JP2002128727A - Method for distilling and purifying lactic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for distilling and purifying lactic acid at a low cost in high productivity. SOLUTION: This method for distilling and purifying lactic acid is characterized in that a solution of lactic acid fermentation is distilled while adding water to the solution so as to make a water concentration in the solution constant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for purifying lactic acid by distillation.

[0002]

2. Description of the Related Art Lactic acid is used in food applications such as brewing and pickles, in chemical raw materials such as pharmaceuticals, agricultural chemicals and cosmetics, and in industrial applications such as fiber finishing, paints, solvents, and biodegradable plastics. Demand is expected to increase.

It is considered that lactic acid is easily denatured by heat, and it is difficult to directly distill lactic acid due to its vapor pressure. For this reason,
Conventionally, a method has been adopted in which lactic acid is esterified with an alcohol, purified by distillation as a lactic acid ester, and then hydrolyzed to obtain lactic acid (JP-A-63-141597, JP-A-6-311886). etc).

However, this method requires three steps of operation, and further requires a catalyst (sulfuric acid, ion exchange resin, etc.) for esterification and hydrolysis,
Running cost increases. Further, a large amount of energy is consumed for performing the heat of the esterification reaction, evaporating excess alcohol, and purifying the used alcohol by distillation. Further, the alcohol used for the esterification reaction also needs to be constantly replenished at a fixed rate.

[0005]

An object of the present invention is to provide a method for purifying lactic acid by distillation at low cost and high productivity.

[0006]

Means for Solving the Problems As a result of diligent research for solving the above-mentioned problems, the present inventor conducted direct distillation of lactic acid by performing distillation while maintaining a certain range of water concentration, thereby reducing the cost. Found that lactic acid can be purified by distillation,
The present invention has been completed.

[0007] That is, the present invention is a method for distilling and purifying lactic acid, comprising distilling a lactic acid fermentation solution while adding water so that the concentration of water in the solution is constant. The concentration of the water is 10% by weight (wt%) or less of the whole solution, and the water concentration is maintained while monitoring the boiling point of the distillate. Hereinafter, the present invention will be described in detail.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As water is removed from an aqueous lactic acid solution, water molecules are removed from hydroxyl groups and carboxyl groups between lactic acid molecules to form an ester bond, thereby producing a polymer. Further, since the water pressure in the steam is higher than the lactic acid partial pressure (Table 1), when the lactic acid aqueous solution is distilled, the lactic acid becomes anhydrous and cannot be distilled because it is polymerized. Therefore, in the prior art, a method of producing a volatile lactic acid ester by an esterification reaction with an alcohol, and distilling and hydrolyzing it is adopted.

[0009]

[Table 1]

On the other hand, the present invention does not distill and hydrolyze the lactic acid ester, but adds water while monitoring the boiling point of the distillate so that the water concentration in the lactic acid fermentation solution in the distillation step becomes constant. This is a method for distilling and purifying lactic acid, which comprises preventing polymerization between lactic acid molecules and performing distillation while maintaining the water concentration within a certain range. Lactic acid to be purified by distillation in the present invention can be prepared as follows.

After washing and crushing the sweet potato, which is a raw material for fermentation, it is mixed with water of the same weight as the raw material, liquefied, and treated with a saccharifying enzyme at a predetermined temperature and time (liquefaction = 90 ° C. × 2 hours, saccharification = 60). C. x 20 hours) to obtain a saccharified solution. The solid content is separated and removed from the saccharified solution to obtain a fermentation medium. A lactic acid-producing bacterium is prepared by incorporating a lactic acid-producing gene into a lactic acid-producing gene and disrupting the alcohol-producing gene. After fermentation for 24 hours, a lactic acid fermentation solution with a concentration of about 10% is obtained. In addition, since yeast has acid resistance, it can be fermented without neutralization with alkali.

After separating the cells from the lactic acid fermentation solution obtained as described above with a filter, the concentrated lactic acid from which the water has been evaporated is subjected to a distillation operation. FIG. 1 shows an outline of a distillation apparatus used in the present invention. In FIG. 1, a distillation stock solution flask 1 is a container for storing a concentrated lactic acid fermentation solution, and includes a stirring blade 3. The oil bath 7 is a device for heating the distillation stock solution flask 1 and the concentrated lactic acid fermentation liquor (including water) therein, and can be set at 60 to 180 ° C. A part of the heated concentrated lactic acid fermentation liquor becomes steam and is stored in the distillate flask 2 through the connecting pipe 5. Since the distillate flask 2 is cooled by the cooler 6, the water vapor and the lactic acid vapor in the distillate flask 2 are cooled and recovered as an aqueous lactic acid solution.

[0013] Here, when distilling in the distillation stock solution flask 1, water is injected from the injection pipe 4 so that the water concentration of the lactic acid fermentation liquor present in the flask becomes constant. As the water used in the present invention, distilled water, deionized water, tap water,
Lactic acid aqueous solution (lactic acid fermentation liquid) and the like can be mentioned. Further, "the water concentration is constant" means that the water concentration in the lactic acid fermentation solution is maintained at a constant level without causing large fluctuations throughout the distillation process. In the present invention, an acceptable water concentration level is 10% by weight or less (0.1 to 10 wt.
%), Preferably 1 to 5% by weight. For this reason, the water concentration depends on the boiling point of the distillation stock solution (124 to 173 ° C, preferably 150 to 1
60 ° C) as an index. The boiling point is monitored in real time by a thermometer 8, a temperature sensor or the like, and water is supplied so as not to deviate from the above-mentioned concentration level, that is, so as not to deviate from the above-mentioned range of the boiling point, to keep the water concentration in the lactic acid fermentation liquor constant. Hold. The above boiling point is a value under atmospheric pressure, and the optimum temperature under reduced pressure is a value corresponding to the pressure.

