroxycarboxylic acids easily undergo polycondensation under heating, making distillation basically difficult to apply. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-169185 Summary of the Invention [Problem to be solved by the invention]

[0009] According to the method described in Patent Document 1, hydroxycarboxylic acid can be purified (produced) with high purity and at a constant yield. However, the purification method of Patent Document 1 has a low recovery rate of 15.2 to 27.5% in one crystallization, and the purity tends to decrease as the crystallization rate increases.

[0010] Therefore, the present invention provides a means for producing a purified α-hydroxycarboxylic acid composition in high yield and with high purity. [Means for solving the problem]

[0011] The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, they have found that the above-mentioned problems can be solved by performing distillation under specific conditions, and have completed the present invention. That is, the present invention is, for example, as follows.

[0012] [1] A method for producing an α-hydroxycarboxylic acid composition by distilling a mixed solution containing an α-hydroxycarboxylic acid, water, and organic impurities, comprising: The distillation is carried out under conditions in which the upper limit temperature of the bottom liquid is 140°C or lower. [2] The method according to [1] above, wherein the α-hydroxycarboxylic acid is 2-hydroxyisobutyric acid. [3] The production method according to the above [2], wherein the content of 2-hydroxyisobutyric acid in the α-hydroxycarboxylic acid composition is 95% or more based on the total mass of the α-hydroxycarboxylic acid composition. [4] The method according to any one of the above [1] to [3], wherein the upper limit temperature of the bottom liquid is 135°C or less. [5] The method according to any one of the above [1] to [4], wherein the bottom liquid after the distillation contains an α-hydroxycarboxylic acid. [6] A method for producing an α,β-unsaturated carboxylic acid, comprising dehydrating an α-hydroxycarboxylic acid produced by the method according to any one of the above [1] to [5]. [7] An α-hydroxycarboxylic acid composition comprising 2-hydroxyisobutyric acid, An α-hydroxycarboxylic acid composition, wherein the content of 2-hydroxyisobutyric acid is 95% or more based on the total mass of the α-hydroxycarboxylic acid composition. [Effects of the Invention]

[0013] According to the present invention, a means for producing a purified α-hydroxycarboxylic acid composition with high yield and high purity is provided. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present invention will be described in detail.

[0015] The method for producing an α-hydroxycarboxylic acid composition of the present invention includes distilling a mixed solution containing an α-hydroxycarboxylic acid, water, and organic impurities, wherein the distillation is carried out under conditions where the upper limit temperature of the bottom liquid is 140°C or less.

[0016] Since all of the α-hydroxycarboxylic acid contained in the mixed solution can be subjected to purification treatment by distillation, an α-hydroxycarboxylic acid composition can be obtained with a high recovery rate. Furthermore, by keeping the upper limit temperature of the bottom liquid at 140°C or less, side reactions such as polycondensation of α-hydroxycarboxylic acid, ester-forming dehydration condensation, and ether-forming dehydration condensation can be prevented, and a high-purity α-hydroxycarboxylic acid composition can be obtained.

[0017] <Mixed solution> The mixed solution contains an α-hydroxycarboxylic acid, water, and organic impurities, and may further contain inorganic impurities.

[0018] [α-Hydroxycarboxylic acid] The α-hydroxycarboxylic acid is not particularly limited, but includes glycolic acid, lactic acid, α-hydroxybutyric acid, α-hydroxyisobutyric acid, α-hydroxyvaleric acid, 2-hydroxy-2-methylbutyric acid, 2-hydroxyisovaleric acid, α-hydroxycaproic acid, 2-hydroxy-2-methylvaleric acid, 2-hydroxy-3-methylvaleric acid, α-hydroxyisocaproic acid, 2-hydroxy-3,3-dimethylbutyric acid, α-hydroxyenanthic acid, α-hydroxycaprylic acid, etc. Among these, the α-hydroxycarboxylic acid preferably includes glycolic acid, lactic acid, α-hydroxybutyric acid, α-hydroxyisobutyric acid, α-hydroxyvaleric acid, more preferably includes glycolic acid, lactic acid, α-hydroxybutyric acid, α-hydroxyisobutyric acid, even more preferably includes α-hydroxybutyric acid, α-hydroxyisobutyric acid, and particularly preferably includes α-hydroxyisobutyric acid.

[0019] The above-mentioned α-hydroxycarboxylic acids may be contained alone or in combination of two or more.

[0020] The content of α-hydroxycarboxylic acid is preferably 10 to 70% by mass, more preferably 40 to 60% by mass, based on the total mass of the mixed solution. An α-hydroxycarboxylic acid content of 10% by mass or more is preferred because it can increase the amount of α-hydroxycarboxylic acid recovered per treatment amount. On the other hand, an α-hydroxycarboxylic acid content of 70% by mass or less is preferred because it can prevent precipitation of α-hydroxycarboxylic acid when the raw material temperature is lowered.

