A method for separating an organic acid from an organic acid salt fermentation broth

Abstract

The present application relates to a kind of methods for separating organic acid from organic acid salt fermentation liquor, the method comprises: organic acid salt fermentation liquor is placed in the salt room of cation displacement dialysis device and is handled by cation displacement dialysis;Liquid phase in the cation displacement dialysis membrane stack in the cation displacement dialysis process is 0.5-5cm / s;Acid liquid is used as displacement medium in the acid room of the cation displacement dialysis device.The method provided by the present application, by using ion exchange membrane as ion transfer medium, organic acid salt fermentation liquor after sterilization and decolorization is directly obtained organic acid and inorganic salt by the method of the present application, the removal rate of the cation corresponding to organic acid salt can reach more than 96%, membrane flux is >2.7mol / m 2 / h, and the recovery rate of organic acid can reach more than 95%.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of separation, in particular to a method for separating organic acid from organic acid salt fermentation liquor. BACKGROUND

[0002] Organic acids are widely used in food, chemical, pharmaceutical, material and other fields, and are an important class of chemicals. The production methods of organic acids mainly include chemical synthesis and microbial fermentation. Chemical synthesis is synthesized by using petrochemical raw materials under the action of catalysts, and petrochemical resources are non-renewable, so other methods need to be found instead. Microbial fermentation utilizes microorganisms to convert carbohydrates into the desired organic acid under mild conditions. The organic acids produced by fermentation mainly include lactic acid, citric acid, succinic acid, gluconic acid and the like. Especially, the invention of biodegradable materials such as polylactic acid and polybutylene succinate has gradually become a hot spot.

[0003] Lactic acid (alpha-hydroxypropionic acid) is an important organic acid, which has been widely used in food, medicine and chemical industry. In recent years, with the successful development and utilization of green solvents (lactic acid esters) and biodegradable plastics (polylactic acid) products synthesized from lactic acid, the demand for lactic acid is increasing year by year. The industrial production of lactic acid mainly includes fermentation method and chemical synthesis method. At present, the extraction methods of lactic acid include calcium acidolysis method, solvent extraction method, ion exchange method, membrane technology and adsorption fermentation method, etc.

[0004] CN104496796A discloses a method for rapidly extracting L-lactic acid from ammonium lactate fermentation broth, which comprises the following steps: (1) ammonium lactate fermentation broth pretreatment; (2) ammonium lactate sulfuric acidolysis; (3) adding the acidolysis broth and the coupling adsorbent into the centrifugal extractor, and coupling adsorption to extract L-lactic acid. The method can rapidly extract L-lactic acid from lactic acid acidolysis broth, changes the existing process route of separating various impurities from L-lactic acid one by one, directly couples and adsorbs L-lactic acid by using the coupling adsorbent, and leaves various impurities in the residual liquid. Since the coupling adsorbent in the application has specific adsorption for L-lactic acid, the purpose of one-step purification of L-lactic acid is achieved, and the existing decolorization process and most of the ion exchange process are removed.

[0005] CN109206312A discloses a method for separating and purifying D-lactic acid from D-ammonium lactate fermentation broth, comprising the following steps in sequence: 1) solid-liquid separation and removal of protein and pigment are performed on the D-ammonium lactate fermentation broth to obtain a clarified fermentation broth; 2) the clarified fermentation broth obtained in step 1) is concentrated; 3) acidification and crystallization are performed on the concentrated fermentation broth obtained in step 2); 4) the liquid-solid mixture obtained in step 3) is filtered to obtain a by-product ammonium sulfate; 5) ion exchange is performed on the fermentation broth containing D-lactic acid after crystallization in step 4); 6) nanofiltration decolorization is performed on the fermentation broth after ion exchange in step 5); and 7) the fermentation broth after nanofiltration is concentrated to obtain D-lactic acid. The above-mentioned lactic acid extraction method is simple, easy to operate, has no waste liquid pollution, has low energy consumption, high recovery rate and high product quality.

[0006] Citric acid is the largest yield among organic acids produced by fermentation method. The traditional production process of citric acid by fermentation method is as follows: citric acid fermentation broth is produced by fermentation, and then sterilization is performed to obtain citric acid-containing fermentation clear liquid, calcium carbonate is added for neutralization to obtain calcium citrate, and then filtration and washing are performed to obtain calcium citrate solid, part of the fermentation clear liquid containing citric acid is added to obtain monohydrogen calcium citrate, sulfuric acid is added for acidolysis, calcium sulfate is removed by filtration, and the obtained solution containing citric acid is purified and concentrated to obtain citric acid product. A large amount of acidic calcium sulfate solid waste is generated in the traditional process of citric acid.

[0007] Succinic acid can be used to produce biodegradable polymer materials, which is an important alternative product to solve the white pollution such as plastic. The traditional production process of succinic acid by fermentation method is as follows: calcium hydroxide is added in the fermentation process to obtain calcium succinate solid, and then concentrated sulfuric acid is added for acidolysis to obtain succinic acid solution and calcium sulfate, the succinic acid solution is purified by activated carbon and ion exchange resin to remove impurity ions, and then concentrated and crystallized to obtain succinic acid solid.

[0008] At present, the industrial production of gluconic acid generally adopts the process of producing sodium gluconate by Aspergillus niger fermentation, in which liquid sodium hydroxide is added in the fermentation process, and after the separation of the bacterial cells and the fermentation broth, the fermentation broth is concentrated and crystallized to obtain sodium gluconate crystals, or is spray-dried to obtain powdered sodium gluconate product. The sodium / potassium gluconate crystals are dissolved, and the sodium / potassium gluconate is converted into gluconic acid by cation exchange, and then the gluconic acid product is obtained by vacuum concentration, crystallization and drying.

[0009] In summary, there are still problems such as complex extraction process, low yield and poor quality in the existing separation and extraction technology of organic acids by fermentation method. At present, electrodialysis is also used to separate organic acids, but ion migration needs to consume electric energy in the process of electrodialysis. Under the joint action of electric field and organic matter and inorganic matter in the fermentation broth, serious membrane pollution will occur, which affects the smooth progress of the process. SUMMARY

[0010] In view of the problems in the prior art, the purpose of the present application is to provide a method for separating organic acid from organic acid salt fermentation liquor, which adopts cation replacement dialysis process to replace the acidolysis and ion exchange steps in the prior art, realizes efficient conversion of organic acid salt to organic acid, and can obtain organic acid and inorganic salt with high purity.

