JP2013121920A - Method of manufacturing purified lactic acid - Google Patents

Abstract

An object of the present invention is to provide a method for producing purified lactic acid for producing lactic acid suitable as a polymer raw material by desalting and purifying lactic acid obtained by fermentation by an ion exchange method.
A lactic acid solution sent from a solid-liquid separation step 22 is supplied to a first cation exchange column 32, then supplied to a second cation exchange column 37, and discharged to a solid-liquid separation step 24. . When the adsorption capacity of the first cation exchange column 32 is consumed, alkali metal ions leak and are adsorbed and removed by the second cation exchange column 37. When calcium ions start to leak from the first cation exchange tower 32, the calcium ion leakage monitor 47 detects this. As a result, the valves 31, 34, 39, 42 are closed, and the valves 51, 54, 59, 62 are opened instead. At the same time, the pumps 36 and 41 are stopped, and the pumps 56 and 61 are operated instead.
[Selection] Figure 5

Description

  The present invention relates to a method for producing purified lactic acid.

  Lactic acid is used as a raw material for producing resins such as polylactic acid, which is an industrial polymer, and lactic acid-based copolymers. These polymers are extremely beneficial because they are biodegradable. In general, polylactic acid concentrates and oligomerizes either L-lactic acid or D-lactic acid, which is a raw material, and converts it into a cyclic dimer (lactide) by depolymerization. It is produced by carrying out ring-opening polymerization of lactide under the conditions (lactide method). In addition, there is a direct polymerization method that does not involve lactide. In any polymerization method, in order to keep the melting point, weather resistance, mechanical properties, etc. of polylactic acid good, it is necessary to keep the optical purity of the lactic acid skeleton in the polylactic acid molecule high. To that end, the optical purity is high. It is necessary to perform ring-opening polymerization of lactide (LL-lactide or DD-lactide). This is because, in the process of producing polylactic acid, the optical purity tends to decrease in each step of oligomerization and subsequent depolymerization. It is known that optical isomers are usually produced via an enolization reaction at the terminal carboxyl group of lactic acid or a lactic acid oligomer. Therefore, in each step of oligomerization and depolymerization, it is necessary to avoid that the terminal carboxyl group of the lactic acid oligomer is easily ionized and easily enolized. Note that a stereocomplex polymer known as a material with higher functionality than a normal homopolymer is a blend of LL-polylactic acid and DD-polylactic acid having a high optical purity, and a polymer having a low optical purity in the polymer backbone itself. Different from lactic acid. In addition, the optical purity of lactic acid affects the crystallization ability of polylactic acid. This affects the secondary processability of the polylactic acid resin into fibers, nonwoven fabrics, films and other final products.

  Of course, lactic acid as a raw material is suitable for polymer raw materials with high optical purity, and is usually produced by fermentation of various saccharides using cells capable of producing lactic acid with high optical purity. In that case, the saccharide used as a raw material is not only a fermentation medium containing purified glucose and the like, but also a mixed sugar system containing pentoses such as galactose, fructose, and xylose, and hexose is often used. The mixed sugar system can be obtained, for example, by hydrolysis of plant biomass containing cellulose. However, the mixed sugar system contains more impurities such as lignin derived from plant biomass than the conventional system using a fermentation medium containing glucose and the like. The concentration of lactic acid in the fermentation liquor varies depending on the process method and the initial raw material concentration such as glucose. In general, 3 to 6% by weight in the case of a process in which raw material addition and extraction of fermentation broth are performed continuously or intermittently, and in the case of a batch process, to maintain the growth conditions of the cells to be fermented It is performed at about 15% by weight (= initial glucose concentration).

  In order to use lactic acid obtained by fermentation as a polymer raw material, a purification step of removing impurities and concentrating is essential. In the method described in (Patent Document 1), a lactic acid fermentation broth containing lactic acid in the form of calcium lactate is heated, and water is evaporated by an evaporator at a temperature of about 60 ° C. to 150 ° C. to concentrate calcium lactate. Then, after adding sulfuric acid and precipitating calcium ions as calcium sulfate, impurities such as minerals and metabolic byproducts are removed by an extraction operation using an organic solvent to obtain purified lactic acid. However, in such a system, since purification is performed by solvent extraction, regeneration processing of an organic solvent or the like is required, the system becomes complicated, and a large amount of secondary waste is generated.

  In addition, (Patent Document 2) discloses an invention relating to a process of performing concentration and distillation purification after removing metal ions and the like by performing ion exchange desalting treatment on a lactic acid fermentation broth. According to the example described in (Patent Document 2), the lactic acid fermentation broth to be desalted is acidic with a pH of 2.25 and contains calcium ions and sulfate ions. From this, as described in (Patent Document 1), the lactic acid fermentation broth to be desalted is promoted while neutralizing lactic acid fermentation by adding calcium, and sulfuric acid is added to the obtained calcium lactate, It is thought that the liquid after removing calcium sulfate precipitation by crystallization is assumed. In addition, the lactic acid to be desalted includes succinic acid, tartaric acid, and pyrubin due to metal ion impurities such as sodium derived from nutrients such as mixed sugar solution used in the fermentation process and metabolic reactions in the cells. Contains organic acid impurities such as acid and acetic acid. Therefore, in the method of (Patent Document 2), metal ion impurities centered on calcium are removed by a cation exchange resin, and anion impurities centered on sulfate ions are removed by an anion exchange resin. To do. In such a system, wastewater containing a large amount of inorganic salt is generated by the regeneration treatment of the ion exchange resin by chemical washing. In the case where the cation is first removed and then the anion is removed, it is desirable to perform treatment with a strongly acidic cation exchange resin tower and a subsequent weakly basic anion exchange resin tower. On the other hand, when an anion is first removed, it is desirable to perform treatment with a strongly basic anion exchange resin tower and a subsequent weakly acidic cation exchange resin tower. Thereby, the amount of waste water generated in the regeneration treatment in the latter ion exchange resin tower is reduced. After the desalting treatment, remaining water and various impurities are removed by distillation, activated carbon treatment, or the like.

