A method for separating lactic acid from kitchen waste lactic acid fermentation liquid

Abstract

The present invention relates to a method for separating lactic acid from food waste lactic acid fermentation liquid, comprising the following steps: (1) passing the food waste lactic acid fermentation liquid through a microfiltration membrane to obtain a microfiltration retentate and a microfiltration permeate, and further passing the microfiltration permeate through an ultrafiltration membrane to obtain an ultrafiltration permeate and an ultrafiltration retentate; (2) the ultrafiltration permeate enters an electric regeneration ion exchanger for treatment to obtain high-purity lactic acid, wherein the electric regeneration ion exchanger comprises a membrane stack and polar chambers on both sides of the membrane stack, wherein the membrane units of the membrane stack are sequentially arranged by a bipolar membrane, a cation exchange membrane, a bipolar membrane, an anion exchange membrane, and a bipolar membrane, and are spaced apart to form an alkali chamber, a cation exchange resin chamber, an anion exchange resin chamber, and an acid chamber. The present invention combines a membrane separation method with an ion exchange adsorption-electrochemical regeneration integrated device to purify lactic acid in food waste fermentation liquid, with a high impurity removal rate, thereby obtaining lactic acid of high purity and high recovery rate. The entire process realizes a closed-loop cycle, shortens the reaction time, realizes resource utilization, and meets the production requirements of green environmental protection.

Description

Technical Field

[0001] The present invention relates to the technical field of organic solid waste resource utilization, and in particular to a method for separating lactic acid from kitchen waste lactic acid fermentation liquid. Background Art

[0002] Lactic acid is one of the most commonly used organic acids in daily life and a key biochemical product, widely used in the food, beverage, daily chemical, pharmaceutical, petrochemical, textile, and tobacco industries. Furthermore, its polymer, polylactic acid (PLA), is a biodegradable plastic favored as a raw material for modern medical materials due to its excellent biocompatibility. Consequently, lactic acid enjoys significant market demand both domestically and internationally. Industrial production of lactic acid typically utilizes microbial fermentation. However, the complex composition of lactic acid fermentation broth, which contains not only the target lactic acid but also a significant amount of bacterial cells, proteins, carbohydrates, acetic acid, and inorganic salts, makes its extraction difficult and costly.

[0003] The traditional method for separating lactic acid from fermentation broth is the "calcium salt method". The disadvantage of this method is that the solubility of calcium lactate is relatively high, which leads to product loss in the crystallization step, low lactic acid recovery rate, and the production of calcium sulfate waste residue with a high impurity content, which affects the quality of the lactic acid product. In addition, a large amount of acid and alkali is consumed, causing serious environmental pollution. The process flow is complicated, the operation is time-consuming and labor-intensive, and it is not suitable for large-scale industrial applications. The prior art also reports the use of membrane separation, ion exchange adsorption, and electrodialysis to separate lactic acid from fermentation broth. However, due to the complex composition of the fermentation broth, it is difficult to ensure the purity of lactic acid, and the regeneration of the membrane and resin requires the consumption of a large amount of acid, alkali, and water, which consumes a lot of energy. Therefore, it is necessary to study a lactic acid purification method with higher lactic acid purity and recovery rate, higher impurity removal rate, and higher efficiency and environmental protection. Summary of the Invention

[0004] The object of the present invention is to provide a method for separating lactic acid from food waste lactic acid fermentation broth, comprising the following steps:

[0005] (1) passing the food waste lactic acid fermentation liquid through a microfiltration membrane to obtain a microfiltration retentate and a microfiltration permeate, and then passing the microfiltration permeate through an ultrafiltration membrane to obtain an ultrafiltration permeate and an ultrafiltration retentate;

[0006] (2) The ultrafiltration permeate enters the electric regeneration ion exchanger, which is composed of a membrane stack and polar chambers on both sides of the membrane stack. The membrane units of the membrane stack are arranged in sequence by a bipolar membrane, a cation exchange membrane, a bipolar membrane, an anion exchange membrane, and a bipolar membrane, which are separated to form an alkali chamber, a cation resin chamber, an anion resin chamber, and an acid chamber;

[0007] The ultrafiltration liquid first enters the cation resin chamber, the effluent from the cation resin chamber is then passed into the alkali chamber, and the effluent from the alkali chamber is again sent into the cation resin chamber, circulating between the cation resin chamber and the alkali chamber; the circulation stops when the pH value of the effluent from the cation resin chamber is lower than 3.0;

