A method for purifying L-lactic acid fermentation broth

Abstract

The application discloses a kind of L-lactic acid fermentation liquor's refining purification method, belongs to lactic acid purification technical field, its technical core is in plate and frame filtration process, take part of fermentation liquor, add filter aid one to it first, then the initial filtrate obtained with filter aid two synergistic effect on the remaining fermentation liquor, secondary filtration is carried out, to form two-stage efficient filtration system, so that different filter aid plays a role for corresponding stage's filtrate characteristics, can significantly reduce the discharge of plate and frame filter residue, obtain high yield L-lactic acid product.The technical scheme of the present application not only improves the extraction quality of target product, but also realizes the double promotion of environmental and economic benefits by reducing the discharge of filter residue, providing a feasible technical path for the optimization of lactic acid purification process.

Description

Technical Field

[0001] This invention relates to the field of lactic acid purification technology, specifically a method for refining and purifying L-lactic acid fermentation broth. Background Technology

[0002] Lactic acid, recognized globally as one of the three major organic acids, has been widely used in many important fields such as food, medicine, cosmetics and chemicals due to its unique chemical properties and excellent performance.

[0003] The industrial production of L-lactic acid in my country mainly employs the calcium salt fermentation method. The fermentation broth obtained using this method has a complex composition, containing various impurities such as bacteria, residual sugars, proteins, pigments, colloids, organic acids, and inorganic salts. Currently, plate and frame filtration is the primary method for solid-liquid separation. To address the problems of high viscosity, small bacterial cells, and slow filtration rates in the fermentation broth, adding filter aids is an effective treatment method. However, traditional filtration methods and conventional filter aids, such as filter cotton, asbestos fiber, fine silica gel, and activated carbon, generate large amounts of plate and frame filter residue, which is extremely difficult to dispose of. These problems place enormous pressure on the environment and have become a bottleneck hindering the sustainable development of the lactic acid industry.

[0004] Therefore, how to improve the filtration performance and filtrate quality of lactic acid fermentation broth, and effectively reduce the amount and cost of filter residue, is a technical problem that urgently needs to be solved in the current industrial production of L-lactic acid. Summary of the Invention

[0005] Therefore, the present invention provides a purification method for L-lactic acid fermentation broth, which can effectively improve the filtration performance of lactic acid fermentation broth, significantly reduce the slag discharge rate, and greatly increase the lactic acid yield.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for purifying L-lactic acid fermentation broth includes the following steps:

[0008] S1. The lactic acid fermentation broth is heated and then subjected to alkalization and flocculation treatment, filtered, and a pretreated broth is obtained.

[0009] S2. Weigh out a portion of the pretreatment liquid, which is 5-10% of the weight of the lactic acid fermentation broth. Add filter aid one to it and perform plate and frame filtration to obtain the initial filtrate.

[0010] S3. Add the initial filtrate and filter aid II to the remaining pretreatment liquid, and perform plate and frame filtration to obtain coarse filtrate;

[0011] S4. The coarse filtrate is sequentially filtered through a membrane filter, concentrated and crystallized, and then acid-hydrolyzed to obtain the final product, L-lactic acid.

[0012] The above scheme can be summarized as follows: pretreatment → primary filtration (establishing a high-quality filter layer) → main filtration (optimization using primary filtrate) → deep purification, optimizing the fermentation broth treatment process in stages. In the solid-liquid separation (plate and frame filtration) stage, the filtration efficiency is effectively improved and the total amount of filter cake is reduced by circulating the primary filtrate and adding filter aids in stages, while simultaneously improving the quality of the filtrate. Filtering filter aid one with a portion of the pretreatment liquid (5-10%, primary filtration) forms a loose pre-coating layer, which acts as a sieving and bridging agent, protecting the filter cloth and retaining solid substances. The primary filtrate, a pre-purified clear liquid, is mixed into the pretreatment liquid to be treated and acts as a "filter initiator," reducing the overall viscosity, solid content, and impurity concentration of the liquid, effectively improving its filtration characteristics. Thus, the primary filtrate and "filter aid two" work together to form a uniform, highly permeable filter cake, preventing filter layer clogging and improving the total filtration throughput and filtrate quality.