[0011] To achieve this purpose, the present application adopts the following technical solutions:

[0012] The present application provides a method for separating organic acid from organic acid salt fermentation liquor, which comprises: placing the organic acid salt fermentation liquor in the salt chamber of a cation replacement dialysis device for cation replacement dialysis treatment.

[0013] The cation replacement dialysis device comprises a cation replacement dialysis membrane stack, and a dialysis membrane is arranged in the membrane stack.

[0014] The linear velocity of the liquid phase in the cation replacement dialysis membrane stack during the cation replacement dialysis treatment is 0.5-5 cm / s.

[0015] An acid solution is used as the displacement medium in the acid chamber of the cation replacement dialysis device.

[0016] The method provided by the present application can directly obtain organic acid and inorganic salt from the sterilized and decolorized organic acid salt fermentation liquor by using ion exchange membrane as ion migration medium, the removal rate of the corresponding cation of the inorganic salt can reach more than 96%, the membrane flux is >2.7 mol / m 2 / h, and the recovery rate of the organic acid can reach 95% or more.

[0017] In the present application, the linear velocity of the liquid phase in the cation replacement dialysis membrane stack during the cation replacement dialysis treatment is 0.5-5 cm / s, for example, it can be 0.5 cm / s, 1 cm / s, 1.5 cm / s, 2 cm / s, 2.5 cm / s, 3 cm / s, 3.5 cm / s, 4 cm / s, 4.5 cm / s or 5 cm / s, but it is not limited to the listed values, and other unlisted combinations within this range are also applicable.

[0018] In the present application, if a higher linear velocity is adopted, the linear velocity of the feed liquid in the membrane stack is larger, and the residence time of the feed liquid in the membrane stack is shorter. Although the membrane flux is higher, the migration rate of inorganic cations in the organic acid salt fermentation liquid is lower. If a too low linear velocity is adopted, the residence time of the feed liquid in the membrane stack can be ensured to be longer, but because the linear velocity of the feed liquid in the membrane stack is lower, the stagnant layer of the liquid on the membrane surface is thicker, so that the membrane flux is greatly reduced. In order to overcome the problems existing in the first operation mode, the single-stage operation of the present application can adopt another operation mode, that is, the feed liquid is circulated into the membrane stack at a higher linear velocity, so that the residence time of the feed liquid in the membrane stack can be greatly increased under the premise that the linear velocity on the membrane surface is maintained, and the membrane flux and the migration rate of inorganic cations are both maintained at a higher level.

[0019] In the present application, the treatment mode of the cation displacement dialysis treatment includes single-stage and multi-stage. For example, it can be 2 stages, 3 stages, 4 stages, 5 stages, 6 stages, 7 stages, 8 stages or 9 stages, but is not limited to the listed values, and other unlisted combinations in this range are also applicable.

[0020] As a preferred technical solution of the present application, the treatment mode of the cation displacement dialysis treatment includes at least 1 stage of cation displacement dialysis treatment.

[0021] As a preferred technical solution of the present application, the cation displacement dialysis treatment includes at least 3 stages of cation displacement dialysis treatment.

[0022] As a preferred technical solution of the present application, the treatment mode of the cation displacement dialysis treatment is countercurrent treatment. The countercurrent refers to that the flow directions of the ammonium lactate fermentation liquid in the salt chamber and the acid liquid in the acid chamber are opposite, that is, the dialysis displacement is carried out between the feed liquid containing high-concentration inorganic cations in the salt chamber and the feed liquid containing low-concentration hydrogen ions in the acid chamber, between the feed liquid containing medium-concentration inorganic cations in the salt chamber and the feed liquid containing medium-concentration hydrogen ions in the acid chamber, and between the feed liquid containing low-concentration inorganic cations in the salt chamber and the feed liquid containing high-concentration hydrogen ions in the acid chamber. This operation mode can maximize the mass transfer driving force of inorganic cations and hydrogen ions, and a higher membrane flux can be obtained.

[0023] The single-stage operation of the present application includes at least two operation modes. One is that the salt chamber feed liquid and the acid chamber feed liquid enter the cation displacement dialysis membrane stack from the membrane stack inlet at a lower linear velocity, and then flow out of the membrane stack from the membrane stack outlet, and the feed liquid does not need to enter the membrane stack again.

[0024] Although single-stage displacement dialysis treatment can achieve certain effects, single-stage cation displacement dialysis operation has the problem that the ion migration driving force gradually decreases. In the early stage of cation displacement dialysis, there is a large concentration difference of hydrogen ions and inorganic cations on both sides of the membrane, and the migration driving force is large; with the ion migration, the inorganic cations in the salt chamber solution migrate into the acid chamber solution, and the hydrogen ions in the acid chamber solution migrate into the salt chamber solution, the concentration difference of the two ions on both sides of the membrane gradually decreases, and the ion migration driving force gradually decreases.

[0025] To solve the above technical problems, a cation displacement dialysis in a multi-stage countercurrent mode is adopted. Taking a three-stage countercurrent operation as an example, the initial salt chamber solution and the acid chamber solution that has undergone partial cation displacement dialysis operation are subjected to cation displacement dialysis operation in the first stage. Compared with the initial acid chamber solution, the hydrogen ion concentration in the acid chamber solution that has undergone partial cation displacement dialysis operation is lower, and it also contains a certain amount of inorganic cations, so the ion migration driving force is lower than that in the initial stage of single-stage operation. Similarly, the initial acid chamber solution and the salt chamber solution that has undergone partial cation displacement dialysis operation are subjected to cation displacement dialysis operation in the third stage, and the salt chamber solution that has completed the first-stage cation displacement dialysis and the acid chamber solution that has completed the third-stage cation displacement dialysis are subjected to cation displacement dialysis operation in the second stage. In this way, a relatively stable concentration difference of hydrogen ions and inorganic cations can be maintained on both sides of the membrane, the ion transmembrane migration driving force of the entire cation displacement dialysis operation can be maintained at a relatively stable level, the ion migration driving force is higher than that of single-stage operation, and the membrane flux is increased.