[0008] The effluent from the cation resin chamber is passed into the anion resin chamber, the effluent from the anion resin chamber is passed into the acid chamber, and the effluent from the acid chamber is again passed into the anion resin chamber, and circulated between the anion resin chamber and the acid chamber; the circulation is stopped when the lactic acid concentration of the effluent from the anion resin chamber is lower than 5 g / L; the effluent from the anion resin chamber is collected and refluxed into the ultrafiltration permeate of step (2);

[0009] (3) Turn on the power supply of the electrically regenerated ion exchanger, introduce pure water into the positive resin chamber and circulate it repeatedly in the positive resin chamber, introduce pure water into the negative resin chamber and circulate it repeatedly in the negative resin chamber, introduce alkali solution into the alkali chamber and circulate it repeatedly in the alkali chamber, introduce lactic acid solution into the acid chamber and circulate it repeatedly in the acid chamber, and regenerate electrically for 1 to 10 hours at an operating voltage of 30 to 40 V, turn off the power supply, collect the water effluent from the acid chamber, and concentrate it in vacuum to obtain the final product.

[0010] In a preferred technical solution of the present invention, the lactic acid concentration in the lactic acid fermentation broth is 30 to 100 g / L, preferably 40 to 90 g / L.

[0011] In a preferred technical solution of the present invention, the acetic acid concentration in the lactic acid fermentation broth is 1 to 10 g / L, preferably 2 to 8 g / L.

[0012] In a preferred technical solution of the present invention, the chloride ion concentration in the lactic acid fermentation broth is 1 to 10 g / L, preferably 2 to 8 g / L.

[0013] In a preferred technical solution of the present invention, the pH of the lactic acid fermentation broth is 5.0-8.0, preferably 6.0-7.0.

[0014] In a preferred technical solution of the present invention, the lactic acid fermentation broth is pretreated to remove oil and bacterial residues, and then subjected to membrane separation treatment.

[0015] In a preferred technical solution of the present invention, the kitchen waste lactic acid fermentation liquid is a fermentation liquid obtained by anaerobic fermentation of kitchen waste by inoculating lactic acid bacteria.

[0016] In a preferred technical solution of the present invention, the microfiltration membrane is made of polyvinylidene fluoride (PVDF) and has a pore size of 0.1 μm.

[0017] In a preferred technical solution of the present invention, the operating pressure of the microfiltration is 0.06-0.12 MPa, and the pH of the lactic acid fermentation liquid is adjusted to 5.0-8.0 before microfiltration.

[0018] In a preferred technical solution of the present invention, the microfiltration retentate is refluxed into the lactic acid fermentation broth.

[0019] In a preferred technical solution of the present invention, the pH of the microfiltration permeate is 5.0-8.0, preferably 6.0-7.0.

[0020] In a preferred technical solution of the present invention, the microfiltration membrane can be cleaned with any one of deionized water, HCl, NaOH, NaClO, or a combination thereof.

[0021] In the preferred technical solution of the present invention, when the membrane flux of microfiltration decreases by 90%, it can be washed with deionized water; under the condition of an operating pressure of 0.10 MPa, reverse washing is performed for 3 minutes; and microfiltration is performed again after the membrane flux is restored.

[0022] In a preferred technical solution of the present invention, the ultrafiltration membrane is any one of a regenerated cellulose (RC) ultrafiltration membrane and a polyethersulfone (PES) ultrafiltration membrane, and has a molecular weight cut-off of 30 to 100 KDa.

[0023] In the preferred technical solution of the present invention, the ultrafiltration operating pressure is 0.080-0.14 MPa, and the pH of the microfiltration permeate is adjusted to 5.0-8.0 before ultrafiltration.

[0024] In a preferred technical solution of the present invention, the ultrafiltration membrane can be cleaned with any one of deionized water, HCl, NaOH, NaClO, or a combination thereof.

[0025] In the preferred technical solution of the present invention, when the ultrafiltration membrane flux is reduced by 90%, it can be cleaned with 1% NaClO. Under the operating pressure of 0.10 MPa, reverse cleaning is performed for 1.5 minutes and forward cleaning is performed for 1.5 minutes. Ultrafiltration can be performed again after the membrane flux is restored.

[0026] In a preferred technical solution of the present invention, the cation exchange resin is a strongly acidic cation exchange resin, preferably any one of type 732, type D001, and type HD-8 resins, or a combination thereof.

[0027] In a preferred technical solution of the present invention, the anion exchange resin is a weakly basic anion exchange resin, preferably any one of D311, D301G, D330, or D330 resins or a combination thereof.

[0028] In a preferred technical solution of the present invention, the alkali solution in step (3) is any one of NaOH and KOH with a concentration of 0.05 to 0.1 mol / L.