[0021] [water] The water content is preferably 30 to 90% by mass, more preferably 40 to 60% by mass, based on the total mass of the mixed solution. A water content of 30% by mass or more is preferred because it can prevent precipitation of α-hydroxycarboxylic acid when the temperature of the raw material drops. On the other hand, a water content of 90% by mass or less is preferred because it can increase the amount of α-hydroxycarboxylic acid recovered per treatment amount.

[0022] [Organic impurities] The organic impurities are not particularly limited, but examples thereof include organic impurities derived from the production process of α-hydroxycarboxylic acid, and organic impurities derived from side reactions of the produced α-hydroxycarboxylic acid.

[0023] Organic impurities derived from the production process of α-hydroxycarboxylic acids include, but are not limited to, raw materials, intermediates, organic catalysts, microbial catalysts, decomposition products thereof, etc. Examples include 1,2-diols, α-cyanohydrins, α-hydroxyamides, α-hydroxycarboxylic acid esters, α,β-unsaturated carboxylic acid esters, etc.

[0024] The 1,2-diol is not particularly limited, but examples thereof include ethylene glycol, 1,2-propanediol, 1,2-butanediol, 2-methyl-1,2-propanediol, and 1,2-pentanediol.

[0025] The α-cyanohydrin is not particularly limited, but examples thereof include formaldehyde cyanohydrin, acetaldehyde cyanohydrin, acetone cyanohydrin (ACH), and propionaldehyde cyanohydrin.

[0026] The α-hydroxyamide is not particularly limited, but examples thereof include glycolamide, N-hydroxyacetamide, lactamide, 2-hydroxypropylamide, 2-hydroxybutyramide, and 2-hydroxyisobutyramide.

[0027] The α-hydroxycarboxylic acid ester is not particularly limited, but examples thereof include methyl glycolate, ethyl glycolate, propyl glycolate, isopropyl glycolate, butyl glycolate, methyl 2-hydroxyacetate, ethyl 2-hydroxyacetate, methyl lactate, ethyl lactate, methyl 2-hydroxybutyrate, ethyl 2-hydroxybutyrate, methyl 2-hydroxyisobutyrate, and ethyl 2-hydroxyisobutyrate.

[0028] The α,β-unsaturated carboxylic acid ester is not particularly limited, but examples thereof include methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, methyl 2-butenoate, ethyl 2-butenoate, methyl 2-methyl-2-butenoate, and ethyl 2-methyl-2-butenoate.

[0029] Organic impurities contained due to side reactions of the produced α-hydroxycarboxylic acid include, but are not limited to, α,β-unsaturated carboxylic acids, polycondensates of α-hydroxycarboxylic acids, dimers or oligomers formed by ester-forming dehydration condensation, and dimers formed by ether-forming dehydration condensation.

[0030] The α,β-unsaturated carboxylic acid is not particularly limited, but examples thereof include acrylic acid, methacrylic acid, 2-butenoic acid, and 2-methyl-2-butenoic acid.

[0031] The organic impurities may be contained alone or in combination of two or more.

[0032] The content of organic impurities is preferably 1.0% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.3% by mass or less, based on the total mass of the mixed solution. A content of organic impurities of 1.0% by mass or less is preferred because a highly pure α-hydroxycarboxylic acid composition can be obtained. When two or more organic impurities are contained, the total content of the organic impurities is preferably within the above range.

[0033] In one embodiment, the contents of α-hydroxycarboxylic acid esters, α,β-unsaturated carboxylic acids, and α-hydroxycarboxylic acid dimers that may be particularly contained as organic impurities in the mixed solution are as follows:

[0034] That is, the content of the α-hydroxycarboxylic acid ester is preferably 1% or less, more preferably 0.5% or less, even more preferably 0.1% or less, and even more preferably 0.01% or less, relative to the total mass of the mixed solution.

[0035] Furthermore, the content of the α,β-unsaturated carboxylic acid is preferably 1% or less, more preferably 0.5% or less, even more preferably 0.1% or less, and even more preferably 0.03% or less, relative to the total mass of the mixed solution.

[0036] Furthermore, the content of α-hydroxycarboxylic acid dimers is preferably 1% or less, more preferably 0.5% or less, even more preferably 0.1% or less, and even more preferably 0.03% or less, based on the total mass of the mixed solution.

[0037] [Inorganic impurities] The inorganic impurities are not particularly limited, but include inorganic catalysts, metal elements, and the like.

[0038] The inorganic catalyst is not particularly limited, but examples thereof include inorganic catalysts derived from the process for producing α-hydroxycarboxylic acid, decomposition products thereof, and the like.

[0039] The metal element is not particularly limited, but examples thereof include Ag, Al, Au, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, Pb, Sn, Sr, Ti, Zn, and Zr.

[0040] The inorganic impurities may be contained alone or in combination of two or more.

[0041] The content of inorganic impurities is preferably 0.1% by mass or less, more preferably 0.05% by mass or less, and even more preferably 0.01% by mass or less, based on the total mass of the mixed solution. A content of inorganic impurities of 0.1% by mass or less is preferred because a highly pure α-hydroxycarboxylic acid composition can be obtained. When two or more inorganic impurities are contained, the total content of the inorganic impurities is preferably within the above range.

