JP2008141981A - Method for producing lactic acid - Google Patents

Abstract

Crude lactic acid is purified by a novel method that minimizes the amount of electric energy consumed and the amount of chemicals used and does not require wastewater treatment.
The crude lactic acid is adjusted to a pH of 3 or less and subjected to a reverse osmosis membrane treatment with a membrane 1 to transfer saccharides to the concentrating side C1 for separation and removal, and this permeate P1 is adjusted to a pH of 8 to 10 to make a membrane 2 By carrying out reverse osmosis membrane treatment, a permeate P2 mainly composed of low-concentration aqueous ammonia and a concentrate C2 mainly composed of ammonium lactate are obtained. Ammonia is removed from the concentrated solution C2 to purify to lactic acid. It is preferable to use a cross-linked polyamide composite film for the films 1 and 2.
[Selection] Figure 2

Description

  The present invention relates to a method for producing lactic acid, and more particularly, to a method for producing lactic acid by purifying crude lactic acid obtained by fermentation using an agricultural product containing rice or starch as a raw material.

  Conventionally, lactic acid is produced by fermentation using agricultural products containing starch and sugar such as rice as raw materials. Lactic acid is used as a food additive, a raw material for chemicals, and the like, and is also used as a raw material for polylactic acid, which is a biodegradable plastic that is now widely used.

  The manufacturing method mainly including such a lactic acid fermentation process is roughly classified into a method of purifying calcium lactate into lactic acid and a method of purifying lactic acid from ammonia-type crude lactic acid obtained by lactic acid fermentation.

  The former is a method in which crude lactic acid generally obtained through lactic acid fermentation using a saccharide raw material is precipitated using calcium salt and recovered as calcium lactate, and then reacted with an acid such as sulfuric acid to be purified to lactic acid. However, this method has been used for producing lactic acid for a long time, but has a drawback that a large amount of calcium sulfate waste is generated due to reaction separation with sulfuric acid when it is produced into lactic acid.

The latter is an alternative method to purify the ammonia-type crude lactic acid obtained by lactic acid fermentation by chemically changing it to lactic acid by electrodialysis or cation exchange. As an example, Patent Document 1 discloses a method for purifying ammonia-type crude lactic acid into lactic acid by electrodialysis using an ion exchange membrane.
JP 7-155191 A

  In the method described in Patent Document 1, lactic acid is purified by a technique of electrodialysis or cation exchange of ammonia-type crude lactic acid (hereinafter referred to as “crude lactic acid”) after lactic acid fermentation. Therefore, the electric energy consumption for the purification process in the electrodialysis apparatus is large, the purification cost is increased, and the price of lactic acid is increased.

  In addition, in the cation exchange resin method, it is necessary to use a large amount of sulfuric acid or hydrochloric acid in the regeneration after adsorption of ammonium ions, and it takes time to handle chemicals and to treat waste water.

  Furthermore, the consumption of electrical energy and the discharge of chemical waste liquid for regeneration are not preferable because they are not economical and give a large load to the environment.

  Therefore, the problem to be solved by the present invention is to purify crude lactic acid by a novel technique that minimizes the amount of electric energy consumed and the amount of chemicals used and does not require waste water treatment.

  In order to solve the above problems, the present inventor applied the reverse osmosis membrane on the condition that the amount of electric energy used is small, the amount of chemicals used is small, and wastewater treatment is unnecessary. As a result of studying application to purification means and repeated testing and research, the present invention has been completed.

  That is, the present invention according to claim 1 is characterized in that a raw material containing starch and saccharide is fermented, and the obtained crude lactic acid is treated with a reverse osmosis membrane to separate the saccharide and purify it into lactic acid. It is a manufacturing method.

  The reverse osmosis membrane used in the reverse osmosis treatment method is preferably a cross-linked polyamide composite membrane (Claim 2). The crosslinked polyamide-based composite membrane is obtained by uniformly forming an ultra-thin crosslinked polyamide functional layer directly on the surface of a support such as a polysulfone porous membrane by an interfacial polycondensation method. There is an advantage that the reverse osmosis membrane method can be easily executed. In addition, this cross-linked polyamide-based reverse osmosis membrane also has the property that the separation performance for the target substance changes depending on the pH condition due to its chargeable nature, so that efficient treatment can be performed as described later using this property. It becomes possible.

