Optimized preparation method of methionine based on direct sulfuric acid acidification method and sodium sulfate washing equipment

Abstract

The present invention relates to the field of methionine production, and in particular to an optimized preparation method of methionine based on a direct sulfuric acid acidification method and a sodium sulfate washing device. Compared with the prior art, the optimized preparation method of methionine based on a direct sulfuric acid acidification method and the sodium sulfate washing device of the present invention are directed to sodium hydroxide hydrolyzate of hydantoin, and ammonia is discharged by adjusting the pH of a sodium sulfate solution to be alkaline, and a methionine concentrate is adjusted to be alkaline to decompose a methionine derivative precursor, and impurities are extracted into beneficial substances by extraction and gas stripping, thereby respectively treating methionine, sodium sulfate, methionine derivatives, formic acid and oil phase impurities generated in methionine production, forming beneficial resources, being environmentally friendly, economical, safe, and having a wide range of market value.

Description

Technical Field

[0001] The invention relates to the field of methionine production, and in particular to an optimized preparation method of methionine based on a sulfuric acid direct acidification method and sodium sulfate washing equipment. Background Art

[0002] D,L-methionine, as an amino acid feed additive in feed, is an animal growth promoter used for protein synthesis, which can improve feed conversion rate, animal growth rate and poultry egg production rate. It can promote the growth of poultry and livestock, increase lean meat, and shorten the feeding cycle. Animal feed with methionine can help animals grow rapidly in a short time and save about 40% of feed.

[0003] At present, the production methods of D,L-methionine mainly include chemical synthesis, biological fermentation, and enzyme catalysis, among which chemical synthesis is the most common. The known methionine production process is to synthesize 5-(β-methylmercaptoethyl)hydantoin, also referred to as hydantoin or hydantoin, from 3-methylmercaptopropionaldehyde, hydrocyanic acid, ammonia, and carbon dioxide as raw materials. Hydantoin is hydrolyzed with alkali to obtain a hydrolyzate of a mixture of methionine salt and carbonate, and the hydrolyzate is acidified to obtain methionine and filtrate. The filtrate contains a large amount of useful components and must be returned to the cycle after treatment; the difference in acidification medium and alkali determines the difference in the return link of the filtrate, and the filtrate is either returned to the hydrolysis step of hydantoin or returned to the crystallization step.

[0004] Hydantoin is an essential intermediate in the mainstream production process of methionine. Hydantoin hydrolysis can use alkalis such as potassium carbonate, sodium carbonate, sodium hydroxide, calcium hydroxide, potassium bicarbonate, and sodium bicarbonate. The methionine production process is relatively long. No matter which alkali is used to hydrolyze hydantoin, the generation of impurities is inevitable, including formic acid, acrolein polymer derivatives, 3-methylthiopropionaldehyde polymer derivatives, methionine hydroxyl analogs, methionine derivative precursors, and polycarboxylic acid impurities. These impurities are similar to the structure of methionine: either carbon chain or amino or carboxyl, so most impurities have a similar effect of similar miscibility with methionine and are difficult to be separated from methionine more thoroughly. During the cycle, the quality of the extracted methionine will decrease and even affect the yield of the reaction, so the separation of impurities is a necessary operation.

[0005] Patent publication CN106748932A uses a microporous membrane filter to remove polymers from a mixed solution of methionine and bicarbonate, and then uses a cation exchange resin to separate the mixture into a methionine solution and a sulfate solution, and uses electrodialysis or stripping / or an anion exchange resin to separate formic acid from the methionine solution. First, the impurities in the crystallization mother liquor are not enriched, and it is a waste to directly use a cation resin to convert alkaline potassium into neutral potassium; second, the impurities in the crystallization mother liquor are still small molecules and have viscosity, and it is difficult for the microporous membrane filter to filter out these impurities and even cause blockage.

[0006] Patent CN102796033B uses an organic solvent to extract the hydrolyzate, extracts part of the impurities into the organic phase, and the organic phase is recycled after distillation, and the residual liquid is treated as waste liquid. First, the concentration of methionine salts and carbonates in the saponified liquid is high, and the organic solvent mixes part of the saponified liquid, resulting in the waste of part of the product; second, the organic solvent is partially dissolved in the saponified liquid, resulting in the accumulation of subsequent organic solvents; third, the saponified liquid has a low impurity ratio, the extraction efficiency is low, and this part of the impurities is basically 3-methylthiopropionaldehyde polymer and is immiscible with the water phase, and TPMA dimer can be controlled to a very low level in the preparation of 5-(2-methylthioethyl)-hydantoin; fourth, the saponified liquid is strongly alkaline, carboxyl impurities are more soluble in the water phase, and the organic extraction effect is not obvious, but this impurity is one of the main components. Comprehensive organic solvent extraction of saponified liquid can only extract a very small amount of impurities in the saponified liquid, and no operation plan is proposed for the enrichment of formic acid.