[0026] In the present application, the number of dialysis membranes arranged between the salt chamber and the acid chamber of the cation displacement dialysis device can be determined as needed, for example, it can be 3, 5, 6, 8, or 10, 20, 30, 40, 50, 100, 200, 300, etc., but is not limited to the listed values.

[0027] In order to ensure that the linear velocity of the liquid phase in the cation displacement dialysis membrane stack is maintained at 0.5-5cm / s, the salt chamber liquid and the acid chamber liquid of each stage are circulated into the salt chamber and acid chamber membrane stack of the stage. Among them, batch multi-stage countercurrent cation displacement dialysis can be used for operation, and the basic process is as follows: the inorganic cations in the organic acid salt fermentation broth in the salt chamber are replaced step by step, the acid chamber and the salt chamber liquid of each stage of cation displacement dialysis are self-circulated, and after the completion (near equilibrium) of each stage of cation displacement dialysis, the acid chamber and the salt chamber liquid are reversely entered into another stage. Taking three-stage countercurrent cation displacement dialysis of ammonium lactate fermentation broth as an example, after the completion (near equilibrium) of the first stage of cation displacement dialysis, the ammonium lactate fermentation broth is entered into the salt chamber of the second stage, after the completion (near equilibrium) of the second stage of cation displacement dialysis, it is entered into the salt chamber of the third stage, and the acid salt ion replacement is continued in the third stage of cation displacement dialysis; the initial acid solution is in the acid chamber of the third stage, after the completion (near equilibrium) of the third stage of cation displacement dialysis, the acid solution is entered into the acid chamber of the second stage, and after the completion (near equilibrium) of the second stage of membrane cation displacement dialysis, the recovered liquid is entered into the acid chamber of the first stage. Or continuous multi-stage countercurrent cation displacement dialysis can be used for operation, and the basic process is as follows: the organic acid salt fermentation broth and the acid chamber liquid are self-circulated in the salt chamber and the acid chamber of each stage, the inorganic cations in the organic acid salt fermentation broth are replaced, the salt chamber liquid is entered into the next stage of salt chamber, and the acid chamber liquid is reversely entered into the previous stage of acid chamber.

[0028] The organic acid salt fermentation broth is treated by multi-stage countercurrent cation displacement dialysis. Taking three-stage countercurrent cation displacement dialysis as an example, the organic acid salt fermentation broth is entered into the cation displacement dialysis device from the inlet of the first stage of salt chamber, the outlet of the first stage of cation displacement dialysis device is connected with the inlet of the second stage of salt chamber, the outlet of the second stage of salt chamber is connected with the inlet of the third stage of salt chamber, and the outlet of the third stage of salt chamber flows out the liquid containing organic acid; the initial acid solution is entered into the cation displacement dialysis device from the inlet of the third stage of acid chamber, the outlet of the third stage of acid chamber is connected with the inlet of the second stage of acid chamber, the outlet of the second stage of acid chamber is connected with the inlet of the first stage of acid chamber, and the outlet of the first stage of acid chamber flows out the liquid of inorganic salt corresponding to the acid radical.

[0029] In the application, in addition to improving the membrane flux of inorganic cations and hydrogen ions, the multi-stage countercurrent operation also has the effects of reducing the transmembrane leakage flux of organic acid and organic acid radical and reducing the loss of organic acid. The results show that, compared with non-staged operation, the transmembrane leakage amount of lactic acid and lactic acid radical is reduced by more than 13% when the cation displacement dialysis operation of ammonium lactate fermentation broth is divided into three stages; the transmembrane leakage amount of gluconic acid and gluconate is reduced by more than 27.6% when the cation displacement dialysis operation of sodium gluconate fermentation broth is divided into three stages; the transmembrane leakage amount of succinic acid and succinate is reduced by more than 25.1% when the cation displacement dialysis operation of sodium succinate fermentation broth is divided into three stages.

[0030] In the present application, the dialysis membrane can be a cation exchange membrane known to those skilled in the art, which can be purchased from the market. For example, a conventional electrodialysis cation exchange membrane, a monovalent selective cation exchange membrane (i.e. an ion exchange membrane that allows monovalent cations to pass through preferentially while blocking divalent and higher valence ions), a diffusion dialysis cation exchange membrane commonly used in conventional diffusion dialysis processes, or a modified ion exchange membrane (doping modification and surface modification) can also be used.

[0031] As a preferred technical solution of the present application, the operating temperature of different processing stages in the cation displacement dialysis process is different. That is, the operating temperature of each stage in the multi-stage dialysis process is different.

[0032] Preferably, the operating temperature of each stage in the cation displacement dialysis process is 5-45°C, for example, it can be 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C or 45°C, etc., but is not limited to the values listed, and other unlisted combinations within this range are also applicable.

[0033] As a preferred technical solution of the present application, the operating temperature of each stage in the cation displacement dialysis process decreases with the increase of the number of processing stages. This is because reducing the operating temperature of cation displacement dialysis can reduce the amount of organic acid in the molecular state permeating through the cation exchange membrane, thereby reducing the loss of organic acid and organic acid root in the salt chamber. For example, the transmembrane migration (leakage) rate of lactic acid and lactate at 5°C is only 40% or less of that at 25°C; the transmembrane migration (leakage) amount of gluconic acid and gluconate at 4°C is only 35% of that at 25°C.

[0034] For example, in the first stage, i.e. in the cation displacement dialysis process in which the inorganic cation concentration in the salt chamber feed solution is high, a higher operating temperature is used, for example, 33°C to 45°C; in the second stage, i.e. in the cation displacement dialysis process in which the inorganic cation concentration in the salt chamber feed solution is at an intermediate level, an intermediate operating temperature is used, for example, 18°C to 30°C; in the third stage, i.e. in the cation displacement dialysis process in which the inorganic cation concentration in the salt chamber feed solution is at a lower level, a lower operating temperature is used, for example, 5°C to 15°C. The reason for choosing variable temperature operation is that performing cation displacement dialysis operation at a lower temperature can effectively reduce the rate of organic acid molecules permeating through the cation membrane into the acid chamber (an undesirable process), while having little effect on the rate of hydrogen ions permeating through the cation membrane into the salt chamber (a desirable process), so that the loss of organic acid during cation displacement dialysis operation can be reduced without significantly affecting the membrane flux.