[0029] In the preferred technical solution of the present invention, the concentration of the lactic acid solution in step (3) is 0.05-0.1 mol / L.

[0030] In the preferred technical solution of the present invention, the electrical regeneration time in step (3) is 2-8 hours, preferably 4-6 hours.

[0031] In a preferred technical solution of the present invention, the concentration in step (3) is 10-15 times of vacuum decompression concentration.

[0032] In the preferred technical solution of the present invention, in step (3), the effluent from the alkali chamber is collected and can be used as a neutralizing agent and refluxed into the fermentation reaction.

[0033] In a preferred technical solution of the present invention, the purity of lactic acid in the final product is greater than 90%, preferably greater than 95%, and more preferably greater than 97%.

[0034] In a preferred technical solution of the present invention, the recovery rate of lactic acid in the final product is greater than 90%, preferably greater than 92%, and more preferably greater than 95%.

[0035] In a preferred technical solution of the present invention, the acetic acid removal rate in the final product is greater than 85%, preferably greater than 88%, and more preferably greater than 90%.

[0036] In a preferred technical solution of the present invention, the chloride ion removal rate in the final product is greater than 90%, preferably greater than 93%, and more preferably greater than 96%.

[0037] Unless otherwise specified, when the present invention relates to the percentage between liquids, the percentages are volume / volume percentages; when the present invention relates to the percentage between liquids and solids, the percentages are volume / weight percentages; when the present invention relates to the percentage between solids and liquids, the percentages are weight / volume percentages; and the rest are weight / weight percentages.

[0038] Unless otherwise stated, the present invention was tested using the following methods:

[0039] 1. Lactic Acid Detection Method (HPLC, LC-20AT): Centrifuge the sample at 12,000 rpm for 10 minutes. Pass the supernatant through a 0.45 μm filter membrane before entering the liquid chromatography column. Separate the sample using a Shodex Sugar SH1011 liquid chromatography column (8.0 mm × 300 mm) and detect with a RID detector. Chromatographic conditions were: column temperature 60°C; mobile phase 5 mM H2SO4; flow rate 1.0 mL / min; injection volume 10 μL.

[0040] 2. Cl ion measurement method (ion chromatograph, ICS 600): The sample to be tested was centrifuged at 12,000 rpm for 10 minutes. The supernatant was filtered through a 0.22 μm filter and diluted appropriately before entering the ion chromatograph. The sample was separated using a Dionex IonPacAS22 ion chromatography column and detected by a RID detector. Chromatographic conditions were: column temperature, 30°C; mobile phase, 4.5 mM Na₂CO₃ / 1.4 mM NaHCO₃; flow rate, 1.2 mL / min; injection volume, 10 μL.

[0041] 3. Lactic acid purity: Lactic acid mass in final product / final product mass × 100%

[0042] 4. Acetic acid removal rate: (acetic acid mass in lactic acid fermentation broth - acetic acid mass in final product) / acetic acid mass in lactic acid fermentation broth × 100%

[0043] 5. Chloride ion removal rate: (Cl in lactic acid fermentation broth - Quality - Cl in final product - mass) / Cl in lactic acid fermentation broth - Mass × 100%

[0044] 6. Lactic acid recovery rate: Lactic acid mass in the final product / Lactic acid mass in the lactic acid fermentation broth × 100%

[0045] Compared with the prior art, the present invention has the following beneficial technical effects:

[0046] 1. The present invention combines membrane separation with ion exchange adsorption-electrochemical regeneration integrated equipment to purify lactic acid in food waste fermentation broth, with a high impurity removal rate, to obtain lactic acid with high purity and high recovery rate.

[0047] 2. The present invention can realize resin adsorption-electrochemical in-situ regeneration, does not consume acid and alkali chemicals, does not generate waste liquid and waste residue, and only consumes a small amount of electricity and pure water. Lactic acid can be directly decomposed from the resin to obtain a purified liquid. At the same time, the regenerated alkaline solution is reused in the lactic acid fermentation process. The entire process realizes a closed-loop cycle, shortens the reaction time, realizes resource utilization, and meets green and environmentally friendly production requirements.

[0048] 3. The method of the present invention is simple and convenient to operate, has low energy consumption and cost, and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 Schematic diagram of the method for separating lactic acid from kitchen waste lactic acid fermentation broth of the present invention;

[0050] Figure 2 This is a schematic diagram of the electrically regenerated ion exchanger of the present invention, in which BPM is a bipolar membrane, CM is a cathodic membrane, and AM is a cathodic membrane.