[0007] Patent CN110678445A uses electrodialysis to remove anions containing 1 to 5 carbon atoms from the mother liquor of methionine crystallization. Electrodialysis cannot achieve this goal well within the acceptable time and energy consumption of industrial production; methionine will enter the anolyte due to osmotic pressure or potential difference, and the anolyte still needs further treatment; in addition, the impurities in the mother liquor of crystallization are enriched, which may cause blockage of the membrane, and ultimately lead to poor efficiency or even collapse of electrodialysis.

[0008] CN401693082A points out that methionine will produce impurities such as dimethyl disulfide, propyleneamine, and 3-methylthiopropylamine during heating, but does not mention the heating time, number of times, and temperature. Alkali metals or alkaline earth metals are used in the hydrolysis of hydantoin. The salt and methionine mixture generated by acidification have different contents and solubilities, so there is a limit on the number of times of subsequent concentration, so it has to be concentrated repeatedly. In order to reduce the number of concentrations, methionine practitioners have proposed the following solution.

[0009] In CN107531621A, the hydrolyzate is first concentrated to extract part of the sodium carbonate and then used for the hydrolysis of hydantoin, and then acidified with sulfuric acid to extract methionine, which can reduce the consumption of alkaline sodium and sulfuric acid for hydrolysis and also reduce the production of sodium sulfate. However, sodium carbonate is easily soluble in water, and it is not easy to concentrate the hydrolyzate to a high multiple and then filter it. Concentration requires a lot of energy, and there is no mention of impurity treatment.

[0010] In CN104693082A, chromatographic separation technology is used to separate a mixed solution of sodium sulfate and methionine, and in CN106432018A, chromatographic separation technology is used to separate a mixed solution of potassium bicarbonate and methionine. However, there are the following defects: the chromatographic separation technology requires the introduction of a large amount of water, which reduces the concentration of the methionine solution; the chromatographic separation investment is large, the separation efficiency is low, and the most important thing is that the impurities generated in the preparation of methionine are not processed, and these impurities (relative to the impurities generated by thermal decomposition) are the ones that need to be processed in the first place; in addition, the separation effect of the chromatographic separation on bicarbonate and methionine is worth considering.

[0011] In CN109734637A, CN103922980A, CN103933861A, CN106432020B, CN104130169A, CN103922980A, and CN105671587A, bipolar membranes are used to separate methionine from carbonate / bicarbonate mixed solutions into methionine and alkali solution. However, there are also the following defects: first, methionine has limited solubility and must be diluted with water, and the separated methionine solution needs to be concentrated and crystallized or crystallized at low temperature; second, the mixed solution contains a lot of impurities, which affects the electronic utilization efficiency of the bipolar membrane and the life of the membrane itself; third, the low concentration of alkali produced by the bipolar membrane still needs to be concentrated for use; fourth, the generated carbon dioxide is a neutral molecule, which leads to an increase in solution resistance, low electrodialysis efficiency, and high investment and operation costs for the main process flow equipment.

[0012] In CN1923807A, CN101602700A, CN101602701A and CN110536881A, the hydrolyzate is acidified with carbon dioxide to extract methionine and mother liquor, a part of the mother liquor is concentrated and then a lower alcohol is added to separate the mixture of methionine and potassium carbonate and returned to the hydrolysis of hydantoin, and the secondary mother liquor is further treated and discarded. However, the introduction of lower alcohols makes the system have residual recovery, which is also a problem.

[0013] In summary, the treatment can be divided into two ideas: extracting impurities or extracting methionine / salt. Because methionine and salt have a large solubility in water, extracting impurities is an option. However, the known disclosed patents still have the following problems:

[0014] (1) The treatment of impurities generated during methionine production is not clearly mentioned;

[0015] (2) Using high-cost and high-energy-consuming equipment and technology to separate methionine and salts in order to reduce the small amount of impurities generated in subsequent processing;

[0016] (3) Treatment of methionine crystallization mother liquor by introducing lower alcohol or coagulant;

[0017] (4) After the methionine crystallization mother liquor is treated, a portion of the crystallization mother liquor still needs to be discarded, and the beneficial substances cannot be recovered;

[0018] (5) Part of the crystallization mother liquor is discarded and processed into low-value substances using beneficial resources, which increases the cost twice. Summary of the invention

[0019] In order to solve the problems mentioned in the background technology, the purpose of the present invention is to provide an optimized preparation method of methionine based on sulfuric acid direct acidification method and sodium sulfate washing equipment, which solves the subsequent treatment problem of sodium hydroxide hydrolysis of hydantoin and the problem that direct elution of sodium sulfate will cause the introduction of a large amount of water and poor washing efficiency.