[0035] As a preferred technical solution of the present application, the concentration of the organic acid root in the organic acid salt fermentation liquor is 0.6-3.0 mol / L, for example, it can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.2 mol / L, 1.3 mol / L, 1.5 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, 2.2 mol / L, 2.4 mol / L, 2.6 mol / L, 2.7 mol / L, 2.8 mol / L, 2.9 mol / L, 3.0 mol / L, etc., but not limited to the listed values, and other unlisted values within the range are also applicable.

[0036] Preferably, the pH value of the organic acid salt fermentation liquor is 5-10, for example, it can be 5, 6, 7, 8, 9, or 10, etc., but not limited to the listed values, and other unlisted values within the range are also applicable.

[0037] In the present application, the organic acid salt includes but is not limited to ammonium lactate, sodium lactate, ammonium citrate, sodium citrate, sodium gluconate, ammonium succinate, and sodium succinate.

[0038] As a preferred technical solution of the present application, the acid includes any one or a combination of at least two of hydrochloric acid, nitric acid, or sulfuric acid.

[0039] As a preferred technical solution of the present application, the inorganic salt obtained by cation exchange dialysis in the acid chamber includes at least one of ammonium chloride, sodium chloride, ammonium sulfate, sodium sulfate, and ammonium nitrate.

[0040] Preferably, the molar concentration of the acid is 0.5-3.5 mol / L, for example, it can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3.0 mol / L, or 3.5 mol / L, etc., but not limited to the listed values, and other unlisted values within the range are also applicable.

[0041] As a preferred technical solution of the present application, the method includes placing the organic acid salt fermentation liquor in the salt chamber of a cation exchange dialysis device for cation exchange dialysis treatment;

[0042] The cation exchange dialysis device includes a cation exchange dialysis membrane stack.

[0043] The cation displacement dialysis treatment comprises at least three stages of cation displacement dialysis treatment, and the operation temperature of each stage of the cation displacement dialysis treatment is different; the operation temperature of each stage of the cation displacement dialysis treatment is 5-45℃; the operation temperature of each stage of the cation displacement dialysis treatment decreases with the increase of the treatment stage number; the cation displacement dialysis treatment is a countercurrent cation displacement dialysis treatment; and the linear velocity of the liquid phase in the cation displacement dialysis membrane stack in the cation displacement dialysis treatment is 0.5-5cm / s.

[0044] The acid liquid is used as the displacement medium in the acid chamber of the cation displacement dialysis device.

[0045] The molar concentration of the organic acid root in the organic acid salt fermentation liquid is 0.5-3.0mol / L; the pH value of the organic acid salt fermentation liquid is 5-10; the acid used in the acid chamber comprises any one or a combination of at least two of hydrochloric acid, nitric acid or sulfuric acid; the molar concentration of the acid used in the acid chamber is 0.5-3.5mol / L; and the dialysis membrane comprises a monovalent selective cation exchange membrane.

[0046] Compared with the prior art, the method provided by the application has at least the following beneficial effects: the method provided by the application directly converts the organic acid salt fermentation liquid into organic acid and inorganic salt by using a specific ion migration medium, the removal rate of inorganic cations can reach more than 96%, the membrane flux is >2.7mol / m 2 / h, and the recovery rate of the organic acid can reach 95% and above. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 is a schematic diagram of the internal structure of the membrane stack of the cation displacement dialysis device described in the application;

[0048] Figure 2 is a schematic diagram of the separation of lactic acid from ammonium lactate fermentation liquid by using three-stage countercurrent cation displacement dialysis described in the application;

[0049] Figure 3 is a schematic diagram of the separation of organic acid from organic acid salt fermentation liquid by using batch three-stage countercurrent cation displacement dialysis described in the application;

[0050] Figure 4 is a schematic diagram of the separation of organic acid from organic acid salt fermentation liquid by using continuous three-stage countercurrent cation displacement dialysis described in the application;

[0051] In the figure, C represents a dialysis membrane, 1 represents the first stage of cation displacement dialysis, 2 represents the second stage of cation displacement dialysis, and 3 represents the third stage of cation displacement dialysis.

[0052] The salt chamber 1 represents a salt chamber of the first stage of the cation-replacement dialysis, the acid chamber 1 represents an acid chamber of the first stage of the cation-replacement dialysis, the salt chamber 2 represents a salt chamber of the second stage of the cation-replacement dialysis, the acid chamber 2 represents an acid chamber of the second stage of the cation-replacement dialysis, the salt chamber 3 represents a salt chamber of the third stage of the cation-replacement dialysis, and the acid chamber 3 represents an acid chamber of the third stage of the cation-replacement dialysis.

[0053] 1-1 represents a salt chamber cylinder of the first stage of the cation-replacement dialysis, 1-2 represents an acid chamber cylinder of the first stage of the cation-replacement dialysis, 2-1 represents a salt chamber cylinder of the second stage of the cation-replacement dialysis, 2-2 represents an acid chamber cylinder of the second stage of the cation-replacement dialysis, 3-1 represents a salt chamber cylinder of the third stage of the cation-replacement dialysis, and 3-2 represents an acid chamber cylinder of the third stage of the cation-replacement dialysis. DETAILED DESCRIPTION

[0054] In order to better illustrate the present application and facilitate the understanding of the technical solutions of the present application, the typical but non-limiting embodiments of the present application are as follows:

[0055] Embodiment 1

[0056] The embodiment provides a method for separating lactic acid from ammonium lactate fermentation liquor, which comprises the following steps: placing the ammonium lactate fermentation liquor in a salt chamber of a cation-replacement dialysis device to perform cation-replacement dialysis treatment.

[0057] Hydrochloric acid is used as the displacement medium in the acid chamber of the cation-replacement dialysis device, and the molar concentration is 1.5 mol / L.

[0058] The membrane stack of the cation-replacement dialysis device is a plate-type membrane stack.

[0059] The cation-replacement dialysis device is provided with 9 cation dialysis membranes, and a conventional partition plate is arranged between adjacent cation dialysis membranes.

[0060] The concentration of lactate in the ammonium lactate fermentation liquor is 1.33 mol / L, and the pH value of the ammonium lactate fermentation liquor is 7.