[0013] Furthermore, filter aid one is perlite; filter aid two is a mixture of perlite and diatomaceous earth.

[0014] In the above scheme, perlite is used as "filter aid one," while a mixture of perlite and diatomaceous earth is used as "filter aid two." Utilizing the physical properties of these two filter aids, combined with a two-stage plate and frame filtration process (primary and coarse filtration), a gradient optimization of the filtration process can be achieved. Perlite, being irregularly granular, is used as "filter aid one" for a small portion of filtration (5-10%, primary filtration). This creates a rigid, loose, and highly permeable porous filter bed framework. The resulting filter cake not only reduces the load on subsequent coarse filtration but also prevents filter media from clogging the filter cloth, effectively reducing the total amount of filter cake. Based on the initial filtration, overall filtration (coarse filtration) is carried out. Perlite continues to maintain the high porosity and flow channels of the filter layer, while diatomaceous earth, with its huge specific surface area and microporous structure, exerts a strong adsorption effect, effectively trapping colloids, smaller particles (down to 0.1-1 micrometers) and some pigments and high molecular weight proteins that were not removed in the first step. This fixes the fine impurities that were originally difficult to trap into the filter cake skeleton. At the same time, the filter aid particles are evenly distributed in the filter cake, which is equivalent to adding countless tiny "filtration units", which can expand the effective filtration area, further promote solid-liquid separation, trap impurities, and allow the effective components in the filtrate to pass through smoothly, thereby improving the overall quality of the filtered clear liquid.

[0015] Furthermore, the filter aid 2 is a mixture of perlite and diatomaceous earth in a mass ratio of 1.8-2.2:1.

[0016] In the above scheme, by controlling the mass ratio of perlite and diatomaceous earth, the complementary advantages of the two can be achieved. The filter cake formed by perlite has a porosity of up to 80%-90%, which can construct a loose, highly permeable skeleton structure, mainly acting as a "bridging" agent to ensure high flow rate. Diatomaceous earth has a unique microporous structure and a larger specific surface area, with strong adsorption capacity, mainly acting as an "adsorption" agent, effectively trapping smaller particles and ensuring extremely high clarity of the filtrate. The specific combination of the two can achieve the best balance between filtration speed and filtration precision, allowing the coarse particles of perlite to open fast channels for the fluid, while the fine particles of diatomaceous earth fill the gaps and deeply adsorb impurities.

[0017] Furthermore, the preparation process of filter aid two includes the following steps:

[0018] A1. Place perlite in a carboxymethyl cellulose solution, soak it thoroughly, and then filter it to obtain wet perlite material;

[0019] A2. Thoroughly mix wet perlite with diatomaceous earth to obtain diatomaceous earth-coated perlite, i.e., filter aid two.

[0020] In the above scheme, the preparation process of "Filter Aid II" is an innovative surface modification process. It's not simply a physical mixture of perlite and diatomaceous earth; instead, it uses carboxymethyl cellulose solution as a binder to firmly and uniformly coat the diatomaceous earth onto the surface of the perlite particles, resulting in a composite filter aid with unique structure and properties. This effectively improves the dispersibility of diatomaceous earth, producing a synergistic effect of "1+1>2". This coated composite filter aid reduces the phenomenon of "earth runoff." Diatomaceous earth, being a fine-grained material, can be used in combination with coarse-grained perlite to form a filter aid with alternating coarse and fine particles. This makes the mixed filter cake structure loose and stable, effectively improving filtration quality, reducing the total amount of filter cake, and increasing product yield. Simultaneously, it effectively avoids the stratification or segregation that may occur between different particles under liquid flow impact and pressure during filtration. The coating structure integrates the "bridging" core and the "adsorption" shell, ensuring that the composite particles possess both functions simultaneously, maintaining the uniformity and stability of the filter cake structure during dynamic filtration.

[0021] Furthermore, the mass ratio of the amount of perlite added in step A1 to the amount of diatomaceous earth added in step A2 is 1.8-2.2:1.