[0051] Figure 3 Comparison of various indicators in the final products obtained in Examples 1-4. DETAILED DESCRIPTION

[0052] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0053] Preparation of kitchen waste fermentation liquid of the present invention: Take 3kg of kitchen waste and 3kg of pure water, mix them, crush and grind them, put them into a fermentation tank, inoculate lactic acid bacteria seed liquid at an inoculation rate of 10%, and perform anaerobic fermentation. The fermentation temperature is maintained at 43°C, and the pH is adjusted to 6.8-7.0 with NaOH solution (10mol / L) every 12 hours. After 84 hours of fermentation, the fermentation product is centrifuged to obtain a liquid phase and a solid phase. The liquid phase is then separated into an oil phase through an extraction funnel, and the remainder is the lactic acid fermentation liquid to be separated in the embodiment of the present invention. After testing, the lactic acid fermentation liquid contains 63.9g / L of lactic acid, 2.5g / L of acetic acid, and Cl - 2.4g / L, protein 0.21g / L, total sugar 3.33g / L.

[0054] The lactic acid bacteria seed liquid culture step comprises: Enterococcus mundtii (CGMCC 22227) stored at -80°C is inoculated into a lactic acid bacteria culture medium at a 10% inoculation rate, cultured at 43°C for 12 hours as an activated seed liquid, and then 10% of the activated seed liquid is inoculated into a lactic acid bacteria culture medium, and cultured at 43°C for 9 hours. The lactic acid bacteria culture medium comprises: 10.0 g of peptone, 8.0 g of beef extract, 4.0 g of yeast powder, 20.0 g of glucose, 5.0 g of sodium acetate trihydrate, 2.0 g of triammonium citrate, 1.0 mL of Tween 80, 2.0 g of K2HPO4, 0.2 g of MgSO4.7H2O, and 0.05 g of MnSO4.H2O per liter of deionized water, with a pH of 7.0.

[0055] The double-stage membrane in the embodiment was purchased from FuMA-Tech of Germany. FBM, positive membrane and negative membrane were purchased from Shandong Tianwei Membrane Technology Co., Ltd., and each membrane had an area of ​​7 cm 2 , the effective area is about 95% of the actual area, and the resins are all commercially available.

[0056] Example 1

[0057] (1) 500 mL of lactic acid fermentation broth was adjusted to pH 6.0 and passed through a microfiltration membrane made of polyvinylidene fluoride (PVDF) with a pore size of 0.1 μm and an operating pressure of 0.10 MPa. The microfiltration permeate and microfiltration retentate were collected, and the microfiltration retentate was refluxed into the fermentation reaction;

[0058] (2) adjusting the pH of the microfiltration permeate obtained in step (1) to 6.0, passing the permeate through an ultrafiltration membrane, wherein the ultrafiltration membrane used is a polyethersulfone (PES) ultrafiltration membrane with a molecular weight cutoff of 50 kDa, and the operating pressure is 0.12 MPa to obtain an ultrafiltration permeate and an ultrafiltration retentate, and the ultrafiltration retentate is refluxed into the fermentation reaction;

[0059] (3) feeding the ultrafiltration permeate obtained in step (2) into an electrically regenerated ion exchanger with the power turned off at a flow rate of 8 ml / s, wherein the membrane units in the electrically regenerated ion exchanger are sequentially arranged by a bipolar membrane, a cationic membrane, a bipolar membrane, a cationic membrane, and a bipolar membrane, and the intervals are composed of an alkali chamber, a cationic resin chamber (filled with 732 type strong acid cation exchange resin), an anionic resin chamber (filled with D311 macroporous weakly basic acrylic anion exchange resin), and an acid chamber;

[0060] The ultrafiltration permeate first enters the cation resin chamber (the operating temperature of the cation exchange resin is 25°C), the effluent from the cation resin chamber is then passed into the alkali chamber, and the effluent from the alkali chamber is again sent into the cation resin chamber, circulating between the cation resin chamber and the alkali chamber; the circulation stops when the pH value of the effluent from the cation resin chamber is lower than 3.0;

[0061] The effluent from the cation resin chamber is passed into the anion resin chamber (the operating temperature of the anion exchange resin is 25° C.), the effluent from the anion resin chamber is then passed into the acid chamber, and the effluent from the acid chamber is again passed into the anion resin chamber, circulating between the anion resin chamber and the acid chamber; when the lactic acid concentration of the effluent from the anion resin chamber is lower than 5 g / L, the circulation is stopped; the effluent from the anion resin chamber is collected and refluxed into the ultrafiltration permeate of step (3);

