TWI450886B - Process for preparing lactic esters with catalysts containing zirconium and aluminum - Google Patents

Description

Method for preparing lactic acid ester by using zirconium aluminum catalyst

The present invention relates to a process for the esterification of lactic acid to form a lactate, and more particularly to the catalyst used in the esterification reaction.

Lactic acid is an important biochemical product widely used in the fields of medicine, food, chemical, leather, synthetic fiber and plastic raw materials. Lactic acid can be synthesized by petrochemical or by fermentation. The future demand for lactic acid will increase mainly from two aspects: polylactic acid and lactate solvent. In recent years, environmental protection issues have attracted attention. With the successful development and utilization of green solvents (lactic acid esters) and biodegradable plastics (polylactic acid) products synthesized from lactic acid, the demand for lactic acid is increasing year by year.

Lactic acid esters are used as green solvents. Lactic acid esters are an excellent and safe high-boiling solvent with excellent solubility and unique solubility for greases and polymers. The use of lactate as a green solvent avoids the environmental pollution caused by traditional organic solvents.

The lactation reaction can also be applied to the process of purifying lactic acid. Since the synthesis of polylactic acid materials requires high-purity lactic acid monomers, the technique of separating and purifying lactic acid from lactic acid fermentation broth has become the key in current lactic acid production. The reactive distillation method is an excellent method for purifying lactic acid and can be used to obtain high-purity lactic acid. The purification of lactic acid by reactive distillation mainly comprises three steps: lactation, distillation under reduced pressure and hydrolysis of lactate, that is, esterification reaction between lactic acid and alcohol is first carried out to form lactate, and then subjected to vacuum distillation. The lactic acid ester and the lactic acid ester are hydrolyzed to obtain purified lactic acid. Therefore, the esterification reaction of lactic acid to form lactate can also be one of the steps of purifying lactic acid.

U.S. Patent No. 2,350,370 (Schopmeyer, H.H., CR Arnold, "Lactic acid purification", 1944) is the first to use the concept of reactive distillation to purify lactic acid, which is an esterification reaction of lactic acid with methanol. Catalyst for esterification.

Choi and Hong (Choi, J., Hong, WH, "Recovery of lactic acid by batch distillation with chemical reactions using ion exchange resin", J. Chemical Eng. Japan, 32(2), P. 184 (1999)), Seo et al. (Seo, Y., Hong, WH, and Hong, TH, "Effects of operation variables on the recovery of lactic acid in a batch distillation process with chemical reactions", Korean J. of Chem. Eng., 16 (5), P. 556 (1999)), and Kim et al. (Kim, JY, Kim, YJ, Hong, WH, and Wozny, G., "Recovery process of lactic acid using two distillation columns", Biotech. & Bioprocess Eng., 5(3), P. 196(2000)), etc. Purification of lactic acid by batch reactive distillation, which uses cation exchange resin as a catalyst to carry out the esterification reaction of methanol with lactic acid, and its subsequent Hydrolysis reaction. Ma et al. (Ma, L., Zhang, Y., and Yang, J., "Purification of lactic acid by heterogeneous catalytic distillation using ion-exchange resins", Chinese J. of Chem. Eng., 13(1) , P. 24 (2005)) In the distillation column, a cation exchange resin is used as a catalyst, methanol is used to esterify lactic acid, and a hydrolysis reaction of methyl lactate is carried out by a reactive distillation method. Kumar et al. (Kumar, R., Nanavati, H., Noronha, SB, Mahajani, SM, "A continuous process for the recovery of lactic acid by reactive distillation", Journal of Chemical Technology & Biotechnology, 81 (11), P. 1767 (2006)) using a two-phase continuous stirred reactor reaction, adding methanol to carry out lactation reaction, and a gas phase product containing methyl lactate, water and methanol, and then feeding it to hydrolysis The tower can obtain relatively pure lactic acid. Kumar and Mahajani (Kumar, R. and Mahajani, SM, Esterification of lactic acid with n-butanol by reactive distillation, Ind. Eng. Chem. Res., 46(21), P. 6873 (2007)) Based on the reaction with lactic acid, the esterification reaction distillation column, the hydrolysis reaction distillation column, and the separation process of the stripping tower complete the purification of lactic acid. The catalyst used by Kumar et al. to catalyze the esterification and hydrolysis of lactic acid is also a cation. Exchange resin. The disadvantage of the cation exchange resin is that it cannot be used at a higher temperature. We have found that the use of a cation exchange resin to catalyze the esterification reaction of lactic acid with butanol above 130 degrees Celsius may cause severe discoloration of the reaction solution.