[0022] In the above scheme, perlite forms a highly permeable framework, with approximately twice the mass of diatomite as the core, ensuring that the composite particles have sufficient rigidity, volume, and porosity, providing a basic channel for rapid filtration; diatomite has a huge specific surface area and microporous structure, and strong adsorption capacity. At this mass ratio, the amount of diatomite used is sufficient to form a continuous and effective functional layer on the surface of perlite, which can give full play to its adsorption advantages without causing particle agglomeration or clogging of the pores of perlite itself due to excessive amount.

[0023] Furthermore, in step A1, the mass fraction of the carboxymethyl cellulose solution is 0.2-1.0%.

[0024] In the above scheme, the mass fraction range of 0.2-1.0% gives the carboxymethyl cellulose solution a moderate viscosity and film-forming property, which can effectively wet and adhere to perlite, without affecting the pore structure and filtration performance of the filter layer due to excessive concentration.

[0025] Furthermore, the ratio of the amount of filter aid 1 added to the mass of lactic acid fermentation broth is 0.03-0.1:100.

[0026] In the above scheme, an appropriate amount of perlite filter aid can reduce filter cake resistance, prevent filtration channel blockage and a sharp increase in resistance caused by the compressibility of the filter cake, reduce the filtration load in the coarse filtration process, and create favorable conditions for subsequent purification processes. If the amount is too low, an effective filter cake skeleton cannot be formed, resulting in filter media deposition and unclear filtrate. If the amount is too high, it will increase the filter cake thickness and subsequent processing volume.

[0027] Furthermore, the ratio of the amount of filter aid II added to the mass of lactic acid fermentation broth is 0.15-0.25:100.

[0028] In the above scheme, the perlite component continues to maintain the high porosity and flowability of the filter layer, while the diatomaceous earth can efficiently adsorb residual fine particles and colloids. This allows filter aid 2 to exert a strong synergistic effect with filter aid 1 when added in an appropriate amount, effectively reducing the overall amount of filter residue and improving the yield of the final product.

[0029] Furthermore, the alkalization product is calcium hydroxide, and the pH is adjusted to 10-11 during the alkalization process.

[0030] In the above scheme, when the pH is set to 10-11, the lactic acid produced by fermentation can be neutralized and converted into a salt form (calcium lactate) that is easy to process later. At the same time, carboxymethyl cellulose can maintain sufficient viscosity, which helps perlite and diatomite to work together.

[0031] Furthermore, in step S1, the heating temperature of the lactic acid fermentation broth is 80-90℃.

[0032] The above scheme can effectively sterilize and denature proteins while minimizing the adverse effects on the heat-sensitive product L-lactic acid. Under subsequent alkalization conditions, it helps to precipitate flocculants and soluble impurities.

[0033] The technical solution of the present invention achieves the following beneficial technical effects:

[0034] 1. Compared with conventional filtration and filter aids used in traditional calcium salt fermentation methods, this invention significantly reduces the residue rate and effectively improves the lactic acid yield through a segmented optimized process of "pretreatment → primary filtration → main filtration → deep purification," particularly the innovative methods of primary filtrate circulation and step-by-step addition of filter aids. During primary filtration, perlite is used as filter aid one to construct a rigid, loose, and highly permeable porous filter layer framework, effectively protecting the filter cloth and reducing the total amount of filter residue. During main filtration, diatomaceous earth coated with perlite is used as a composite filter aid two, which forms a filter aid with alternating coarse and fine particles. The high porosity of perlite ensures the filtration speed, while the large specific surface area and microporous structure of diatomaceous earth enhance adsorption capacity. This synergistic effect significantly reduces the generation of plate and frame filter residue, thereby reducing the difficulty of filter residue treatment and environmental pressure.

[0035] 2. Through a composite filter aid system composed of perlite and diatomaceous earth, a high-quality filter layer is formed in the primary filtration. In the main filtration, the diatomaceous earth component of filter aid two, with its strong adsorption effect, can effectively retain colloids, small particles, some pigments, and high molecular weight proteins, achieving targeted adsorption and filtration, effectively reducing the total amount of filter residue. The introduction of the primary filtrate reduces the viscosity, solid content, and impurity concentration of the pretreatment liquid, further optimizing the filtration characteristics. This results in a higher lactic acid permeate rate in the final coarse filtrate, laying a good foundation for subsequent deep purification steps such as membrane filtration, concentration, and crystallization, and significantly improving the yield of finished L-lactic acid.