[0062] (4) Turn on the power supply of the electric regeneration ion exchanger, and at a flow rate of 8 ml / s, introduce pure water into the positive resin chamber and circulate it repeatedly in the positive resin chamber, introduce pure water into the negative resin chamber and circulate it repeatedly in the negative resin chamber, introduce a NaOH solution with a concentration of 0.05 mol / L into the alkali chamber and circulate it repeatedly in the alkali chamber, and introduce a lactic acid solution with a concentration of 0.05 mol / L into the acid chamber and circulate it repeatedly in the acid chamber. The electric regeneration is carried out for 6 hours under the condition of an operating voltage of 30 V, and the power is turned off. The water effluent from the acid chamber is collected and distilled and concentrated 13 times under vacuum conditions with the pressure reduced to 2.67 KPa (20 mmHg) to obtain the final product; the water effluent from the alkali chamber can be used as a neutralizer and refluxed into the fermentation reaction. Figure 1-2 .

[0063] Example 2

[0064] (1) 500 mL of lactic acid fermentation broth was adjusted to pH 6.0 and passed through a microfiltration membrane made of polyvinylidene fluoride (PVDF) with a pore size of 0.1 μm and an operating pressure of 0.10 MPa. The microfiltration permeate and microfiltration retentate were collected, and the microfiltration retentate was refluxed into the fermentation reaction;

[0065] (2) adjusting the pH of the microfiltration permeate obtained in step (1) to 6.0, passing the permeate through an ultrafiltration membrane, wherein the ultrafiltration membrane used is a polyethersulfone (PES) ultrafiltration membrane with a molecular weight cutoff of 50 kDa, and the operating pressure is 0.12 MPa to obtain an ultrafiltration permeate and an ultrafiltration retentate, and the ultrafiltration retentate is refluxed into the fermentation reaction;

[0066] (3) feeding the ultrafiltration permeate obtained in step (2) into an electrically regenerated ion exchanger with the power turned off at a flow rate of 8 ml / s, wherein the membrane units in the electrically regenerated ion exchanger are sequentially arranged by a bipolar membrane, a cationic membrane, a bipolar membrane, an anionic membrane, and a bipolar membrane, and the intervals constitute an alkali chamber, a cationic resin chamber (filled with 732 type strong acid cation exchange resin), an anionic resin chamber (filled with D345 macroporous weak alkaline phenolic anion exchange resin), and an acid chamber;

[0067] The ultrafiltration permeate first enters the cation resin chamber (the operating temperature of the cation exchange resin is 25°C), the effluent from the cation resin chamber is then passed into the alkali chamber, and the effluent from the alkali chamber is again sent into the cation resin chamber, circulating between the cation resin chamber and the alkali chamber; the circulation stops when the pH value of the effluent from the cation resin chamber is lower than 3.0;

[0068] The effluent from the cation resin chamber is passed into the anion resin chamber (the operating temperature of the anion exchange resin is 25° C.), the effluent from the anion resin chamber is then passed into the acid chamber, and the effluent from the acid chamber is again passed into the anion resin chamber, circulating between the anion resin chamber and the acid chamber; when the lactic acid concentration of the effluent from the anion resin chamber is lower than 5 g / L, the circulation is stopped; the effluent from the anion resin chamber is collected and refluxed into the ultrafiltration permeate of step (3);

[0069] (4) Turn on the power supply of the electrically regenerated ion exchanger, and introduce pure water into the positive resin chamber at a flow rate of 8 ml / s and circulate it repeatedly in the positive resin chamber, introduce pure water into the negative resin chamber and circulate it repeatedly in the negative resin chamber, introduce a NaOH solution with a concentration of 0.05 mol / L into the alkali chamber and circulate it repeatedly in the alkali chamber, and introduce a lactic acid solution with a concentration of 0.05 mol / L into the acid chamber and circulate it repeatedly in the acid chamber. The electroregeneration is carried out for 6 hours under the condition of an operating voltage of 30 V, and the power supply is turned off. The water effluent from the acid chamber is collected and distilled and concentrated 13 times under vacuum conditions with the pressure reduced to 2.67 kPa (20 mmHg) to obtain the final product; the water effluent from the alkali chamber can be collected and refluxed into the fermentation reaction as a neutralizer.