[0061] The linear velocity of the ammonium lactate fermentation liquor and the acid liquor in the membrane stack in the cation-replacement dialysis treatment is 1.5 cm / s, and the mode of the cation-replacement dialysis treatment is countercurrent, as shown in Figure 1 . Figure 1 The partition plate is not shown in

[0062] The number of stages of the cation-replacement dialysis treatment is batch three-stage countercurrent, as shown in Figure 3 . The initial volume of the feed liquid of the first-stage salt chamber and the third-stage acid chamber is 2.0 L.

[0063] The feed solution into the salt chamber of the first stage cation displacement dialysis membrane stack is the original ammonium lactate fermentation broth, the lactate concentration of which is 1.33 mol / L, and the ammonium ion concentration is about 1.35 mol / L. When the ammonium ion concentration in the solution of the salt chamber of this stage is reduced to 0.85 mol / L, the solution is pumped into the salt chamber of the second stage cation displacement dialysis membrane stack. When the ammonium ion concentration in the solution of the second stage salt chamber is reduced to 0.4 mol / L, the solution is pumped into the third stage salt chamber. When the ammonium ion concentration in the solution of the third stage salt chamber is reduced to 0.05 mol / L, the cation displacement dialysis operation is stopped.

[0064] The feed solution into the third stage acid chamber is 1.5 mol / L hydrochloric acid. When the ammonium ion concentration in the solution of the third stage acid chamber is increased to 0.48 mol / L, the solution is pumped into the second stage acid chamber. When the ammonium ion concentration in the solution of the second stage acid chamber is increased to 0.9 mol / L, the solution is pumped into the first stage acid chamber.

[0065] The operation temperature of each stage cation displacement dialysis in this embodiment is different. The operation temperature of the first stage is 35-40℃, the operation temperature of the second stage is 20-25℃, and the operation temperature of the third stage is 10-15℃.

[0066] The ammonium ion removal rate of this embodiment is 93%, the average membrane flux of ammonium ion across the cation exchange membrane is 2.6 mol / m 2 / h, the lactate recovery rate is about 95%, the lactate concentration in the end solution of the third stage salt chamber is 1.22 mol / L, and the residual ammonium ion concentration in the end solution of the salt chamber is less than 0.05 mol / L.

[0067] Embodiment 2

[0068] This embodiment provides a method for separating lactate from sodium lactate fermentation broth, which comprises: placing the sodium lactate fermentation broth in the salt chamber of a cation displacement dialysis device for cation displacement dialysis treatment;

[0069] The membrane stack of the cation displacement dialysis device is a plate type membrane stack.

[0070] Sulfuric acid is used as the displacement medium in the acid chamber of the cation displacement dialysis device, and the molar concentration is 2.0 mol / L;

[0071] Twelve dialysis membranes are arranged between the salt chamber and the acid chamber of the cation displacement dialysis device; and a baffle is arranged between adjacent dialysis membranes.

[0072] The number of stages of the cation displacement dialysis treatment is 5 stages;

[0073] The concentration of lactate in the sodium lactate fermentation broth is 2.0 mol / L; and the pH value of the sodium lactate fermentation broth is 6;

[0074] The linear velocity of sodium lactate fermentation broth and acid liquid in the membrane stack in the cation displacement dialysis treatment is 2.5 cm / s, and the cation displacement dialysis treatment mode is countercurrent;

[0075] The cation displacement dialysis treatment has 5 stages, the initial volume of the liquid in the first-stage salt chamber is 2.0 L, and the initial volume of the liquid in the fifth-stage acid chamber is 1.0 L.

[0076] The liquid entering the first-stage cation displacement dialysis membrane stack salt chamber is the original sodium lactate fermentation broth, the lactate ion concentration of which is 2.0 mol / L, and the sodium ion concentration is about 2.05 mol / L. When the sodium ion concentration in the liquid of the salt chamber is reduced to 1.66 mol / L, the liquid in the salt chamber is pumped into the second-stage cation displacement dialysis membrane stack salt chamber. When the sodium ion concentration in the liquid of the second-stage salt chamber is reduced to 1.24 mol / L, the liquid in the salt chamber is pumped into the third-stage salt chamber. When the sodium ion concentration in the liquid of the third-stage salt chamber is reduced to 0.8 mol / L, the liquid in the salt chamber is pumped into the fourth-stage salt chamber. When the sodium ion concentration in the liquid of the fourth-stage salt chamber is reduced to 0.4 mol / L, the liquid in the salt chamber is pumped into the fifth-stage salt chamber. When the sodium ion concentration in the liquid of the fifth-stage salt chamber is less than 0.02 mol / L, the cation displacement dialysis operation is stopped.

[0077] The liquid entering the fifth-stage acid chamber is 2.2 mol / L sulfuric acid. When the sodium ion concentration in the liquid of the fifth-stage acid chamber is increased to 0.78 mol / L, the liquid in the acid chamber is pumped into the fourth-stage acid chamber. When the sodium ion concentration in the liquid of the fourth-stage acid chamber is increased to 1.55 mol / L, the liquid in the acid chamber is pumped into the third-stage acid chamber. When the sodium ion concentration in the liquid of the third-stage acid chamber is increased to 2.36 mol / L, the liquid in the acid chamber is pumped into the second-stage acid chamber. When the sodium ion concentration in the liquid of the second-stage acid chamber is increased to 3.17 mol / L, the liquid in the acid chamber is pumped into the first-stage acid chamber until the cation displacement dialysis is completed.

[0078] The cation displacement dialysis of each stage in this embodiment uses different operating temperatures. The operating temperature of the first stage is 35-40°C, the operating temperature of the second stage is 25-30°C, the operating temperature of the third stage is 15-20°C, the operating temperature of the fourth stage is 10-15°C, and the operating temperature of the fifth stage is 5-10°C.

[0079] The sodium ion removal rate of this embodiment is 96%, the average membrane flux of sodium ions across the cation exchange membrane is 2.7 mol / m 2 / h, the lactic acid recovery rate is about 96.6%, the lactate ion concentration in the liquid at the end of the fifth-stage salt chamber is 1.88 mol / L, and the residual sodium ion concentration in the liquid at the end of the salt chamber is less than 0.03 mol / L.

