A method for refining and purifying L-lactic acid fermentation liquid

Abstract

The present invention discloses a method for refining and purifying L-lactic acid fermentation broth, comprising the following steps: heating sterilization, flocculation filtration, concentrated acid hydrolysis filtration, activated carbon decolorization, ion exchange, nanofiltration membrane filtration, sequential simulated moving bed, MVR concentration and molecular distillation. The present invention replaces the second ion exchange system with a sequential simulated moving bed after nanofiltration membrane filtration to remove miscellaneous sugars, salts and other organic miscellaneous acids, thereby reducing the amount of heavy phase lactic acid in the molecular distillation process and greatly improving the quality of the finished L-lactic acid product.

Description

Technical Field

[0001] The invention relates to the technical field of lactic acid purification, in particular to a method for refining and purifying L-lactic acid fermentation liquid. Background Art

[0002] Lactic acid, as an important organic acid, is widely present in human body, animals and plants. Lactic acid, lactate and its derivatives are widely used in food, feed, chemical industry and medicine. Recently, poly-L-lactic acid produced by polymerization of L-lactic acid is used as a new material to manufacture biodegradable materials, green packaging materials and household films, which solves the increasingly serious white pollution problem of the environment. It is considered to be the most promising new material in the new century and has a very broad application prospect.

[0003] At present, in most production processes, the purification process after the crude L-lactic acid solution is as follows: the acid solution is first decolorized by activated carbon and then subjected to the first ion exchange to remove polyvalent ions, then the low molecular weight sugars and polyvalent ions are removed by nanofiltration membrane, and finally the second ion exchange and molecular distillation are carried out in sequence to remove impurities. This process has the advantages of easy control and simple equipment requirements, but the product extraction rate is low and the purity is not high. The reasons for the low extraction rate and low purity of lactic acid are: the sugars, pigments, polyvalent ions and other organic acids in the fermentation broth cannot be effectively removed, which greatly affects the yield and purity of lactic acid; the sugar removal is not sufficient during the refining process, resulting in residual sugar or other reducing substances in the finished lactic acid, affecting the product quality. Summary of the invention

[0004] In order to solve the deficiencies mentioned in the above background technology, the purpose of the present invention is to provide a method for refining and purifying L-lactic acid fermentation broth, which uses a sequential simulated moving bed to replace the second ion exchange system after nanofiltration membrane filtration to remove miscellaneous sugars, salts and other organic miscellaneous acids, thereby reducing the amount of heavy phase lactic acid in the molecular distillation process and greatly improving the quality of the finished L-lactic acid.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A method for refining and purifying L-lactic acid fermentation broth, comprising the following steps:

[0007] (1) Sterilization by heating: heating the lactic acid fermentation liquid to 80-90° C. to sterilize the fermented milk, adding calcium hydroxide to adjust the pH to 10-12, keeping the temperature and stirring for 15-60 minutes to separate the solid and liquid, and collecting the fermentation clear liquid;

[0008] (2) Flocculation and filtration: Add a flocculant, polyphenylene amide, to the fermentation liquid, let it stand for 1-3 hours, and then filter the mycelium residues by plate and frame filtration to obtain a calcium lactate concentrate;

[0009] (3) Concentration, acid hydrolysis and filtration: The calcium lactate concentrate is concentrated by MVR evaporation, sulfuric acid is added for acid hydrolysis and then filtered by belt type to obtain crude lactic acid;

[0010] (4) Activated carbon decolorization: Use granular activated carbon to decolorize the crude lactic acid, the temperature is controlled at 40-50°C, and the decolorization time is 45-60 minutes;

[0011] (5) Ion exchange: The ion exchange column is composed of a cation column and an anion column connected in series. The above decolorizing solution is subjected to cation exchange and anion exchange in sequence to obtain an ion exchange solution;

[0012] (6) Nanofiltration: Use nanofiltration to remove low molecular weight sugars and multivalent ions in the filtrate to obtain membrane clear solution and membrane concentrate;

[0013] (7) Sequential simulated moving bed: the above-mentioned membrane clear liquid continues to flow into the sequential simulated moving bed device to obtain an extract with a high L-lactic acid content and a residual liquid with a high impurity component;

[0014] (8) MVR concentration: evaporating the extract obtained from the sequential simulated moving bed chromatography separation device until the L-lactic acid concentration is 85%;

[0015] (9) Molecular distillation: Molecular distillation equipment is used to evaporate the low-boiling impurities in the concentrated refined L-lactic acid to obtain a light phase of finished L-lactic acid and a heavy phase of high-impurity lactic acid.