[0042] [Method of manufacturing the mixed solution] The method for producing the mixed solution is not particularly limited, and the mixed solution can be produced by a known method.

[0043] For example, glycolic acid can be produced by a method including the steps of reacting formaldehyde and hydrocyanic acid (hydrogen cyanide) to obtain formaldehyde cyanohydrin and hydrolyzing the cyano group of formaldehyde cyanohydrin to obtain glycolic acid. In this case, each step may use an organic catalyst, a microbial catalyst, or an inorganic catalyst.

[0044] Lactic acid can be produced by a method including the steps of hydrolyzing lactonitrile to obtain crude lactic acid, reacting the crude lactic acid with an alcohol to obtain a lactic acid ester, and hydrolyzing the lactic acid ester to obtain lactic acid. In this case, the lactic acid ester is preferably purified by distillation or the like before hydrolysis.

[0045] Lactic acid can also be produced by a method including a step of microbial fermentation of carbohydrates such as sucrose, in which the microorganisms may be genetically modified.

[0046] Furthermore, α-hydroxyisobutyric acid can be produced by a process (e.g., the new ACH process) that includes the steps of reacting acetone with hydrocyanic acid (hydrogen cyanide) to obtain acetone hydric cyanohydrin (ACH), hydrolyzing the cyano group of acetone hydric cyanohydrin to obtain α-hydroxyisobutyramide, esterifying α-hydroxyisobutyramide to obtain α-hydroxyisobutyl ester, and hydrolyzing α-hydroxyisobutyl ester to obtain α-hydroxyisobutyric acid. In this process, each process may use an organic catalyst, a microbial catalyst, or an inorganic catalyst.

[0047] Alternatively, α-hydroxycarboxylic acids can be produced by selective oxidation of the primary alcohol in 1,2-diols, usually using a catalyst such as TEMPO (2,2,6,6-tetramethylpiperidine 1-oxyl).

[0048] The reaction solution containing the α-hydroxycarboxylic acid produced as described above is subjected to distillation as a mixed solution.

[0049] The resulting reaction solution may be pretreated for the purpose of adjusting the components of the mixed solution, etc. Examples of the pretreatment include, but are not limited to, preliminary purification, pH adjustment, etc.

[0050] Examples of preliminary purification include filtration, centrifugation, chromatography, and simple distillation. Filtration can remove solid impurities such as insoluble matter contained in the reaction solution. Centrifugation can remove impurities with different specific gravities. Chromatography can remove impurities with different polarities. Simple distillation can remove impurities with different boiling points (preferably water contained in excess in the reaction solution). These preliminary purification methods may be used alone or in combination of two or more.

[0051] The pH may be adjusted to the acidic side using an acidic compound, or to the basic side using a basic compound.

[0052] <Distillation> By distilling the mixed solution described above, water and at least a portion of the organic impurities are removed, and an α-hydroxycarboxylic acid composition can be produced.

[0053] Here, distillation is a process of applying heat to a mixed solution to concentrate substances with high relative volatility into a vapor phase and substances with low relative volatility into a liquid phase, and then recovering them separately to separate the components. Specific examples of distillation include distillation in which the generated vapor is distilled directly without partial condensation, such as simple distillation (batch distillation) with no reflux; equilibrium flash distillation (continuous distillation); and fractional distillation (rectification) in which the condensate is refluxed and sequential mass transfer is performed between the reflux and the vapor. In this case, a packed column, a plate column, or the like is used for mass transfer in the fractional distillation (rectification). Of these, simple distillation is preferred. Simple distillation is preferred because it is more economical than equilibrium flash distillation and rectification.

[0054] In this case, the distillation is carried out under conditions where the upper limit temperature of the bottoms liquid is 140° C. or less. The upper limit temperature of the bottoms liquid is preferably 138° C. or less, more preferably 135° C. or less, even more preferably 130° C. or less, particularly preferably 125° C. or less, and most preferably 120° C. or less. The lower limit temperature of the bottoms liquid is not particularly limited as long as it is a temperature at which the target component evaporates, but is preferably equal to or higher than the melting point of α-hydroxycarboxylic acid.

[0055] In this specification, the term "bottom liquid" refers to the liquid phase (liquid present in the bottom column) in which at least a portion of the substances with low relative volatility has been concentrated during distillation. The "temperature of the bottom liquid" is measured using a resistance temperature detector or a K-type thermocouple. For example, in simple distillation and rectification, the temperature of the bottom liquid is usually the temperature of the liquid present in the evaporator (the bottom of the distillation column) after the start of evaporation of the substances with high relative volatility. In equilibrium flash distillation, the mixed solution is usually separated into gas and liquid in a flash drum, producing a liquid phase in which the substances with low relative volatility have been concentrated. The temperature of this liquid phase is the temperature of the bottom liquid. Since the distillation defines the "upper limit temperature of the bottom liquid," the upper limit temperature of the bottom liquid is usually controlled. On the other hand, distillation without temperature control of the bottom liquid, such as continuous distillation in which a liquid sample is introduced from above, is not included in the distillation. For example, in continuous distillation in which a liquid sample is introduced from above, evaporation and condensation occur continuously, and the temperature of the liquid phase (bottom liquid) in which the substances with low relative volatility have been concentrated is not controlled. In continuous distillation where a liquid sample is introduced from the top, the desired α-hydroxycarboxylic acid may not be obtained with high purity and high recovery rate under the conditions for distillation (temperature conditions, pressure conditions, etc.).