[0080] Example 3

[0081] The linear velocity of ammonium lactate fermentation broth and acid liquid in the membrane stack of this embodiment is 0.5 cm / s. The operating temperature of the first stage is 36-38℃, the operating temperature of the second stage is 22-23℃, the operating temperature of the third stage is 11-13℃, and three-stage countercurrent treatment is used, as shown in Figure 2 The other operating conditions are the same as in Example 1.

[0082] The ammonium ion removal rate of this embodiment is 92.6%, the average membrane flux of ammonium ions across the cation exchange membrane is 2.1 mol / m 2 / h, the lactic acid recovery rate is about 96%, the lactate concentration in the end liquid of the third stage salt chamber is 1.26 mol / L, and the residual ammonium ion concentration in the end liquid of the salt chamber is less than 0.05 mol / L.

[0083] Example 4

[0084] The linear velocity of ammonium lactate fermentation broth and acid liquid in the membrane stack of this embodiment is 5.0 cm / s. The operating temperature of the first stage is 35℃, the operating temperature of the second stage is 19℃, the operating temperature of the third stage is 8℃, and three-stage continuous countercurrent treatment is used, as shown in Figure 4 The other operating conditions are the same as in Example 1.

[0085] The ammonium ion removal rate of this embodiment is 93.8%, the average membrane flux of ammonium ions across the cation exchange membrane is 2.9 mol / m 2 / h, the lactic acid recovery rate is about 97%, the lactate concentration in the end liquid of the third stage salt chamber is 1.27 mol / L, and the residual ammonium ion concentration in the end liquid of the salt chamber is about 0.045 mol / L.

[0086] Example 5

[0087] This embodiment provides a method for separating citric acid from ammonium citrate fermentation broth, which comprises: the method comprises: placing the ammonium citrate fermentation broth in the salt chamber of a cation displacement dialysis device for cation displacement dialysis treatment;

[0088] The membrane stack of the cation displacement dialysis device is a plate-type membrane stack.

[0089] Sulfuric acid is used as the displacement medium in the acid chamber of the cation displacement dialysis device, and the molar concentration is 2.0 mol / L;

[0090] Twelve dialysis membranes are arranged between the salt chamber and the acid chamber of the cation displacement dialysis device; and a partition plate is arranged between adjacent dialysis membranes.

[0091] The number of stages of the cation displacement dialysis treatment is 5 stages.

[0092] The concentration of citrate in the ammonium citrate fermentation liquor is 1.15 mol / L; the pH value of the ammonium citrate fermentation liquor is 7.6;

[0093] The linear velocity of the ammonium citrate fermentation liquor and the acid liquor in the membrane stack in the cation displacement dialysis treatment is 3.0 cm / s, and the mode of the cation displacement dialysis treatment is countercurrent.

[0094] The number of stages of the cation displacement dialysis treatment is 5, the volume of the initial liquor in the first-stage salt chamber is 2.0 L, and the volume of the initial liquor in the fifth-stage acid chamber is 1.0 L.

[0095] The liquor entering the first-stage cation displacement dialysis membrane stack salt chamber is the original ammonium citrate fermentation liquor, the concentration of citrate in which is 1.15 mol / L, and the concentration of ammonium ion is about 3.45 mol / L; when the concentration of ammonium ion in the liquor of the salt chamber is reduced to 2.80 mol / L, the liquor of the salt chamber is pumped into the second-stage cation displacement dialysis membrane stack salt chamber; when the concentration of ammonium ion in the liquor of the second-stage salt chamber is reduced to 2.1 mol / L, the liquor of the salt chamber is pumped into the third-stage salt chamber; when the concentration of ammonium ion in the liquor of the third-stage salt chamber is reduced to 1.4 mol / L, the liquor of the salt chamber is pumped into the fourth-stage salt chamber; when the concentration of ammonium ion in the liquor of the fourth-stage salt chamber is reduced to 0.7 mol / L, the liquor of the salt chamber is pumped into the fifth-stage salt chamber; when the concentration of ammonium ion in the liquor of the fifth-stage salt chamber is lower than 0.04 mol / L, the cation displacement dialysis operation is stopped.

[0096] The liquor entering the fifth-stage acid chamber is 2.0 mol / L sulfuric acid; when the concentration of ammonium ion in the liquor of the fifth-stage acid chamber is increased to 1.35 mol / L, the liquor of the acid chamber is pumped into the fourth-stage acid chamber; when the concentration of ammonium ion in the liquor of the fourth-stage acid chamber is increased to 2.69 mol / L, the liquor of the acid chamber is pumped into the third-stage acid chamber; when the concentration of ammonium ion in the liquor of the third-stage acid chamber is increased to 4.96 mol / L, the liquor of the acid chamber is pumped into the second-stage acid chamber; when the concentration of ammonium ion in the liquor of the second-stage acid chamber is increased to 5.33 mol / L, the liquor of the acid chamber is pumped into the first-stage acid chamber until the cation displacement dialysis is completed.

[0097] The cation displacement dialysis of each stage in the embodiment adopts different operation temperatures; the operation temperature of the first stage is 35-40℃, the operation temperature of the second stage is 25-30℃, the operation temperature of the third stage is 15-20℃, the operation temperature of the fourth stage is 10-15℃, and the operation temperature of the fifth stage is 5-10℃.

[0098] The ammonium ion removal rate of the embodiment is 97%, and the average membrane flux of ammonium ion across the cation exchange membrane is 3.6 mol / m 2The concentration of citric acid in the end liquid of the fifth salt chamber is 1.08 mol / L, and the concentration of ammonium ion in the end liquid of the salt chamber is less than 0.04 mol / L.

[0099] Example 6

[0100] The method for separating succinic acid from a succinic acid sodium fermentation liquor comprises the following steps: placing the succinic acid sodium fermentation liquor in a salt chamber of a cation displacement dialysis device to perform cation displacement dialysis treatment;

[0101] Hydrochloric acid is used as the displacement medium in the acid chamber of the cation displacement dialysis device, and the molar concentration is 2.2 mol / L.

[0102] The membrane stack of the cation displacement dialysis device is a plate-type membrane stack.

[0103] The cation displacement dialysis device is provided with 9 cation dialysis membranes, and a conventional spacer is arranged between adjacent cation dialysis membranes.

[0104] The concentration of succinate in the succinic acid sodium fermentation liquor is 0.51 mol / L, and the pH value of the succinic acid sodium fermentation liquor is 7.

