JP2004182643A - METHOD FOR MANUFACTURING alpha-HYDROXYCARBOXYLATE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently manufacturing an α-hydroxycarboxylate. <P>SOLUTION: The method for manufacturing the α-hydroxycarboxylate comprises the following steps: step 1 for reacting (i) 1,2-diols with each other or reacting (ii) a 1,2-diol with an alcohol in the presence of oxygen to obtain the α-hydroxycarboxylate and step 2 for distilling the reaction liquid obtained in step 1 under a reduced pressure to obtain the α-hydroxycarboxylate. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing an α-hydroxycarboxylic acid ester. Α-Hydroxycarboxylic acid esters such as glycolic acid esters are used as raw materials for various synthetic resins such as polyglycolic acid, and are industrially useful compounds as cleaning agents for boilers, etching agents, and the like. .
[0002]
[Prior art]
As a method for producing an α-hydroxycarboxylic acid ester such as a glycolic acid ester, various methods have been developed so far. A method of synthesizing polyglycolide from formaldehyde and carbon monoxide in the presence of a heteropolyacid and subjecting it to alcoholysis (for example, see Patent Document 1), synthesizing glycolic acid from formaldehyde and carbon monoxide, and subsequently performing esterification with an alcohol (See, for example, Patent Document 2), a method of performing oxidative esterification of glyoxal and alcohol in the presence of a catalyst (for example, see Patent Document 3), and a method of hydrogenating oxalic acid diester (for example, Patent Document 4) Is known as a manufacturing method.
[0003]
In response to these production methods, the present applicant has developed a method based on an oxidative esterification reaction of alcohol (for example, refer to Unpublished Patent Document 1). This method is a method for producing an α-hydroxycarboxylic acid ester by reacting a 1,2-diol with an alcohol in the presence of oxygen. According to this production method, it becomes possible to produce the α-hydroxycarboxylic acid ester more efficiently.
[0004]
[Patent Document 1]
JP-A-6-228045 (Claims)
[Patent Document 2]
Republic of Korea Public Patent No. 9511114
[Patent Document 3]
JP-A-8-104665 (Claims)
[Patent Document 4]
JP-A-6-135895 (Claims)
[Undisclosed patent document 1]
Japanese Patent Application No. 2002-204748 (Claims)
[0005]
[Problems to be solved by the invention]
However, the prior art is insufficient for consistently and efficiently producing α-hydroxycarboxylic acid ester from synthesis to purification, and a method for more efficiently producing α-hydroxycarboxylic acid ester is required. Had been.
[0006]
The present invention provides a method capable of producing an α-hydroxycarboxylic acid ester more efficiently.
[0007]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to achieve the above object, and as a result, have found that by optimally combining a reaction step and a distillation step, an α-hydroxycarboxylic acid ester can be produced more efficiently, thereby completing the present invention. Reached.
[0008]
That is, the present invention provides a reaction step of obtaining an α-hydroxycarboxylic acid ester by reacting (i) 1,2-diols or (ii) a 1,2-diol with an alcohol in the presence of oxygen, and a reaction step. The present invention relates to a method for producing an α-hydroxycarboxylic acid ester comprising a distillation step of distilling the obtained reaction solution at a pressure of 13 to 80000 Pa and a tower bottom temperature of 30 to 250 ° C. to obtain an α-hydroxycarboxylic acid ester.
[0009]
Further, the present invention can be obtained by a reaction step of reacting (i) 1,2-diols or (ii) a 1,2-diol with an alcohol in the presence of oxygen to obtain an α-hydroxycarboxylic acid ester, and a reaction step. The unreacted alcohol contained in the reaction solution obtained in the reaction step obtained by distilling the reaction solution obtained at a pressure of 13 to 80000 Pa and a column bottom temperature of 30 to 250 ° C. to obtain an α-hydroxycarboxylic acid ester is removed. The present invention relates to a method for producing an α-hydroxycarboxylic acid ester comprising a step of recovering and recycling an alcohol having a water content of 0 to 20% by mass to a reaction step.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the method for producing the α-hydroxycarboxylic acid ester according to the present invention will be described in detail.