[0036] 3. By controlling the amount of filter aid added and optimizing the mass ratio of perlite and diatomaceous earth and the mass fraction of carboxymethyl cellulose solution in the preparation of filter aid II, the efficient utilization of filter aid was achieved. This not only avoided the problems of insufficient filter aid dosage failing to form an effective filter cake skeleton or excessive dosage increasing the amount of filter residue, but also ensured filtration efficiency and filtrate quality through the synergistic effect of the composite filter aid. Controlling process parameters such as heating temperature and pH effectively sterilizes and promotes protein denaturation, minimizing the adverse effects on L-lactic acid, while also promoting the precipitation of flocculants and dissolved impurities. At the same time, it maintains a suitable viscosity of carboxymethyl cellulose to assist the filter aid in its function, creating favorable conditions for subsequent filtration and purification, and improving the efficiency and reliability of the entire refining and purification process. Detailed Implementation

[0037] Example 1

[0038] A method for purifying L-lactic acid fermentation broth includes the following steps:

[0039] S1. Heat 200t of lactic acid fermentation broth to 85℃, add calcium hydroxide to adjust the pH to 10-11, carry out alkalization and flocculation treatment, filter, and obtain pretreated liquid;

[0040] S2. Take 15t of pretreated liquid, add 100kg of perlite to it, and perform plate and frame filtration to obtain the initial filtrate;

[0041] S3. Add the initial filtrate and 400 kg of filter aid II to the remaining pretreated liquid, and perform plate and frame filtration to obtain coarse filtrate;

[0042] S4. The coarse filtrate is sequentially subjected to membrane filtration, concentration and crystallization, and acid hydrolysis filtration to obtain the finished product L-lactic acid;

[0043] In step S3, the preparation process of filter aid two includes the following steps:

[0044] A1. Place 500 kg of perlite in 2000 kg of carboxymethyl cellulose solution with a mass fraction of 0.5%, soak thoroughly, and then filter to obtain wet perlite material;

[0045] A2. Thoroughly mix wet perlite with 250 kg of diatomaceous earth to obtain diatomaceous earth-coated perlite, i.e., filter aid two.

[0046] Example 2

[0047] A method for purifying L-lactic acid fermentation broth includes the following steps:

[0048] S1. Heat 200t of lactic acid fermentation broth to 80℃, add calcium hydroxide to adjust the pH to 10-11, carry out alkalization and flocculation treatment, filter, and obtain pretreated liquid;

[0049] S2. Take 10t of pretreated liquid, add 60kg of perlite to it, and perform plate and frame filtration to obtain the initial filtrate;

[0050] S3. Add the initial filtrate and 300 kg of filter aid II to the remaining pretreated liquid, and perform plate and frame filtration to obtain coarse filtrate;

[0051] S4. The coarse filtrate is sequentially subjected to membrane filtration, concentration and crystallization, and acid hydrolysis filtration to obtain the finished product L-lactic acid;

[0052] In step S3, the preparation process of filter aid two includes the following steps:

[0053] A1. Place 500 kg of perlite in 2000 kg of carboxymethyl cellulose solution with a mass fraction of 0.2%, soak thoroughly, and then filter to obtain wet perlite material;

[0054] A2. Mix the wet perlite with 277.8 kg of diatomaceous earth to obtain diatomaceous earth-coated perlite, i.e., filter aid two.

[0055] Example 3

[0056] A method for purifying L-lactic acid fermentation broth includes the following steps:

[0057] S1. Heat 200t of lactic acid fermentation broth to 90℃, add calcium hydroxide to adjust the pH to 10-11, carry out alkalization and flocculation treatment, filter, and obtain pretreated liquid;

[0058] S2. Take 20t of pretreated liquid, add 200kg of perlite to it, and perform plate and frame filtration to obtain the initial filtrate;

[0059] S3. Add the initial filtrate and 500 kg of filter aid II to the remaining pretreated liquid, and perform plate and frame filtration to obtain coarse filtrate;

[0060] S4. The coarse filtrate is sequentially subjected to membrane filtration, concentration and crystallization, and acid hydrolysis filtration to obtain the finished product L-lactic acid;

[0061] In step S3, the preparation process of filter aid two includes the following steps:

[0062] A1. Place 500 kg of perlite in 2000 kg of carboxymethyl cellulose solution with a mass fraction of 1.0%, soak thoroughly, and then filter to obtain wet perlite material;

[0063] A2. Mix the wet perlite with 227.3 kg of diatomaceous earth to obtain diatomaceous earth-coated perlite, i.e., filter aid two.

