CN101759580B - A method for preparing threonine crystals from threonine fermentation broth - Google Patents

Abstract

The invention relates to a method for preparing threonine crystal by threonine fermentation liquid, comprising the steps of: sterilizing the threonine fermentation liquid, and the carrying out plate-type or tube-type film ultrafiltration, concentration, azeotropic crystallization and other steps to prepare the threonine crystal; and the prepared threonine crystal has the purity of 98.5%, the threonine film ultrafiltration yield of more than 96%, and the azeotropic crystallization yield of more than 95%. The preparation method is an environment-friendly new production technique which has high efficiency, low energy consumption, low cost, simple method and easy popularization.

Description

A method for preparing threonine crystals from threonine fermentation broth

technical field

The invention belongs to the technical field of amino acid separation and purification production, and in particular relates to a method for preparing threonine crystals from threonine fermentation broth.

Background technique

Threonine is an essential amino acid for humans and animals, which can restore human fatigue and promote growth and development. However, the human body and animals cannot synthesize threonine by themselves, and must obtain it from external sources such as food. Therefore, threonine is widely used as a food fortifier, feed additive, pharmaceutical preparation, health care product, etc., with broad application prospects and strong market demand.

The production methods of threonine include protein hydrolysis, synthesis and direct fermentation. Direct fermentation is currently the main method for producing threonine, which has the advantages of low raw material cost and easy large-scale production. The traditional threonine fermentation production includes fermentation culture, bacteria separation, ion exchange, activated carbon decolorization, evaporation concentration, isopoint electrocrystallization, recrystallization and other steps. Among them, bacteria separation, ion exchange, activated carbon decolorization, evaporation concentration, Isoelectric crystallization and recrystallization are key steps in the separation and purification of threonine. Traditional threonine fermentation broth cell separation methods use flocculation and centrifugation, often the cells and other particles are not completely separated, and the quality of the filtrate is poor. The primary crystallization of threonine generally adopts the isoelectric point method, that is, the pH value of the threonine aqueous solution is adjusted to the isoelectric point of threonine 6.16, the threonine gradually crystallizes out, and the crystallization solution is filtered to obtain the crude product of the primary crystallization of threonine. Due to the poor quality of incoming materials, the quality of primary crystallization products often cannot meet the quality standards, and recrystallization must be carried out to ensure product quality. The crystallization method has long steps, low yield, a large amount of crystallization mother liquor, and large amount of sewage discharge. In addition, since threonine is soluble in water, about 7% of threonine remains in the crystallization mother liquor. In order to improve the yield of threonine, the crystallization mother liquor should be recycled, which further reduces the product quality and forms a vicious circle. It is necessary to develop a threonine crystallization method with high yield, high quality, low cost and low pollution.

The patent application CN200610014324.4 of Tianjin University of Science and Technology discloses a method for separating and extracting L-threonine from the fermentation broth. The method uses a metal tubular microfiltration membrane to filter the fermentation broth. Compared with the traditional method, the quality of the filtrate is improved. However, the removal rate of pigment and protein by the microfiltration membrane needs to be improved, and activated carbon decolorization is required to further improve the quality of the feed solution, and the crystallization method still adopts the isoelectric point method of adjusting the pH value of the solution for one crystallization and the ethanol precipitation method for recrystallization twice. method, the crystallization mother liquor still needs to be applied mechanically, therefore, the technology of this method is long, the yield is low, and the crystallization mother liquor discharge volume is big.

The patent application CN200710097998.1 of Changchun Dacheng Industrial Group Co., Ltd. discloses a method for extracting threonine from threonine fermentation broth. This method uses inorganic ceramic membranes to filter the fermentation broth, which can improve the quality of the filtrate, but requires activated carbon for further decolorization; The crystallization method adopts the method of cooling from 70°C to 5°C. The crystallization mother liquor still uses water as the solvent, which has a small dissolving ability for impurities such as pigments. A large amount of threonine is also dissolved in the mother liquor, and the crystallization yield is low. It is necessary to concentrate the crystallization mother liquor for two Secondary crystallization or reuse of mother liquor has disadvantages such as low yield and high energy consumption.

Contents of the invention

The purpose of the present invention is to provide a method for preparing threonine crystals from threonine fermentation broth with high efficiency, low energy consumption and low cost.