[0011]
(1) Raw materials
The synthesis of the α-hydroxycarboxylic acid ester in the present invention is carried out by reacting (i) 1,2-diols or (ii) 1,2-diol with an alcohol in the presence of oxygen as a raw material. 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 a trihydric or higher polyhydric alcohol, for example. Specific examples of the 1,2-diol include, for example, aliphatic 1,2-carbondiols such as ethylene glycol, 1,2-propylene glycol, 1,2-butanediol, and 1,2-hexanediol. 2-diols; aliphatic polyhydric alcohols having about 1 to 10 carbon atoms, such as glycerin, erythritol, xylitol, and sorbitol, having a hydroxyl group at the 1- and 2-positions; and derivatives of these 1,2-diols. . Examples of the derivative of 1,2-diol include aliphatic 1,2-diol having about 2 to 10 carbon atoms containing halogen such as 3-chloro-1,2-propanediol; 2-phenyl-1,2- An aliphatic 1,2-diol having about 2 to 10 carbon atoms and having an aromatic ring, such as ethanediol, may be used. As the 1,2-diol, an aliphatic diol having about 2 to 6 carbon atoms can be suitably used, and ethylene glycol can be most preferably used. These 1,2-diols can be used alone or in combination of two or more.
[0012]
The alcohol used as the raw material may be any alcohol other than 1,2 diol, as long as it has a hydroxyl group in the molecule. The type thereof is not particularly limited, and may be a monohydric alcohol or a dihydric alcohol. The above polyhydric alcohols may be used. Specific examples of the alcohol include aliphatic alcohols having about 1 to 10 carbon atoms such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 1-hexanol, and 1-octanol; 1,3-butanediol; Aliphatic polyhydric alcohol having about 2 to 10 carbon atoms such as 1,4-butanediol; aliphatic unsaturated alcohol having about 3 to 10 carbon atoms such as allyl alcohol and methallyl alcohol; having an aromatic ring such as benzyl alcohol; Alcohol and the like. Of these, primary alcohols are preferable, and aliphatic primary alcohols having 1 to 4 carbon atoms such as methanol, ethanol, 1-propanol and 1-butanol can be suitably used. Methanol, ethanol, 1-propanol and 1-butanol Are particularly preferred. One or more alcohols can be used.
[0013]
In the production method of the present invention, the types of the 1,2-diol and the alcohol may be appropriately selected according to the type of the target ester and the like. For example, when ethylene glycol is used as the 1,2-diol and methanol, ethanol, 1-propanol, 1-butanol, or the like is used as the alcohol, a glycolic acid ester of the alcohol can be produced. Alternatively, when only 1,2-diol is used and the 1,2-diol is ethylene glycol, 2-hydroxyethyl glycolate can be produced.
[0014]
When 1,2-diol and alcohol are used as raw materials, the reaction ratio is not particularly limited, but the molar ratio of alcohol to 1,2-diol is usually about 1: 1 to 50, and about 1: 2 to 20. Is more preferred. When the content is within the above range, the α-hydroxycarboxylic acid ester can be produced more efficiently.
[0015]
(2) Catalyst
The above reaction may be performed in the presence of a catalyst. When a catalyst is used in the above reaction, the type of the catalyst is not particularly limited, but it is preferable to use a catalyst in which a metal as an active component is supported on a carrier, that is, a supported metal catalyst.
[0016]
The metal that is the active ingredient is not particularly limited, but is preferably a noble metal, for example, gold, palladium, ruthenium, rhodium, iridium, platinum and the like, among which gold, palladium, ruthenium and the like can be exemplified. More preferred, especially gold is preferred.
[0017]
The catalyst that can be used in this reaction contains the above-mentioned noble metal as an essential component, and further contains, in addition to the noble metal, the fourth to sixth cycles of the periodic table (“Chemical Analysis Handbook Revised 5th Edition” Maruzen (2001)). At least one element selected from the group consisting of Group 2B, Group 3B, Group 4B, Group 5B and Group 6B, and Group 8 of the fourth period (hereinafter, these elements may be referred to as "second elements" )). Specific examples of the second element include, for example, Group 2B such as Zn, Cd, and Hg; Group 3B such as Ga, In, and Tl; Group 4B such as Ge, Se, and Pb; Group 5B such as As, Sb, and Bi; Group 6B such as Se, Te, and Po; Group 8 such as Fe, Co, and Ni can be exemplified.
