CN112679397B - Preparation method of DL-methionine - Google Patents
Preparation method of DL-methionine Download PDFInfo
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Abstract
The invention relates to the field of methionine production, in particular to a preparation method of DL-methionine. In the continuous production process of methionine, the sodium sulfate mother liquor is concentrated to improve the sodium sulfate concentration and reduce the methionine content, the saponification liquid is used for regulating the concentrated mother liquor, the temperature is reduced and crystallization is carried out to obtain high-quality mirabilite, and the crystallization mother liquor is reused in the production process of methionine after impurity removal according to the impurity content in the crystallization mother liquor after mirabilite separation. The crystallization mother liquor can be completely recycled, no waste liquid is generated, and the continuous production process of methionine is ensured, so that impurities are not accumulated due to repeated use of the crystallization mother liquor, and the stability of the quality of methionine is not affected; meanwhile, the precipitation of sodium sulfate byproduct mirabilite reduces the water content in the crystallization mother liquor, and increases the concentration of methionine in the crystallization mother liquor, so that the time cost and the energy cost for concentrating the sodium sulfate mother liquor in the methionine production process are saved.
Description
Technical Field
The invention relates to the field of methionine production, in particular to a preparation method of DL-methionine.
Background
Methionine, also known as methionine, abbreviated Met, is one of the basic units of biosynthetic proteins, also essential and limiting amino acids. Methionine is the only sulfur-containing amino acid in the essential amino acid, and animal ingestion of a small amount can obviously promote growth, shorten feeding period, increase egg and milk yield, and if insufficient ingestion can cause insufficient utilization of other amino acids in the body, the unused amino acid is converted into energy molecules and urea through deamination, and the burden of livers and kidneys is increased. Methionine is not only used in the feed industry, but also widely used in the fields of medicine, food, cosmetics and the like. Chinese is taken as one of a main production area and a main consumption area of methionine, along with gradual release of new productivity of companies such as winning, alumni and the like in 2018-2020, the competition in the methionine industry is more and more intense, and the improvement of the methionine preparation process is particularly important.
One of the main preparation processes of Met in the prior art is a Rona-Planck process, wherein hydrocyanic acid or sodium cyanide is used for preparing 5- (beta-methylthioethyl) hydantoin solution, then hydrolysis and deamination are carried out on sodium alkaline compound to generate saponified solution, sulfuric acid is used for acidizing the saponified solution to separate methionine, sodium sulfate mother liquor containing saturated methionine is repeatedly concentrated at high temperature to saturate sodium sulfate, so that sodium sulfate solid is separated out, and concentrated residual liquid is returned to an acidizing step to complete the preparation of methionine.
On one hand, a large amount of sodium sulfate mother liquor is repeatedly concentrated at high temperature for a long time, so that various chemical reactions can be caused, and malodorous substances are generated to pollute the environment;
on the other hand, 3-methylthio-propanal, 2-acrylic acid and the intermediate of acrolein and the polymer, formate, methionine dipeptide, pigment and other impurities can be accumulated in the treatment process, so that the purity of precipitated sodium sulfate is extremely poor and cannot be recycled, and the concentrated residual liquid also contains a large amount of impurities, so that the quality of the methionine finished product is poor after the concentrated residual liquid is returned to an acidification step, the problem can be solved only by a method for discharging the concentrated residual liquid periodically, and the method is unfavorable for environmental protection and maximization of economic benefit.
In the technical scheme disclosed in publication number CN104693082a, in order to avoid repeated high-temperature concentration of sodium sulfate mother liquor containing methionine, continuous chromatographic separation technology is used to separate methionine and sodium sulfate in the sodium sulfate mother liquor, and high-temperature concentration crystallization is separately performed on the sodium sulfate solution to obtain sodium sulfate byproduct, but the scheme still has the following disadvantages:
1. the concentration of methionine and sodium sulfate solution after chromatographic separation is diluted, so that the concentration cost of the sodium sulfate solution is increased;
2. the chromatographic separation device has very high price and extremely low efficiency for separating methionine from sodium sulfate;
3. the separated sodium sulfate solution contains not only sodium sulfate but also a small amount of other impurities, and the concentration and crystallization mode finally leads to poor purity of sodium sulfate byproducts.
In the technical scheme disclosed in publication number CN106432020B, carbon dioxide is introduced into a saponification liquid to obtain methionine and a potassium bicarbonate aqueous solution containing methionine, and the saponification liquid is treated by removing salts in the potassium bicarbonate aqueous solution using an electrodialysis technique and then recycling the potassium bicarbonate aqueous solution. On the one hand, however, the electrodialysis technology used in the scheme has extremely high electricity consumption and high cost; on the other hand, the methionine interception rate and the desalination rate of the electrodialysis technology are low, and the solution desalination requirement in the industrial production cannot be met; furthermore, the scheme can only remove salt, and cannot remove impurities generated in methionine production, and recycling of methionine solution can cause impurity accumulation, so that the quality of methionine is affected.