The method for preparing threonine crystals from threonine fermentation broth provided by the present invention comprises the following steps:

1) Filtration: The threonine fermentation broth is sterilized and filtered through an ultrafiltration membrane to remove impurities such as bacteria, protein, and macromolecular pigments to obtain a clarified threonine fermentation filtrate;

The ultrafiltration membrane is a plate-type or tube-type membrane separation system, the material of the membrane is an organic polymer, the molecular weight cut-off is 5000-50000MW, the pH value is 0-14, and the operating temperature is controlled at 10-45°C;

The material of the membrane is an organic polymer, including: polycellulose and its derivatives, polycarbonate, polyvinyl chloride, polyvinylidene fluoride, polysulfone, polyacrylonitrile, polyamide, polysulfone amide, Sulfonated polysulfone, cross-linked polyvinyl alcohol, modified acrylic polymer;

2) Concentration: Concentrate the clarified filtrate obtained in step 1) until a concentrated solution with a threonine mass concentration of 20 wt% or more is obtained; adjust the pH value of the concentrated solution to 4.0-8.0 with ammonia water;

Preferably, the mass concentration of threonine in the concentrated solution is 20-25wt%;

Preferably, the pH value of the concentrated solution is adjusted to 5.8-6.3 with ammonia water;

The concentration method is concentrated by evaporation under reduced pressure, concentrated by evaporation under normal pressure or concentrated by nanofiltration;

3) Azeotropic: The concentrated solution of threonine in step 2) is mixed with the entraining agent in a volume ratio of 1:0.3-1:1, and azeotropic crystallization is carried out under stirring until the water content in the mixed solution is reduced to 0.8-15% (calculus moisture content); then cool the mixed solution to 5-20°C, filter out the crystals, wash the crystals with the same entrainer to remove impurities on the crystal surface, and dry to obtain the required threonine Crystals;

The azeotropic crystallization is azeotropic crystallization under reduced pressure or azeotropic crystallization under normal pressure, preferably azeotropic crystallization under reduced pressure;

Described entrainer is the alcohols and/or esters solvent that can form azeotropic system with water;

The alcohol entrainer is straight-chain aliphatic alcohol, branched-chain aliphatic alcohol, cyclic alcohol or their mixtures containing carbon number C2-C8, including: ethanol, n-propanol, isopropanol, n-butanol, isopropanol Butanol, tert-butanol, n-pentanol, n-hexanol, cyclohexanol, n-heptanol, n-octanol, etc., preferably n-butanol;

The ester entraining agent is an ester entraining agent containing carbon number C2-C8, including: ethyl acetate, butyl acetate, etc., preferably butyl acetate;

The entrainer is a mixture of alcohols and esters with carbon number C2-C8.

According to the preparation method of the invention, the purity of the obtained threonine crystals can reach 98.5%, the yield of threonine membrane ultrafiltration can reach more than 96%, and the yield of azeotropic crystallization can reach more than 95%.

The present invention prepares threonine crystals by performing steps such as plate or tubular membrane ultrafiltration, concentration, and azeotropic crystallization after sterilizing the threonine fermentation broth. Compared with the prior art, the present invention has the following advantages:

1) Compared with the method using microfiltration membrane (patent application CN200610014324.4), the present invention adopts plate or tubular membrane ultrafiltration, thereby improving the quality and yield of filtrate, and solving the problem of difficult filtration and quality of threonine fermentation broth. Poor and low yield problems;

2) Compared with the use of isoelectric point crystallization and ethanol precipitation recrystallization (patent application CN200610014324.4) or cooling crystallization (patent application CN200710097998.1), the present invention improves the yield of threonine crystallization through azeotropic crystallization and quality and reduced energy consumption, the purity of the primary crystallization product reaches 98.5%;

Therefore, the preparation method of the present invention is a new green production process with high efficiency, low energy consumption and low cost, and its method is simple and easy to popularize.

Detailed ways

Example 1:

(1) Take 20L of sterilized threonine fermentation broth and add it to the fermentation broth storage tank of the plate ultrafiltration membrane system. Control at 35±5°C, check whether the equipment is in a normal state, start the membrane equipment, control the membrane inlet pressure below 5kg/ ^cm2 , and adjust the membrane inlet and outlet pressure difference at about 2kg/ ^cm2 . The ultrafiltration membrane has different interception rates for substances with different molecular weights, so that impurities such as bacteria, protein, and macromolecular pigments are trapped in the filter residue, and the clarified ultrafiltrate is collected. When the pressure difference between the inlet and outlet is lower than 1kg/ ^cm2 , add an appropriate amount of deionized water. At the end of the filtration, 27 L of threonine ultrafiltrate was obtained, and the ultrafiltration yield reached 96%.