[0018]
When a catalyst is used in this reaction, for example, fine particles of gold and / or at least one of the 2B group, 3B group, 4B group, 5B group, 6B group and the 8th group of the fourth period of the fourth to sixth periods of the periodic table are used. A catalyst in which fine particles composed of one kind of second element and gold are supported on a carrier can be suitably used.
[0019]
The metal which is the active ingredient may contain the above-mentioned noble metal alone, or may contain two or more kinds. When two or more noble metals are contained, some or all of them may form an alloy, an intermetallic compound or the like as long as the effect is obtained.
[0020]
When the metal as the active component contains a noble metal and a second element, some or all of them may form an alloy, an intermetallic compound, or the like as long as the effect is obtained.
[0021]
The particle diameter of the metal fine particles as the active ingredient is not limited as long as a predetermined catalytic activity is obtained, but the average particle diameter is usually about 10 nm or less, preferably about 6 nm or less, more preferably about 5 nm or less, and particularly preferably. Is about 1 to 5 nm.
[0022]
As the carrier, those conventionally used as catalyst carriers can be used, and are not particularly limited. For example, a commercially available product can be used. Further, those obtained by a known production 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.), zeolites (ZSM-5, beta, etc.), mesoporous silicates ( Inorganic oxides such as MCM-41, etc .; natural minerals (clay, diatomaceous earth, pumice, etc.); and various carriers of carbon materials (activated carbon, graphite, etc.), among which inorganic oxides are preferred.
[0023]
The method for producing the catalyst is not limited as long as the above-mentioned carrier is obtained. For example, it can be obtained by heat-treating a carrier containing at least one of a desired metal and a compound thereof. The metal compound may be any of hydroxide, chloride, carboxylate, nitrate, alkoxide, acetylacetonate and the like.
[0024]
Specifically, for example, when gold particles are supported, the method is not particularly limited as long as the method is capable of immobilizing the gold particles on a carrier. As the loading method itself, for example, known methods such as a coprecipitation method, a precipitation method, an impregnation method, a vapor deposition method and the like can be used, but a coprecipitation method, a precipitation method and the like can be preferably used, and particularly the precipitation method is preferred. preferable. When a catalyst is produced by a precipitation method, for example, an aqueous solution of a water-soluble compound containing gold and an inorganic oxide carrier are mixed, and the recovered solid is calcined to obtain the catalyst.
[0025]
(3) Reaction process of α-hydroxycarboxylic acid ester
The above reaction may be any of a liquid phase reaction and a gas phase reaction, but a liquid phase reaction is preferred. It is preferable to use molecular oxygen as oxygen. Oxygen (oxygen gas) may be diluted with an inert gas such as nitrogen gas, argon gas, helium gas, or carbon dioxide gas. Further, an oxygen-containing gas such as air can be used. The method for supplying the oxygen-containing gas to the reaction system is not particularly limited, and a known method can be employed. The oxygen-containing gas may be supplied in the liquid or may be supplied to the gas phase.
[0026]
The reaction mode may be any of a continuous system, a batch system, and a semi-batch system, and is not particularly limited. The catalyst may be in any form of a fixed bed, a fluidized bed, a suspension bed and the like.
[0027]
Specific examples of the reaction format are listed. When the catalyst is used in a fixed bed, for example, (i) the catalyst is fixed in the reactor, the raw material in which the oxygen-containing gas is dissolved is continuously supplied thereto, and the oxygen-containing gas is again added to the extracted reaction solution. External circulation type reactor which dissolves and circulates to the reactor. (Ii) A tubular reactor in which a catalyst is fixed in a tubular reactor and a raw material and an oxygen-containing gas are continuously supplied. The reaction efficiency can be improved by dividing the oxygen-containing gas and supplying it to the reactor inlet, the intermediate portion, and a plurality of locations. (Iii) An irrigation packed tower reactor in which a catalyst is packed in a tower reactor and a raw material and an oxygen-containing gas are continuously supplied. The reaction efficiency can be improved by making the gas a continuous phase and making the liquid a dispersed phase.