[0070] Example 3

[0071] (1) 500 mL of lactic acid fermentation broth was adjusted to pH 6.0 and passed through a microfiltration membrane made of polyvinylidene fluoride (PVDF) with a pore size of 0.1 μm and an operating pressure of 0.10 MPa. The microfiltration permeate and microfiltration retentate were collected, and the microfiltration retentate was refluxed into the fermentation reaction;

[0072] (2) adjusting the pH of the microfiltration permeate obtained in step (1) to 6.0, passing the permeate through an ultrafiltration membrane, wherein the ultrafiltration membrane used is a polyethersulfone (PES) ultrafiltration membrane with a molecular weight cutoff of 50 kDa, and the operating pressure is 0.12 MPa to obtain an ultrafiltration permeate and an ultrafiltration retentate, and the ultrafiltration retentate is refluxed into the fermentation reaction;

[0073] (3) The ultrafiltration permeate obtained in step (2) is fed into an electrically regenerated ion exchanger with the power turned off at a flow rate of 8 ml / s, wherein the membrane units in the electrically regenerated ion exchanger are sequentially arranged by a bipolar membrane, a cationic membrane, a bipolar membrane, an anionic membrane, and a bipolar membrane, and the intervals are composed of an alkali chamber, a cationic resin chamber (filled with 732 type strong acid cation exchange resin), an anionic resin chamber (filled with D301G macroporous weak base styrene anion exchange resin), and an acid chamber;

[0074] The ultrafiltration permeate first enters the cation resin chamber (the operating temperature of the cation exchange resin is 25°C), the effluent from the cation resin chamber is then passed into the alkali chamber, and the effluent from the alkali chamber is again sent into the cation resin chamber, circulating between the cation resin chamber and the alkali chamber; the circulation stops when the pH value of the effluent from the cation resin chamber is lower than 3.0;

[0075] The effluent from the cation resin chamber is passed into the anion resin chamber (the operating temperature of the anion exchange resin is 25° C.), the effluent from the anion resin chamber is then passed into the acid chamber, and the effluent from the acid chamber is again passed into the anion resin chamber, circulating between the anion resin chamber and the acid chamber; when the lactic acid concentration of the effluent from the anion resin chamber is lower than 5 g / L, the circulation is stopped; the effluent from the anion resin chamber is collected and refluxed into the ultrafiltration permeate of step (3);

[0076] (4) Turn on the power supply of the electrically regenerated ion exchanger, and introduce pure water into the positive resin chamber at a flow rate of 8 ml / s and circulate it repeatedly in the positive resin chamber, introduce pure water into the negative resin chamber and circulate it repeatedly in the negative resin chamber, introduce a NaOH solution with a concentration of 0.05 mol / L into the alkali chamber and circulate it repeatedly in the alkali chamber, and introduce a lactic acid solution with a concentration of 0.05 mol / L into the acid chamber and circulate it repeatedly in the acid chamber. The electroregeneration is carried out for 6 hours under the condition of an operating voltage of 30 V, and the power supply is turned off. The water effluent from the acid chamber is collected and distilled and concentrated 13 times under vacuum conditions with the pressure reduced to 2.67 kPa (20 mmHg) to obtain the final product; the water effluent from the alkali chamber can be collected and refluxed into the fermentation reaction as a neutralizer.

[0077] Example 4

[0078] (1) 500 mL of lactic acid fermentation broth was adjusted to pH 6.0 and passed through a microfiltration membrane made of polyvinylidene fluoride (PVDF) with a pore size of 0.1 μm and an operating pressure of 0.10 MPa. The microfiltration permeate and microfiltration retentate were collected, and the microfiltration retentate was refluxed into the fermentation reaction;

[0079] (2) adjusting the pH of the microfiltration permeate obtained in step (1) to 6.0, passing the permeate through an ultrafiltration membrane, wherein the ultrafiltration membrane used is a polyethersulfone (PES) ultrafiltration membrane with a molecular weight cutoff of 50 kDa, and the operating pressure is 0.12 MPa to obtain an ultrafiltration permeate and an ultrafiltration retentate, and the ultrafiltration retentate is refluxed into the fermentation reaction;

[0080] (3) The ultrafiltration permeate obtained in step (2) is fed into an electrically regenerated ion exchanger with the power turned off at a flow rate of 8 ml / s, wherein the membrane units in the electrically regenerated ion exchanger are sequentially arranged by a bipolar membrane, a cationic membrane, a bipolar membrane, a cationic membrane, and a bipolar membrane, and the intervals are composed of an alkali chamber, a cationic resin chamber (filled with 732 type strong acid cation exchange resin), an anionic resin chamber (filled with D330 weak basic epoxy anion exchange resin), and an acid chamber;

[0081] The ultrafiltration permeate first enters the cation resin chamber (the operating temperature of the cation exchange resin is 25°C), the effluent from the cation resin chamber is then passed into the alkali chamber, and the effluent from the alkali chamber is again sent into the cation resin chamber, circulating between the cation resin chamber and the alkali chamber; the circulation stops when the pH value of the effluent from the cation resin chamber is lower than 3.0;