[0056] The distillation pressure may be normal pressure (101 kPaA) or reduced pressure, but reduced pressure is preferred because lowering the heating temperature can prevent side reactions of α-hydroxycarboxylic acid. Specifically, the distillation pressure is preferably 0.2 to 30.0 kPaA, more preferably 4.0 to 30.0 kPaA, and even more preferably 4.0 to 6.0 kPaA. A distillation pressure of 0.2 kPaA or more is preferred because of its excellent economic efficiency. On the other hand, a distillation pressure of 30.0 kPaA or less is preferred because it can lower the upper limit temperature of the bottom liquid. Note that vacuum distillation can also be performed by applying a vacuum to the pressure.

[0057] In the distillation, it is preferable to use a carrier gas. Examples of the carrier gas include inert gases such as hydrogen gas, nitrogen gas, helium gas, and argon gas. Steam distillation may also be performed using heated steam as the carrier gas. Among these, from the viewpoint of preventing oxidation, it is preferable to use an inert gas as the carrier gas, and it is more preferable to use nitrogen gas.

[0058] The α-hydroxycarboxylic acid composition may be obtained as an evaporate (the α-hydroxycarboxylic acid is contained in the solidified liquid after distillation) or as a residue (the α-hydroxycarboxylic acid is contained in the bottom liquid after distillation).

[0059] When the α-hydroxycarboxylic acid composition is obtained as an evaporant, any of simple distillation, equilibrium flash distillation, and rectification can be suitably applied.

[0060] In the case of simple distillation, the process is as follows. That is, when the mixed solution charged in the evaporator (the bottom of the distillation column) is heated, the α-hydroxycarboxylic acid evaporates. The evaporated α-hydroxycarboxylic acid then passes through the distillation column and is cooled in a condenser to become a solid or liquid. After distillation, the solidified product (evaporated product) is collected to obtain an α-hydroxycarboxylic acid composition.

[0061] In the case of equilibrium flash distillation, the process is as follows: the mixed solution charged in an evaporator is heated under pressure. The heated mixed solution is then blown into a flash drum operated at low pressure. This causes the α-hydroxycarboxylic acid in the mixed solution to evaporate. Gas-liquid separation occurs in the flash drum, and evaporated α-hydroxycarboxylic acid is obtained from the top of the flash drum. The evaporated α-hydroxycarboxylic acid is then cooled in a condenser to become a solid or liquid, and the solidified product (evaporated product) is collected to obtain an α-hydroxycarboxylic acid composition.

[0062] Furthermore, in the case of rectification, the process is as follows. Specifically, when the mixed solution charged in the evaporator (the bottom of the distillation tower) is heated, the α-hydroxycarboxylic acid evaporates. The evaporated α-hydroxycarboxylic acid is then fed to a packed tower, plate tower, or other distillation tower. The lower part of the packed tower, plate tower, or other distillation tower is heated to generate steam, and the upper part is cooled to generate reflux. Sequential mass transfer between the reflux and the steam occurs within the packed tower, plate tower, or other tower, thereby further purifying the evaporated α-hydroxycarboxylic acid. The vapor passing through the distillation tower is cooled in a condenser to become a solid or liquid. The α-hydroxycarboxylic acid composition can be obtained by recovering the solidified product (evaporate) derived from the vapor in the distillation tower or the evaporate derived from the reflux liquid of the distillation tower. The number of plates in the distillation tower and the reflux ratio (reflux volume / fraction withdrawal volume) can be set appropriately.

[0063] When the α-hydroxycarboxylic acid composition is obtained as a residue, simple distillation or equilibrium flash distillation can be suitably applied.

[0064] In the case of simple distillation, the process is as follows: When the mixed solution charged in the evaporator (the bottom of the distillation column) is heated, water and organic impurities are volatilized. The water and organic impurities then pass through the distillation column, are cooled in a condenser, and are discharged. After distillation, the residue (bottom liquid) remaining in the evaporator can be recovered to obtain an α-hydroxycarboxylic acid composition.

[0065] In the case of equilibrium flash distillation, the process is as follows: the mixed solution charged in an evaporator is heated under pressure. The heated mixed solution is then blown into a flash drum operated at low pressure. This causes the water and organic impurities in the mixed solution to evaporate. Gas-liquid separation in the flash drum allows the α-hydroxycarboxylic acid composition to be obtained from the bottom of the flash drum. The evaporated water and organic impurities are discharged from the top.