[0028]
When the catalyst is used in a suspension bed or a fluidized bed, for example, (iv) a tank-type reactor in which a raw material and a catalyst are charged into a tank-type reactor and reacted while continuously supplying an oxygen-containing gas. The raw material and the catalyst may be reacted in a batch system in which the raw materials are initially charged together, or may be reacted in a semi-batch system in which a part of the raw material is continuously or temporarily supplied during the reaction. Alternatively, the reaction may be performed in a continuous manner in which the reaction solution and the gas are continuously extracted while continuously supplying the raw material and the oxygen-containing gas. In the case where the reaction is performed continuously, the reaction efficiency can be improved by using a continuous tank reactor in which a plurality of reactors are connected in series and reacted. (V) Using a tower-type reactor provided with a partition therein, the raw material and the catalyst are continuously supplied from the upper part of the column, the oxygen-containing gas is continuously supplied from the lower part of the column, and both are counter-currently supplied. A vertical, continuous tank reactor that reacts upon contact. The reaction liquid may be withdrawn as it is or may be supplied to the reactor again. (Vi) A bubble column reactor or the like that continuously supplies a raw material and an oxygen-containing gas from the lower portion of the column reactor can be exemplified.
[0029]
The amount used when a catalyst is used may be appropriately determined according to the type of the raw material 1,2-diol or alcohol, the type of the catalyst, the reaction conditions, and the like. It is about 1 to 100 g, preferably about 2 to 60 g.
[0030]
The reaction time is not particularly limited and varies depending on the set conditions. However, the reaction time or the residence time (the amount of liquid retained in the reactor / the amount of liquid supplied) is usually about 0.5 to 20 hours, and preferably 1 to 20 hours. It may be set to about 10 hours.
[0031]
Various conditions such as the reaction temperature and the reaction pressure may be appropriately determined depending on the type of the raw material 1,2-diol or alcohol, the type of the catalyst, and the like. The reaction temperature is usually about 0 to 200 ° C, preferably about 50 to 180 ° 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 pressurized pressure, but is usually preferably about 0.05 to 10 MPa (gauge pressure), particularly preferably about 0.1 to 5 MPa.
[0032]
Further, for example, when only 1,2-diol ethylene glycol is used as a raw material, 2-hydroxyethyl glycolate is generated. By adding an alcohol to the reaction solution and performing transesterification of 2-hydroxyethyl glycolate and the alcohol, a glycolic acid ester of the alcohol can be produced. According to this method, there are advantages such as a reduction in alcohol-derived by-products and a reduction in size of the reactor. Of course, the same reaction can be carried out using 1,2-diols other than ethylene glycol.
[0033]
At the time of transesterification, a catalyst may be used. Examples of the catalyst include an acid; a base; and a metal compound such as titanium, lead, and tin. Among them, an acid is preferable. Specific examples of the acid catalyst include a homogeneous catalyst such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, heteropolyacid, p-toluenesulfonic acid, and acetic acid; a heterogeneous catalyst such as acidic ion exchange resin, zeolite, and clay. Among them, a heterogeneous catalyst is preferable because of easy separation.
[0034]
Regarding the transesterification reaction conditions, the molar ratio of alcohol / 2-hydroxyethyl glycolate is preferably 1 or more, more preferably 2 or more. The reaction temperature is preferably in the range of 30 to 200C.
[0035]
(4) α-Hydroxycarboxylic acid ester distillation step
Since the reaction solution obtained by the above reaction contains unreacted 1,2-diol and alcohol, by-product water and the like in addition to the target product α-hydroxycarboxylic acid ester, The α-hydroxycarboxylic acid ester can be purified from the reaction solution by distillation.
[0036]
The reaction solution may be distilled as it is, or distillation may be performed after performing another step. Other steps include, for example, a separation step of separating solids such as a catalyst, an evaporation step of removing a low-boiling component, a reaction step of converting a by-product in a reaction solution into an active ingredient, and a stable distillation. For this purpose, a distillation pretreatment step of adjusting the composition of the reaction solution and the like can be mentioned.
