KR20130057540A - Methods for purifying lactic acid - Google Patents

Abstract

PURPOSE: A method for purifying lactic acid is provided to increase distillation yield by preventing the formation of an oligomer of lactic acid through low temperature distillation, and to purify the lactic acid with high purity by ion exchanging and distillation. CONSTITUTION: A method for purifying lactic acid comprises: a step of manufacturing an ion-exchanged lactic acid solution by an ion exchanging process of a lactic ferment solution; and a step of manufacturing lactic acid by distilling the ion-exchanged lactic acid solution in a reactor. The ion exchanging is conducted by a cation exchange resin and the cation exchange resin is strong acidic cation exchange resin. [Reference numerals] (AA) Ammonium hydroxide; (BB) Medium; (CC) Fermentation; (DD) Centrifugation or membrane filtration; (EE) Mycobiont; (FF) Ammonium lactate solution; (GG) Hydrochloric acid or sulfuric acid; (HH) Cation exchange; (II) Ammonium chloride or ammonium sulfide; (JJ) Bleaching; (KK) Lactic acid; (LL) Distillation; (MM) Other impurities; (NN) High purity lactic acid

Description

Method for Purifying Lactic Acid {Methods for Purifying Lactic Acid}

The present invention relates to a method for purifying lactic acid from lactic acid fermentation broth produced by fermentation of microorganisms, and more particularly, to remove high ionic substances in fermentation broth through ion exchange and distill the resulting lactic acid-containing solution to produce high purity lactic acid. It is about a method.

Lactic acid is a basic chemical with a variety of applicability obtained from renewable biomass. Lactic acid is produced by chemical synthesis prepared by hydrolysis of Lactonitrile by sulfuric acid and by fermentation which ferments a substrate containing glucose with lactic acid. Recently, the technology of refining lactic acid produced by fermentation has been developed, so that lactic acid having almost the same quality as lactic acid produced by chemical synthesis can be produced.

Lactic acid produced through fermentation produces different lactates depending on the pH regulator added to the culture medium during the lactic acid fermentation microorganism culture. A pH adjuster is added to maintain a pH at which microorganisms can efficiently metabolize, and when calcium hydroxide or calcium carbonate is added, calcium lactate is produced, and when ammonium hydroxide is added, ammonium lactate is produced. Lactate may be purified through various purification methods depending on the type of lactate according to the pH adjusting agent.

Purification of lactic acid produced through fermentation includes Precipitation, Extraction, Adsorption, Reactive Distillation, Electrodialysis and Nano filtration. have.

Precipitation is performed by neutralizing calcium lactate solution produced by using calcium hydroxide or calcium carbonate as a pH adjusting agent with sulfuric acid to convert calcium ions into calcium sulfate ( It is precipitated in the form of Calcium sulfate) and filtered to remove it. This method has the disadvantage of generating waste of calcium sulfate, but it has the advantage of relatively simple process and low purification cost.

Purification of lactic acid by extraction is a method of purifying lactic acid using a solvent having a large partition coefficient for lactic acid and a low partition coefficient for other impurities. The fermentation broth in the form of calcium lactate was neutralized with sulfuric acid to precipitate calcium sulfate. The lactic acid was extracted into the solvent layer using an amine extractant to separate the impurities from the impurities, and the back extracted from the solvent layer to the aqueous layer to purify the lactic acid. (US2006-7144977, US2003-0004375, JP2003-511360, US2002-6472559 and KP2002-7004319). This method may cause environmental problems since organic solvents are used, and it is difficult to select an appropriate solvent.

The adsorption method is a method of adsorbing and purifying lactic acid to a solid adsorbent or ion exchange resin, which is an advantageous process for purifying lactic acid in a complex solution such as low concentration lactic acid or fermentation broth. However, this adsorption method has a disadvantage of low purity because not only lactic acid but also other by-products are adsorbed together, other purification methods that can increase the purity is required.