After distilling out the aqueous lactic acid solution, the water is concentrated by heating and evaporating the water to obtain purified lactic acid of a desired concentration. Low boiling components (ethanol,
When an aqueous lactic acid solution containing acetic acid or the like is obtained, it is preferable to remove low-boiling components in the lactic acid concentration process. Further, when the impurities in the distillate are gradually increased by performing the distillation treatment of the lactic acid fermentation liquor continuously, it is desirable to discard a part of the distillate undiluted solution so that the impurity concentration does not exceed a certain level. . The impurity concentration level is set according to the product purity specification. After the distillation operation, impurities can be removed from the distillate by ion-exchange resin, activated carbon, chromatographic separation or the like, if necessary, to obtain lactic acid with higher purity.

[0015]

The present invention will be described more specifically with reference to the following examples. However, the technical scope of the present invention is not limited to these examples. [Reference Example 1] Preparation of lactic acid fermentation liquid After washing and crushing sweet potato (40 kg), which is a raw material of lactic acid fermentation, mixed with 40 L of water and 20 g of liquefaction enzyme (Nova, Tamamil) in a liquefaction / saccharification tank, and Treated at a temperature of ° C. for 2 hours. Next, after cooling to 60 ° C., 80 g of a saccharifying enzyme (Nippon Chemical Co., Sumiteam) was added, and the mixture was kept at a temperature of 60 ° C. for 15 to 24 hours to saccharify the raw material.

The stock solution obtained as described above was applied to a filtration device (filter press) to separate solids (lignin and the like). As a lactic acid-producing bacterium, a lactic acid-producing gene was incorporated and a yeast in which the alcohol-producing gene was disrupted was used for the following fermentation. The above-mentioned sweet potato saccharified solution was used as a medium. The fermentation was performed at a temperature of 30 ° C., a cell density of 25% (wet weight basis), a substrate concentration of 10% (initial concentration of batch fermentation), and a fermentation time of 20 to 24 hours. As a result, 5 to 10% of lactic acid was obtained. Since the yeast has acid resistance, it can be fermented without neutralization with an alkali.

Example 1 Distillation and Purification of Lactic Acid Fermentation Liquid The cells were separated from the lactic acid fermentation liquid obtained in Reference Example 1 using a filter, and the water was evaporated to obtain concentrated lactic acid.
When the concentrated lactic acid was analyzed by liquid chromatography, the lactic acid concentration was 90 wt%, and the main impurities contained glucose 0.1 wt%, malic acid 0.8 wt%, succinic acid 0.4 wt%, and glutamic acid 0.3 wt%. (The rest is moisture). 500 g of the concentrated lactic acid was placed in the distillation stock solution flask 1, heated by the oil bath 7, and further concentrated until a 45 cc distillate was distilled in the distillate flask 2. At this time, the boiling point of the distillation stock solution increased with concentration and reached 160 ° C. After removing the distillate, the undistilled solution flask 1 is heated again in an oil bath, and distillation is performed while injecting water from the injection tube 4 so that the boiling point becomes constant at 160 ° C. (so that the lactic acid concentration becomes constant). went. The distillate obtained by this distillation has a lactic acid concentration of
14.7 wt%, and the above impurities were not detected (10
0 ppm or less).

Example 2 The same 90% concentrated lactic acid as in Example 1 was heated in an oil bath 7 and further concentrated until the boiling point reached 150 ° C. (40 cc of distillate was obtained), and the boiling point was constant at 150 ° C. Distillation was performed while injecting a lactic acid fermentation solution having a concentration of 10% from the injection tube 4 so that The distillate obtained by this distillation had a lactic acid concentration of 10% by weight, and the above impurities were not detected. Incidentally, low boiling impurities were removed during the lactic acid concentration process after distillation.

[Comparative Example 1] This comparative example shows a test example in which distillation was performed without adding water. 90% lactic acid aqueous solution 50
0 g was placed in the distillation flask 1 and vacuum distillation was performed. Connect a vacuum pump from the end of the cooling pipe 6 with a vacuum hose, and 1.
Distillation was performed at a pressure of 3 kPa. The liquid distilled smoothly up to 50 cc of distillate, but the distilling amount gradually decreased thereafter, and distilling stopped after about 70 cc of distillate. When the distillation residue was examined, a lactic acid polymer insoluble in water at room temperature was found to have formed.

[0020]

According to the present invention, a method for purifying lactic acid by distillation is provided. Since the method of the present invention performs direct distillation of the lactic acid fermentation liquor, it does not require an alcohol or a catalyst as in the conventional esterification reaction, can reduce the running cost, and has three conventional purification steps. The operation is simple because one step is performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of a method of the present invention.

[Explanation of symbols]

1: Distillate stock flask, 2: Distillate flask, 3:
Stirring blade, 4: injection tube, 5: connecting tube, 6: cooler,
7: Oil bath, 8: Thermometer

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yasuo Matsuo 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F-term (reference) 4B064 AD33 CA06 CA19 CA21 CC03 CC24 CD22 CE01 DA10 4D076 AA16 AA22 BB01 CB01 EA01Y EA02X EA02Y EA12X EA20Y GA03 HA11 JA05 4H006 AA02 AD11 BB31 BC37 BN10 BS10

Claims (3)

[Claims] 1. A method for distilling and purifying lactic acid, comprising distilling a lactic acid fermentation solution while adding water so that the concentration of water in the solution is constant. 2. The distillation purification method according to claim 1, wherein the concentration of water is 10% by weight or less of the whole solution. 3. The distillation purification method according to claim 1, wherein the maintenance of the water concentration is performed while monitoring the boiling point of the distillate.