  On the other hand, in (Patent Document 3), when polylactic acid is produced by the lactide method using lactic acid containing a cationic impurity such as sodium, a significant decrease in optical purity occurs before the lactic acid is converted to lactide. It is described that the obtained lactide contains a large amount of so-called meso lactide. This is presumably because when a large amount of cationic impurities such as sodium is contained in lactic acid, the terminal carboxyl group of lactic acid or a lactic acid oligomer is ionized and an enolization reaction is likely to occur. Therefore, it is desirable to remove cationic impurities such as sodium as much as possible in the raw lactic acid used for the production of polylactic acid. From such a viewpoint, the ion exchange desalting technique described in (Patent Document 2) is considered to be one of the techniques suitable for the production of lactic acid for polymer raw materials. However, the following problems remain in the application of the above technique.

  That is, when the cation exchange resin tower breaks through, the treatment liquid is discharged from the resin tower without removing cation impurities thereafter. In order to avoid this, it is necessary to perform a regeneration treatment before the resin tower breaks through. However, there is actually no appropriate method for monitoring breakthrough of the resin tower during operation on site. In particular, alkali metal ions, which are trace impurities, are difficult to monitor due to the presence of lactic acid and calcium ions, which are major impurities. This is due to the fact that ion exchange resins usually have different adsorption selectivity depending on the type of ions to be removed. It is known that the adsorption selectivity is usually larger as the ion concentration and valence are larger and the hydrated ion radius is smaller. For example, when each cation of sodium, potassium, and calcium is contained in lactic acid, if there is no difference in concentration, it leaks from the resin tower in the order of sodium, potassium, and calcium. Since calcium leakage is a major impurity, it may be detected by monitoring electrical conductivity. However, since the concentration of sodium and potassium is low, it is difficult to detect by monitoring. When the breakthrough of the resin tower is determined based on the detectable leakage of calcium, sodium or potassium is not contained in the treatment liquid discharged so far. Potassium is leaking. When polylactic acid is polymerized using such lactic acid as a raw material, the optical purity of lactide obtained in the intermediate step is remarkably lowered by the action of these alkali metal ions, so that an appropriate polymer cannot be obtained.

Japanese translation of PCT publication No. 2003-511360 US Pat. No. 6,489,508 Japanese Patent No. 3258324

  An object of the present invention is to provide a method for producing purified lactic acid for producing lactic acid suitable as a polymer raw material by desalting and purifying lactic acid obtained by fermentation by an ion exchange method in view of the above circumstances. And

  As a result of intensive studies to solve the above-mentioned object, the present inventors connected a plurality of cation exchange resin towers in series when desalting a lactic acid fermentation broth containing cation impurities with an ion exchange resin. I thought it was necessary. This is because, at the time when the first stage resin tower breaks through due to leakage of calcium ions, the cation that easily leaks than calcium, such as alkali metals that have leaked so far, can be adsorbed and removed by the subsequent cation exchange resin tower. It is. FIG. 1 conceptually shows the features of the present invention compared to the prior art. According to the present invention, it is possible to suppress the occurrence of an event in which a cationic impurity contains an unacceptably high concentration in the treatment liquid after desalting. The first-stage cation exchange resin tower desirably uses a resin having a relatively high adsorption selectivity for calcium ions. As such a resin, it is usually preferable to select a resin having a crosslinking degree of about 8 to 14%. In addition, regarding leakage of cationic impurities, the present inventors monitor alkali metal ions, which are trace components, while monitoring leakage of calcium ions, which are main components, based on electrical conductivity and the like. I found that it was possible. Therefore, when using a system in which a plurality of cation exchange resin towers are connected in series, electrical connection is made between a specific resin tower and a subsequent resin tower, for example, between the first resin tower and the second resin tower. By monitoring the conductivity or the like, it is possible to detect the time when the first stage resin tower breaks through and the regeneration process is necessary. In this case, the latter resin tower may be regenerated as necessary. Furthermore, in a system in which a plurality of cation exchange resin towers are connected in series, a more efficient system can be obtained by using an ion exchange resin having lower adsorption selectivity between ions in the latter resin tower than in the first resin tower. I found out that it can be built. The purpose of the latter resin tower is mainly to remove alkali metal ions with low adsorption selectivity. Even if the first resin tower breaks through and calcium ions flow into the latter resin tower, the alkali metal ions can be removed. This is to prevent the removal of ions as much as possible. As shown in FIG. 2, such an ion exchange resin having a relatively low adsorption selectivity for calcium ions usually has a low degree of crosslinking of the resin, and particularly preferably has a degree of crosslinking of 4% or less. Moreover, in the continuous operation of the lactic acid production plant, it is desirable to provide a plurality of systems in which the cation exchange resin towers are installed in series as described above in parallel. As a result, at the stage where regeneration treatment is required in a certain resin tower system, the processing system can be switched to another resin tower system through which liquid can flow, and the continuous operation of the entire plant can be maintained. As a result, it has been found that the concentration of cationic impurities contained in the treatment liquid can be suppressed to a minimum, and problems associated with a decrease in optical purity in the polylactic acid polymerization step can be reduced, and the present invention has been completed.