  That is, when a cross-linked polyamide composite membrane is used as a reverse osmosis membrane, it is preferable to adjust the pH of the liquid to be treated for the reverse osmosis membrane treatment to 3 or less (claim 3). When a raw material (processed liquid) mainly composed of lactic acid and saccharides adjusted to pH 3 or less is treated with a reverse osmosis membrane using a crosslinked polyamide composite membrane, the crosslinked polyamide composite membrane substantially contains lactic acid. Since it permeates, a permeate rich in lactic acid is obtained, and saccharides in the liquid to be treated are separated and left in the concentrate. Therefore, lactic acid can be purified efficiently by using this permeate.

  In a preferred embodiment of the present invention, the reverse osmosis membrane treatment is performed in stages. That is, the liquid to be treated adjusted to pH 3 or lower is separated and removed by transferring the saccharide to the concentration side by the first reverse osmosis membrane treatment, and after adjusting the first permeate to pH 8 to 10, The second reverse osmosis membrane treatment separates the second permeate mainly composed of low-concentration aqueous ammonia and the second concentrate mainly composed of ammonium lactate. Then, the lactic acid can be purified by removing ammonia from the second concentrated liquid obtained by the second reverse osmosis membrane treatment (Claim 5).

  Here, the second permeate obtained by the second reverse osmosis membrane treatment can be reused as dilution water in the fermentation treatment (Claim 6).

  Further, the reverse osmosis membrane treatment can be executed in more stages. That is, the saccharide-rich first concentrated solution obtained by the first reverse osmosis membrane treatment is used to increase the third permeate and saccharide from which the saccharide is substantially separated and removed by the third reverse osmosis membrane treatment. Separated into a third concentrated solution contained at a concentration (Claim 7). In this case, the third concentrated liquid obtained by the third reverse osmosis membrane treatment can be reused as a fermentation raw material (claim 8). In addition, the third permeate obtained by the third reverse osmosis membrane treatment is subjected to the first reverse osmosis membrane treatment, and a circulation treatment for recovering a small amount of lactic acid remaining in the third concentrated liquid. And can also be used to adjust the pH of the fermentation raw material (claim 9).

  The present invention also provides a method of fermenting a raw material containing starch and saccharides, subjecting the obtained crude lactic acid to reverse osmosis membrane separation to separate saccharides and purify them into lactic acid. It has the property of separating and concentrating the lactic acid in the treatment liquid without permeating the saccharide in the treatment liquid, and in the second predetermined pH range different from the first predetermined pH range. The reverse osmosis membrane is prepared by adjusting the crude lactic acid to the first predetermined pH range using a reverse osmosis membrane having a property of allowing saccharides to substantially permeate but not allowing lactic acid in the treatment liquid to permeate. The first stage reverse osmosis membrane treatment is carried out, the saccharides are transferred to the concentration side, separated and removed, the first permeate is adjusted to the second predetermined pH range, and then the second stage by the reverse osmosis membrane The reverse osmosis membrane treatment of the second consisting mainly of low-concentration ammonia water It can be defined as a method for producing lactic acid characterized by separating ammonia into a second concentrated liquid mainly composed of ammonium lactate and removing ammonia from the obtained second concentrated liquid. This problem is solved (claim 10).

  It is preferable to use a crosslinked polyamide-based composite membrane as the reverse osmosis membrane in the first stage and second stage reverse osmosis treatment methods. In this case, the first predetermined pH range is pH 3 or less, and the second predetermined pH range is The pH is 8 or more (claim 11). Moreover, it is preferable to return the sugar-rich first concentrated liquid to the fermentation raw material and reuse it.

  As described above, in the prior art, an electrodialysis method or a cation exchange resin method is employed for purifying ammonia-type crude lactic acid after lactic acid fermentation. Electric energy consumption is large, and the cost of refining is high, leading to an increase in the price of lactic acid. In addition, in the cation exchange resin method, it is necessary to use a large amount of sulfuric acid or hydrochloric acid in the regeneration after adsorption of ammonium ions, which requires time and effort for handling chemicals and treating waste water. Furthermore, the consumption of electrical energy and the discharge of chemical waste liquid for regeneration are not preferable because they are not economical and give a large load to the environment.