[0105] The linear velocity of the succinic acid sodium fermentation liquor and the acid liquid in the membrane stack during the cation displacement dialysis treatment is 2.0 cm / s, and the cation displacement dialysis treatment is performed in a countercurrent manner, as shown in Figure 1 . Figure 1 The spacer is not shown in

[0106] The number of stages of the cation displacement dialysis treatment is 3, as shown in Figure 3 , the volume of the initial feed liquid of the first salt chamber is 2.0 L, and the volume of the initial feed liquid of the third acid chamber is 1.0 L.

[0107] The feed liquid entering the salt chamber of the first cation displacement dialysis membrane stack is the original succinic acid sodium fermentation liquor, the concentration of succinate in the feed liquid is 0.51 mol / L, and the concentration of sodium ions is about 1.02 mol / L. When the concentration of sodium ions in the feed liquid of the first salt chamber is reduced to 0.71 mol / L, the feed liquid of the first salt chamber is pumped into the salt chamber of the second cation displacement dialysis membrane stack. When the concentration of sodium ions in the feed liquid of the second salt chamber is reduced to 0.33 mol / L, the feed liquid of the second salt chamber is pumped into the third salt chamber. When the concentration of sodium ions in the feed liquid of the third salt chamber is reduced to 0.04 mol / L, the cation displacement dialysis operation is stopped.

[0108] The feed liquid entering the third acid chamber is 2.2 mol / L hydrochloric acid. When the concentration of sodium ions in the feed liquid of the third acid chamber is increased to 0.68 mol / L, the feed liquid of the third acid chamber is pumped into the second acid chamber. When the concentration of sodium ions in the feed liquid of the second acid chamber is increased to 1.35 mol / L, the feed liquid of the second acid chamber is pumped into the first acid chamber.

[0109] The cation displacement dialysis of each stage in the embodiment adopts different operating temperatures, the operating temperature of the first stage is 35-40℃, the operating temperature of the second stage is 20-25℃, and the operating temperature of the third stage is 10-15℃.

[0110] The sodium ion removal rate of the embodiment is 94%, the average membrane flux of sodium ion across the cation exchange membrane is 2.8 mol / m 2 / h, the recovery rate of succinic acid is about 96%, the concentration of succinate in the end-point liquid of the salt chamber of the third stage is 0.45 mol / L, and the concentration of residual sodium ion in the end-point liquid of the salt chamber is less than 0.04 mol / L.

[0111] Embodiment 7

[0112] The embodiment provides a method for separating gluconic acid from sodium gluconate fermentation liquor, and the method comprises the following steps: placing the sodium gluconate fermentation liquor in a salt chamber of a cation displacement dialysis device to perform cation displacement dialysis treatment;

[0113] The membrane stack of the cation displacement dialysis device is a plate-type membrane stack.

[0114] Hydrochloric acid is used as the displacement medium in the acid chamber of the cation displacement dialysis device, and the molar concentration is 1.6 mol / L;

[0115] Twelve dialysis membranes are arranged between the salt chamber and the acid chamber of the cation displacement dialysis device; and a baffle is arranged between adjacent dialysis membranes.

[0116] The number of stages of the cation displacement dialysis treatment is five;

[0117] The concentration of gluconate in the sodium gluconate fermentation liquor is 1.48 mol / L; and the pH value of the sodium gluconate fermentation liquor is 6.0;

[0118] The linear velocity of the sodium gluconate fermentation liquor and the acid liquid in the membrane stack in the cation displacement dialysis treatment is 2.0 cm / s, and the mode of the cation displacement dialysis treatment is countercurrent.

[0119] The number of stages of the cation displacement dialysis treatment is five, the volume of the initial feed liquid of the salt chamber of the first stage is 2.0 L, and the volume of the initial feed liquid of the acid chamber of the fifth stage is 2.0 L.

[0120] The feed solution into the first stage cation displacement dialysis membrane stack salt chamber is the original sodium gluconate fermentation broth, the gluconate concentration of which is 1.48 mol / L, and the sodium ion concentration is about 1.47 mol / L. When the sodium ion concentration in the solution of the salt chamber of this stage is reduced to 1.18 mol / L, the solution is pumped into the salt chamber of the second stage cation displacement dialysis membrane stack; when the sodium ion concentration in the solution of the second stage salt chamber is reduced to 0.9 mol / L, the solution is pumped into the third stage salt chamber; when the sodium ion concentration in the solution of the third stage salt chamber is reduced to 0.62 mol / L, the solution is pumped into the fourth stage salt chamber; when the sodium ion concentration in the solution of the fourth stage salt chamber is reduced to 0.31 mol / L, the solution is pumped into the fifth stage salt chamber; when the sodium ion concentration in the solution of the fifth stage salt chamber is less than 0.04 mol / L, the cation displacement dialysis operation is stopped.

[0121] The feed solution into the fifth stage acid chamber is 1.6 mol / L hydrochloric acid; when the sodium ion concentration in the solution of the fifth stage acid chamber is increased to 0.32 mol / L, the solution is pumped into the fourth stage acid chamber; when the sodium ion concentration in the solution of the fourth stage acid chamber is increased to 0.64 mol / L, the solution is pumped into the third stage acid chamber; when the sodium ion concentration in the solution of the third stage acid chamber is increased to 0.92 mol / L, the solution is pumped into the second stage acid chamber; when the sodium ion concentration in the solution of the second stage acid chamber is increased to 1.2 mol / L, the solution is pumped into the first stage acid chamber, until the cation displacement dialysis is completed.

[0122] The cation displacement dialysis of each stage in this embodiment uses different operating temperatures; the operating temperature of the first stage is 35-40°C, the operating temperature of the second stage is 25-30°C, the operating temperature of the third stage is 15-20°C, the operating temperature of the fourth stage is 10-15°C, and the operating temperature of the fifth stage is 5-10°C.

[0123] The sodium ion removal rate of this embodiment is 96.6%, the average membrane flux of sodium ion across the cation exchange membrane is 4.4 mol / m 2 / h, the glucose acid recovery rate is about 94.9%, the gluconate concentration in the solution of the fifth stage salt chamber at the end point is 1.35 mol / L, and the residual sodium ion concentration in the solution of the salt chamber at the end point is less than 0.04 mol / L.