[0037]
When the reaction solution contains a component having a lighter boiling point (such as water or alcohol) and a component having a higher boiling point (such as ethylene glycol) than the α-hydroxycarboxylic acid ester, when performing purification by distillation, the number of distillation columns is particularly large. Not limited. After removing the light-boiling components in the first column using two distillation columns, the α-hydroxycarboxylic acid ester may be distilled in the second column, or the high-boiling components may be removed in the first column. Thereafter, the low boiling point component may be distilled off in the second column, and the α-hydroxycarboxylic acid ester may be extracted from the bottom of the column. Further, the α-hydroxycarboxylic acid ester may be extracted from the middle stage of the column by side cutting using one distillation column.
[0038]
When the proportion of the light-boiling component in the reaction solution is large, flashing or evaporation may be performed before distillation to reduce the amount of the light-boiling component before distillation.
[0039]
As the distillation method, rectification using a simple distillation or a multistage distillation column is possible, but rectification is preferably performed. Further, the distillation system can be suitably carried out in either a batch system or a continuous system.
[0040]
When a multi-stage distillation column is used, the number of stages of the distillation column is not particularly limited, but the number of stages excluding the top (top) and the bottom (bottom) may be two or more. preferable. As such a distillation column, for example, a packed column filled with packing materials such as Raschig ring, pole ring, interlock saddle, Dickson packing, McMahon packing, and sludge packing; trays such as bubble bell tray, sieve tray, and valve tray A commonly used distillation column such as a plate column using (plate plate) can be used. Further, a combined distillation column having both a tray and a packed bed can also be used. Further, a plurality of multi-stage distillation columns may be used in combination. The above-mentioned number of plates indicates the number of plates in a tray column, and indicates the number of theoretical plates in a packed tower.
[0041]
In addition, in order to suppress a side reaction in the distillation column, it is preferable to minimize the heat history of the reaction solution in the distillation column. As a device for heating the liquid, a device capable of reducing the heat history, such as a liquid film reboiler, is preferable.
[0042]
The α-hydroxycarboxylic acid ester has a hydroxyl group and an ester group in the molecule, is a highly reactive compound, and easily causes a side reaction when heated during the reaction or distillation. For example, α-hydroxycarboxylic acid ester molecules may undergo an ester exchange reaction to form an oligomer in which a plurality of α-hydroxycarboxylic acid ester molecules are connected by an ester bond. When an alcohol other than the alcohol R-OH corresponding to the ester group —C (＝ O) OR (where R is an organic residue) of the α-hydroxycarboxylic acid ester is present, a transesterification reaction occurs with the alcohol, In some cases, α-hydroxycarboxylic acid esters having different ester groups are produced. Further, when water coexists, α-hydroxycarboxylic acid ester is hydrolyzed to generate α-hydroxycarboxylic acid. These side reactions result in a decrease in the desired α-hydroxycarboxylic acid ester in each case. Further, since the α-hydroxycarboxylic acid generated by hydrolysis in the presence of water is a carboxylic acid, it acts as an acid catalyst for the side reaction, and the side reaction is further promoted. Particularly, in the reaction step of the present invention, since 2 mol of water is by-produced with respect to 1 mol of the α-hydroxycarboxylic acid ester, hydrolysis is very likely to occur when distilling the reaction solution, and therefore, Side reactions are very likely.
[0043]
In addition, any of the above side reactions is a reaction in which the alcohol R-OH corresponding to the ester group -C (= O) OR (where R is an organic residue) of the α-hydroxycarboxylic acid ester is released. Therefore, when the alcohol is a component having a lighter boiling point than that of the α-hydroxycarboxylic acid ester, if the alcohol is preferentially distilled off in the distillation step, the equilibrium of the side reaction is shifted, and the side reaction further proceeds.
[0044]
In the present invention, the operation pressure and the bottom temperature in the distillation column when distilling the α-hydroxycarboxylic acid ester are important for obtaining a product with good purity, good yield and little coloring. In order to suppress a side reaction in the distillation column, the side reaction can be suppressed by performing distillation at a pressure of 13 to 80000 Pa. In addition, by performing distillation at a column bottom temperature of 30 to 250 ° C., side reactions can be suppressed.