(2) The clarified threonine fermentation filtrate obtained in the previous step was evaporated under reduced pressure until the concentration of threonine was 20 wt%, and the evaporation was stopped, and the pH of the threonine concentrate was adjusted to 6.16 with ammonia water.

(3) The concentrated solution obtained by the previous step and n-butanol (entrainer) are mixed in a volume ratio of 1: 1, and azeotropic crystallization is carried out under stirring until the moisture content in the mixed solution reaches 1-2% (cal. formula water content); then the crystallization solution is cooled to 10°C, the crystals are filtered out and washed with n-butanol to remove impurities on the crystal surface, and dried to obtain the required threonine crystals. The purity of the threonine crystals is 98.5%. Threonine The crystallization yield of acid reaches 95%, and the total yield of threonine reaches 91.2%.

Example 2:

(1) Take 20L of sterilized threonine fermentation liquid and add it to the fermentation liquid storage tank of the tubular ultrafiltration membrane system. The material of the tubular ultrafiltration membrane is polysulfone, the molecular weight cut-off is 30000-50000MW, and the pH value is 5.0. The operating temperature is controlled at 25±5°C, check whether the equipment is in a normal state, start the membrane equipment, control the membrane inlet pressure below 5kg/ ^cm2 , and adjust the membrane inlet and outlet pressure difference at about 2kg/ ^cm2 . The ultrafiltration membrane has different interception rates for substances with different molecular weights, so that impurities such as bacteria, protein, and macromolecular pigments are trapped in the filter residue, and the clarified ultrafiltrate is collected. When the pressure difference between the inlet and outlet is lower than 1kg/ ^cm2 , add an appropriate amount of deionized water. At the end of the filtration, 29 L of threonine ultrafiltrate was obtained, and the ultrafiltration yield reached 96.2%.

(2) The clarified threonine fermentation filtrate obtained in the previous step was evaporated under reduced pressure until the concentration of threonine was 25 wt%, and the evaporation was stopped, and the pH of the threonine concentrate was adjusted to 6.0 with ammonia water.

(3) The concentrated solution obtained in the previous step and isopropanol (entrainer) are mixed in a volume ratio of 1:0.3, and azeotropic crystallization under reduced pressure is carried out under stirring until the water content in the mixed solution reaches 1-2 % (Cat formula moisture content); then the crystallization solution is cooled to 10°C, the crystal is filtered out and washed with isopropanol to remove crystal surface impurities, and dried to obtain the required threonine crystals, the purity of the threonine crystals is 98.6% , the crystallization yield of threonine reaches 95.1%, and the total yield of threonine reaches 91.5%.

Example 3:

(1) Take 20L of sterilized threonine fermentation broth and add it to the fermentation broth storage tank of the plate ultrafiltration membrane system. Control the temperature at about 25±5℃, check whether the equipment is in normal state, start the membrane equipment, control the membrane inlet pressure below 5kg/ ^cm2 , and adjust the membrane inlet and outlet pressure difference at about 2kg/ ^cm2 . The ultrafiltration membrane has different interception rates for substances with different molecular weights, so that impurities such as bacteria, protein, and macromolecular pigments are trapped in the filter residue, and the clarified ultrafiltrate is collected. When the pressure difference between the inlet and outlet is lower than 1kg/ ^cm2 , add an appropriate amount of deionized water. At the end of the filtration, 29 L of threonine ultrafiltrate was obtained, and the ultrafiltration yield reached 96.1%.

(2) Concentrate the clarified threonine fermentation filtrate obtained in the previous step by nanofiltration until the concentration of threonine is 20 wt%, stop concentrating, and adjust the pH of the threonine concentrate to 5.8 with ammonia water.

(3) The concentrate obtained in the previous step and butyl acetate (zeotropic agent) are mixed in a volume ratio of 1:1, and azeotropic crystallization under reduced pressure is carried out under stirring until the water content in the mixed solution reaches 1-2 % (Cat formula moisture content); then the crystallization solution is cooled to 10°C, the crystals are filtered out and washed with butyl acetate to remove impurities on the crystal surface, and dried to obtain the required threonine crystals, the purity of the threonine crystals is 98.5% , the crystallization yield of threonine reached 95.0%, and the total yield of threonine reached 91.3%.