That is, the gist of the present invention is as follows.
(1) A method for producing purified lactic acid by concentrating and purifying a calcium lactate-containing solution containing lactic acid obtained by fermentation in the form of calcium lactate, wherein sulfuric acid is added to the calcium lactate-containing solution, and calcium ions are converted into calcium sulfate. The method for producing purified lactic acid, comprising a step of separating, and a step of removing impurities by supplying a solution obtained by separating calcium sulfate to a plurality of cation exchange resin towers and anion exchange resin towers arranged in series.
(2) In a plurality of cation exchange resin towers installed in series, leakage of calcium ions into the solution is detected between the resin tower and the resin tower at the subsequent stage. Production method.
(3) In a plurality of cation exchange resin towers installed in series, the purification selectivity according to the above (1) or (2), in which the adsorption selectivity for calcium ions of the latter resin tower is lower than that of the first resin tower. A method for producing lactic acid.

  According to the present invention, the process for desalting and purifying lactic acid fermentation broth is improved, and lactic acid having an impurity concentration reduced to an appropriate level or less is produced as a raw material for producing a high-quality polymer from the viewpoint of optical purity. be able to. In addition, since the timing for regenerating the cation exchange resin tower can be properly grasped, the amount of waste water generated in the regenerating process can be suppressed to the minimum necessary. Furthermore, by appropriately removing salts containing metal ions, the equipment scale and required energy amount in the subsequent distillation purification process can be reduced, and the cost for producing purified lactic acid can be reduced. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

It is the conceptual diagram which compared the conventional system and the system of this invention. It is a graph which shows the correlation with the selection coefficient of each ion in a cation exchange resin, and the crosslinking degree of resin. It is a figure which shows a saccharification and fermentation process among the manufacturing processes of refined lactic acid. It is a figure which shows a refinement | purification process among the manufacturing processes of refinement | purification lactic acid. It is a figure which shows one Embodiment of the manufacturing method of the refinement | purification lactic acid of this invention.

Hereinafter, a method for producing purified lactic acid according to the present invention will be described in detail with reference to the drawings.
One embodiment of the method for producing purified lactic acid according to the present invention includes a calcium lactate-containing solution containing lactic acid obtained by fermentation in the form of calcium lactate at a predetermined temperature, and is contained in the calcium lactate-containing solution by a reverse osmosis membrane. A step of concentrating calcium lactate by removing the generated water. Here, the calcium lactate-containing solution can be obtained by a fermentation process using a microorganism having lactic acid fermentation ability. The fermentation process refers to a step of producing lactic acid by lactic acid fermentation by the microorganism using the sugar contained in the medium as a substrate.

  In addition, although the saccharide which the said microorganisms utilize as a substrate in this fermentation process is not specifically limited, The polysaccharide, oligosaccharide, and monosaccharide obtained by a saccharification process from various saccharification raw materials can be mentioned. The saccharification process is generally a step of converting a fermentation raw material containing a carbon source, a nitrogen source, and other nutrients into a sugar suitable for lactic acid fermentation. Examples of the saccharification raw material include starches such as corn starch and potato starch, garbage including amylose, cellulose such as plant biomass, and the like. These saccharified raw materials may be subjected to a pretreatment such as crushing with a crusher or the like and subdividing.

  In the saccharification process, a part or all of the saccharification raw material can be decomposed into polysaccharides, oligosaccharides or monosaccharides by introducing an enzyme that digests the fragmented saccharification raw material. Examples of digestive enzymes include amylase and cellulase. The decomposition treatment with these digestive enzymes is performed at an optimum temperature of the digestive enzymes, for example, about 40 ° C to about 60 ° C. As a result, the saccharification raw material is hydrolyzed and converted into glucose, maltose, oligosaccharide or polysaccharide. Amylase can be industrially obtained as a product of microorganisms such as Aspergillus oryzae and Bacillus subtilis. Moreover, impurities other than saccharides are contained in the obtained solution containing saccharides. In this case, for example, the solids such as starch and amylose that have not been saccharified are removed by solid-liquid separation by, for example, centrifugation, and the oil film is removed by a decanter, and then liquid chromatography is performed to mainly remove sugars. A solution can be produced. This solution can be used in the fermentation process. Moreover, molasses, such as sucrose, sugar beet sugar, and molasses, can also be used as a raw material instead of producing | generating the solution containing saccharides through a saccharification process.

  As an example of a suitable raw material for lactic acid fermentation, in addition to the fermentation medium containing saccharides obtained in the saccharification process, a recirculation system containing lactic acid material obtained in the production process of polylactic acid, or a solution containing lactic acid material is prepared. Therefore, hydrolyzed recycled polylactic acid (for example, waste collected from consumers (post-consumer waste) or waste produced in the production process of polylactic acid) can be used.

  In the fermentation process, biosynthesized lactic acid is produced in the solution as calcium lactate by performing lactic acid fermentation using saccharides as a raw material in the presence of calcium carbonate and / or calcium hydroxide. In this case, the concentration of saccharide is usually preferably 10 to 20% by weight.