In the prior art, a treatment method using ion exchange resin is also used, the saponification liquid is separated into methionine solution and sodium sulfate solution, the methionine solution is crystallized to obtain a product, and the sodium sulfate solution is concentrated at a high temperature to obtain a byproduct.
However, this solution has the following drawbacks:
1. methionine has low solubility, and a large amount of water is required to be added into the saponified solution for dilution, so that a large amount of time and energy are consumed in the subsequent concentration treatment;
2. the ion exchange resin only can separate sodium sulfate, and the intermediate of 3-methylthiopropanal, 2-acrylic acid and acrolein, polymer thereof, formate, methionine dipeptide, pigment and other impurities are mainly remained in methionine solution, so that mother liquor after methionine crystallization is concentrated, and the impurities are accumulated, thereby causing the quality of methionine to be poor;
3. although the sodium sulfate mother liquor contains only a small amount of impurities, concentrating and crystallizing sodium sulfate eventually also leads to poor quality of sodium sulfate byproducts.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a preparation method of DL-methionine, which can not generate discharged wastewater, and avoid the accumulation effect of impurities caused by recycling residual liquid, which affects the quality of methionine finished products and sodium sulfate byproducts; meanwhile, the cost in the methionine preparation process can be reduced.
In order to solve the technical problems, the invention provides the following technical scheme:
a preparation method of DL-methionine comprises the following specific steps:
s100, performing S100; preparing 4-methylthio-2-hydroxybutyronitrile by using hydrocyanic acid and 3-methylthio propanal, generating 5- (beta-methylthioethyl) hydantoin by using 4-methylthio-2-hydroxybutyronitrile to react with ammonia and carbon dioxide, hydrolyzing the 5- (beta-methylthioethyl) hydantoin by using an alkali solution of sodium, and deaminizing to obtain a saponified solution;
s200, performing S200; acidifying the saponified solution, cooling, crystallizing and separating to obtain methionine crystals and sodium sulfate mother liquor;
s300, performing S300; concentrating the sodium sulfate mother liquor, cooling and crystallizing, and then carrying out solid-liquid separation to obtain mixed solid and concentrated mother liquor;
s350, performing operation; returning the mixed solid to the step S200, and dissolving the mixed solid into the saponified solution;
s400, performing S400; adding saponification liquid into the concentrated mother liquor, crystallizing at low temperature, and performing solid-liquid separation to obtain crystallization mother liquor and mirabilite;
s500, performing control; and (3) removing impurities from the crystallization mother liquor, returning the crystallization mother liquor after the impurity removal to the step S200, mixing the crystallization mother liquor with the saponification liquid, and performing acidification again to separate methionine crystals.
Preferably, the specific steps of the step S200 are as follows:
s210, performing S210; heating the saponification liquid at constant temperature to keep the temperature of the saponification liquid at 60-120 ℃, acidifying the saponification liquid by sulfuric acid, keeping the pH value of the acidified saponification liquid at 5-7, and keeping the temperature for 10-30 min to obtain acidified liquid;
s220, performing operation; the temperature of the acidizing fluid is reduced to 35-45 ℃, and the temperature is kept for 20-60 min;
s230, performing S230; and (3) carrying out solid-liquid separation on the acidized liquid to obtain methionine crystals and sodium sulfate mother liquor.
Preferably, the sulfuric acid concentration in the step S210 is 20 to 98wt%.
Preferably, the specific steps of the step S300 are as follows:
s310; heating the sodium sulfate mother liquor to 90-120 ℃ and concentrating under reduced pressure;
s320; the temperature is reduced to 10 to 60 ℃ and kept for 10 to 40 minutes;
s330; and (3) carrying out solid-liquid separation at 35-45 ℃ to obtain mixed solid and concentrated mother liquor.
Preferably, in the step S310, the sodium sulfate mother solution is concentrated under reduced pressure until the sodium sulfate content in the sodium sulfate mother solution is more than 20wt%.
Preferably, the specific steps of the step S400 are as follows: adding saponification liquid into the concentrated mother liquor, wherein the molar ratio of sodium carbonate in the added saponification liquid to methionine in the concentrated mother liquor is 1-2:1, adding the saponification liquid, then adding the concentrated mother liquor, reducing the pH value to be more than or equal to 8, reducing the temperature to-10 ℃, and carrying out solid-liquid separation after preserving the heat for 20-100 min to obtain crystallization mother liquor and mirabilite.