[0082] The effluent from the cation resin chamber is passed into the anion resin chamber (the operating temperature of the anion exchange resin is 25° C.), the effluent from the anion resin chamber is then passed into the acid chamber, and the effluent from the acid chamber is again passed into the anion resin chamber, circulating between the anion resin chamber and the acid chamber; when the lactic acid concentration of the effluent from the anion resin chamber is lower than 5 g / L, the circulation is stopped; the effluent from the anion resin chamber is collected and refluxed into the ultrafiltration permeate of step (3);

[0083] (4) Turn on the power supply of the electrically regenerated ion exchanger, and introduce pure water into the positive resin chamber at a flow rate of 8 ml / s and circulate it repeatedly in the positive resin chamber, introduce pure water into the negative resin chamber and circulate it repeatedly in the negative resin chamber, introduce a NaOH solution with a concentration of 0.05 mol / L into the alkali chamber and circulate it repeatedly in the alkali chamber, and introduce a lactic acid solution with a concentration of 0.05 mol / L into the acid chamber and circulate it repeatedly in the acid chamber. The electroregeneration is carried out for 6 hours under the condition of an operating voltage of 30 V, and the power supply is turned off. The water effluent from the acid chamber is collected and distilled and concentrated 13 times under vacuum conditions with the pressure reduced to 2.67 kPa (20 mmHg) to obtain the final product; the water effluent from the alkali chamber can be collected and refluxed into the fermentation reaction as a neutralizer.

[0084] Test Example 1

[0085] The final products obtained in Examples 1-4 were tested for lactic acid purity, lactic acid recovery rate, acetic acid removal rate, Cl - Removal rate, see Figure 3 .

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for separating lactic acid from food waste lactic acid fermentation broth, comprising the following steps: (1) passing the kitchen waste lactic acid fermentation liquid through a microfiltration membrane to obtain a microfiltration retentate and a microfiltration permeate, and further passing the microfiltration permeate through an ultrafiltration membrane to obtain an ultrafiltration permeate and an ultrafiltration retentate; wherein the lactic acid concentration in the lactic acid fermentation liquid is 30 to 100 g / L, the acetic acid concentration is 1 to 10 g / L, and the chloride ion concentration is 1 to 10 g / L; (2) The membrane permeate enters the electrically regenerated ion exchanger, which is composed of a membrane stack and polar chambers on both sides of the membrane stack. The membrane units of the membrane stack are arranged in sequence by a bipolar membrane, a cation exchange membrane, a bipolar membrane, an anion exchange membrane, and a bipolar membrane, which are separated by an alkali chamber, a cation exchange resin chamber, an anion exchange resin chamber, and an acid chamber; The cation exchange resin is a strongly acidic cation exchange resin, The anion exchange resin is a weakly basic anion exchange resin; The ultrafiltration liquid first enters the cation resin chamber, the effluent from the cation resin chamber is then passed into the alkali chamber, and the effluent from the alkali chamber is again sent into the cation resin chamber, circulating between the cation resin chamber and the alkali chamber; the circulation stops when the pH value of the effluent from the cation resin chamber is lower than 3.0; The effluent from the cation resin chamber is passed into the anion resin chamber, the effluent from the anion resin chamber is passed into the acid chamber, and the effluent from the acid chamber is again passed into the anion resin chamber, and circulated between the anion resin chamber and the acid chamber; the circulation is stopped when the lactic acid concentration of the effluent from the anion resin chamber is lower than 5 g / L; the effluent from the anion resin chamber is collected and refluxed into the ultrafiltration permeate of step (2); (3) Turn on the power supply of the electrically regenerated ion exchanger, introduce pure water into the positive resin chamber and circulate it repeatedly in the positive resin chamber, introduce pure water into the negative resin chamber and circulate it repeatedly in the negative resin chamber, introduce alkali solution into the alkali chamber and circulate it repeatedly in the alkali chamber, introduce lactic acid solution into the acid chamber and circulate it repeatedly in the acid chamber, and regenerate electrically for 1 to 10 hours at an operating voltage of 30 to 40 V, turn off the power supply, collect the water effluent from the acid chamber, and concentrate it in vacuum to obtain the final product.

2. The method according to claim 1, wherein The lactic acid concentration in the lactic acid fermentation liquid is 40-90 g / L.

3. The method according to claim 1, wherein The acetic acid concentration in the lactic acid fermentation liquid is 2-8 g / L.

4. The method according to claim 1, wherein The chloride ion concentration in the lactic acid fermentation liquid is 2-8 g / L.

5. The method according to claim 1, wherein The pH of the lactic acid fermentation liquid is 5.0-8.

0.