Purification of lactic acid using reactive distillation involves first producing lactic acid by reacting lactic acid with an appropriate alcohol to produce ester and then hydrolyzing the ester obtained by distillation to obtain pure lactic acid. The fermentation broth in the form of ammonium lactate is reacted with ethanol or butanol to hydrolyze the resulting lactic acid ester to purify the lactic acid through distillation (WO2007-013259, US2003-6569989). This method has the advantage of obtaining high purity lactic acid but is not suitable for primary purification of lactic acid from fermentation broth.

Purification of lactic acid by electrodialysis is performed by desalination electrodialysis to remove impurities present in the fermentation broth, and then lactate (Lactate) form in water decomposition electrodialysis to recover lactic acid. The advantage is that it does not cause pollution problems. However, the purification method using electrodialysis has the disadvantages of membrane contamination and equipment investment cost.

Finally, the purification of lactic acid by nanofiltration is a method of obtaining a lactic acid desired by excluding the nonionic substances present in the fermentation broth by the size difference using a nanofiltration membrane and effectively excluding the ionic substances by the characteristics of the membrane. It has the advantage that continuous process is possible and does not cause environmental pollution problem. However, as with electrodialysis, purification methods using membranes such as nanofiltration have disadvantages such as membrane contamination and equipment investment costs.

Lactic acid purified by various methods as described above is mainly applicable to the fields of food, cosmetics, pharmaceuticals and polymers depending on the quality. In particular, in order to produce lactic acid, which is used as a raw material for poly lactic acid, a biodegradable polymer, a high-purity lactic acid purification process in which impurities are completely excluded is required. However, solvent extraction or reaction distillation, which can obtain high purity lactic acid, can cause economic and environmental problems due to the complicated process, long reaction time, and the use of organic solvents. Therefore, high purity lactic acid can be produced in a relatively simple process by removing ammonium ions which occupy the largest proportion of impurities through an ion exchange process suitable for primary purification of lactic acid and purifying through distillation to increase the purity of lactic acid.

Numerous papers and patent documents are referenced and cited throughout this specification. The disclosures of the cited papers and patent documents are incorporated herein by reference in their entirety to better understand the state of the art to which the present invention pertains and the content of the present invention.

The present inventors have tried to produce high purity lactic acid from lactic acid fermentation broth produced by microbial fermentation. As a result, the present invention has been completed by elucidating that the purpose of the present invention for producing high-purity lactic acid can be achieved by preparing lactic acid through a distillation process for removing the major ionic substances in the fermentation broth through ion exchange and increasing the purity. It was.

It is therefore an object of the present invention to provide a lactic acid purification method.

Other objects and advantages of the present invention will become more apparent from the following detailed description of the invention, claims and drawings.

According to one aspect of the present invention, there is provided a method for purifying lactic acid from lactic acid fermentation broth containing lactic acid salt comprising the following steps:

(a) preparing a lactic acid solution in which the lactic acid fermentation solution including lactic acid salt is ion exchanged through an ion exchange process; And

(b) distilling the ion exchanged lactic acid solution in a reactor to produce lactic acid.

The present inventors have tried to prepare high purity lactic acid from lactic acid fermentation broth produced by microbial fermentation. As a result, it was found that the purpose of the present invention for producing high-purity lactic acid can be achieved by preparing lactic acid through a distillation process for removing major ionic substances in fermentation broth through ion exchange and increasing purity.

The lactic acid production method from the lactic acid fermentation broth containing lactic acid of the present invention will be described in detail by dividing each step as follows:

Step (a): preparing an ion exchanged lactic acid solution

According to the present invention, a lactic acid fermentation solution containing lactic acid is prepared by ion exchange resin lactic acid solution.

Preferably, the lactic acid fermentation broth comprises L type lactic acid or D type lactic acid.

Preferably, the method further includes the step of adding salt to the lactic acid fermentation medium before step (a) and then lactic acid fermentation to produce lactic acid salt.