[0016] Further preferably, in step (4), the feeding mode of the granular activated carbon decolorization is low-in and high-out, the residence time of the crude lactic acid in the activated carbon column is 45 min-60 min, and the color value of the obtained decolorized liquid is less than 30 hazen.

[0017] Further preferably, in step (5), the cation column uses a strongly acidic cation exchange resin as a filler, and the anion column uses a weakly basic anion exchange resin as a filler.

[0018] Further preferably, the eluent during sequential simulated moving bed separation is deionized water, the operating temperature is 60°C, the sequential simulated moving bed chromatographic columns are 6 columns, and the different zones of the columns are switched through a dual-channel automatic valve. The stationary phase adsorbent loaded in the column is a weak positive exchange resin, and the feed rate is set to 45.5ml / min-47.5ml / min.

[0019] Further preferably, in step (7), after passing through the sequential simulated moving bed, the extract obtained has an ion content of calcium ion ≤2ppm, magnesium ion ≤1ppm, sodium ion ≤1ppm, sulfate ion ≤2ppm, chloride ion ≤2ppm, chromaticity <15hazen, and total sugar content ≤80ppm.

[0020] Beneficial effects of the present invention:

[0021] The present invention replaces the second ion exchange system with a sequential simulated moving bed (SSMB) after nanofiltration membrane filtration to remove sugars, salts and other organic acids, thereby reducing the amount of heavy phase lactic acid in the molecular distillation process. Currently, the amount of L-lactic acid in the heavy phase lactic acid generally accounts for 15-30% of the L-lactic acid feed in short-path distillation. The process flow of the present application not only reduces the amount of this part to less than 10%, but also greatly improves the quality of the finished L-lactic acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described below in conjunction with the accompanying drawings.

[0023] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0024] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are within the scope of protection of the present invention.

[0025] Example 1

[0026] like Figure 1 As shown, a method for refining and purifying L-lactic acid fermentation broth comprises the following steps:

[0027] S1: Pretreatment of L-lactic acid fermentation broth

[0028] (1) Sterilization by heating: heating the lactic acid fermentation liquid to 80° C. to sterilize the fermented milk, adding calcium hydroxide to adjust the pH to 11.5, keeping the temperature and stirring for 60 min to separate the solid and liquid, and collecting the fermentation clear liquid;

[0029] (2) Flocculation and filtration: Add the flocculant polybenzene amide to the fermentation liquid, let it stand for 2 hours, and then filter the mycelium residue by plate and frame filtration to obtain a calcium lactate concentrate;

[0030] S2: L-lactic acid extraction

[0031] (1) The fermentation supernatant containing calcium L-lactate is concentrated, and the concentrated material temperature is controlled at 76.5° C. to obtain a fermentation supernatant concentrate.

[0032] (2) Adding concentrated sulfuric acid to the fermentation supernatant to carry out double decomposition reaction, the pH value of the acidolysis solution is controlled at 1.8, and the acidolysis temperature is controlled at 85° C. The acidolysis solution obtained by the double decomposition reaction contains L-lactic acid and calcium sulfate.

[0033] (3) The acid hydrolysis solution is subjected to solid-liquid separation through a belt filter to obtain calcium sulfate solid, and the obtained acid hydrolysis filtration clear liquid is processed into the next step.

[0034] S3: L-lactic acid refining

[0035] (1) Activated carbon decolorization: Use granular activated carbon to decolorize the crude lactic acid, the temperature is controlled at 45°C, and the decolorization time is 60 minutes;

[0036] (2) Ion exchange: The ion exchange column is composed of a cation column and an anion column connected in series. The decolorizing solution is subjected to cation exchange and anion exchange in sequence to obtain an ion exchange solution. The cation column uses a strongly acidic cation exchange resin as a filler, and the anion column uses a weakly basic anion exchange resin as a filler.

[0037] (3) Nanofiltration: Use nanofiltration to remove low molecular weight sugars and multivalent ions in the filtrate to obtain membrane clear solution and membrane concentrate;

[0038] (4) Sequential simulated moving bed (SSMB): The above membrane supernatant continues to flow into the sequential simulated moving bed device to obtain an extract with a high L-lactic acid content and a residual liquid with a high impurity component. The SSMB separation conditions and parameters are as follows: the eluent is deionized water, the operating temperature is 60°C, the simulated moving bed chromatographic column is 6 columns, and the columns are switched in different zones through a dual-channel automatic valve. The stationary phase adsorbent filled in the column is a weak positive exchange resin, and the feed rate is set to 46.0 ml / min;

[0039] (5) MVR concentration: evaporating the extract obtained from the sequential simulated moving bed chromatography separation device until the L-lactic acid concentration is 85%;

[0040] (6) Molecular distillation: Molecular distillation equipment is used to evaporate low-boiling impurities in the concentrated refined L-lactic acid to obtain high-purity L-lactic acid with an L-lactic acid content of 99.5%, which can be used to produce polylactic acid or as high-purity food-grade lactic acid.