Preferably, in the step S500, before the impurity is removed from the crystallization mother liquor, the impurity content in the crystallization mother liquor is detected, when the ratio of the impurity content to the methionine content in the crystallization mother liquor exceeds 3%, the impurity removal is performed on the crystallization mother liquor, and when the ratio of the impurity content to the methionine content in the crystallization mother liquor does not exceed 3%, the crystallization mother liquor is directly returned to the step S200 to be mixed with the saponification liquid.
Preferably, in the step S500, the crystallization mother liquor is divided into two parts, one part of the crystallization mother liquor is subjected to impurity removal, and the impurity-removed crystallization mother liquor is mixed with the other part of the crystallization mother liquor, and then the mixture is returned to the step S200 to be mixed with the saponification liquid.
Preferably, in the step S500, the specific steps of removing impurities from the crystallization mother liquor are as follows: adding sulfuric acid into the crystallization mother liquor, wherein the pH value of the crystallization mother liquor after adding sulfuric acid is 2-3, standing for 30min at the temperature of 10-40 ℃, separating oil phase impurities and aqueous phase liquid, filtering the aqueous phase liquid to remove solid impurities, and removing formic acid by a stripping method.
Preferably, the concentration of sulfuric acid added in the step S500 for removing impurities from the crystallization mother liquor is 20-98%.
The invention has the beneficial effects that:
1. the invention prepares saponified solution by using raw materials such as hydrocyanic acid, acidizing, cooling and crystallizing the saponified solution, then carrying out solid-liquid separation to obtain methionine crystal and sodium sulfate mother liquor, concentrating and cooling the sodium sulfate mother liquor, separating out part of methionine, sodium sulfate and a small amount of impurities remained in the sodium sulfate mother liquor to form mixed solids, directly dissolving the mixed solids in the saponified solution, acidifying and extracting methionine finished product again, leaving more impurities in the concentrated mother liquor, adding the saponified solution into the concentrated mother liquor, then cooling to separate out sodium sulfate in the concentrated mother liquor in a mirabilite mode, adding sulfuric acid into filtrate (namely crystallization mother liquor) after solid-liquid separation, condensing and separating out oil phase impurities in the crystallization mother liquor from the concentrated mother liquor, and filtering out part of solid impurities separated out in aqueous phase liquor. Thereby completing the removal of impurities generated in the preparation process of DL-methionine, so that the impurities in the continuous preparation process of DL-methionine can not generate accumulation effect, and the quality of methionine is affected.
2. The crystallization mother liquor after impurity removal can also be used as an acidulant of saponification liquid after formic acid is removed by steam stripping, so that the cost of the saponification liquid in the acidulation process is saved, and meanwhile, because a large amount of water is brought out by precipitation of mirabilite, the time and energy of the concentration process of sodium sulfate mother liquor can be saved, and the single extraction rate of methionine can be improved.
3. On one hand, the solubility of methionine and oil phase impurities is relatively high in an alkaline environment, and the quality of mirabilite cannot be influenced in the process of crystallization precipitation of mirabilite; on the other hand, alkaline environments do not create a great deal of corrosiveness to the equipment.
According to the technical scheme provided by the invention, impurities generated in the methionine preparation process can be separated out for treatment, the accumulated effect in the methionine production along with the recycling of the crystallization mother liquor is avoided, the quality of a methionine finished product is reduced, the influence of the impurities on the methionine quality is not required to be reduced by a mode of periodically discharging the crystallization mother liquor, the crystallization mother liquor can be continuously recycled in the methionine production completely, the maximum economic benefit is achieved, and the pollution to the environment is reduced.
Drawings
FIG. 1 is a schematic flow chart of the present invention.
Detailed Description
The invention will be further described with reference to examples and drawings, to which reference is made, but which are not intended to limit the scope of the invention. It will be understood by those skilled in the art that various changes and substitutions of details and forms of the technical solution of the present invention may be made without departing from the spirit and scope of the present invention, but these changes and substitutions fall within the scope of the present invention. The following experimental methods, in which specific conditions are not specified, were conducted under conventional conditions.
Example 1; a preparation method of DL-methionine comprises the following specific steps:
s100, performing S100; preparing 4-methylthio-2-hydroxybutyronitrile by using hydrocyanic acid and 3-methylthio propanal, generating 5- (beta-methylthioethyl) hydantoin by using 4-methylthio-2-hydroxybutyronitrile to react with ammonia and carbon dioxide, hydrolyzing the 5- (beta-methylthioethyl) hydantoin by using an alkali solution of sodium, and deaminizing to obtain a saponified solution;
the specific steps of hydrolyzing 5- (beta-methylthioethyl) hydantoin with sodium alkali solution are as follows:
s110, performing S110; heating 5- (beta-methylthioethyl) hydantoin to 120-200 ℃, and adding sodium alkali solution, wherein the molar ratio of alkaline sodium in the sodium alkali solution to the 5- (beta-methylthioethyl) hydantoin is 1.5-4:1;
s120, performing operation; preserving heat for 10-60 min.