[0045]
The reflux ratio at the top of the distillation column is not limited, but is preferably 0.1 to 100, and more preferably 0.3 to 50. Other operating conditions may be in accordance with known distillation conditions.
[0046]
5) Recycling of unreacted raw materials
In the synthesis of the α-hydroxycarboxylic acid ester, when the conversion of the raw material has not reached 100%, the unreacted raw material may be recovered and recycled to the reaction step. The unreacted raw material alcohol is distilled off as a light-boiling component together with by-products such as water during the distillation of the glycolic acid ester. By recycling the alcohol as a raw material in the reaction step, an α-hydroxycarboxylic acid ester can be efficiently produced.
[0047]
At this time, the alcohol to be collected and recycled preferably has a water content controlled in the range of 0 to 20% by mass. The content of water in the alcohol can be controlled by distillation or the like. When an alcohol having a water content of more than 20% by mass is used in the reaction, the α-hydroxycarboxylic acid ester generated during the reaction may be hydrolyzed, and the yield of α-hydroxycarboxylic acid ester may be reduced.
[0048]
In general, new alcohol is added to recycled alcohol as a reaction raw material. At that time, the amount of water in the raw alcohol obtained by mixing the recycled alcohol and the new alcohol is 20 mass% of the alcohol. It is preferable to adjust the amount of water in the recycled alcohol so as to be less than or equal to%. It is more preferably at most 15% by mass. If the amount of water exceeds 20% by mass, the α-hydroxycarboxylic acid ester generated during the reaction may be hydrolyzed, and the yield of α-hydroxycarboxylic acid ester may be reduced.
[0049]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited thereto.
[0050]
Reference Example (Preparation of Au / TiO2-SiO2 catalyst)
TiO 2 —SiO 2 (molar ratio TiO 2 / SiO 2 = 5/95, firing temperature 600 ° C., 50-250 mesh) prepared by a coprecipitation method was used as a carrier.
[0051]
40 L of tetrachloroauric acid having a concentration of 20 mmol / l was adjusted to pH 7 using a 0.5 N sodium hydroxide solution in the range of 65 to 75 ° C. 1 kg of the TiO2-SiO2 carrier was added to this aqueous solution with stirring, and stirring was continued for 1 hour while maintaining the temperature at 65 to 70C. Thereafter, a washing step of removing the supernatant by removing the supernatant, adding 20 L of ion-exchanged water to the remaining immobilized gold, stirring at room temperature for 5 minutes, and removing the supernatant was repeated three times. Finally, the gold-immobilized product obtained by filtration was dried at 110 ° C. for 8 hours, and further calcined in air at 400 ° C. for 3 hours to obtain a catalyst (Au / TiO 2 −) having gold supported on a TiO 2 —SiO 2 support. SiO2) was obtained.
[0052]
The amount of gold supported on the carrier in this catalyst was 5.4% by mass. When the particle diameter of the gold particles was observed, almost all particles were highly dispersed with a particle diameter of 6 nm or less, had a narrow particle diameter distribution having a maximum around 2-3 nm, and had an average particle diameter of 6 nm or less. .
[0053]
Example 1 Production of α-hydroxycarboxylic acid ester (production of methyl glycolate)
Methyl glycolate was synthesized using the Au / TiO2-SiO2 catalyst obtained in Reference Example. Into a 100 L reactor equipped with a rotary stirrer and a condenser, 9.6 kg of ethylene glycol, 50.0 kg of methanol and 4.3 kg of the catalyst of Reference Example were charged and pressurized to 0.7 MPa with nitrogen. Thereafter, the internal temperature was raised to 120 ° C., and the pressure was adjusted to 1 MPa. While maintaining the pressure at 1 MPa, air was blown into the liquid at a flow rate of 2.5 Nm 3 / hr, and the reaction was carried out at 120 ° C. for 8 hours.