  In the method of the present invention, we conducted extensive experiments to investigate the properties of reverse osmosis membrane materials such as cross-linked polyamide composite membranes and the separation performance of sugars, lactic acid, and ammonia due to pH fluctuations, and found the appropriate conditions and combinations. As a result, there is provided an economical and environmentally friendly method for purifying lactic acid without wasting electric energy and without even generating waste liquid.

  Furthermore, in a preferred implementation of the method of the present invention, a method has been proposed in which the permeate and / or concentrate obtained by the reverse osmosis membrane treatment performed in multiple stages is effectively reused in a series of treatment cycles. It is highly useful as an extremely efficient lactic acid purification method.

  As a reverse osmosis membrane for performing lactic acid purification in the lactic acid production method according to the present invention, a crosslinked polyamide composite membrane is suitable. As described above, the crosslinked polyamide composite membrane is obtained by uniformly forming an ultrathin crosslinked polyamide functional layer directly on the surface of a support such as a polysulfone porous membrane by an interfacial polycondensation method or the like. There is an advantage that the reverse osmosis membrane method can be easily executed even when the treatment liquid is pressurized.

  The present inventor prepared two kinds of membrane materials, a cation-rich membrane and an anion-rich membrane, as a cross-linked polyamide composite membrane, and changed the pH of lactic acid, ammonia, and saccharides that are the main components of the lactic acid fermentation broth. In order to confirm the change in separation performance, a reverse osmosis membrane treatment test was performed under the following conditions.

(Test Example 1)
(1) Description of Test Apparatus A schematic configuration of the reverse osmosis membrane experimental apparatus used in this test example is shown in FIG. Each test solution A put in the test solution tank 1 was supplied to the reverse osmosis membrane 3 with a pump 2 at a constant pressure, and separated into a concentrate B and a permeate C there. All tests are performed under constant pressure supply and operation conditions with a fixed flow rate of concentrated water, and the test solution can be continuously supplied to the membrane device 3 while maintaining a constant liquid quality in a total circulation system. Yes. In the figure, reference numerals 4a and 4b indicate pressure gauges, and reference numerals 5a and 5b indicate flow meters.

(2) Test conditions SU-210 (low pressure, cross-linked polyamide composite composite membrane, 4-inch type) manufactured by Toray Industries, Inc. was used for the reverse osmosis membrane 3 as a representative cation-rich membrane. The supply conditions were fixed at 0.75 MPa and a concentrated water flow rate of 1200 l / h, and the treatment liquid A in the test liquid tank 1 was set at a water temperature of 22 ° C. at room temperature. The pressure and flow rate of the supply conditions were detected by the pressure gauges 4a and 4b and the flow meters 5a and 5b, and controlled by control means (not shown).

  In the lactic acid separation test, 1% lactic acid was used as a feed solution, the pH was adjusted to 10 with aqueous ammonia, and samples were collected and analyzed at each pH. The ammonia concentration at that time was also analyzed, and the result was expressed as a concentration ratio as in the case of lactic acid. Glucose (glucose) and sucrose (sucrose) were similarly adjusted at 1% concentration by adding aqueous ammonia when increasing the pH and adding lactic acid when decreasing the pH.

(3) Test results Table 1 shows the test results.

  From the results shown in Table 1, when the pH is 3 or less, lactic acid is hardly concentrated in this cation-rich membrane, most of it is lost to the permeation side C, and 94% of the saccharide remains on the concentration side B. I understood that. Therefore, it was found that the sugar was removed from the liquid A to be treated if the pH was adjusted to 3 or less in this membrane. Moreover, since the concentrated liquid B at this time contains saccharides at a high concentration, it was found that this can be reused as a fermentation raw material.

  In this test, ammonia was not added at a pH of 3 or less, but when ammonia was added to increase the pH of the lactic acid treatment solution A (pH 5 or more), the concentration was about 80% and the concentrate B was added. It was found from the results of Table 1 that In the first place, when ammonia ions are present in the treatment liquid A as in the case of crude lactic acid after fermentation, most of the ions cannot pass through the membrane 3 and remain in the concentrated liquid B at a high concentration. It can be reused as an alkali for adjusting the pH of the liquid (adjusting to pH 3 or lower). However, on the other hand, it was also found that when the pH was 10, the separation performance for ammonia was lowered. This is because when the pH is 10, the gas tends to be gasified and water-soluble and permeates through the reverse osmosis membrane 3 and is contained in the permeate C.