S200, performing S200; acidifying the saponified solution, cooling, crystallizing and separating to obtain methionine crystals and sodium sulfate mother liquor;
s210, performing S210; heating the saponified solution at constant temperature to keep the temperature of the saponified solution at 60-120 ℃, acidifying the saponified solution by using sulfuric acid or using sulfuric acid and mixed solution of the crystallized mother solution obtained in the step S500 after impurity removal, wherein the pH value of the saponified solution after acidification is 5-7, and preserving the temperature for 10-30 min to obtain acidified solution; in actual operation, in order to save time and energy in the subsequent concentration process, the concentration of the sulfuric acid is 20-98wt%.
S220, performing operation; the temperature of the acidizing fluid is reduced to 35-45 ℃, and the temperature is kept for 20-60 min;
s230, performing S230; performing solid-liquid separation on the acidized liquid to obtain methionine crystals and sodium sulfate mother liquor;
according to the precipitation speed and quality of methionine crystals in the mixed mother liquor, the heat preservation time is controlled, so that more methionine crystals can be precipitated under the condition of not wasting time and energy, the precipitated methionine crystals are washed and dried to obtain qualified methionine products, meanwhile, the solubility of sodium sulfate is maximum under the condition of 35-45 ℃, and the solubility of methionine is relatively low, so that the methionine crystals can be separated.
S310; heating the sodium sulfate mother liquor to 90-120 ℃ and concentrating under reduced pressure;
in the concrete implementation, the sodium sulfate mother liquor is concentrated until the sodium sulfate content in the sodium sulfate mother liquor is more than 20 weight percent, so that the sodium sulfate can be more crystallized to form sodium sulfate byproduct mirabilite in the subsequent step.
S320; the temperature is reduced to 10 to 60 ℃ and kept for 10 to 40 minutes;
s330; carrying out solid-liquid separation at 35-45 ℃ to obtain mixed solid and concentrated mother liquor;
s350, performing operation; returning the mixed solid to the step S200, and dissolving the mixed solid into the saponified solution; the mixed solid contains methionine, sodium sulfate and a small amount of impurities, and the mixed solid is redissolved into the saponified solution to further purify the methionine, so that the yield of the methionine is increased.
S400, performing S400; adding saponification liquid into the concentrated mother liquor, crystallizing at low temperature, and performing solid-liquid separation to obtain crystallization mother liquor and mirabilite; the molar ratio of sodium carbonate in the saponified solution to methionine in the concentrated mother solution is 1-2:1, and then the concentrated mother solution is kept at the temperature of minus 10-10 ℃ for 20-100 min and then subjected to solid-liquid separation to obtain crystallization mother solution and mirabilite. The pH value of the concentrated mother liquor after the saponification liquid is added is more than or equal to 8, under the condition, methionine exists in the form of sodium methionine, when the sodium sulfate is subjected to low-temperature crystallization, the methionine cannot be separated out, and meanwhile, oily impurities in the concentrated mother liquor after the saponification liquid is added have larger solubility in an alkaline environment, so that the quality of the separated-out sodium sulfate cannot be influenced.
S500, performing control; detecting the impurity content in the crystallization mother liquor, when the ratio of the impurity content to the methionine content in the crystallization mother liquor exceeds 3%, performing impurity removal on the crystallization mother liquor, and when the ratio of the impurity content to the methionine content in the crystallization mother liquor does not exceed 3%, directly returning the crystallization mother liquor to the step S200 for mixing with the saponification liquid. When the ratio of the impurity content in the crystallization mother liquor to the methionine content is not more than 3%, the influence of the impurity on the methionine crystallization quality is in an acceptable range, the crystallization mother liquor can be directly recycled without impurity removal, the impurity removal cost of the crystallization mother liquor is saved, and the economic benefit is increased.
And in the specific implementation, the crystallization mother liquor is divided into two parts, impurity removal is carried out on one part of the crystallization mother liquor, and the impurity-removed crystallization mother liquor is mixed with the other part of the crystallization mother liquor and then returned to the step S200 to be mixed with the saponification liquor. The ratio of the impurity-removed crystallization mother liquor to the non-impurity-removed crystallization mother liquor may be: 1:9, 2:8, 3:7 or 4:6. Not only ensures the recycling of crystallization mother liquor, but also ensures that impurities are not accumulated in the continuous production process, so that the quality of the produced methionine finished product is stable under the condition that waste water is not discharged in the preparation of methionine; meanwhile, the cost of the impurity removal process can be reduced by partially removing impurities, and the economic benefit of methionine production and preparation is increased.