  Lactic acid fermentation can be performed using microorganisms that produce lactic acid by metabolism, such as bacteria, fungi, or yeast. As such a microorganism, either a microorganism that inherently has lactic acid fermentation ability or a microorganism to which a gene (gene group) involved in lactic acid fermentation has been introduced and to which lactic acid fermentation ability has been imparted can be used.

  As the microorganism having lactic acid fermentation ability, bacteria of the genus Lactobacillus are usually used. For fungi, fungi of the genus Rhizopus are used. Suitable yeasts include those belonging to the genus Saccharomyces such as Saccharomyces cerevisiae.

  Lactic acid fermentation is usually performed in a temperature range of about 30 ° C. to about 60 ° C. for bacterial fermentation and usually about 20 ° C. to about 45 ° C. for yeast fermentation. For fungal fermentation, the temperature range is broad but often is in the range of about 25 ° C to about 50 ° C.

  In the fermentation process, the function of the microorganism may be reduced due to a decrease in pH accompanying the generation of lactic acid. In order to prevent this, generally, as a pH adjuster, usually an alkali hydroxide or alkaline earth hydroxide (calcium hydroxide), calcium carbonate, lime milk, ammonia water, or ammonia gas is added as a pH adjuster, Keep neutral. Along with the addition of the pH adjuster, the cation of the pH adjuster is combined with dissociated lactic acid to produce lactate. Particularly in the present invention, a calcium salt, that is, calcium carbonate, calcium hydroxide or the like is added to the lactic acid fermentation solution as a pH adjuster. Thereby, the lactic acid produced | generated by fermentation exists in the form of calcium lactate, and since the fall of pH by lactic acid fermentation is prevented, lactic acid fermentation can be continued.

  As described above, by fermenting the fermentation raw material with microorganisms, a calcium lactate-containing solution containing lactic acid in the form of calcium lactate is obtained. Usually, since the calcium lactate-containing solution contains a compound other than lactic acid called impurities, solid-liquid separation is performed using a method such as centrifugation to remove the solid content. Examples of impurities include cell debris, residual carbohydrates, nutrients and the like. Impurities are appropriately removed so as to be a predetermined concentration or less depending on the use of the finally obtained purified lactic acid. The concentration of lactic acid in the fermentation broth depends on the production method. In the case of the batch method, saccharides are converted into lactic acid with a yield of almost 100%, but in the case of the continuous method (fermented liquor is continuously extracted and sugar is continuously supplied), the concentration is 3 to 6% by weight. Is efficient.

  Next, prior to the purification process according to the present invention using an ion exchange resin tower, the calcium lactate-containing solution from which impurities have been removed is concentrated as necessary. This concentration step is a process for increasing the concentration of calcium lactate contained in the calcium lactate-containing solution, and a method of concentrating without using large thermal energy with a reverse osmosis membrane (RO membrane) or the like is desirable. As a result, the yield of lactic acid during purification can be increased, and at the same time, the amount of liquid to be treated in the distillation step in the subsequent purification process can be reduced, and the processing energy cost in the entire purification process can be reduced. . Further, although concentration in the distillation column is excellent in separability, it is necessary to keep the liquid to be treated at a high temperature, which may cause not only a problem of thermal energy but also a decrease in optical purity of lactic acid. By adopting the desalting method of the present invention, deterioration of lactic acid in the distillation process is suppressed, and the raw material yield during the production of polylactic acid is improved. In addition, the concentration of impurities in the lactic acid fermentation liquor increases by concentrating calcium lactate before the desalting step by ion exchange. As a result, there is an advantage that the adsorption rate of the impurity metal ions to the ion exchange resin is increased and the desalting treatment can be performed at a high superficial velocity. However, in the concentration by the RO membrane, it is necessary to consider that the concentration of calcium lactate to be concentrated does not exceed the solubility and precipitate. In addition, the said concentration process can be abbreviate | omitted as needed, and lactic acid concentration can also be concentrated in the latter distillation process.

  Concentration using RO membranes does not require heating / cooling of the calcium lactate-containing solution after lactic acid fermentation, so that no unnecessary heat history is added to the calcium lactate-containing solution. The optical isomerization of lactic acid can be reduced. Here, optical isomerization means a conversion (isomerization) reaction between L-type lactic acid and D-type lactic acid. Depending on the industrial application, the optical purity of lactic acid is important. As an example, the L-type optical purity needs to be 95% or more for food use. In the fermentation by microorganisms, any optical isomer is mainly produced. For example, Lactobacillus delbrucchi mainly produces D-lactic acid, and Lactobacillus casei mainly produces L-lactic acid. The optical purity of 95% means that 95% of the contained lactic acid or lactate is one of two optical isomers (L-type and D-type).

  For this reason, the optical purity of lactic acid is important depending on the application, and may be lowered by heat treatment in the concentration step or distillation step. Therefore, the above-described concentration step using the RO membrane is preferable because the thermal history can be minimized, optical isomerization can be suppressed, and the optical purity of lactic acid can be maintained high.