[0064] Example 4

[0065] The only difference between this embodiment and Embodiment 1 is that the filter aid 2 is a mixture of perlite and diatomaceous earth. Specifically:

[0066] A method for purifying L-lactic acid fermentation broth includes the following steps:

[0067] S1. Heat 200t of lactic acid fermentation broth to 85℃, add calcium hydroxide to adjust the pH to 10-11, carry out alkalization and flocculation treatment, filter, and obtain pretreated liquid;

[0068] S2. Take 15t of pretreated liquid, add 100kg of perlite to it, and perform plate and frame filtration to obtain the initial filtrate;

[0069] S3. Add the initial filtrate and 400 kg of filter aid II to the remaining pretreated liquid. Filter aid II is a mixture of 266.7 kg of perlite and 133.3 kg of diatomaceous earth. Perform plate and frame filtration to obtain coarse filtrate.

[0070] S4. The coarse filtrate is sequentially filtered through a membrane filter, concentrated and crystallized, and then acid-hydrolyzed to obtain the final product, L-lactic acid.

[0071] Example 5

[0072] The only difference between this embodiment and Embodiment 1 is that the filter aid 2 is perlite. Details are as follows:

[0073] A method for purifying L-lactic acid fermentation broth includes the following steps:

[0074] S1. Heat 200t of lactic acid fermentation broth to 85℃, add calcium hydroxide to adjust the pH to 10-11, carry out alkalization and flocculation treatment, filter, and obtain pretreated liquid;

[0075] S2. Take 15t of pretreated liquid, add 100kg of perlite to it, and perform plate and frame filtration to obtain the initial filtrate;

[0076] S3. Add the initial filtrate and 400 kg of perlite to the remaining pretreated liquid, and perform plate and frame filtration to obtain coarse filtrate;

[0077] S4. The coarse filtrate is sequentially filtered through a membrane filter, concentrated and crystallized, and then acid-hydrolyzed to obtain the final product, L-lactic acid.

[0078] Comparative Example 1

[0079] The difference between this comparative example and Example 1 is that the filter aid two is a mixture of perlite and diatomaceous earth, and no initial filtration treatment was performed. Specifically:

[0080] A method for purifying L-lactic acid fermentation broth includes the following steps:

[0081] S1. Heat 200t of lactic acid fermentation broth to 85℃, add calcium hydroxide to adjust the pH to 10-11, carry out alkalization and flocculation treatment, filter, and obtain pretreated liquid;

[0082] S2. Add 100 kg of perlite to the pretreatment liquid, mix well, and then add 400 kg of filter aid II, which is a mixture of 266.7 kg of perlite and 133.3 kg of diatomaceous earth. Perform plate and frame filtration to obtain coarse filtrate.

[0083] S3. The coarse filtrate is sequentially filtered through a membrane filter, concentrated and crystallized, and then acid-hydrolyzed to obtain the final product, L-lactic acid.

[0084] Comparative Example 2

[0085] The only difference between this comparative example and Example 1 is that no initial filtration treatment was performed. Specifically:

[0086] A method for purifying L-lactic acid fermentation broth includes the following steps:

[0087] S1. Heat 200t of lactic acid fermentation broth to 85℃, add calcium hydroxide to adjust the pH to 10-11, carry out alkalization and flocculation treatment, filter, and obtain pretreated liquid;

[0088] S2. Add 100 kg of perlite to the pretreatment liquid, mix well, then add 400 kg of filter aid II, and perform plate and frame filtration to obtain coarse filtrate.