[0066] Among the above, from the viewpoints of economy and suppression of deterioration due to heating, it is preferable to obtain the α-hydroxycarboxylic acid composition as a residue. That is, in a preferred embodiment, it is preferable that the α-hydroxycarboxylic acid is contained in the bottom liquid after distillation. In particular, when the α-hydroxycarboxylic acid is α-hydroxybutyric acid or α-hydroxyisobutyric acid, the distillation pressure and temperature conditions set for obtaining the α-hydroxycarboxylic acid as a residue are suitable for purification, and therefore are preferred.

[0067] The distillation may be batch distillation or continuous distillation. In the case of continuous distillation, simple distillation may be repeated, equilibrium flash distillation may be repeated, rectification may be repeated, or simple distillation, equilibrium flash distillation, and rectification may be combined. In the case of continuous distillation, the α-hydroxycarboxylic acid composition may be obtained either as a distillate or as a residue, or a combination of these.

[0068] The recovery rate of α-hydroxycarboxylic acid in the above distillation is preferably 90% or more, more preferably 95% or more, even more preferably 99% or more, particularly preferably 99.4% or more, and most preferably 99.5% or more.

[0069] <α-Hydroxycarboxylic acid composition> The α-hydroxycarboxylic acid composition can be produced by distilling the mixed solution. Thus, according to one aspect of the present invention, an α-hydroxycarboxylic acid composition is provided. The α-hydroxycarboxylic acid composition contains α-hydroxycarboxylic acid. In addition, the α-hydroxycarboxylic acid composition may contain water, organic impurities, inorganic impurities, etc.

[0070] The content of α-hydroxycarboxylic acid (purity of α-hydroxycarboxylic acid) is preferably 90% or more, more preferably 95% or more, even more preferably 97% or more, particularly preferably 99%, and most preferably 100% based on the total mass of the α-hydroxycarboxylic acid composition. When the content of α-hydroxycarboxylic acid (purity of α-hydroxycarboxylic acid) is 100%, the α-hydroxycarboxylic acid composition refers to α-hydroxycarboxylic acid itself.

[0071] In a preferred embodiment, the α-hydroxycarboxylic acid includes 2-hydroxyisobutyric acid. That is, the content of 2-hydroxyisobutyric acid (purity of 2-hydroxyisobutyric acid) is preferably 90% or more, more preferably 95% or more, even more preferably 97% or more, particularly preferably 99%, and most preferably 100% based on the total mass of the α-hydroxycarboxylic acid composition.

[0072] The water content is preferably 5% or less, more preferably 3% or less, even more preferably 1% or less, particularly preferably 0.5% or less, and most preferably 0.2% or less, based on the total mass of the α-hydroxycarboxylic acid composition.

[0073] The organic impurities include those contained in the mixed solution described above and those produced by distillation.

[0074] Examples of organic impurities produced by distillation include organic impurities that are derived from side reactions of the α-hydroxycarboxylic acid produced by the above-mentioned method.

[0075] Among the above-mentioned organic impurities, the α-hydroxycarboxylic acid composition may particularly contain α-hydroxycarboxylic acid esters, α,β-unsaturated carboxylic acids, and dimers of α-hydroxycarboxylic acids, which have boiling points similar to those of α-hydroxycarboxylic acids.

[0076] The content of the α-hydroxycarboxylic acid ester is preferably 3% or less, more preferably 1% or less, even more preferably 0.5% or less, even more preferably 0.1% or less, and most preferably 0.01% or less, based on the total mass of the α-hydroxycarboxylic acid composition.

[0077] The content of the α,β-unsaturated carboxylic acid is preferably 3% or less, more preferably 1% or less, even more preferably 0.5% or less, even more preferably 0.1% or less, and most preferably 0.03% or less, based on the total mass of the α-hydroxycarboxylic acid composition.

[0078] The content of α-hydroxycarboxylic acid dimers is preferably 3% or less, more preferably 1% or less, even more preferably 0.5% or less, even more preferably 0.1% or less, and most preferably 0.03% or less, based on the total mass of the α-hydroxycarboxylic acid composition.

[0079] The total content of organic impurities is preferably 3% or less, more preferably 1% or less, even more preferably 0.5% or less, even more preferably 0.1% or less, and most preferably 0.07% or less, based on the total mass of the α-hydroxycarboxylic acid composition.

[0080] The α-hydroxycarboxylic acid composition has high purity and little or no side reactions, and therefore has high storage stability. In particular, the α-hydroxycarboxylic acid composition can maintain high purity even in a high-temperature environment.

[0081] <Uses of α-hydroxycarboxylic acid composition> The α-hydroxycarboxylic acid composition can be used in a variety of applications.

[0082] In one embodiment, the α-hydroxycarboxylic acid composition is used in applications such as food, cosmetics, fragrances, preservatives, pH adjusters, and the like.

[0083] In another embodiment, the α-hydroxycarboxylic acid composition is used as a chemical raw material or intermediate.

[0084] In a preferred embodiment, the α-hydroxycarboxylic acid composition is applied to a polymer raw material. For example, when the α-hydroxycarboxylic acid is glycolic acid or lactic acid, polyglycolic acid, polylactic acid, or a copolymer containing these as monomer units is produced. That is, in one embodiment, there is provided a method for producing a polymer, which includes polymerizing the α-hydroxycarboxylic acid composition produced by the above-mentioned method.