[0041] Example 2

[0042] A method for refining and purifying L-lactic acid fermentation broth, comprising the following steps:

[0043] S1: Pretreatment of L-lactic acid fermentation broth

[0044] (1) Sterilization by heating: Heat the lactic acid fermentation liquid to 85° C. to sterilize the fermented milk, add calcium hydroxide to adjust the pH to 10, keep warm and stir for 15 min to separate the solid and liquid, and collect the fermentation clear liquid;

[0045] (2) Flocculation and filtration: Add the flocculant polybenzene amide to the fermentation liquid, let it stand for 1 hour, and then filter the mycelium residue by plate and frame filtration to obtain a calcium lactate concentrate;

[0046] S2: L-lactic acid extraction

[0047] (1) The fermentation supernatant containing calcium L-lactate is concentrated, and the concentrated material temperature is controlled at 75° C. to obtain a fermentation supernatant concentrate.

[0048] (2) Adding concentrated sulfuric acid to the fermentation liquid concentrate for double decomposition reaction, the pH value of the acid hydrolyzate is controlled at 1.5, and the acid hydrolysis temperature is controlled at 75° C. The acid hydrolyzate obtained by the double decomposition reaction contains L-lactic acid and calcium sulfate.

[0049] (3) The acid hydrolysis solution is subjected to solid-liquid separation through a belt filter to obtain calcium sulfate solid, and the obtained acid hydrolysis filtration clear liquid is processed into the next step.

[0050] S3: L-lactic acid refining

[0051] (1) Activated carbon decolorization: Use granular activated carbon to decolorize the crude lactic acid, the temperature is controlled at 40°C, and the decolorization time is 45 minutes;

[0052] (2) Ion exchange: The ion exchange column is composed of a cation column and an anion column connected in series. The decolorizing solution is subjected to cation exchange and anion exchange in sequence to obtain an ion exchange solution. The cation column uses a strongly acidic cation exchange resin as a filler, and the anion column uses a weakly basic anion exchange resin as a filler.

[0053] (3) Nanofiltration: Use nanofiltration to remove low molecular weight sugars and multivalent ions in the filtrate to obtain membrane clear solution and membrane concentrate;

[0054] (4) Sequential simulated moving bed (SSMB): The above membrane supernatant continues to flow into the sequential simulated moving bed device to obtain an extract with a high L-lactic acid content and a residual liquid with a high impurity component. The SSMB separation conditions and parameters are as follows: the eluent is deionized water, the operating temperature is 60°C, the simulated moving bed chromatographic column is 6 columns, and the columns are switched in different zones through a dual-channel automatic valve. The stationary phase adsorbent filled in the column is a weak positive exchange resin, and the feed rate is set to 45.5 ml / min;

[0055] (5) MVR concentration: evaporating the extract obtained from the sequential simulated moving bed chromatography separation device until the L-lactic acid concentration is 85%;

[0056] (6) Molecular distillation: Molecular distillation equipment is used to evaporate low-boiling impurities in the concentrated refined L-lactic acid to obtain high-purity L-lactic acid with an L-lactic acid content of 98.0%, which can be used to produce polylactic acid or as high-purity food-grade lactic acid.

[0057] Example 3

[0058] like Figure 1 As shown, a method for refining and purifying L-lactic acid fermentation broth comprises the following steps:

[0059] S1: Pretreatment of L-lactic acid fermentation broth

[0060] (1) Sterilization by heating: Heat the lactic acid fermentation liquid to 90° C. to sterilize the fermented milk, add calcium hydroxide to adjust the pH to 12, keep warm and stir for 40 min to separate the solid and liquid, and collect the fermentation clear liquid;

[0061] (2) Flocculation and filtration: Add the flocculant polybenzene amide to the fermentation liquid, let it stand for 3 hours, and then filter the mycelium residue by plate and frame to obtain a calcium lactate concentrate;

[0062] S2: L-lactic acid extraction

[0063] (1) The fermentation supernatant containing calcium L-lactate is concentrated, and the concentrated material temperature is controlled at 80° C. to obtain a fermentation supernatant concentrate.

[0064] (2) Adding concentrated sulfuric acid to the fermentation supernatant to carry out double decomposition reaction, the pH value of the acidolysis solution is controlled at 2.0, and the acidolysis temperature is controlled at 90° C. The acidolysis solution obtained by the double decomposition reaction contains L-lactic acid and calcium sulfate.