The specific steps of impurity removal of the crystallization mother liquor are as follows: adding sulfuric acid into the crystallization mother liquor, wherein the pH value of the crystallization mother liquor after adding sulfuric acid is 2-3, standing for 30min at the temperature of 10-40 ℃, layering oily impurities and water in the crystallization mother liquor, standing and separating to obtain aqueous phase liquid and oil phase impurities, wherein the oil phase impurities can be subjected to clean incineration treatment, and meanwhile, a small amount of impurities remained in the aqueous phase liquid can be recrystallized, and one or more of diatomite, silica gel, activated carbon and activated clay are used as additives to filter and remove the impurities. The aqueous phase after filtration is stripped of formic acid, and the saponification agent may be acidified together with sulfuric acid as an acidifying agent. Impurity is removed from the crystallization mother liquor, so that the influence on methionine products is weakened; and simultaneously, the water content in the crystallization mother liquor can be reduced by stripping to remove the formic acid, and the cost of concentrating the sodium sulfate mother liquor in continuous production is reduced. The concentration of sulfuric acid added in the process of removing impurities from the crystallization mother liquor is 20-98wt%.
In the continuous production process of methionine, the sodium sulfate mother liquor is concentrated to increase the concentration of sodium sulfate, partial methionine is separated, the saponification liquor is used for regulating the concentrated mother liquor, the temperature is reduced and crystallization is carried out to obtain high-quality mirabilite, and the crystallization mother liquor is reused in the production process of methionine after impurity removal according to the impurity content in the crystallization mother liquor after the separation of mirabilite. The crystallization mother liquor can be completely recycled, waste liquid containing beneficial components is not generated, and the continuous production process of methionine is ensured, impurities are not accumulated due to repeated use of the crystallization mother liquor, and the stability of the quality of methionine is not affected; meanwhile, the precipitation of sodium sulfate byproduct mirabilite reduces the water content in the crystallization mother liquor, namely increases the concentration of sulfuric acid in the crystallization mother liquor, so that the time cost and the energy cost for concentrating the sodium sulfate mother liquor in the process of producing methionine are saved when the crystallization mother liquor is used as an acidulant. And simultaneously, the single extraction rate of methionine is improved.
The following provides specific examples of production practice using the technical scheme provided by the invention, and practical operation is carried out in sequence, so that the process of industrial continuous production using the invention is simulated.
4-methylthio-2-hydroxybutyronitrile is prepared from hydrocyanic acid and 3-methylthio propanal, 5000g of 5- (beta-methylthioethyl) hydantoin solution with the concentration of 21.39wt% is produced by the reaction of 4-methylthio-2-hydroxybutyronitrile, ammonia and carbon dioxide, 1474g of 30wt% sodium hydroxide solution is added, the temperature is raised to 155-160 ℃ in a high-pressure reaction kettle, the temperature is kept for 20min, the pressure is released to atmospheric pressure, the ammonia content is stripped to less than 50ppm at the normal pressure at the temperature of 100 ℃ to obtain 5365g of saponified solution, and the methionine content in the saponified solution is 16.95wt%.4.74
Example 2-a;
1000g of saponified solution is taken, constant temperature heating is carried out to ensure that the temperature of the saponified solution is stabilized at 70 ℃, 96.7g of 98wt% sulfuric acid is dripped into the saponified solution, and after dripping is finished, the temperature is kept for 20min to obtain an acidizing solution, and the pH value of the acidizing solution is 6.5; cooling the acidized solution to 35 ℃, preserving heat, stirring for 30min, filtering to obtain methionine crystals and sodium sulfate mother liquor, washing and drying the methionine crystals to obtain 149.5g of methionine with the content of 99.1wt%, and obtaining the yield of 87.4%; 576g of sodium sulfate mother liquor, wherein the methionine content is 2.48wt% and the sodium sulfate content is 18.84wt%. 500g of sodium sulfate mother liquor is taken, reduced pressure distillation is carried out at 90 ℃ until the content of sodium sulfate is more than 25 weight percent, then the temperature is reduced to 35 ℃ and the temperature is kept for 30min, and then 12g of mixed solid and 251.65g of concentrated mother liquor are obtained after filtration. In the concentrated mother liquor, the methionine content is 1.1wt%, and the sodium sulfate content is 26.42wt%. 84.9g of saponification liquid is taken and mixed with the concentrated mother liquor uniformly, the pH value of the mixed solution is 8.6, then the temperature is reduced to 10 ℃, cooling crystallization is carried out for 30min, and 113.7g of mirabilite and 140.8g of crystallization mother liquor are obtained by filtering. The sodium sulfate content in mirabilite is 38.21wt%, the water content is 61.23wt%, methionine is not detected, and the sodium sulfate yield is 76.84%; the methionine content in the mother liquor was 6.22wt% and the sodium sulfate content was 7.75wt%.