The esterification of lactic acid is a reversible reaction and is typically represented by the following chemical reaction formula:

CH ₃ CH(OH)COOH+ROH=CH ₃ CH(OH)COOR+H ₂ O

(Lactic acid + alkyl alcohol = lactate + water)

Based on the theory of chemical kinetics, a catalyst capable of catalyzing the esterification reaction of lactic acid (ie, a positive reaction) can also be used to catalyze the hydrolysis reaction of a lactate (ie, a reverse reaction). This reversible reaction is an endothermic reaction, so an increase in temperature favors an increase in the equilibrium constant and an increase in the yield of lactic acid ester. It is known from the above literature that liquid acid and cation exchange resins can catalyze the esterification reaction of lactic acid and alcohol and catalyze the hydrolysis reaction of lactic acid ester. The disadvantage of using liquid acid as a catalyst is that it is easy to corrode the reaction equipment and cause environmental pollution problems. The disadvantage of using a cation exchange resin as a catalyst is that it is not resistant to high temperatures. Therefore, a solid catalyst is needed, which can effectively catalyze the esterification reaction of lactic acid with alcohol and the hydrolysis reaction of lactic acid at high temperature, and is applied to the synthesis of green solvent (lactic acid ester) and to the purification of lactic acid by reactive distillation. In the process.

SUMMARY OF THE INVENTION The primary object of the present invention is to provide an improved process for the synthesis of lactic acid esters which comprises esterifying a lactic acid and a liquid containing an alkyl alcohol in the presence of a catalyst system comprising zirconium and aluminum to form a lactate. . Unexpectedly, under the same reaction conditions, the zirconium-aluminum mixed catalyst has a higher lactate yield than the zirconium catalyst alone or the aluminum catalyst alone.

The zirconium-aluminum mixed catalyst of the present invention can be produced by a coprecipitation method, a sol-gel method, an impregnation method or a solid-state reaction, and is preferably a coprecipitation method. The coprecipitation method is to change the pH value in the solution or change the temperature of the solution to coprecipitate the zirconium compound and the aluminum compound, and then to form a zirconium-aluminum mixed catalyst by filtration, drying and calcination.

A preferred method of coprecipitation is to use a mixed solution containing a zirconium precursor and an aluminum precursor in contact with an aqueous alkaline solution to produce an insoluble zirconium aluminum hydroxide or an insoluble zirconium aluminum carbonate, such hydroxides and carbonic acid. The salt is heated to form a zirconium-aluminum mixed oxide.

Titanium precursors suitable for use in the present invention include zirconium halides, zirconium oxides, zirconium esters, zirconium sulfides, zirconium sulfates, zirconium oxalates, zirconium nitrides, zirconium hydrides, zirconium carbides, preferably zirconium halides and zirconium esters, more preferably It is zirconium chloride.

Aluminum precursors suitable for use in the present invention include aluminum halides, aluminum oxides, aluminum esters, aluminum sulfides, aluminum sulfates, aluminum oxalates, aluminum nitrides, aluminum hydrides, aluminum carbides, preferably aluminum halides and aluminum esters, more preferably. It is aluminum chloride.

The esterification reaction of lactic acid of the present invention comprises esterifying lactic acid and a monoalkyl alcohol in the presence of a catalyst system comprising zirconium and aluminum prepared as described above to form a lactate. Suitable alkyl alcohols contain from one to seven carbons, preferably methanol, ethanol, propanol and butanol.

The esterification reaction of the present invention can be carried out in a batch reactor or a continuous reactor or a reactive distillation column. The continuous reactor can be a continuously stirred slurry reactor or a trickle-bed reactor. ) or a fixed bed reactor. The reaction temperature of the esterification reaction is between 20 and 300 ° C, preferably between 50 and 200 ° C.

The following examples are intended to further illustrate the method of the invention, but are not intended to limit the scope of the invention.

Example 1

The esterification catalyst used in this practical example is a catalyst having a zirconium aluminum molar ratio of 1:1.