[0065] (3) The acid hydrolysis solution is subjected to solid-liquid separation through a belt filter to obtain calcium sulfate solid, and the obtained acid hydrolysis filtration clear liquid is processed into the next step.

[0066] S3: L-lactic acid refining

[0067] (1) Activated carbon decolorization: The crude lactic acid was decolorized with granular activated carbon, the temperature was controlled at 50°C, and the decolorization time was 55 min;

[0068] (2) Ion exchange: The ion exchange column is composed of a cation column and an anion column connected in series. The decolorizing solution is subjected to cation exchange and anion exchange in sequence to obtain an ion exchange solution. The cation column uses a strongly acidic cation exchange resin as a filler, and the anion column uses a weakly basic anion exchange resin as a filler.

[0069] (3) Nanofiltration: Use nanofiltration to remove low molecular weight sugars and multivalent ions in the filtrate to obtain membrane clear solution and membrane concentrate;

[0070] (4) Sequential simulated moving bed (SSMB): The above membrane supernatant continues to flow into the sequential simulated moving bed device to obtain an extract with a high L-lactic acid content and a residual liquid with a high impurity component. The SSMB separation conditions and parameters are as follows: the eluent is deionized water, the operating temperature is 60°C, the simulated moving bed chromatographic column is 6 columns, and the columns are switched in different zones through a dual-channel automatic valve. The stationary phase adsorbent filled in the column is a weak positive exchange resin, and the feed rate is set to 47.5 ml / min;

[0071] (5) MVR concentration: evaporating the extract obtained from the sequential simulated moving bed chromatography separation device until the L-lactic acid concentration is 85%;

[0072] (6) Molecular distillation: Molecular distillation equipment is used to evaporate low-boiling impurities in the concentrated refined L-lactic acid to obtain high-purity L-lactic acid with an L-lactic acid content of 99.0%, which can be used to produce polylactic acid or as high-purity food-grade lactic acid.

[0073] Comparative Example 1

[0074] The conventional lactic acid refining process is used to prepare high-purity L-lactic acid, which includes the following steps:

[0075] S1: Pretreatment of L-lactic acid fermentation broth

[0076] (1) Sterilization by heating: heating the lactic acid fermentation liquid to 80° C. to sterilize the fermented milk, adding calcium hydroxide to adjust the pH to 11.5, keeping the temperature and stirring for 60 min to separate the solid and liquid, and collecting the fermentation clear liquid;

[0077] (2) Flocculation and filtration: Add the flocculant polybenzene amide to the fermentation liquid, let it stand for 2 hours, and then filter the mycelium residue by plate and frame filtration to obtain a calcium lactate concentrate;

[0078] S2: L-lactic acid extraction

[0079] (1) The fermentation supernatant containing calcium L-lactate is concentrated, and the concentrated material temperature is controlled at 76.5° C. to obtain a fermentation supernatant concentrate.

[0080] (2) Adding concentrated sulfuric acid to the fermentation supernatant to carry out double decomposition reaction, the pH value of the acidolysis solution is controlled at 1.8, and the acidolysis temperature is controlled at 85° C. The acidolysis solution obtained by the double decomposition reaction contains L-lactic acid and calcium sulfate.

[0081] (3) The acid hydrolysis solution is subjected to solid-liquid separation through a belt filter to obtain calcium sulfate solid, and the obtained acid hydrolysis filtration clear liquid is processed into the next step.

[0082] S3: L-lactic acid refining

[0083] (1) Activated carbon decolorization: Use granular activated carbon to decolorize the crude lactic acid, the temperature is controlled at 45°C, and the decolorization time is 60 minutes;

[0084] (2) Ion exchange: The ion exchange column is composed of a cation column and an anion column connected in series. The decolorizing solution is subjected to cation exchange and anion exchange in sequence to obtain an ion exchange solution. The cation column uses a strongly acidic cation exchange resin as a filler, and the anion column uses a weakly basic anion exchange resin as a filler.

[0085] (3) Nanofiltration: Use nanofiltration to remove low molecular weight sugars and multivalent ions in the filtrate to obtain membrane clear solution and membrane concentrate;

[0086] (4) The nanofiltration membrane clear liquid enters the second ion exchange column in the continuous ion exchange system for secondary ion exchange. Similarly, the second ion exchange column is composed of a cation column and an anion column connected in series, wherein the cation column and the anion column can be arranged in parallel in multiples, wherein the cation column uses a strongly acidic cation exchange resin as a filler, and the anion column uses a weakly alkaline anion exchange resin as a filler. The nanofiltration membrane clear liquid is sequentially subjected to cation exchange and anion exchange to obtain a secondary ion exchange liquid, and the secondary ion exchange can remove a small amount of enriched ions and impurities.