[0124] Comparative Example 1

[0125] This comparative example does not use a staged operation; the operating temperature of the cation displacement dialysis is room temperature 25°C, and the linear velocity of the sterilized and decolorized fermentation broth and the acid solution in the membrane stack is 0.01 cm / s. Other operating conditions are the same as in Example 1.

[0126] The ammonium ion removal rate of this comparative example is 82%, the average membrane flux of ammonium ion across the cation exchange membrane is 1.4 mol / m 2The lactic acid recovery rate is approximately 90% per hour, the lactate concentration in the final solution of the third-stage salt chamber is 1.0 mol / L, and the residual ammonium ion concentration in the final solution of the salt chamber is less than 0.05 mol / L.

[0127] Comparative Example 2

[0128] This comparative example employed a three-stage dialysis process, with each stage of cation exchange dialysis operating at room temperature (25°C). Other operating conditions were the same as in Example 1.

[0129] In this comparative example, the ammonium ion removal rate was 83%, and the average membrane flux of ammonium ions across the cation exchange membrane was 2.72 mol / m³. 2 The lactic acid recovery rate is approximately 85% per hour. The lactate concentration in the final solution of the third-stage salt chamber is 1.2 mol / L, and the residual ammonium ion concentration in the final solution of the salt chamber is greater than 0.1 mol / L.

[0130] Comparative Example 3

[0131] This comparative example does not employ countercurrent operation. Other operating conditions are the same as in Example 1.

[0132] In this comparative example, the ammonium ion removal rate was 90%, and the average membrane flux of ammonium ions across the cation exchange membrane was 2.4 mol / m. 2 The lactic acid recovery rate is approximately 90% per hour. The lactate concentration in the final solution of the third-stage salt chamber is 1.18 mol / L, and the residual ammonium ion concentration in the final solution of the salt chamber is approximately 0.09 mol / L.

[0133] The results from the above embodiments and comparative examples demonstrate that the method provided by this invention, using a specific dialysis system and a specific ion migration medium, can directly obtain organic acids and inorganic salts. The removal rate of cations corresponding to organic acid salts can reach over 96%, and the membrane flux is >2.7 mol / m³. 2 / h, the recovery rate of organic acids can reach 95% or more.

[0134] The applicant declares that the detailed structural features of the present invention are illustrated through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components selected in the present invention, additions of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0135] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0136] It should be further noted that any technically feasible combination of the various technical features described in the above embodiments is possible, provided that there is no contradiction, and the present application does not make any further statement on the various possible combinations.

[0137] Furthermore, any combination of the various embodiments of the present application is possible, provided that there is no contradiction, and it should be considered as disclosed by the present application.

Claims

1. A method for separating an organic acid from an organic acid salt fermentation broth, characterized by, The method comprises placing the organic acid salt fermentation liquor in a salt chamber of a cation displacement dialysis device for cation displacement dialysis treatment; The cation displacement dialysis device comprises a cation displacement dialysis membrane stack, and a dialysis membrane is arranged in the membrane stack; the dialysis membrane is a cation exchange membrane; The linear velocity of the liquid phase in the cation displacement dialysis membrane stack in the cation displacement dialysis treatment is 0.5-5 cm / s; An acid solution is used as the displacement medium in the acid chamber of the cation displacement dialysis device; The acid used in the acid chamber is selected from any one or a combination of at least two of hydrochloric acid, nitric acid or sulfuric acid; The cation displacement dialysis treatment comprises at least three stages of cation displacement dialysis treatment; The cation displacement dialysis treatment is countercurrent treatment.

2. The method of separating an organic acid from an organic acid salt fermentation broth according to claim 1, wherein, The operating temperatures of different treatment stages in the cation displacement dialysis treatment are different.

3. The method of separating an organic acid from an organic acid salt fermentation broth according to claim 2, wherein, The operating temperature range of different treatment stages in the cation displacement dialysis treatment is 5-45°C.

4. The method of separating an organic acid from an organic acid salt fermentation broth according to claim 2, wherein, The operating temperature of each stage in the cation displacement dialysis treatment decreases with an increase in the number of treatment stages.

5. The method of separating an organic acid from an organic acid salt fermentation broth according to any one of claims 1 to 4, characterized in that, The molar concentration of the organic acid root in the organic acid salt fermentation liquor is 0.5-3.0 mol / L.

6. The method of separating an organic acid from an organic acid salt fermentation broth according to any one of claims 1 to 4, wherein, The pH value of the organic acid salt fermentation liquor is 5-10.

7. The method of separating an organic acid from an organic acid salt fermentation broth according to any one of claims 1 to 4, wherein, The molar concentration of the acid used in the acid chamber is 0.5-3.5 mol / L.

8. The method of separating an organic acid from an organic acid salt fermentation broth according to any one of claims 1 to 4, wherein, The dialysis membrane comprises a monovalent selective cation exchange membrane.

9. The method of separating an organic acid from an organic acid salt fermentation broth according to any one of claims 1 to 4, wherein, The method comprises placing the organic acid salt fermentation liquor in a salt chamber of a cation displacement dialysis device for cation displacement dialysis treatment; The cation displacement dialysis device comprises a cation displacement dialysis membrane stack; The cation displacement dialysis treatment comprises at least three stages of cation displacement dialysis treatment, the operating temperatures of different treatment stages in the cation displacement dialysis treatment are different, the operating temperature of each stage in the cation displacement dialysis treatment is 5-45°C, the operating temperature of each stage in the cation displacement dialysis treatment decreases with an increase in the number of treatment stages, the cation displacement dialysis treatment is countercurrent cation displacement dialysis treatment, and the linear velocity of the liquid phase in the cation displacement dialysis membrane stack in the cation displacement dialysis treatment is 0.5-5 cm / s; An acid solution is used as the displacement medium in the acid chamber of the cation displacement dialysis device; The molar concentration of the organic acid root in the organic acid salt fermentation liquor is 0.5-3.0 mol / L, the pH value of the organic acid salt fermentation liquor is 5-10, the acid used in the acid chamber comprises any one or a combination of at least two of hydrochloric acid, nitric acid or sulfuric acid, the molar concentration of the acid used in the acid chamber is 0.5-3.5 mol / L, and the dialysis membrane comprises a monovalent selective cation exchange membrane.

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