Example 2-b;
1000g of saponification liquid is taken, the mixed solid in the embodiment 2-a is dissolved into the saponification liquid, the temperature of the saponification liquid is stabilized at 70 ℃ by constant-temperature heating, the mixed liquid of sulfuric acid and the crystallization mother liquor in the embodiment 2-a is dripped into the saponification liquid, the acidification liquid is obtained after the dripping is completed and the temperature is kept for 20min, and the pH value of the acidification liquid is 6.2; cooling the acidized solution to 35 ℃, preserving heat, stirring for 30min, filtering to obtain methionine crystals and sodium sulfate mother liquor, washing and drying the methionine crystals to obtain 152.6g of methionine with the content of 99.18wt%, and obtaining 88.6% of yield; 612g of sodium sulfate mother liquor, wherein the methionine content is 2.35wt% and the sodium sulfate content is 17.63wt%. 500g of sodium sulfate mother liquor is taken, reduced pressure distillation is carried out at 90 ℃ until the content of sodium sulfate is more than 25 weight percent, then the temperature is reduced to 35 ℃ and the temperature is kept for 30min, and then 10.5g of mixed solid and 223.78g of concentrated mother liquor are obtained after filtration. The concentrated mother liquor contains 1.2wt% of methionine and 26.76wt% of sodium sulfate. Mixing 78.8g of saponification liquid with concentrated mother liquor uniformly, cooling to 10 ℃ and crystallizing for 30min, and filtering to obtain 109.3g of mirabilite and 131.3g of crystallization mother liquor, wherein the pH value of the mixed solution is 8.8. 38.35% of sodium sulfate in mirabilite, 60.93% of water, undetected methionine and 77.03% of sodium sulfate yield; the methionine content in the mother liquor was 6.16wt% and the sodium sulfate content was 7.57wt%.
Example 2-c;
1000g of saponification liquid is taken, the mixed solid in the embodiment 2-b is dissolved into the saponification liquid, the temperature of the saponification liquid is stabilized at 70 ℃ by constant-temperature heating, the mixed liquid of sulfuric acid and the crystallization mother liquor in the embodiment 2-b is dripped into the saponification liquid, the acidification liquid is obtained after the dripping is completed and the temperature is kept for 20min, and the pH value of the acidification liquid is 6.4; cooling the acidized solution to 35 ℃, preserving heat, stirring for 30min, filtering to obtain methionine crystals and sodium sulfate mother liquor, washing and drying the methionine crystals to obtain 150.23g of methionine with the content of 99.02wt%, and obtaining the yield of 87.9%; 608g of sodium sulfate mother liquor, wherein the methionine content is 2.38wt% and the sodium sulfate content is 18.23wt%. 500g of sodium sulfate mother liquor is taken, reduced pressure distillation is carried out at 90 ℃ until the content of sodium sulfate is more than 25 weight percent, then the temperature is reduced to 35 ℃ and the temperature is kept for 30min, and then 10.7g of mixed solid and 230.34g of concentrated mother liquor are obtained after filtration. In the concentrated mother liquor, the methionine content is 1.1wt%, and the sodium sulfate content is 26.83wt%. Mixing 80.3g of saponification liquid with concentrated mother liquor uniformly, cooling to 10 ℃ for cooling crystallization for 30min, and filtering to obtain 110.8g of mirabilite and 139.2g of crystallization mother liquor, wherein the pH value of the mixed solution is 8.7. The sodium sulfate content in mirabilite is 38.24wt%, the water content is 60.87wt%, methionine is not detected, and the sodium sulfate yield is 76.56%; the methionine content in the mother liquor was 6.14wt% and the sodium sulfate content was 7.48wt%.
The ratio of the impurity content to the methionine content in the crystallization mother liquor is detected to be more than 3%, so that the yield and the purity of methionine and sodium sulfate are reduced, the crystallization mother liquor is subjected to impurity removal, 1.4g of 98wt% sulfuric acid is added into the crystallization mother liquor, the pH value of the concentrated mother liquor is 2.5 after the sulfuric acid is added, the aqueous phase liquid and the oil phase impurities are obtained through liquid separation, diatomite is used as an auxiliary agent, the aqueous phase liquid is filtered to remove solid impurities, and then the stripping method is used to remove formic acid, so that 76.5g of the crystallization mother liquor after impurity removal is obtained, the methionine content in the crystallization mother liquor after impurity removal is 11.0wt% and the sodium sulfate content is 13.1wt%.