[0089] S3. The coarse filtrate is sequentially subjected to membrane filtration, concentration and crystallization, and acid hydrolysis filtration to obtain the finished product L-lactic acid;

[0090] In step S2, the preparation process of filter aid two includes the following steps:

[0091] A1. Place 500 kg of perlite in 2000 kg of carboxymethyl cellulose solution with a mass fraction of 0.5%, soak thoroughly, and then filter to obtain wet perlite material;

[0092] A2. Thoroughly mix wet perlite with 250 kg of diatomaceous earth to obtain diatomaceous earth-coated perlite, i.e., filter aid two.

[0093] In the above embodiments and comparative examples, the lactic acid fermentation broth, perlite, and diatomaceous earth were provided by the Henan Provincial Lactic Acid Engineering Technology Research Center.

[0094] Proof of effectiveness

[0095] After treating the lactic acid fermentation broth according to the methods described in Examples 1-5 and Comparative Examples 1-2, the slag discharge rate (drying treatment) and lactic acid yield were tested. The specific test results are shown in Table 1.

[0096] Table 1

[0097]

[0098] As can be seen from Examples 1-5 and Comparative Examples 1-2, and in conjunction with the data in Table 1, after treating the lactic acid fermentation broth using the methods described in Examples 1-5, the sludge discharge rate does not exceed 4.3%, and the lactic acid yield reaches over 83.4%. The test results are significantly better than those of the comparative examples, indicating that the purification method for L-lactic acid fermentation broth provided by this invention can effectively improve the filtration performance of the lactic acid fermentation broth. At the same time, the preferred scheme of this invention (Examples 1-3) has a sludge discharge rate of no more than 3.3% and a lactic acid yield of over 84.9%, which can significantly reduce the sludge discharge rate and greatly improve the lactic acid yield.

[0099] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of the claims of this patent application.

Claims

1. A method for purifying L-lactic acid fermentation broth, characterized in that, Includes the following steps: S1. The lactic acid fermentation broth is heated and then subjected to alkalization and flocculation treatment to obtain a pretreated solution; S2. Weigh out a portion of the pretreatment liquid, based on 5-10% of the weight of the lactic acid fermentation broth, add filter aid one to it, and perform plate and frame filtration to obtain the initial filtrate. S3. Add the initial filtrate and filter aid II to the remaining pretreatment liquid, and perform plate and frame filtration to obtain coarse filtrate; S4. The coarse filtrate is sequentially filtered through a membrane filter, concentrated and crystallized, and then acid-hydrolyzed to obtain the final product, L-lactic acid.

2. The method for purifying L-lactic acid fermentation broth according to claim 1, characterized in that, Filter aid one is perlite; filter aid two is a mixture of perlite and diatomaceous earth.

3. The method for purifying L-lactic acid fermentation broth according to claim 2, characterized in that, Filter aid 2 is a mixture of perlite and diatomaceous earth in a mass ratio of 1.8-2.2:

1.

4. The method for purifying L-lactic acid fermentation broth according to claim 2, characterized in that, The preparation process of filter aid two includes the following steps: A1. Place perlite in a carboxymethyl cellulose solution, soak it thoroughly, and then filter it to obtain wet perlite material; A2. Thoroughly mix wet perlite with diatomaceous earth to obtain diatomaceous earth-coated perlite, i.e., filter aid two.

5. The method for purifying L-lactic acid fermentation broth according to claim 4, characterized in that, The mass ratio of perlite added in step A1 to diatomite added in step A2 is 1.8-2.2:

1.

6. The method for purifying L-lactic acid fermentation broth according to claim 5, characterized in that, In step A1, the mass fraction of the carboxymethyl cellulose solution is 0.2-1.0%.

7. The method for purifying L-lactic acid fermentation broth according to claim 4, characterized in that, The ratio of the amount of filter aid 1 added to the mass of lactic acid fermentation broth is 0.03-0.1:

100.

8. The method for purifying L-lactic acid fermentation broth according to claim 4, characterized in that, The ratio of the amount of filter aid II added to the mass of lactic acid fermentation broth is 0.15-0.25:

100.

9. The method for purifying L-lactic acid fermentation broth according to claim 4, characterized in that, The alkalization treatment material is calcium hydroxide, and the pH is adjusted to 10-11 during the alkalization process.

10. The method for purifying L-lactic acid fermentation broth according to claim 1, characterized in that, In step S1, the heating temperature of the lactic acid fermentation broth is 80-90℃.

Images