  Furthermore, the reverse osmosis membrane 3 has a concentration of 92% or higher when the pH is 8 or higher in the separation performance for lactic acid, contrary to the case where the pH is 3 or lower. I also found out that it would move.

(Test Example 2)
(1) Description of Test Apparatus As in Test Example 1, the configuration shown in FIG.

(2) Test conditions In this test example, SU-610 (ultra-low pressure, cross-linked polyamide composite composite membrane, 4-inch type) manufactured by Toray Industries, Inc. was used for the reverse osmosis membrane 3 as a representative of the anion-rich membrane. The supply conditions were fixed at 0.35 MPa and a concentrated water flow rate of 1200 l / h, and the treatment liquid A in the test liquid tank 1 was set at a water temperature of 22 ° C. at room temperature. The pressure and flow rate of the supply conditions were detected by the pressure gauges 4a and 4b and the flow meters 5a and 5b, and controlled by control means (not shown).

  Similarly to Test Example 1, in the lactic acid separation test, 1% lactic acid was used as a feed solution, the pH was adjusted to 10 with aqueous ammonia, and samples were collected at each pH and analyzed. The ammonia concentration at that time was also analyzed, and the result was expressed as a concentration ratio as in the case of lactic acid. Glucose (glucose) and sucrose (sucrose) were similarly adjusted at 1% concentration by adding aqueous ammonia when increasing the pH and adding lactic acid when decreasing the pH.

(3) Test results Table 2 shows the test results.

  From the results shown in Table 2, if the pH is 3 or less, lactic acid is hardly concentrated in this anion-rich membrane, most of it is lost to the permeation side C, and 88% of the saccharide remains on the concentration side B. I understood that. On the other hand, it was found that if the pH is 8 or higher, lactic acid can be concentrated at 94% or higher by this anion-rich membrane, exhibiting the separation performance opposite to that at pH 3 or lower.

  As for the separation performance of ammonia (ion), when the pH reaches 10, gasification and water-solubility tend to occur rapidly and permeate through the reverse osmosis membrane and be contained in the permeate C. Since it moves to the concentration side B as ions, the concentrated solution B contains a high concentration of lactic acid in the form of ammonium lactate.

  It was also found that the permeate C was diluted ammonia water from which ammonia was substantially removed, so that it could be used as dilution water without waste in the fermenter.

(Summary of separation performance)
From the above test results, the separation performance for lactic acid, saccharides and ammonia by reverse osmosis membrane treatment using a crosslinked polyamide composite membrane can be evaluated as follows.

  First, the lactic acid separation performance varies greatly depending on the change in pH of the test solution. As is clear from Tables 1 and 2, the cation rich membrane (SU-210) used in Test Example 1 has a large change in lactic acid separation rate of 35 to 96% at pH 3 to 10, and the anion used in Test Example 2 Even in the rich membrane (SU-610), the lactic acid separation rate is greatly changed at 22 to 95% at pH 3 to 10. Therefore, in any of the cation-rich membrane and the anion-rich membrane, the lower the pH of the treatment liquid, the smaller the lactic acid separation rate (larger lactic acid permeability), and the higher the treatment solution pH, the larger the lactic acid separation rate (lactic acid). It is understood that the transmittance is small). This means that the lactic acid in the liquid can be distributed to the permeate side and the concentrate side by adjusting the pH of the treatment liquid and performing a two-step reverse osmosis membrane treatment. In the present invention, this two-stage processing method is adopted as a preferred embodiment.

  Normally, stable ions such as caustic soda are used in pH fluctuation tests, but it is clear from the inventors' tests that similar fluctuations occur even when unstable ions are used as alkaline materials such as ammonia. It has become.

  Next, the cross-linked polyamide composite membrane is excellent in the action of separating and removing saccharides in both the cation rich membrane (SU-210) and the anion rich membrane (SU-610), and stable separation performance in the pH range of 3-10. (Refer to the glucose inhibition rate (separation rate) in Tables 1 and 2). Especially, in the case of cation-rich membranes, the concentration performance is extremely excellent at 95% or more in the pH range of 3 to 10. I found out.