Example 2-d;
1000g of saponification liquid is taken, the mixed solid in the embodiment 2-c is dissolved into the saponification liquid, the temperature of the saponification liquid is stabilized at 70 ℃ by constant-temperature heating, the mixed liquid of sulfuric acid and the crystallized mother liquid after impurity removal in the embodiment 2-c is dripped into the saponification liquid, the temperature is kept for 20min after the dripping is finished, and an acidizing liquid is obtained, and the pH value of the acidizing liquid is 6.5; cooling the acidizing fluid to 35 ℃, preserving heat, stirring for 30min, filtering to obtain methionine crystals and sodium sulfate mother liquor, washing and drying the methionine crystals to obtain 153.3g of methionine with the content of 99.23wt%, and obtaining the yield of 90.31%; 579g of sodium sulfate mother liquor, wherein the methionine content is 2.36wt% and the sodium sulfate content is 19.39wt%. 500g of sodium sulfate mother liquor is taken, reduced pressure distillation is carried out at 90 ℃ until the content of sodium sulfate is more than 25 weight percent, then the temperature is reduced to 35 ℃ and the temperature is kept for 30min, and then 9.8g of mixed solid and 235.7g of concentrated mother liquor are obtained after filtration. In the concentrated mother liquor, the methionine content is 1.4wt%, and the sodium sulfate content is 27.21wt%. Mixing 83.2g of saponified solution with concentrated mother liquor uniformly, cooling to 10 ℃ and crystallizing for 30min, and filtering to obtain 121.8g of mirabilite and 126.4g of crystallization mother liquor, wherein the pH value of the mixed solution is 8.8. The sodium sulfate content in the mirabilite is 39.24 weight percent, the water content is 60.68 weight percent, methionine is not detected, and the sodium sulfate yield is 78.35 percent; the methionine content in the mother liquor of crystallization was 6.21wt% and the sodium sulfate content was 7.69wt%.
Example 2-e;
1000g of saponification liquid is taken, the mixed solid in the embodiment 2-d is dissolved into the saponification liquid, the temperature of the saponification liquid is stabilized at 70 ℃ by constant-temperature heating, the mixed liquid of sulfuric acid and the crystallized mother liquid after impurity removal in the embodiment 2-d is dropwise added into the saponification liquid, and after the dropwise addition is completed, the temperature is kept for 20min to obtain an acidizing liquid, and the pH value of the acidizing liquid is 6.2; cooling the acidizing fluid to 35 ℃, preserving heat, stirring for 30min, filtering to obtain methionine crystals and sodium sulfate mother liquor, washing and drying the methionine crystals to obtain 151.4g of methionine with the content of 99.21wt%, and obtaining 90.18%; 597g of sodium sulfate mother liquor, wherein the methionine content is 2.35wt%, and the sodium sulfate content is 18.21wt%. 500g of sodium sulfate mother liquor is taken, reduced pressure distillation is carried out at 90 ℃ until the content of sodium sulfate is more than 25 weight percent, then the temperature is reduced to 35 ℃ and the temperature is kept for 30min, and then 10.8g of mixed solid and 230.7g of concentrated mother liquor are obtained after filtration. In the concentrated mother liquor, the methionine content is 1.1wt%, and the sodium sulfate content is 26.79wt%. Mixing 80.9g of saponified solution with concentrated mother solution uniformly, cooling to 10deg.C, cooling for crystallization for 30min, and filtering to obtain 117.1g of Natrii sulfas and 135.3g of crystallization mother solution. The sodium sulfate content in mirabilite is 39.13wt%, the water content is 60.66wt%, methionine is not detected, and the sodium sulfate yield is 78.03%; the methionine content in the mother liquor was 6.13wt% and the sodium sulfate content was 7.49wt%.
From the above examples 2-a to 2-e, it is apparent that the yield of methionine and the yield of sodium sulfate can be effectively improved in the continuous production process using the technical scheme provided by the invention. In example 2-c, i.e., three times of continuous production, the impurity was slightly accumulated to slightly lower the methionine yield and the sodium sulfate yield, and the ratio of the impurity content to the methionine content in the resulting crystallization mother liquor was detected to be more than 3%, so that the crystallization mother liquor was once purified and then used in example 2-d. So in the embodiment 2-d, the yield of methionine is improved to more than 90wt%, and the yield of sodium sulfate is also improved; in example 2-e, the methionine yield was also 90wt% or more. By setting the planned value or the regular period of the impurities in the crystallization mother liquor, the impurity of the crystallization mother liquor is removed, so that the methionine yield can be effectively improved and kept stable, the crystallization mother liquor containing methionine is not discharged in the production and preparation process of methionine, the economic benefit maximization is ensured, and the pollution to the environment is reduced.