[0087] (5) MVR concentration: evaporating the extract obtained from the sequential simulated moving bed chromatography separation device until the L-lactic acid concentration is 85%;

[0088] (6) Molecular distillation: Molecular distillation equipment is used to evaporate low-boiling impurities in the concentrated refined L-lactic acid to obtain high-purity L-lactic acid with an L-lactic acid content of 97.5%, which can be used to produce polylactic acid or as high-purity food-grade lactic acid.

[0089] Data Detection

[0090] The parameters in the L-lactic acid refining process and the quality test of the lactic acid product in Examples 1-3 and the comparative example were tested, and the impurity contents before and after molecular distillation were tested respectively, and the data obtained were shown in Tables 1 and 2 below:

[0091] Table 1 Comparison of impurity contents before molecular distillation

[0092]

[0093] Table 2 Comparison of impurity contents after molecular distillation

[0094]

[0095] As can be seen from Table 1-2, Examples 1-3 of the present invention use a sequential simulated moving bed instead of the second ion exchange process, and use chromatographic separation technology to remove sugars, salts and other organic acids, thereby improving the yield of the overall process and obtaining better product quality, so that the purity of the final product L-lactic acid reaches 99.6%, which meets the quality requirements of L-lactic acid as a PLA raw material.

[0096] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0097] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A method for refining and purifying L-lactic acid fermentation broth, It is characterized in that The following steps are involved: (1) Sterilization by heating: heating the lactic acid fermentation broth to 80-90° C. to sterilize the fermentation broth, adding calcium hydroxide to adjust the pH to 10-12, keeping the temperature and stirring for 15-60 minutes to separate the solid and liquid, and collecting the fermentation clear liquid; (2) Flocculation and filtration: Add the flocculant polybenzene amide to the fermentation liquid, let it stand for 1-3 hours, and then filter the mycelium residue by plate and frame to obtain a calcium lactate concentrate; (3) Concentration, acid hydrolysis and filtration: The calcium lactate concentrate is concentrated by MVR evaporation, sulfuric acid is added for acid hydrolysis, and then crude lactic acid is obtained by belt filtration; (4) Activated carbon decolorization: Use granular activated carbon to decolorize the crude lactic acid, the temperature is controlled at 40-50°C, and the decolorization time is 45-60 minutes; (5) Ion exchange: The ion exchange column is composed of a cation column and an anion column connected in series. The decolorizing solution is subjected to cation exchange and anion exchange in sequence to obtain an ion exchange solution; (6) Nanofiltration: Use nanofiltration to remove low molecular weight sugars and multivalent ions in the filtrate to obtain membrane clear solution and membrane concentrate; (7) Sequential simulated moving bed: the above-mentioned membrane clear liquid continues to flow into the sequential simulated moving bed device to obtain an extract with a high L-lactic acid content and a residual liquid with a high impurity component; (8) MVR concentration: evaporating the extract obtained from the sequential simulated moving bed chromatography separation device until the L-lactic acid concentration is greater than 85 wt %; (9) Molecular distillation: using molecular distillation equipment to evaporate low-boiling impurities in the concentrated refined L-lactic acid to obtain a light phase of finished L-lactic acid and a heavy phase of high-impurity lactic acid; The eluent for the sequential simulated moving bed separation is deionized water, the operating temperature is 55-65°C, the sequential simulated moving bed chromatographic columns are 6 columns, and the columns are switched in different zones through a dual-channel automatic valve. The stationary phase adsorbent filled in the columns is a weak positive exchange resin, and the feed rate is set to 45.5ml / min-47.5ml / min; The extract obtained after the sequential simulated moving bed in step (7) has an ion content of calcium ion ≤2ppm, magnesium ion ≤1ppm, sodium ion ≤1ppm, sulfate ion ≤2ppm, chloride ion ≤2ppm, chromaticity <15hazen, and total sugar content ≤80ppm.

2. The method for refining and purifying L-lactic acid fermentation broth according to claim 1, It is characterized in that In the step (4), the granular activated carbon decolorization feeding mode is low in and high out, the residence time of the crude lactic acid in the activated carbon column is 45min-60min, and the color value of the obtained decolorized liquid is less than 30hazen.

3. The method for refining and purifying L-lactic acid fermentation broth according to claim 1, It is characterized in that In the step (5), the cation column of the ion exchange uses a strongly acidic cation exchange resin as a filler, and the anion column uses a weakly basic anion exchange resin as a filler.

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