Example 4:

(1) Take 20L of sterilized threonine fermentation liquid and add it to the fermentation liquid storage tank of the tubular ultrafiltration membrane system. The material of the tubular ultrafiltration membrane is polyamide, the molecular weight cut-off is 30000-50000MW, and the pH value is 5.3. The operating temperature is controlled at about 30±5°C, check whether the equipment is in a normal state, start the membrane equipment, control the membrane inlet pressure below 5kg/ ^cm2 , and adjust the pressure difference between the inlet and outlet of the membrane at about 2kg/ ^cm2 . The ultrafiltration membrane has different interception rates for substances with different molecular weights, so that impurities such as bacteria, protein, and macromolecular pigments are trapped in the filter residue, and the clarified ultrafiltrate is collected. When the pressure difference between the inlet and outlet is lower than 1kg/ ^cm2 , add an appropriate amount of deionized water. At the end of the filtration, 29 L of threonine ultrafiltrate was obtained, and the ultrafiltration yield reached 96.2%.

(2) The clarified threonine fermentation filtrate obtained in the previous step was evaporated under reduced pressure until the concentration of threonine was 25 wt%, and the concentration was stopped, and the pH of the threonine concentrate was adjusted to 6.3 with ammonia water.

(3) The concentrate obtained in the previous step and n-butanol/butyl acetate (entrainer) are mixed in a volume ratio of 1: 0.5: 0.5, and carry out azeotropic crystallization under reduced pressure under stirring until the moisture content in the mixed solution is The content reaches 1-2% (calculus moisture content); then the crystallization solution is cooled to 10°C, the crystals are filtered out and washed with n-butanol to remove impurities on the crystal surface, and dried to obtain the desired threonine crystals, threonine crystallization The purity of the method is 98.5%, the crystallization yield of threonine reaches 95.1%, and the total yield of threonine reaches 91.5%.

Claims (7)

1. method that is prepared threonine crystal by threonine fermentation liquid may further comprise the steps:

1) filters: threonine fermentation liquid is entered ultrafiltration membrance filter through sterilization is laggard, remove impurity, the Threonine Fermentation filtrate that obtains clarifying; The ultra-filtration membrane molecular weight cut-off is 5000-50000MW;

2) concentrated: with step 1) clear filtrate that obtains is concentrated, is the above concentrated solution of 20wt% until obtain the Threonine mass concentration; The pH value of regulating concentrated solution with ammoniacal liquor is 4.0-8.0;

The concentrated solution of Threonine 3) azeotropic: with step 2) and entrainer are with volume ratio 1: 0.3-1: 1 ratio is mixed, and under agitation carries out azeotropic crystalization, is 0.8-15% until the moisture content in the mixed solution reduces to the cassette moisture content; Then mixed solution is cooled to 5-20 ℃, leach crystal, to remove the impurity of plane of crystal, drying obtains required threonine crystal body with same entrainer washing crystal;

Described entrainer is the mixture of ethanol, n-propyl alcohol, Virahol, propyl carbinol, isopropylcarbinol, the trimethyl carbinol, Pentyl alcohol, n-hexyl alcohol, hexalin, n-Heptyl alcohol, n-Octanol, ethyl acetate, butylacetate or above-mentioned alcohols and ester class.

2. the method that is prepared threonine crystal by threonine fermentation liquid according to claim 1, it is characterized in that: ultra-filtration membrane described step 1) is the film separating system of board-like or tubular type, the material of film is organic high molecular polymer, and the pH value is 0-14, and service temperature is controlled at 10-45 ℃.

3. the method that is prepared threonine crystal by threonine fermentation liquid according to claim 1 and 2 is characterized in that: the material of the film of ultra-filtration membrane described step 1) is polyvinyl alcohol or the modified acrylic polymer of poly-Mierocrystalline cellulose, polycarbonate, polyvinyl chloride, polyvinylidene difluoride (PVDF), polysulfones, polyacrylonitrile, polymeric amide, polysulfonamides, SPSF, interlinkage.

4. the method that is prepared threonine crystal by threonine fermentation liquid according to claim 1, it is characterized in that: the mass concentration of the Threonine in the concentrated solution described step 2) is 20-25wt%.

5. the method that is prepared threonine crystal by threonine fermentation liquid according to claim 1 is characterized in that: described step 2) to regulate its pH value with ammoniacal liquor be 5.8-6.3 to concentrated solution.

6. the method that is prepared threonine crystal by threonine fermentation liquid according to claim 1 is characterized in that: concentration method described step 2) is that reduction vaporization is concentrated, atmospheric evaporation is concentrated or nanofiltration is concentrated.

7. the method that is prepared threonine crystal by threonine fermentation liquid according to claim 1 is characterized in that: azeotropic crystalization described step 3) is the decompression azeotropic crystalization.