The foregoing embodiments are preferred embodiments of the present invention, and other embodiments are included, without departing from the spirit of the present invention.
Claims (4)
1. The preparation method of DL-methionine is characterized by comprising the following specific steps:
s100, performing S100; preparing 4-methylthio-2-hydroxybutyronitrile by using hydrocyanic acid and 3-methylthio propanal, generating 5- (beta-methylthioethyl) hydantoin by using 4-methylthio-2-hydroxybutyronitrile to react with ammonia and carbon dioxide, hydrolyzing the 5- (beta-methylthioethyl) hydantoin by using an alkali solution of sodium, and deaminizing to obtain a saponified solution;
s200, performing S200; acidifying the saponified solution, cooling, crystallizing and separating to obtain DL-methionine crystals and sodium sulfate mother liquor;
s210, performing S210; heating the saponification liquid at a constant temperature to keep the temperature of the saponification liquid at 60-120 ℃, acidifying the saponification liquid by sulfuric acid, keeping the pH value of the acidified saponification liquid at 5-7, and keeping the temperature for 10-30 min to obtain an acidified liquid;
s220, performing operation; reducing the temperature of the acidizing fluid to 35-45 ℃, and preserving heat for 20-60 min;
s230, performing S230; performing solid-liquid separation on the acidized liquid to obtain methionine crystals and sodium sulfate mother liquor;
s300, performing S300; concentrating the sodium sulfate mother liquor, cooling and crystallizing, and then carrying out solid-liquid separation to obtain mixed solid and concentrated mother liquor;
s310; heating the sodium sulfate mother liquor to 90-120 ℃, concentrating under reduced pressure, and concentrating under reduced pressure until the sodium sulfate content in the sodium sulfate mother liquor is more than 20wt%;
s320; reducing the temperature to 10-60 ℃, and preserving the heat for 10-40 min;
s330; carrying out solid-liquid separation at 35-45 ℃ to obtain mixed solids and concentrated mother liquor;
s350, performing operation; returning the mixed solid to the step S200, and dissolving the mixed solid into the saponified solution;
s400, performing S400; adding saponification liquid into the concentrated mother liquor, crystallizing at low temperature, and performing solid-liquid separation to obtain crystallization mother liquor and mirabilite; the specific operation is as follows: adding saponification liquid into the concentrated mother liquor, wherein the molar ratio of sodium carbonate in the added saponification liquid to methionine in the concentrated mother liquor is 1-2:1, adding the saponification liquid, then adding the saponification liquid, concentrating the mother liquor to have a pH value of greater than or equal to 8, reducing the temperature to-10 ℃, preserving the heat for 20-100 min, and then performing solid-liquid separation to obtain crystallization mother liquor and mirabilite
S500, performing control; removing impurities from the crystallization mother liquor, returning the crystallization mother liquor after the impurity removal to the step S200, mixing the crystallization mother liquor with saponification liquid, and acidifying again to separate DL-methionine crystals, wherein the specific operation is as follows: before impurity removal of the crystallization mother liquor, detecting the impurity content in the crystallization mother liquor, performing impurity removal on the crystallization mother liquor when the ratio of the impurity content to the methionine content in the crystallization mother liquor exceeds 3%, and directly returning the crystallization mother liquor to step S200 for mixing with the saponification liquid when the ratio of the impurity content to the methionine content in the crystallization mother liquor does not exceed 3%;
the specific steps of impurity removal of the crystallization mother liquor are as follows: and adding sulfuric acid into the crystallization mother liquor, wherein the pH value of the crystallization mother liquor after adding sulfuric acid is 2-3, standing for 30min at 10-40 ℃, separating oil phase impurities and aqueous phase liquid, filtering the aqueous phase liquid to remove solid impurities, and removing formic acid by a stripping method.
2. The method for producing DL-methionine according to claim 1, wherein the sulfuric acid concentration in the step S210 is 20 to 98% by weight.
3. The method for producing DL-methionine according to claim 1, wherein the step S500 comprises the following steps: dividing the crystallization mother liquor into two parts, removing impurities from one part of the crystallization mother liquor, mixing the impurity-removed crystallization mother liquor with the other part of crystallization mother liquor, and returning to the step S200 to be mixed with the saponification liquid.
4. The method for producing DL-methionine according to claim 1, wherein the concentration of sulfuric acid added in the step S500 for removing impurities from the mother liquor of crystallization is 20 to 98%.
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| EP2641898A1 (en) * | 2012-03-20 | 2013-09-25 | Evonik Industries AG | Method for manufacturing methionine |
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