[0085] In one preferred embodiment, the α-hydroxycarboxylic acid composition is used as a raw material for an α,β-unsaturated carboxylic acid. For example, when the α-hydroxycarboxylic acid is 2-hydroxypropionic acid or α-hydroxyisobutyric acid, acrylic acid or methacrylic acid is produced. That is, in one aspect, there is provided a method for producing an α,β-unsaturated carboxylic acid, which includes dehydrating the α-hydroxycarboxylic acid composition produced by the above-mentioned method. [Example]

[0086] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these. Unless otherwise specified, "%" is based on mass.

[0087] [Example 1] Purification was carried out by vacuum distillation.

[0088] (Preparation of mixed solution) Using acetone and hydrocyanic acid (hydrogen cyanide) obtained from formamide as raw materials, they were sequentially converted into acetone hydricyanhydrin (ACH), α-hydroxyisobutyramide, and α-hydroxyisobutyl ester, and then 2-hydroxyisobutyric acid was synthesized (new ACH method). This was then diluted with water to prepare a mixed solution containing 2-hydroxyisobutyric acid (HBA), water, and methyl 2-hydroxyisobutyrate (HBM).

[0089] The content of HBA was 50.4 mass % and the content of HBM was 0.14 mass % relative to the total mass of the mixed solution.

[0090] (distillation) 301.9 g of the mixed solution prepared above was placed in a flask equipped with a thermometer, a condenser, and a pressure reducing device. Distillation was initiated under a pressure of 30 kPaA while blowing in nitrogen at 2.0 mL / min. After the temperature of the bottom liquid reached 90°C, the temperature was controlled to 90-100°C and the pressure was reduced to 4.0 kPaA. After confirming that the temperature of the gas phase in the flask had reached 100°C, distillation was terminated and the bottom liquid was recovered as an HBA composition.

[0091] In addition to the methyl 2-hydroxyisobutyrate (HBM) contained in the mixed solution, the α-hydroxycarboxylic acid composition also contained methacrylic acid (MAA) and 2-hydroxyisobutyric acid dimer (HBA dimer), which were produced by a side reaction of 2-hydroxyisobutyric acid (HBA).

[0092] The upper limit temperature of the bottom liquid until the end of the distillation was 135° C. The time from when the temperature reached 120° C. until the end of the distillation was 12 minutes.

[0093] The contents of water, methyl 2-hydroxyisobutyrate (HBM), methacrylic acid (MAA), and 2-hydroxyisobutyric acid dimer (HBA dimer) in the composition were measured by the following method.

[0094] Specifically, it was measured by the standard addition method using gas chromatography (hydrogen flame ionization detector: GC-FID, thermal conductivity detector: GC-TCD).

[0095] <Preparation of Analytical Sample> The first analytical sample and the second analytical sample were prepared. The first analytical sample was prepared by dissolving 7 g of 2-hydroxyisobutyric acid (HBA) in 17.5 g of acetonitrile. The second analytical sample was prepared by adding 0.2 mL of a standard addition sample (water / methyl 2-hydroxyisobutyrate (HBM) / methacrylic acid (MAA) = 30 / 1 / 1, volume ratio) to 15 mL of the first analytical sample.

[0096] <Quantification of Moisture (GC-TCD)> Samples: The first analytical sample, the second analytical sample Apparatus: GC-2030 (Shimadzu Corporation) Column: Agilent, DB-WAX (length: 30 m, inner diameter: 0.25 mm, film thickness: 0.25 μm) Carrier: He (30 cm / sec) Inlet: 250 °C (split 1:10) Detector: 250 °C Sample: 0.5 μL Oven: 60 °C (0 min) → 4 °C / min → 80 °C (0 min) → 30 °C / min → 230 °C (10 min) Retention time: 3.8 min (water)

[0097] <Quantification of HBM, MAA, and HBA Dimer (GC-FID)> Apparatus: GC-2025 (Shimadzu Corporation) Column: Agilent, DB-FFAP (length: 30 m, inner diameter: 0.25 mm, film thickness: 0.25 μm) Carrier: He (30 cm / sec) Inlet: 250 °C (split 1:50) Detector: 250 °C Sample: 0.2 μL Oven: 60°C (0 min) → 4°C / min → 80°C (0 min) → 30°C / min → 230°C (10 min) Retention times: 5.9 min (HBM), 9.2 min (MAA), 9.5 min (HBA dimer) The content of HBA dimer is calculated assuming the same sensitivity as acetonitrile.

[0098] As a result, the water content was 0.12%, the HBM content was 0.01%, the MAA content was 0.02%, and the HBA dimer content was 0.05%.

[0099] The content of 2-hydroxyisobutyric acid (HBA) in the composition (HBA purity) was calculated by subtracting the sum of the contents of water, HBM, MAA, and HBA dimer from 100. The result was 99.8%.

[0100] The recovery rate of 2-hydroxyisobutyric acid (HBA) was calculated using the following formula and was found to be 99.6%.