  Regarding ammonia, both the cation-rich membrane (SU-210) and the anion-rich membrane (SU-610) are almost stable up to pH 8 and exhibit separation performance of 80% or more. When it becomes 10, it gasifies and becomes water-soluble and permeates the membrane. Therefore, in order to leave ammonia on the concentration side, it is necessary to adjust the pH of the treatment liquid to 10 or less.

  In addition, ammonia is not only a pH adjuster in the reverse osmosis membrane treatment in the method of the present invention, but also an agent used as a pH adjuster in the fermentation process, which is a pre-treatment, so if concentration and separation are possible here, It is economical to return to the fermenter for reuse. Therefore, as will be described later, in a preferred embodiment of the present invention, a method is proposed in which the processing solution is distributed in consideration of the reuse in the second stage reverse osmosis processing by changing the type of membrane and pH. is doing.

  Based on the test results and analysis described above, fermentation crude lactic acid was used to purify lactic acid by reverse osmosis membrane treatment according to the treatment flow shown in FIG. This process flow is described in detail below with reference to Table 3 showing the liquid analysis values of the respective treatment liquids.

  Acid was added to the fermented crude lactic acid solution containing 32.5 g of lactic acid, 31.5 g of glucose and 19.0 g of ammonia per liter to adjust the pH to 3 or less. Lactic acid was used for pH adjustment here. As will be described later, when the permeate P3 after the reverse osmosis membrane treatment by the membrane 3 is added to the fermented crude lactic acid, the lactic acid contained in the permeate P3 works to lower the pH of the fermented crude lactic acid solution. There is an advantage that the amount of the acid used for adjusting the pH is small (or unnecessary).

  A treatment liquid (fermented crude lactic acid liquid) adjusted to pH 3 or lower was supplied to the membrane 1 at a supply pressure of 1 MPa and a flow rate of 800 liters / h to perform reverse osmosis membrane treatment. This treatment is performed to transfer and separate saccharides in the treatment liquid to the concentration side. Therefore, the membrane 1 substantially permeates lactic acid in the treatment liquid within this predetermined pH range. Has a property of substantially separating and removing saccharides in the treatment liquid. In this example, the cation-rich cross-linked polyamide composite membrane SU-210 used in Test Example 1 was used. As described above, it has been found that, among the crosslinked polyamide-based composite membranes, the cation-rich membrane exhibits extremely excellent concentration performance of 95% or more in the pH range of 3 to 10.

  Saccharides may remain in the crude lactic acid obtained at the end of the fermentation or during the fermentation, and it is preferable to remove these saccharides in order to interfere with the reaction in the ester reaction or the synthesis reaction when producing the lactic acid derivative. . By carrying out the reverse osmosis membrane treatment with the membrane 1, the saccharide remaining in the crude lactic acid is separated and removed, so that the above-mentioned reaction interference can be prevented in advance. If only saccharides can be concentrated and separated here, it can be returned to the fermenter and reused, which is a more economical method (details will be described later).

  Since the membrane 1 separates saccharides, the saccharide content in the permeate P1 that has passed through the membrane 1 is greatly reduced, and the saccharides are concentrated in the concentrated solution C1. This is shown in Table 3 (glucose content 31.5 g / l in the treatment liquid decreases to 2.3 g / l for P1 and increases to 39.0 g / l for C1).

  The pH of the permeate P1 that passed through the membrane 1 was adjusted to 8 or more by adding an alkali. Ammonia water was used as an alkali added for pH adjustment.

  Next, the permeate P1 whose pH was adjusted to 8 or more was subjected to reverse osmosis membrane treatment with the membrane 2 to separate the permeate P2 and the concentrate C2. This second-stage reverse osmosis membrane treatment is performed to concentrate the treatment liquid (permeate P1) with lactic acid, and in this pH range, both the cation-rich membrane and the anion-rich membrane show a very high lactic acid concentration rate. Therefore, any type of cross-linked polyamide composite membrane can be suitably used, but an anion-rich cross-linked polyamide composite membrane was used as the membrane 2 in this example.

  As a result of the reverse osmosis membrane treatment by the membrane 2, as shown in Table 3, most of the lactic acid contained in the permeate P1 moves to the concentrate side and remains in the concentrate C2, so that glucose and lactic acid are contained in the permeate P2. However, only a very small amount remains, and it can be said that it is a dilute ammonia water. This ammonia water can be used without waste as dilution water for the raw material solution in the fermenter.