Catalyst preparation

11.65 g of zirconium tetrachloride (ZrCl ₄ ) and 12.07 g of aluminum trichloride (AlCl ₃ ‧6H ₂ O) were respectively dissolved in 25 ml of absolute alcohol, and these solutions were mixed. Then, 150 ml of 28% aqueous ammonia was slowly dropped into the mixed alcohol solution to cause a coprecipitation reaction, and stirring was continued for two hours to complete the coprecipitation reaction. After filtering, washing with water, drying (110 ° C, 12 hours), and then calcining (heating to a temperature of 1 degree Celsius per minute to 500 degrees Celsius, then maintaining at 500 degrees Celsius for three hours), that is, zirconium aluminum Mixed catalyst with ear ratio 1:1.

Esterification reaction

2.8 g of lactic acid (88% purity) and 30 ml of butanol were added to a 100 ml high pressure reactor, and 0.64 g of the zirconium aluminum catalyst prepared above was added, followed by heating to bring the reactor to the set temperature. The stirring rate was set to 200 rpm. After the reaction has reached the set time, the reactor is cooled to room temperature, the reacted solution is taken, and the component analysis is carried out by gas chromatography (GC) to measure the molar number of the remaining lactic acid and the produced butyl lactate. The number of moles. From this, the conversion of lactic acid and the yield of butyl lactate can be calculated by the following equation: conversion of lactic acid = (mole of lactic acid reaction) / (mole of lactic acid) × 100%; butyl lactate Yield = (molar number of butyl lactate) / (molar number of lactic acid added) × 100%. The results of the lactic acid conversion rate are shown in Table 1. The results of the butyl lactate yield are shown in Table 2.

Example 2

The esterification catalyst used in this practical example is a 3:1 catalyst of zirconium aluminum molar ratio.

The catalyst was prepared as in Example 1, except that 17.48 grams of zirconium tetrachloride and 6.04 grams of aluminum trichloride (AlCl ₃ ‧6H ₂ O) were used. The esterification reaction was also carried out in the same manner as in Example 1. The results of the lactic acid conversion were also shown in Table 1. The results of the butyl lactate yield are also shown in Table 2.

Example 3

The esterification catalyst used in this practical example is a catalyst of zirconium aluminum molar ratio of 1:3.

The catalyst was prepared in the same manner as in Example 1, except that 5.83 g of zirconium tetrachloride and 18.11 g of aluminum trichloride (AlCl ₃ ‧6H ₂ O) were used. The esterification reaction was also carried out in the same manner as in Example 1. The results of the lactic acid conversion were also shown in Table 1. The results of the butyl lactate yield are also shown in Table 2.

Comparative example 1

The esterification catalyst used in this comparative example was an aluminum-free zirconium catalyst. The zirconium catalyst was prepared in the same manner as in Example 1, except that 23.303 g of zirconium tetrachloride and 0 g of aluminum trichloride were used. The esterification reaction was also carried out in the same manner as in Example 1. The results of the lactic acid conversion were also shown in Table 1. The results of the butyl lactate yield are also shown in Table 2.

Comparative example 2

The esterification catalyst used in this comparative example was an aluminum catalyst containing no zirconium. The aluminum catalyst was prepared in the same manner as in Example 1, except that 24.14 g of aluminum trichloride and 0 g of zirconium tetrachloride were used. The esterification reaction was also carried out in the same manner as in Example 1. The results of the lactic acid conversion were also shown in Table 1. The results of the butyl lactate yield are also shown in Table 2.

It can be seen from the data of Tables 1 and 2 that the zirconium-aluminum mixed catalyst (Examples 1 to 3) is higher than the zirconium catalyst alone or the aluminum catalyst alone (Comparative Example 1 and Comparative Example 2). The lactic acid conversion rate and the lactic acid ester yield, this result is clearly unexpected.

It can be understood from the above description that the method of the present invention has an improved effect and is indeed a new invention which is of industrial value.

Claims (8)

A method for synthesizing lactic acid ester, which comprises esterifying lactic acid with a monoalkyl alcohol in the presence of a catalyst system containing zirconium-oxygen-aluminum bonds to form a lactate, the catalyst being zirconium halide and The aluminum halide is prepared as a precursor. The method of claim 1, wherein the alkyl alcohol is an alcohol having one to seven carbon numbers. The method of claim 1, wherein the alkyl alcohol is an alcohol having one to four carbon numbers. The method of claim 1, wherein the alkyl alcohol is butanol. The method of claim 1, wherein the esterification reaction has a temperature between 20 and 300 °C. The method of claim 1, wherein the esterification reaction has a temperature between 50 and 200 °C. The method of claim 1, wherein the zirconium halide is zirconium tetrachloride. The method of claim 1, wherein the aluminum halide is aluminum trichloride.