In the present specification, the term "lactic acid salt" is ammonium lactate produced by fermentation by adding an alkali that can adjust the pH of the fermentation broth, such as ammonium hydroxide, sodium hydroxide, calcium hydroxide, potassium hydroxide, calcium oxide and calcium carbonate, to the culture medium of lactic acid fermentation microorganisms. , Sodium lactate, calcium lactate, potassium lactate, and the like, preferably ammonium lactate produced by adding ammonium hydroxide.

In the culturing of the lactic acid fermentation microorganism of the present invention, different lactates are produced depending on the pH adjuster added to the culture. The pH adjusting agent is added to maintain an optimal pH at which microorganisms can efficiently metabolize, and when calcium hydroxide or calcium carbonate is added, calcium lactate is produced, and when ammonium hydroxide is added, ammonium lactate is produced. Lactate may be purified through various purification methods depending on the type of lactate according to the pH adjusting agent.

When calcium hydroxide or calcium carbonate is used as the pH adjusting agent, the calcium lactate produced is low in solubility in water, causing precipitation from the fermentation broth to hinder the agitation of the fermentation broth and thus lowering the fermentation yield. In addition, since the solubility of calcium hydroxide or calcium carbonate in water is low, it is difficult to adjust the pH of the fermentation broth so that microorganisms can efficiently produce lactic acid.

Preferably, the pH adjuster used in the present invention is ammonium hydroxide or ammonia water, more preferably ammonium hydroxide. In addition to facilitating the pH control of the lactic acid fermentation broth using high solubility ammonium hydroxide (NH ₄ OH or ammonia water), the ammonium lactate produced by the lactic acid fermentation process has high solubility in water, which leads to the lactic acid fermentation process and the growth of lactic acid bacteria. Since it does not interfere, the lactic acid fermentation yield is greatly improved.

When ammonium hydroxide is added to the lactic acid fermentation broth in the present invention, the pH of the lactic acid broth is preferably pH 3 to pH 12, more preferably pH 5 to pH 10, and most preferably pH 6 to pH 8. .

In the present specification, the term "lactic acid fermentation broth" is a product produced through the lactic acid fermentation process, preferably, the lactic acid fermentation broth is lactic acid fermentation from a culture solution containing microorganisms after lactic acid fermentation or a culture solution containing microorganisms after the lactic acid fermentation. Fermentation broth from which microorganisms are isolated.

According to a preferred embodiment, the lactic acid fermentation broth used in the present invention is separated from the lactic acid fermentation microorganisms from the lactic acid fermentation broth containing ammonium lactate produced by the lactic acid fermentation of lactic acid fermentation microorganism culture medium containing ammonium hydroxide and the remaining ammonium lactate Lactic acid fermentation broth containing.

In the present invention, the separation of microorganisms from the lactic acid fermentation broth is removed by centrifugation or filtration.

The ion exchange in step (a) can be carried out using various ion exchange resins known in the art, such as cation exchange resins and anion exchange resins. Preferably, the ion exchange in step (a) is made by a cation exchange resin.

As used herein, the term “strongly acidic cation exchange resin” refers to an ion exchange resin commonly understood in the art, for example Kirk-Othmer Encyclopedia Of Chemical Technology, Volume 14, pages 737-783 (1995). It means what is described in "ion exchange" described in. Strongly acidic cation exchange resins maintain a substantially fully ionized form over a wide pH range, which is a distinct distinction from weakly acidic cation exchange resins, and weakly acidic cation exchange resins maintain ionized forms in a narrow pH range. Strongly acidic cation exchange resins suitable for the present invention are those in which a sulfo, sulfoalkyl (such as sulfomethyl, sulfoethyl and sulfopropyl), phospho or phosphoalkyl functional group is bonded to a polymer (such as polysaccharide) matrix. Preferably, the strongly acidic cation exchange resin has a sulfo or sulfoalkyl functional group, most preferably one having a sulfo functional group.

Preferably, the liquid-flowing amount of lactic acid salt in the strongly acidic cation exchange step is 10-200 g, more preferably 50-185 g, most preferably 80-100 g.

Preferably, the rate of liquid passing through the lactic acid salt in the strongly acidic cation exchange step is 1-5 BV / h, more preferably 1-3 BV / h, most preferably 1-1.5 BV / h.