  After the concentration step as described above, sulfuric acid is added to the obtained calcium lactate concentrate to separate calcium ions as calcium sulfate. That is, the calcium lactate concentrate is acidified to convert lactic acid contained in the solution in the form of calcium lactate from a dissociated form, that is, from a salt form to a non-dissociated acid form. Examples of a method for converting calcium lactate to free lactic acid include a method of adding a strong mineral acid such as sulfuric acid to a concentrated solution. By adding sulfuric acid to the calcium lactate concentrate, free lactic acid is produced together with calcium sulfate. Since calcium sulfate is almost insoluble in water, it can be easily removed by crystallization. Known methods for crystallizing and filtering calcium sulfate can be used. For example, calcium sulfate can be removed by a rotary drum type vacuum filter, a centrifugal separator or the like.

  Next, after removing calcium sulfate, in order to remove impurity ions contained in the solution, a desalting step using a series cation exchange resin tower and an anion exchange resin tower is performed. First, calcium ions remaining in the solution from which calcium sulfate has been removed and metal cations such as sodium, potassium and magnesium contained as impurities in the fermentation raw material are removed by cation exchange. If necessary, a fine particle adsorption step using activated carbon may be inserted before the cation exchange. In cation exchange, the metal cation in the lactic acid solution is removed by contacting with an ion exchange resin that substitutes with hydrogen ions. As a result of the cation exchange, the metal ions deposited as solids are separated from the solution by solid-liquid separation using sedimentation separation or the like. Sulfate ions other than lactic acid and organic acid anions with relatively low molecular weight, such as acetate ions and formate ions, that are contained in the solution from which metal ions have been removed, are removed by anion exchange. Can do. Sulfate ions and organic acid anions are removed by contacting the sulfate ions and organic acid anions with an anion exchange resin that replaces the hydroxyl ions. Anion exchange is usually performed in a single-stage resin tower, but may be performed in a plurality of stages of resin towers as necessary.

  In this desalting step, the metal cation is removed from the lactic acid solution obtained by fermentation using a system in which a plurality of resin towers using a cation exchange resin are installed in series. At that time, the above-mentioned resin tower system is characterized in that calcium ions are adsorbed and removed in the first resin tower, and the remaining cations are removed in the latter resin tower. Treatment liquid in which cations such as alkali metal ions having lower adsorption selectivity than calcium ions are discharged from the first stage resin tower when the breakthrough state in which calcium ion leakage occurs in the first stage resin tower Leaking inside. At that time, the latter cation exchange resin tower functions as a backup and can adsorb and remove them, and the lactic acid treatment liquid after the desalting process contains an unacceptably high concentration of cationic impurities. Is suppressed. The first-stage cation exchange resin having a relatively high adsorption selectivity for calcium ions is usually selected from those having a crosslinking degree of about 8 to 14%. In an ion exchange resin having a certain degree of cross-linking, the adsorption pore diameter on the resin surface is small and dense. A small pore size means that ions that can be adsorbed are limited to those having a small hydration radius. On the contrary, it is desirable to use a cation exchange resin having low adsorption selectivity for calcium ions in the latter resin tower, and it is preferable to select such an ion exchange resin having a crosslinking degree of 4% or less. This is because a resin having a low degree of crosslinking has a relatively large adsorption pore diameter on the surface, and the influence of the hydrated ion radius on the adsorption selectivity tends to be small. Further, in a plurality of cation exchange resin towers, it is discharged from the first stage resin tower between a specific resin tower and the latter resin tower, for example, between the first stage resin tower and the second stage resin tower. By performing measurement for detecting leakage of calcium ions into the processing solution, it is possible to determine when the first stage resin tower breaks through and regeneration processing is necessary. In this case, the latter resin tower may be regenerated as necessary. In the above system, the latter resin tower is basically intended for backup of the first stage, and if the amount of metal ions other than calcium ions mixed in the lactic acid fermentation process and the pH of the desalting solution are clear, it is Thus, the scale of the latter resin tower can be minimized. In addition, since the calcium ion concentration is substantially controlled by the solubility of calcium sulfate, it does not depend on the amount of calcium mixed in the lactic acid fermentation process. Regarding the scale of the latter resin tower, for example, the sodium ion concentration per unit quantity of lactic acid fermentation liquor is 1, and it occurs when breakthrough of the first stage resin tower by calcium ions reaches 100 unit quantity as the treatment amount of lactic acid fermentation liquor. In this case, when the sodium ion adsorption capacity of the subsequent resin tower at the pH value is set to a scale of 100, the subsequent regeneration process can be performed in accordance with the first regeneration process (actually, there is a little more margin). It is preferable to set the scale of the equipment to be small). As a simple measurement / monitoring method for detecting calcium ion leakage between the first-stage resin tower and the second-stage resin tower, there is a method of measuring electrical conductivity, pH, sugar content (refractive index), etc. It is done. Among these, the method based on electric conductivity is desirable because of its high sensitivity to calcium ion leakage. In continuous operation of a lactic acid production plant, it is desirable to provide such a system having a plurality of cation exchange resin towers arranged in series in parallel. Thereby, at the stage where the regeneration treatment of a certain resin tower becomes necessary, it is possible to prevent the continuous operation of the plant from being hindered by switching the treatment system to another resin tower system through which liquid can flow.