  The concentrated solution C2 of the membrane 2 is rich in lactic acid and hardly contains saccharides but contains a lot of ammonia (see Table 3), so this was put into an ammonia removing device to remove ammonia. Ammonia removal is performed to separate ammonia using a gas-liquid separation method by a physicochemical method such as heat treatment or vacuum deaeration treatment, and change it into lactic acid. In this embodiment, vacuum treatment deaeration treatment is performed. Was used to remove about 95% of the ammonia contained in the concentrate C2.

  On the other hand, the concentrated solution C1 of the membrane 1 contains a large amount of saccharides in the crude lactic acid solution, but a small amount of lactic acid that could not permeate the membrane 1 remains, and this is used as a treatment solution for the membrane 3 for reverse osmosis. Membrane treatment was performed. Since the reverse osmosis membrane treatment with this membrane 3 is mainly intended to further concentrate saccharides and use them in the fermentation broth, like the membrane 1, a cation-rich cross-linked polyamide composite membrane (especially excellent in saccharide separation performance) SU-210) was used as membrane 3.

  As a result of the treatment by the membrane 3, as shown in Table 3, most of the glucose in the treatment liquid C1 was separated and removed and left in the concentrate C3, and a permeate P3 containing lactic acid and a small amount of ammonia was obtained. Therefore, if this permeate P3 is mixed with the fermented crude lactic acid solution and reprocessed, the remaining lactic acid can be recovered in the concentrated solution C2 after the membrane 2 treatment, and an extremely efficient circulation process becomes possible. Further, mixing and using the permeate P3 containing lactic acid in the fermentation crude lactic acid solution also lowers the pH of the fermentation crude lactic acid solution, and therefore works advantageously in adjusting the pH of the treatment solution for the membrane 1.

  As shown in Table 3, lactic acid and saccharides are considerably concentrated in the concentrated solution C3 after the treatment of the membrane 3, and the amount of saccharides is significantly reversed from that of the lactic acid as compared with that before the treatment according to the method of the present invention. Therefore, effective reprocessing is performed by returning this to the lactic acid fermenter and using it as a fermentation raw material. In this way, the lactic acid recovery rate can be further increased, and the lactic acid concentration rate in the concentrate C2 in the membrane 2 can be increased.

  As described above, according to the embodiment of the present invention, the saccharides which become interference substances in the second stage reverse osmosis membrane treatment are removed by the first stage reverse osmosis membrane treatment, and the second stage reverse osmosis membrane is obtained. Not only can lactic acid be efficiently purified by the treatment, but also the saccharide removed by the reverse osmosis membrane treatment in the first stage can be separated and concentrated and reused as a lactic acid fermentation raw material.

  Furthermore, according to the present invention, a great advantage can be obtained with respect to the power consumption in the electrodialysis method, which is a conventional lactic acid purification method, the amount of chemical used in the ion exchange method, and the amount of waste liquid generated. In order to demonstrate this, the following tests were conducted.

(Test Example 3)
In this test, in order to convert ammonia lactate into lactic acid, a two-chamber bipolar membrane electrodialysis method was carried out by a constant voltage method, 0.83 Kwh / kg lactic acid as a reference processing required electric quantity, and a current efficiency of 0. 90 was applied (refer to the monthly "Food Chemical" June 1996 issue "Bipolar Membrane Electrodialysis Method for Converting Salts to Their Acids and Bases"). In addition, cation exchange resin (trade name “AmberliteIR-120B” manufactured by Rohm & Haas Co., Ltd.) is used for ion exchange, the exchange capacity is 1.9 mgeq / ml, and the capacity coefficient in organic acid treatment is 0.700. Was calculated assuming that it was 5% sulfuric acid.

  Compared with the conventional electrodialysis method and ion exchange method, the amount of electricity consumed, the amount of chemicals used, and the amount of waste liquid when 100 liters of crude lactic acid (lactic acid 3%) is purified according to the above conditions. I did it. The results are shown in Table 4.

  As shown in Table 4, the method of the present invention requires very little power consumption compared to the conventional electrodialysis method, and may produce a large amount of waste liquid that requires treatment like the ion exchange method. Absent. Therefore, it has been proved that the purification method can be said not only to have a small impact on the environment but also to be excellent in terms of manufacturing cost.