[0054]
After completion of the reaction, the reaction solution was cooled and extracted, and the catalyst was filtered. After that, the reaction solution was analyzed by gas chromatography, liquid chromatography and Karl Fischer moisture meter. The reaction solution contained 7.5 kg of methyl glycolate, 3.5 kg of ethylene glycol, 43.2 kg of methanol, 4.9 kg of water, and 0.7 kg of glycolic acid. The conversion of ethylene glycol was 63.5 mol%, The yield of methyl glycolate based on ethylene glycol was 53.8 mol%.
[0055]
The reaction solution was applied to a rotary thin film evaporator to remove light boiling components. The low boiling point component was removed at a jacket temperature of 140 ° C. and a pressure of 533 hpa. The composition of the resulting low boiling cut solution was 47.0% by mass of methyl glycolate, 26.0% by mass of methanol, 17.0% by mass of water, 7.0% by mass of ethylene glycol, and 2.6% by mass of glycolic acid. there were.
[0056]
3050 g of the obtained light boiling cut liquid was charged into a 3 L glass flask equipped with a distillation column filled with Sumitomo / Sulzer Lab Packing to a height of 90 cm, and subjected to batch distillation. First, at a reflux ratio of 0.5 and a top pressure of 133 hPa, methanol and water, which are light boiling components, were removed. Thereafter, a fraction containing methyl glycolate was withdrawn at a reflux ratio of 1 and an overhead pressure of 13 hPa. The top temperature at that time was 46 to 47 ° C. Analysis of the obtained fraction containing methyl glycolate contained 98.9% by mass of methyl glycolate, 0.10% by mass of methanol, and 0.31% by mass of water.
[0057]
Example 2
A mixture of the light-boiling components distilled off in the rotary thin-film evaporator of Example 1 and the initial distillation obtained by distilling methyl glycolate was added to the bottom of the column, and batch distillation was performed in a 15-stage Oldershaw distillation column. Was. The operation was performed at a reflux ratio of 1, and a fraction of 97% by mass of methanol and 3% by mass of water was obtained from the top of the column.
[0058]
In a 500 mL autoclave equipped with a rotary stirrer and a condenser, 24.1 g of ethylene glycol, 127.8 g of the fraction obtained by the above distillation, and 18.0 g of the catalyst of Reference Example were charged, and pressurized to 0.7 MPa with nitrogen. . Thereafter, the internal temperature was raised to 120 ° C., and the pressure was adjusted to 1 MPa. While maintaining the pressure at 1 MPa, a mixed gas consisting of 8% by volume of oxygen and 92% by volume of nitrogen was blown into the liquid at a flow rate of 1 normal L per minute, and the reaction was carried out at 120 ° C. for 4 hours.
[0059]
After completion of the reaction, the reaction solution was cooled and extracted, and the catalyst was filtered. After that, the reaction solution was analyzed by gas chromatography and liquid chromatography. The reaction solution contained 19.9 g of methyl glycolate, 3.9 g of ethylene glycol, and 114.2 g of methanol. The conversion of ethylene glycol was 83.7 mol%, and the yield of methyl glycolate based on ethylene glycol was 83.7 mol%. Was 56.9 mol%.
[0060]
【The invention's effect】
According to the method for producing an α-hydroxycarboxylic acid ester of the present invention, an α-hydroxycarboxylic acid ester having high reactivity and easily causing a side reaction can be efficiently produced with good yield.

Claims (2)

A method for producing an α-hydroxycarboxylic acid ester comprising the following steps.
Step 1: (i) a reaction step of reacting 1,2-diols with each other or (ii) reacting a 1,2-diol with an alcohol in the presence of oxygen to obtain an α-hydroxycarboxylic acid ester;
Step 2: A distillation step of distilling the reaction solution obtained in Step 1 under the conditions of a pressure of 13 to 80000 Pa and a tower bottom temperature of 30 to 250 ° C. to obtain an α-hydroxycarboxylic acid ester. The method for producing an α-hydroxycarboxylic acid ester according to claim 1, further comprising the following steps.
Step 3: a step of collecting unreacted alcohol contained in the reaction solution obtained in Step 1 and recycling the alcohol having a water content of 0 to 20% by mass to Step 1.