  Next, after removing impurities, water contained in the solution is removed to concentrate lactic acid. In this concentration step, a method such as heat concentration by decompression, centrifugal thinning, or the like can be used. The temperature of the concentration step is preferably about 60 ° C. to about 150 ° C., and the pressure is preferably about 4 kPa to 10 kPa. An 80% by weight lactic acid solution can be obtained by the concentration step. After the concentration, further organic impurities can be removed by distillation purification. For the distillation, known means such as a distillation column can be used. When a distillation column is used, it is desirable that the distillation temperature is 60 ° C. to 130 ° C. and the distillation pressure is about 500 Pa to 2000 Pa. A plurality of distillation columns can be used, and usually about 1 to 5 groups are used. A 90% by weight lactic acid solution can be obtained by distillation purification. In the present invention, when concentration using a reverse osmosis membrane is performed on the above-mentioned calcium lactate-containing solution, the amount of water removed by concentration and distillation by heating is reduced compared to the case where reverse osmosis membrane concentration is not used. Therefore, energy saving can be realized. Since a high temperature treatment is required in the distillation purification process, a slight amount of optical isomers may be generated due to the heat history during distillation. Moreover, the color tone of a solution may become deep with the thermal deterioration of the impurity contained in a solution. As a finishing process for these, the following method can be used. That is, the generated optical isomer can be removed using an ultrafiltration membrane. For example, an optical purity of 99% or more can be obtained by sequentially passing ultrafiltration membranes having a diameter of 1 to 2 μm and a diameter of 0.2 to 0.5 μm. Regarding the thermal deterioration of impurities, an additional separation step using activated carbon, ion exchange resin, or the like may be performed as necessary for the purpose of reducing coloring. Depending on the purpose of use, if necessary, further purification and concentration may be performed by distillation, liquid chromatography or the like.

  The saccharification process and fermentation process included in the method for producing purified lactic acid as described above, and the flowcharts of one embodiment of the purification process are shown in FIGS. 3 and 4, respectively. As shown in FIGS. 3 and 4, saccharification raw materials such as starch are first crushed in the raw material crushing step 1, and saccharification is performed by adding a saccharifying enzyme such as amylase in the saccharification step 2, and unreacted starch is solid-liquid separated. Removed in step 3. In the lactic acid fermentation step 11 in the subsequent fermentation process, lactic acid bacteria and calcium hydroxide as a pH adjuster are added to the obtained saccharified solution, and a calcium lactate-containing solution containing lactic acid as calcium lactate is obtained by fermentation. The solid content contained in the calcium lactate-containing solution is separated in the solid-liquid separation step 12, and moisture is removed in the reverse osmosis membrane concentration step 13. Next, in the purification process of FIG. 4, the concentrated solution is acidified with sulfuric acid in the acidification step 21 to crystallize calcium ions as calcium sulfate and separated in the solid-liquid separation step 22. Next, the obtained acidified solution is passed through a cation exchange step 23, and metal ions derived from fermentation raw materials such as sodium and magnesium and calcium ions that could not be removed by precipitation are converted into metal salts, and the solid-liquid separation step 24 is performed. To remove. Further, in the anion exchange step 25, organic acid ions and the like due to impurities are removed, and a 90% by weight lactic acid solution is obtained through a heat concentration step 26 and a distillation purification step 27 using a distillation tower. Since the cation exchange process 23 and the anion exchange process 25 do not stop the plant during the regeneration process, it is desirable to have a plurality of systems in parallel. Finally, the optical isomer contained in the obtained purified lactic acid solution can be removed by the finishing step 28 to obtain a purified lactic acid solution having an optical purity of 99.5% or more.

  FIG. 5 is a diagram showing details of the cation exchange step 23. First, valves 31, 34, 39, 42 are open and valves 33, 35, 38, 40, 51, 53, 54, 55, 58, 59, 60, 62, 72, 73, 76 are closed And In addition, the pumps 45, 46, 56, 61, 65, 66, and 74 are stopped, and the pumps 30, 36, and 41 are operating. The first cation exchange column 32 and the third cation exchange column 52 are mainly for removing calcium ions in the lactic acid solution, and it is desirable to use a cation exchange resin having a crosslinking degree of about 8 to 14%. . The second cation exchange tower 37 and the fourth cation exchange tower 57 are mainly for removing cations other than calcium, and it is desirable to use a cation exchange resin having a crosslinking degree of 4% or less.

  The lactic acid solution sent from the solid-liquid separation step 22 is supplied to the upper part of the first cation exchange column 32 by the pump 30. The lactic acid solution flows down inside the first cation exchange column 32 due to gravity and is discharged from the lower part of the first cation exchange column 32, and then supplied to the upper part of the second cation exchange column 37 by the pump 36. The lactic acid solution flows down inside the second cation exchange column 37 due to gravity and is discharged from the lower part of the second cation exchange column 37, and then supplied to the solid-liquid separation step 24 by the pump 41. In the first cation exchange column 32, all cations are first removed by adsorption. However, when the adsorption capacity in the column is consumed, leakage starts from the first cation exchange column 32 in order from the cation such as alkali metal having a small adsorption selectivity. Cations leaking from the first cation exchange column 32 are adsorbed and removed in the second cation exchange column 37. When calcium ions begin to leak from the first cation exchange column 32, the calcium ion leakage monitor 47 detects the electrical conductivity and the like. Thereby, upon receipt of calcium ion leakage confirmation from the first cation exchange tower 32, the valves 31, 34, 39, 42 are closed, and the valves 51, 54, 59, 62 are opened instead. At the same time, the pumps 36 and 41 are stopped, and the pumps 56 and 61 are operated instead. Thereby, the lactic acid solution sent from the solid-liquid separation step 22 is supplied to the upper part of the third cation exchange column 52 by the pump 30. The lactic acid solution flows down inside the third cation exchange column 52 due to gravity and is discharged from the lower part of the third cation exchange column 52, and then supplied to the upper part of the fourth cation exchange column 57 by the pump 56. The lactic acid solution flows down inside the fourth cation exchange column 57 due to gravity and is discharged from the lower part of the fourth cation exchange column 57, and then supplied to the solid-liquid separation step 24 by the pump 61.