[0101]

number

[0102] [Example 2] An HBA composition was produced in the same manner as in Example 1, except that 304.3 g of the mixed solution prepared in Example 1 was used, and the distillation was terminated after it was confirmed that the temperature of the bottom liquid had reached 120°C (upper limit temperature of the bottom liquid: 120°C).

[0103] The contents of water, HBM, MAA, and HBA dimer were measured using the same method as in Example 1 and were found to be 0.28%, 0.02%, 0.02%, and 0.02%, respectively. The HBA content (HBA purity) was 99.7%. The HBA recovery rate was calculated using the same method as in Example 1 and was found to be 99.4%.

[0104] [Example 3] (Preparation of mixed solution) Using acetone and hydrocyanic acid (hydrogen cyanide) obtained from formamide as raw materials, they were sequentially converted into acetone hydricyanhydrin (ACH), α-hydroxyisobutyramide, and α-hydroxyisobutyl ester, and then 2-hydroxyisobutyric acid was synthesized (new ACH method). This was then diluted with water to prepare a mixed solution containing 2-hydroxyisobutyric acid (HBA), water, and methyl 2-hydroxyisobutyrate (HBM).

[0105] The content of HBA was 51.2 mass % and the content of HBM was 0.15 mass % relative to the total mass of the mixed solution.

[0106] (distillation) 800.1 g of the mixed solution prepared above was placed in a flask equipped with a thermometer, a condenser, and a pressure reducing device. Simple distillation was initiated while blowing in nitrogen at 5.0 mL / min under a pressure of 30 kPaA. After confirming that the temperature of the bottom liquid had reached 140°C, the distillation was terminated (upper limit temperature of the bottom liquid: 140°C), and the bottom liquid was recovered as an HBA composition (413.5 g).

[0107] The time from when the temperature of the bottom liquid reached 120°C until the end of the distillation was 19 minutes.

[0108] The contents of water, HBM, MAA, and HBA dimer were measured using the same method as in Example 1 and were found to be 1.25%, 0.15%, 0.05%, and 0.15%, respectively. The HBA content (HBA purity) was 98.4%. The HBA recovery rate was calculated using the same method as in Example 1 and was found to be 99.3%.

[0109] [Comparative Example 1] Purification was carried out under conditions where the upper limit temperature of the bottom liquid was over 140° C. HBA did not remain in the bottom liquid, but was obtained from the distillate.

[0110] 262.2 g of the mixed solution prepared in Example 1 was placed in a flask equipped with a thermometer and a condenser. After recovering 188.5 g of initial distillate by atmospheric distillation (101 kPaA), 59.6 g of main distillate was recovered. At this time, the distillation line was heated to 80°C or higher to prevent solidification of HBA. The temperature of the bottom liquid during recovery of the main distillate was 232 to 276°C, and the temperature of the gas phase in the flask was 191 to 211°C. The resulting main distillate was used as an HBA composition.

[0111] The contents of water, HBM, MAA, and HBA dimer were measured using the same method as in Example 1 and were found to be 0.08%, 0%, 5.45%, and 64.6%, respectively. The HBA content (HBA purity) was 29.9%. The HBA recovery rate was calculated using the same method as in Example 1 and was found to be 13.5%.

[0112] Comparative Example 2 Purification was carried out under conditions where the upper limit temperature of the bottom liquid exceeded 140° C. HBA did not remain in the bottom liquid, but was obtained from the distillate.

[0113] 264.3 g of the mixed solution prepared in Example 1 was placed in a flask equipped with a thermometer, a condenser, and a pressure reducing device. After recovering 137.9 g of initial distillate by atmospheric distillation (101 kPaA), the pressure was reduced to 30 kPaA and 89.6 g of main distillate was recovered. During this process, the distillation line was heated to 80°C or higher to prevent solidification of HBA. The temperature of the bottom liquid during main distillate recovery was 183 to 235°C, and the temperature of the gas phase in the flask was 155 to 171°C. The resulting main distillate was used as an HBA composition.

[0114] The contents of water, HBM, MAA, and HBA dimer were measured using the same method as in Example 1 and were found to be 0.09%, 0%, 0.40%, and 14.2%, respectively. The HBA content (HBA purity) was 85.3%. The HBA recovery rate was calculated using the same method as in Example 1 and was found to be 57.4%.

[0115] Comparative Example 3 Purification was carried out by spray drying.

[0116] 500 g of the mixed solution prepared in Example 1 was sprayed into a spray dryer (SB39) equipped with a two-fluid nozzle under conditions of a spray pressure of 0.5 MPa and a spray rate of 496 g / h. The operation was carried out with an inlet temperature of 90°C and an outlet temperature of 54 to 60°C. 166.7 g of powder obtained by evaporation of the water in the mixed solution was recovered as an HBA composition.

[0117] The contents of water, HBM, MAA, and HBA dimer were measured using the same method as in Example 1 and were found to be 0.09%, 0%, 0.01%, and 0%, respectively. The HBA content (HBA purity) was 99.9%. The HBA recovery rate was calculated using the same method as in Example 1 and was found to be 66.6%.