According to a preferred embodiment, the pH of the lactic acid solution in which the lactic acid fermentation broth including lactic acid is ion exchanged in the ion exchange process of step (a) through a strong acid cation exchange resin process is pH 1.0-pH 3.86, and more preferably pH 1.0. -pH has a value of 2.0.

According to the ion exchange process, the conversion rate from lactic acid to lactic acid is 85-100%, more preferably 90-100%, and most preferably 95-98%.

The ion exchange resin which has undergone the ion exchange process in step (a) of the present invention can be regenerated with sulfuric acid, hydrochloric acid or sodium hydroxide, preferably with sulfuric acid and the sulfuric acid concentration is 5-15%, more preferably. Is 7-10%.

Step (b): distillation in a reactor to produce lactic acid

The ion exchanged lactic acid solution obtained from step (a) is then distilled in a reactor to produce lactic acid.

The distillation is a method of separating the mixture using the difference in volatility of the components constituting the boiling mixture.

Preferably, the distillation of step (b) is carried out at a temperature of 80-140 ° C., more preferably at 90-120 ° C.

Preferably, the distillation of step (b) is carried out at 1-20 torr, more preferably 1-5 torr. The 1-20 torr is 1.315 × 10 ⁻³ to 2.632 × 10 ⁻² atm, and 1-5 torr is 1.315 × 10 ⁻³ atm to 6.575 × 10 ⁻³ atm.

Preferably, the initial lactic acid concentration of the lactic acid solution of step (b) is 10-80% by weight, more preferably 30-50% by weight.

Preferably, the initial amount of lactic acid solution to be distilled in step (b) and the amount of lactic acid solution remaining in the reactor is 1-30% by volume of the reactor volume, and the amount of the lactic acid solution is equal to the amount of the reactor volume. The lactic acid solution is continuously injected into the reactor to maintain 1-30% by volume.

According to a preferred embodiment of the present invention, L-lactic acid or D-lactic acid produced by the lactic acid production method of the present invention has an optical purity of 95% or more.

The features and advantages of the present invention are summarized as follows:

(a) The present invention provides a method for purifying lactic acid from a lactic acid fermentation broth comprising lactate.

(b) The present invention has a merit of purifying low purity lactic acid purified through an ion exchange process, which is a kind of adsorption method, in a conventional purification process of lactic acid with high purity through distillation.

(c) The present invention provides a minimum amount of lactic acid solution for initial distillation of lactic acid, which has a high boiling point and is difficult to distill in the existing lactic acid distillation process, and continuously distilled while injecting, thereby increasing the heat transfer rate of the material at a relatively low temperature. Can be distilled. Distillation at low temperature has the advantage of preventing oligomer formation of lactic acid to improve the distillation yield, and to prevent deterioration due to carbonization of impurities during high temperature distillation.

(d) The present invention can use a relatively simple equipment compared to other separation and purification process, using the equipment that has already been spread is excellent in the ease of use and maintenance of the equipment.

(e) The present invention can be applied to high value-added products such as bioplastic using optical lactic acid of high purity in addition to cosmetics and food additives and polylactic acid.

Figure 1 shows a schematic diagram of the purification process of lactic acid from ammonium lactate through ion exchange and distillation.

Hereinafter, the present invention will be described in more detail with reference to Examples. It is to be understood by those skilled in the art that these embodiments are only for describing the present invention in more detail and that the scope of the present invention is not limited by these embodiments in accordance with the gist of the present invention .

Example

Throughout this specification, "%" used to denote the concentration of a particular substance is intended to include solids / solids (wt / wt), solid / liquid (wt / The liquid / liquid is (vol / vol)%.

Example  1: Ion Exchange of Lactic Acid Fermentation Solution Containing Ammonium Lactate

Lactobacillus coriniformis coryniformis ; KCTC 3535) medium (glucose 11%, yeast extract 1.5%, corn steep liquor 6%, sodium acetate 0.1%, MgSO ₄ 0.02%, MnSO ₄ 0.006%, K ₂ HPO ₄ 0.07% and KH ₂₎ 0.05% of PO ₄ ) was added to pH 6.0 by addition of ammonium hydroxide and incubated at 32 ° C. for about 50 hours.