6. The method according to claim 5, wherein The pH of the lactic acid fermentation liquid is 6.0-7.

0.

7. The method according to claim 1, wherein The lactic acid fermentation liquid is pretreated to remove grease and bacterial residues, and then subjected to membrane separation treatment.

8. The method according to claim 1, wherein The lactic acid fermentation liquid is the fermentation liquid obtained by anaerobic fermentation of kitchen waste by inoculating lactic acid bacteria.

9. The method according to claim 1, wherein The microfiltration membrane is made of polyvinylidene fluoride (PVDF) and has a pore size of 0.1 μm.

10. The method according to claim 1, wherein The operating pressure of the microfiltration is 0.06-0.12 MPa, and the pH of the lactic acid fermentation liquid is adjusted to 5.0-8.0 before microfiltration.

11. The method according to claim 1, wherein The microfiltration retentate is returned to the lactic acid fermentation broth.

12. The method according to claim 1, wherein The pH of the microfiltration permeate is 5.0-8.

0.

13. The method according to claim 12, wherein: The pH of the microfiltration permeate is 6.0-7.

0.

14. The method according to claim 1, wherein The microfiltration membrane can be cleaned with any one of deionized water, HCl, NaOH, NaClO, or a combination thereof.

15. The method according to claim 1, wherein When the membrane flux of microfiltration is reduced by 90%, it can be cleaned with deionized water; under the operating pressure of 0.10MPa, reverse cleaning is performed for 3 minutes; microfiltration can be carried out again after the membrane flux is restored.

16. The method according to claim 1, wherein The ultrafiltration membrane is any one of a regenerated cellulose (RC) ultrafiltration membrane and a polyethersulfone (PES) ultrafiltration membrane, and has a molecular weight cut-off of 30 to 100 KDa.

17. The method according to claim 1, wherein The ultrafiltration operating pressure is 0.080-0.14 MPa, and the pH of the microfiltration permeate is adjusted to 5.0-8.0 before ultrafiltration.

18. The method according to claim 1, wherein The ultrafiltration membrane can be cleaned with any one of deionized water, HCl, NaOH, NaClO, or a combination thereof.

19. The method according to claim 1, wherein When the ultrafiltration membrane flux is reduced by 90%, it can be cleaned with 1% NaClO. Under the operating pressure of 0.10 MPa, reverse cleaning is performed for 1.5 minutes and forward cleaning is performed for 1.5 minutes. Ultrafiltration can be performed again after the membrane flux is restored.

20. The method of claim 1, wherein The cation exchange resin is any one of 732 type, D001 type, HD-8 type resin or a combination thereof.

21. The method according to claim 1, wherein The anion exchange resin is any one of D345, D301G, D311, and D330 resins or a combination thereof.

22. The method of claim 1, wherein The alkali solution in step (3) is any one of NaOH and KOH with a concentration of 0.05 to 0.1 mol / L.

23. The method of claim 1, wherein The concentration of the lactic acid solution in step (3) is 0.05-0.1 mol / L.

24. The method of claim 1, wherein The electrical regeneration time in step (3) is 2 to 8 hours.

25. The method of claim 24, wherein: The electrical regeneration time in step (3) is 4 to 6 hours.

26. The method of claim 1, wherein The concentration in step (3) is 10-15 times of vacuum concentration.

27. The method of claim 1, wherein: In the step (3), the effluent from the alkali chamber is collected and can be used as a neutralizing agent to flow back into the fermentation reaction.

28. The method according to any one of claims 1 to 27, wherein The purity of lactic acid in the final product is greater than 90%.

29. The method of claim 28, wherein The purity of lactic acid in the final product is greater than 95%.

30. The method of claim 29, wherein: The purity of lactic acid in the final product is greater than 97%.

31. The method according to any one of claims 1 to 27, wherein The recovery rate of lactic acid in the final product is greater than 90%.

32. The method of claim 31, wherein The recovery rate of lactic acid in the final product is greater than 92%.

33. The method of claim 32, wherein: The recovery rate of lactic acid in the final product is greater than 95%.

34. The method according to any one of claims 1 to 27, wherein The acetic acid removal rate in the final product is greater than 85%.

35. The method of claim 34, wherein: The acetic acid removal rate in the final product is greater than 88%.

36. The method of claim 35, wherein: The acetic acid removal rate in the final product is greater than 90%.

37. The method according to any one of claims 1 to 27, wherein The chloride ion removal rate in the final product is greater than 90%.

38. The method of claim 37, wherein The chloride ion removal rate in the final product is greater than 93%.

39. The method of claim 38, wherein The chloride ion removal rate in the final product is greater than 96%.

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