  The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to these embodiments, and various modifications can be made within the scope of the invention described in the claims.

The schematic block diagram which shows the experimental apparatus of the reverse osmosis membrane test used for Test Example 1,2. It is a processing flowchart of the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Test liquid tank 2 Pump 3 Reverse osmosis membrane 4a, 4b Pressure gauge 5a, 5b Flowmeter A Processing liquid B Concentrate C Permeate P1 Permeate C1 of membrane 1 Concentrate P2 of membrane 1 Permeate C2 of membrane 2 Membrane 2 Concentrate of liquid P3 Permeate of membrane 3 C3 Concentrate of membrane 3

Claims (12)

A method for producing lactic acid, comprising fermenting a raw material containing starch and saccharides, treating the obtained crude lactic acid with a reverse osmosis membrane, separating the saccharides and purifying the lactic acid. The method for producing lactic acid according to claim 1, wherein the reverse osmosis membrane used in the reverse osmosis treatment method is a crosslinked polyamide composite membrane. The method for producing lactic acid according to claim 2, wherein the pH of the liquid to be treated for the reverse osmosis membrane treatment is adjusted to 3 or less. The reverse osmosis membrane treatment is performed stepwise, and the liquid to be treated adjusted to pH 3 or lower is separated and removed by transferring the saccharide to the concentration side by the first reverse osmosis membrane treatment, and this first permeate is removed from pH 8 to 10 3. After being adjusted to, this is separated into a second permeate mainly composed of low-concentration aqueous ammonia and a second concentrate mainly composed of ammonium lactate by a second reverse osmosis membrane treatment. The lactic acid manufacturing method as described. The method for producing lactic acid according to claim 4, wherein ammonia is removed from the second concentrated solution obtained by the second reverse osmosis membrane treatment to purify lactic acid. The method for producing lactic acid according to claim 4 or 5, wherein the second permeate obtained by the second reverse osmosis membrane treatment is reused as dilution water in the fermentation treatment. The saccharide-rich first concentrated liquid obtained by the first reverse osmosis membrane treatment is used to add a high concentration of the third permeate and saccharide from which the saccharide has been substantially separated and removed by the third reverse osmosis membrane treatment. The method for producing lactic acid according to claim 3, wherein the lactic acid is separated into a third concentrated solution. The method for producing lactic acid according to claim 7, wherein the third concentrated liquid obtained by the third reverse osmosis membrane treatment is reused as a fermentation raw material. The third permeate obtained by the third reverse osmosis membrane treatment is subjected to the first reverse osmosis membrane treatment, and a circulation treatment is performed to recover a small amount of lactic acid remaining in the third concentrated liquid. The method for producing lactic acid according to claim 7 or 8, which is also used for pH adjustment of the fermentation raw material. In a method of fermenting a raw material containing starch and saccharide, and subjecting the obtained crude lactic acid to reverse osmosis membrane separation to separate saccharide and purify it into lactic acid, the lactic acid in the treatment liquid is substantially reduced within the first predetermined pH range. In the second predetermined pH range different from the first predetermined pH range, and the saccharide in the processing liquid is substantially allowed to permeate. Using a reverse osmosis membrane having a property of allowing permeation but separation of lactic acid without allowing permeation of lactic acid in the treatment liquid, after adjusting the crude lactic acid to the first predetermined pH range, A reverse osmosis membrane treatment is performed to separate and remove saccharides, and after adjusting the first permeate to a second predetermined pH range, a second-stage reverse osmosis membrane treatment with this reverse osmosis membrane is carried out. Mainly composed of a second permeate consisting of concentrated ammonia water and ammonium lactate The second is separated into a concentrated liquid, resulting lactic acid producing method characterized by removing the ammonia from the second concentrate that. The reverse osmosis membrane used for the first stage and the second stage reverse osmosis treatment method is a crosslinked polyamide composite membrane, the first predetermined pH range is pH 3 or less, and the second predetermined pH range is pH 8 or more, The method for producing lactic acid according to claim 10. The method for producing lactic acid according to claim 10 or 11, wherein the saccharide-rich first concentrated liquid is returned to the fermentation raw material and reused.

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