  On the other hand, about the 1st cation exchange column 32, the reproduction | regeneration process by an acid is performed in the meantime. The valves 72, 33, and 35 are opened, and the pumps 74 and 45 are operated. A regenerative chemical (such as sulfuric acid) is supplied from the regenerative chemical supply tank 71 through the nozzle 43 from the upper portion of the first cation exchange column 32 by the pump 74. The supplied regenerative chemical flows down inside the first cation exchange column 32 due to gravity and is discharged from the lower part of the first cation exchange column 32, and is then supplied to the acid waste liquid tank 75 by the pump 45. When the predetermined regeneration process is completed, the valves 72, 33, and 35 are closed and the pumps 74 and 45 are stopped. The second cation exchange column 37 is also subjected to a regeneration treatment with an acid in the same manner as the first cation exchange column 32 as necessary. The valves 72, 38 and 40 are opened, and the pumps 74 and 46 are operated. A regenerative drug (sulfuric acid or the like) is supplied from the regenerative drug supply tank 71 by the pump 74 via the nozzle 44 from the upper part of the second cation exchange tower 37. The supplied regenerative chemical flows down inside the second cation exchange column 37 due to gravity and is discharged from the lower part of the second cation exchange column 37, and then supplied to the acid waste liquid tank 75 by the pump 46. When the predetermined regeneration process is completed, the valves 72, 38, 40 are closed and the pumps 74, 46 are stopped.

  Similarly, the calcium ion leakage monitor 67 detects the calcium ion leakage from the third cation exchange column 52, closes the valves 51, 54, 59, 62, and opens the valves 31, 34, 39, 42 instead. . At the same time, the pumps 56 and 61 are stopped, and the pumps 36 and 41 are operated instead. As a result, the lactic acid solution sent from the solid-liquid separation step 22 is supplied again to the upper portion of the first cation exchange column 32 by the pump 30. The lactic acid solution flows down inside the first cation exchange column 32 due to gravity and is discharged from the lower part of the first cation exchange column 32, and then supplied to the upper part of the second cation exchange column 37 by the pump 36. The lactic acid solution flows down inside the second cation exchange column 37 due to gravity and is discharged from the lower part of the second cation exchange column 37, and then supplied to the solid-liquid separation step 24 by the pump 41. And about the 3rd cation exchange column 52, the reproduction | regeneration process by an acid is performed in the meantime. The valves 72, 53, and 55 are opened, and the pumps 74 and 65 are operated. A regenerative chemical (such as sulfuric acid) is supplied from the regenerative chemical supply tank 71 through the nozzle 63 from the upper part of the third cation exchange column 52 by the pump 74. The supplied regenerative chemical flows down inside the third cation exchange column 52 due to gravity and is discharged from the lower part of the third cation exchange column 52, and then supplied to the acid waste liquid tank 75 by the pump 65. When the predetermined regeneration process is completed, the valves 72, 53, and 55 are closed and the pumps 74 and 65 are stopped. As with the third cation exchange column 52, the fourth cation exchange column 57 is also regenerated with an acid as necessary. The valves 72, 58 and 60 are opened, and the pumps 74 and 66 are operated. A regenerative drug (sulfuric acid or the like) is supplied from the regenerative drug supply tank 71 from the upper part of the fourth cation exchange column 57 via the nozzle 64 by the pump 74. The supplied regenerative chemical flows down in the fourth cation exchange column 57 due to gravity and is discharged from the lower part of the fourth cation exchange column 57, and then is supplied to the acid waste liquid tank 75 by the pump 66. When the predetermined regeneration process is completed, the valves 72, 58, 60 are closed and the pumps 74, 66 are stopped.

  When the amount of the acid waste liquid stored in the acid waste liquid tank 75 reaches a predetermined value, the valve 76 is opened to discharge the acid waste liquid. After discharging the acid waste liquid, the valve 76 is closed. The acid waste liquid discharged from the acid waste liquid tank 75 is mixed and neutralized with the waste liquid of the regenerated chemical (usually alkaline waste liquid such as caustic soda) similarly generated in the anion exchange step 25, and the inorganic salt (sodium sulfate etc.) is mixed. It is discharged out of the system as waste liquid.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, the technical scope of this invention is not limited to a following example.
Example 1
An aqueous glucose solution was used as a raw material, which was introduced into a fermenter together with bacteria of the genus Lactobacillus, and fermented. Calcium hydroxide was added as a neutralizing agent to the fermentor, and the pH was maintained at 6.2 to 6.8. The fermentation temperature was set to 52 ° C. and fermented for 72 hours. The lactic acid concentration in the obtained lactic acid fermentation broth was 4.5% by weight when measured as the calcium lactate concentration. In addition, about the density | concentration of calcium lactate, it measured using the liquid chromatography (The Hitachi High-Technologies company make, LaChrom L-7000). Water was removed from the lactic acid fermentation liquor at a pressure of 3 MPa using a reverse osmosis membrane (manufactured by GE Water Technologies, Duratherm HWS RO HR) while maintaining the fermentation temperature at 50 ° C. As a result, a concentrated lactic acid fermentation broth having a lactic acid concentration of 20% by weight measured as the calcium lactate concentration was obtained. The obtained lactic acid fermentation broth was cooled to 42 ° C., a 98% sulfuric acid solution was added, and calcium ions in the solution were crystallized as calcium sulfate. The calcium sulfate crystals were separated by centrifugation. The solubility of calcium sulfate at 42 ° C. is 3 g / L, and calcium sulfate having a solubility or higher can be separated as a solid.