[0118] Comparative Example 4 Purification was carried out by spray drying.

[0119] 1040 g of the mixed solution prepared in Example 1 was sprayed into a spray dryer (SB39) equipped with a two-fluid nozzle under conditions of a spray pressure of 0.2 MPa and a spray rate of 520 g / h. The operation was carried out with an inlet temperature of 90°C and an outlet temperature of 38 to 50°C. 347.9 g of powder obtained by evaporation of the water in the mixed solution was recovered as an HBA composition.

[0120] The contents of water, HBM, MAA, and HBA dimer were measured using the same method as in Example 1 and were found to be 0.40%, 0.01%, 0.02%, and 0%, respectively. The HBA content (HBA purity) was 99.6%. The HBA recovery rate was calculated using the same method as in Example 1 and was found to be 66.0%.

[0121] Comparative Example 5 Purification was carried out by thin film distillation. Using a short-path distillation apparatus (KDL-5), 299.4 g of the mixed solution prepared in Example 1 was purified under the conditions of a vacuum of 40 kPaA, an evaporator temperature of 150°C, an internal condenser temperature of -5°C, a wiper speed of 400 rpm, and a feed rate of 300 g / h. During this process, the bottoms piping was heated to 100°C to prevent solidification of HBA. 123.3 g of the resulting bottoms was obtained as an HBA composition.

[0122] The contents of water, HBM, MAA, and HBA dimer were measured using the same method as in Example 1 and were found to be 0.37%, 0.02%, 0.02%, and 0%, respectively. The HBA content (HBA purity) was 99.6%. The HBA recovery rate was calculated using the same method as in Example 1 and was found to be 81.3%.

[0123] The results of Examples 1 to 3 and Comparative Examples 1 to 5 are shown in Table 1 below.

[0124] [Table 1]

[0125] The results in Table 1 show that in Examples 1 to 3, a highly purified HBA composition was obtained in high yield.

[0126] On the other hand, in Comparative Examples 1 and 2, the upper limit temperature of the bottom liquid was high, which is thought to have resulted in the production of MAA due to the dehydration reaction of HBA and HBA dimers due to the dimerization of HBA, resulting in a decrease in the recovery rate and HBA purity.

[0127] Furthermore, in Comparative Examples 3 and 4, the particle size of the approximately powdered HBA composition obtained by evaporating the water content of the mixed solution by spray drying was small. This is thought to have resulted in the reduced recovery rate because the approximately powdered HBA composition was discharged without being recovered or captured by a powder collector, cyclone, or the like. Note that in Comparative Examples 3 and 4, the sprayed droplets were made small to ensure that the water content of the mixed solution was evaporated by spray drying, resulting in a small particle size of the obtained approximately powdered HBA composition.

[0128] Furthermore, the short-path distillation apparatus (KDL-5) used in Comparative Example 5 was a vertical evaporator-type distillation apparatus equipped with a built-in wiper. This distillation method involves introducing a liquid sample from the top, forming a thin film on the inner wall of the evaporator using a roller wiper, and performing continuous distillation. The condensation surface is positioned relatively close to the evaporation surface. Under the conditions of thin-film distillation using this short-path distillation apparatus, it is believed that the recovery rate decreased due to partial volatilization of HBA during the evaporation process.

[0129] [Heat storage test of α-hydroxycarboxylic acid composition] The stability of a 2-hydroxyisobutyric acid (HBA) composition containing water and methacrylic acid (MAA) under heating conditions was confirmed. The HBA content of the composition was 99.6%, the water content was 0.43%, and the MAA content was 0.01%.

[0130] Specifically, 50 g of the HBA composition was placed in a flask equipped with a thermometer, a condenser, and a pressure reducing device, and the flask was heated and maintained at 120°C or 140°C while nitrogen was blown in at 2.0 mL / min under normal pressure, and the change in the HBA composition over time was observed. The results are shown in Table 2 below.

[0131] [Table 2]

[0132] The results in Table 2 show that a high-purity HBA composition can maintain its high purity even in a high-temperature environment of 120°C or 140°C.

Claims

1. A method for producing an α-hydroxycarboxylic acid composition by distilling a mixed solution containing an α-hydroxycarboxylic acid, water, and organic impurities under reduced pressure, comprising the steps of: the α-hydroxycarboxylic acid includes 2-hydroxyisobutyric acid; The distillation is carried out under conditions in which the upper limit temperature of the bottom liquid is 140°C or lower.

2. 2. The method according to claim 1, wherein the content of 2-hydroxyisobutyric acid in the α-hydroxycarboxylic acid composition is 95% or more based on the total mass of the α-hydroxycarboxylic acid composition.

3. The method according to claim 1 or 2, wherein the upper limit temperature of the bottom liquid is 135°C or less.

4. The method according to any one of claims 1 to 3, wherein the bottom liquid after distillation contains an α-hydroxycarboxylic acid.

5. A method for producing an α,β-unsaturated carboxylic acid, comprising dehydrating an α-hydroxycarboxylic acid produced by the method according to any one of claims 1 to 4.

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