The lactic acid fermentation broth containing 10% by weight of ammonium lactate was removed by centrifugation at a speed of 4000 rpm or more. For conversion of ammonium lactate to lactic acid, 4 L of the cell-free ammonium lactate fermentation broth was added to a strongly acidic cationic resin column having 4 L volume of sulfuric acid functional group (ie, sulfo group) pre-conditioned with H ^+. Pass at BV / h speed. The resin is regenerated by passing 150 g of sulfuric acid per liter. According to these conditions, the conversion rate from ammonium lactate to lactic acid was 97%, and the analysis of the lactic acid solution is shown in Table 1.

- Lactate Concentration (%) Ammonia Ion Concentration (%) pH Ammonium Lactate Fermentation Solution 10.0 2.1 6.0 Ion-Exchanged Lactic Acid Solution 8.0  ≤ 0.01 1.8

Example  2: distillation of lactic acid at various concentrations and temperatures

The boiling point of lactic acid is 122 ° C. under 12 mmHg and about 250 ° C. under atmospheric pressure. As such, lactic acid has a very high boiling point, low volatility, and oligomerization due to self-polymerization at high temperatures, and thus, distillation under reduced pressure is required to distill lactic acid.

300 g of lactic acid solution concentrated to 10-80% is distilled in a 500 ml round flask. At this time, distillation under reduced pressure at a reactor temperature of 80-140 ° C at a pressure of 1.0-4.0 torr. The amount of lactic acid solution in the initial reactor is 30 g (6% of the reactor volume), and the remaining 270 g is continuously distilled while continuously injecting the liquid amount in the reactor while maintaining 30 g. The optical purity of the lactic acid solution treated under these conditions is 95% or more, the final purity of the lactic acid solution is 98% or more, and the distillation yield according to the conditions is shown in Table 2.

Lactic acid concentration
(weight%) Concentration temperature
(℃) Distillate temperature
(℃) pressure
(torr) Distillation time
(minute) Distillation yield
(%) 10 80 60-80 1.0-4.0 100 91.05 10 80 70-90 10.0-20.0 200 80.07 50 100 80-100 1.0-4.0 150 94.11 50 100 90-110 10.0-20.0 270 65.59 80 140 110-120 1.0-4.0 90 82.25

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the same is by way of illustration and example only and is not to be construed as limiting the scope of the present invention. It is therefore intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

Claims (9)

A method for purifying lactic acid from lactic acid fermentation broth containing lactic acid salt comprising the following steps:
(a) preparing a lactic acid solution in which the lactic acid fermentation solution including lactic acid salt is ion exchanged through an ion exchange process; And
(b) distilling the ion exchanged lactic acid solution in a reactor to produce lactic acid.
The method according to claim 1, wherein the lactic acid fermentation broth of step (a) is L-lactic acid or D-lactic acid.
The method of claim 1 wherein the lactic acid salt of step (a) is ammonium lactate.
The method of claim 1, wherein the ion exchange in step (a) is made by a cation exchange resin.
The method of claim 4, wherein the cation exchange resin is a strong acid cation exchange resin.
6. The method of claim 5, wherein the strongly acidic cation exchange resin has a sulfo functional group.
The process of claim 1 wherein the distillation of step (b) is carried out at a temperature of 80-140 ° C. and 1-20 torr.
The method of claim 1, wherein the initial lactic acid concentration of the lactic acid solution of step (b) is 10-80% by weight.
According to claim 1, wherein the initial amount of lactic acid solution to be distilled in step (b) and the amount of lactic acid solution remaining in the reactor is 1-30% by volume of the reactor volume, the amount of the lactic acid solution is the amount of the reactor The lactic acid solution is continuously injected into the reactor to maintain 1-30% by volume of volume.

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