  The acidified lactic acid solution (pH 1.5) from which the calcium sulfate solid was separated was mixed with the first cation exchange resin tower (manufactured by Mitsubishi Chemical Corporation, strongly acidic cation exchange resin Diaion PK220, degree of crosslinking 11%) and the second cation. The polymer was passed through an exchange resin tower (manufactured by Mitsubishi Chemical Corporation, strongly acidic cation exchange resin Diaion PK208, degree of cross-linking 4%). Thereafter, the metal salt was removed by centrifugation. Subsequently, the mixture was passed through an anion exchange resin tower (Mitsubishi Chemical Co., Ltd., weakly basic anion exchange resin Diaion WA30), and then sulfate and organic acid salt were removed by centrifugation. For anion exchange resins, in order to avoid the effects of rapid swelling of the resin accompanying the flow of a high-concentration lactic acid solution, a gentle 1% concentration of lactic acid aqueous solution is circulated through the resin as a pretreatment. Induced. By purification using the ion exchange resin as described above, residual calcium ions, cations derived from fermentation raw materials such as sodium, potassium and magnesium, sulfate ions as impurities generated during fermentation, and organic acid ions up to 50 meq / L It was possible to reduce.

  In the first cation exchange resin tower, ion leakage started in the order of sodium, potassium, and calcium after a time period in which there was no cation leakage at first. However, even at that time, no leakage of various cations was observed from the treatment liquid that passed through the second cation exchange resin tower. In the first cation exchange resin tower, the leakage start time of calcium ions was recognized after about twice as long as the leakage start time of sodium ions, and the ion concentration reached approximately 140 ppm. At that time, as the calcium concentration increased, the monitored electrical conductivity increased significantly. At this stage, the ion exchange resin was regenerated with sulfuric acid. In addition, the second cation exchange resin tower was also subjected to regeneration treatment of the ion exchange resin. Thereby, the adsorption capacity of each cation exchange resin tower was recovered.

  The solution after the ion exchange treatment was heated and concentrated at 100 ° C. and 10 kPa to obtain an 80% by weight lactic acid solution. The concentrated lactic acid solution was distilled at 130 ° C. and 1 kPa to remove impurities and obtain a 90% by weight lactic acid solution. The obtained 90% by weight lactic acid solution was passed through an ultrafiltration membrane having a diameter of 2 μm and a diameter of 0.5 μm in order to obtain an optical purity of 99.5%. The measurement was performed by liquid chromatography.

  In addition, this invention is not limited to above-described embodiment, Various modifications are included. For example, although FIG. 5 etc. demonstrated the case where two cation exchange resin towers were installed in series, it is not limited to this, You may install three or more cation exchange resin towers in series. In this case, leakage of calcium ions into the solution is usually detected between the first resin tower and the second resin tower, but if necessary, the second and subsequent resin towers and the subsequent stages. Detection may be performed with the resin tower. In addition, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. In addition, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

DESCRIPTION OF SYMBOLS 1 Raw material crushing process 2 Saccharification process 3 Solid-liquid separation process 11 Lactic acid fermentation process 12 Solid-liquid separation process 13 Reverse osmosis membrane concentration process 21 Acidification process 22 Solid-liquid separation process 23 Cation exchange process 24 Solid-liquid separation process 25 Anion exchange Step 26 Heat concentration step 27 Distillation purification step 28 Finishing step 31, 33, 34, 35, 38, 39, 40, 42, 51, 53, 54, 55, 58, 59, 60, 62, 72, 73, 76 Valve 30, 36, 41, 45, 46, 56, 61, 65, 66, 74 Pump 32 First cation exchange tower 37 Second cation exchange tower 52 Third cation exchange tower 57 Fourth cation exchange tower 47, 67 Calcium ion leakage monitor 71 Recycled chemical supply tank 75 Acid waste liquid tank

Claims (3)

A method for producing purified lactic acid by concentrating and purifying a calcium lactate-containing solution containing lactic acid obtained by fermentation in the form of calcium lactate,
A step of adding sulfuric acid to a calcium lactate-containing solution to separate calcium ions as calcium sulfate, and supplying the separated solution of calcium sulfate to a plurality of cation exchange resin towers and anion exchange resin towers installed in series And a method for producing the purified lactic acid, comprising a step of removing impurities.   The method for producing purified lactic acid according to claim 1, wherein leakage of calcium ions into the solution is detected between the resin tower and a resin tower at a subsequent stage in a plurality of cation exchange resin towers installed in series.   3. The method for producing purified lactic acid according to claim 1, wherein, in a plurality of cation exchange resin towers installed in series, the adsorption selectivity for calcium ions of the latter resin tower is lower than that of the first resin tower.

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