[0020] The key to the optimized preparation method of methionine based on the direct acidification method of sulfuric acid is to include the following steps:

[0021] S1. The sodium hydrolyzate of 5-(2-methylmercaptoethyl)-hydantoin is acidified with sulfuric acid and separated into crude methionine and crystallization mother liquor;

[0022] S2. The crude methionine is mixed with water and beaten, separated and dried to obtain methionine, and the beating water is returned to S1 and combined with the crystallization mother liquor;

[0023] S3 adjusts the crystallization mother liquor pH> 8.5, concentrates and separates into sodium sulfate and concentrated mother liquor; sodium sulfate is washed using sodium sulfate washing equipment, and the washing water returns to S3 and is combined with the crystallization mother liquor to adjust the pH;

[0024] S4. Acidification and crystallization of the concentrated mother liquor to separate into secondary methionine and impurity-enriched liquid;

[0025] S5. The secondary methionine is returned to S2 and washed with the crystallization mother liquor of S2 to form a secondary mother liquor. Part of the secondary mother liquor is extracted to perform S3 operation, and the remaining secondary mother liquor is returned to S1 for acidification of the hydrolyzate;

[0026] S6. The impurity-enriched liquid is divided into two parts. The first part of the impurity-enriched liquid is returned to S3 to be combined with the crystallization mother liquor, and the second part of the impurity-enriched liquid is subjected to impurity removal treatment after acid adjustment.

[0027] Preferably, S1 is as follows: the sodium hydrolyzate of 5-(2-methylmercaptoethyl)-hydantoin is adjusted to pH 5-8 using sulfuric acid, kept at 25-40° C. for 10-100 min, and centrifuged to separate into crude methionine and crystallization mother liquor.

[0028] Preferably, S3 specifically comprises: using a hydrolyzate to adjust the pH of the crystallization mother liquor to greater than 8.5, concentrating at 60-120° C. until the methionine content is greater than 7% wt, and centrifuging to separate into sodium sulfate and concentrated mother liquor.

[0029] Preferably, S4 specifically comprises: controlling the pH of the concentrated mother liquor to 6-10, keeping the concentrated mother liquor at 25-40° C. for 10-100 min, and separating the concentrated mother liquor into secondary methionine and impurity-enriched liquid.

[0030] Preferably, the secondary mother liquor extracted in S5 is 10-30%wt of the total secondary mother liquor, the extracted secondary mother liquor contains all methionine solids, and the remaining secondary mother liquor does not contain methionine solids.

[0031] Preferably, the mass ratio of the first part of the impurity-enriched solution to the second part of the impurity-enriched solution in S6 is 3:1-7:1.

[0032] Preferably, in S6, sulfuric acid is used to adjust the pH of the second part of the impurity-enriched liquid to less than 3, and then an impurity removal treatment is performed.

[0033] Preferably, the impurity removal treatment in S6 is specifically as follows: steam / carbon dioxide is used for stripping / gas stripping, the formic acid-containing gas is absorbed by alkali solution and then returned to the stripping / gas stripping process, and the alkali solution is concentrated to prepare formate; the impurity-enriched liquid after formic acid removal is separated into an oil phase and an aqueous phase by stratification or organic solvent extraction, the oil phase is adjusted to pH>10 with calcium oxide, and can be solidified for use as a soil conditioner or used as a soil conditioner after fermentation; the aqueous phase is returned to S1 for acidification of the hydrolyzate or returned to S4 for adjusting the pH of the concentrate.

[0034] A sodium sulfate washing device, which mainly comprises a washing tank, a settling tank, a thickening tank and a centrifuge connected in sequence by pipelines;

[0035] The upper part of the washing tank is connected to the lower pipeline of the settling tank, and the lower part of the washing tank is connected to the upper overflow pipe of the settling tank; a reflux pipeline is provided between the upper and lower parts of the settling tank for separating sodium sulfate and washing water; the filtrate outlet of the centrifuge is connected to the upper pipeline of the settling tank.

[0036] Preferably, a water supply pipe and a precision filter are provided on the reflux pipeline;

[0037] Preferably, the settling tank is a cylindrical tank body, and the bottom of the settling tank is conical;

[0038] Preferably, a stirring device is provided in the washing tank and the thickening tank;

[0039] Preferably, the circulation inlet of the reflux pipeline is located at the upper layer of the settling tank, and the circulation outlet is located at the lower layer of the settling tank.

[0040] Beneficial effects: Compared with the prior art, the optimized preparation method of methionine based on the direct sulfuric acid acidification method and the sodium sulfate washing equipment of the present invention, for the sodium hydroxide hydrolyzate of hydantoin, adjusts the pH of the sodium sulfate solution to be alkaline to discharge ammonia, adjusts the pH of the methionine concentrate to be alkaline to decompose the methionine derivative precursor, and extracts the impurities into beneficial substances through extraction and gas stripping, thereby separately treating the methionine, sodium sulfate, methionine derivatives, formic acid and oil phase impurities generated in the methionine production to form beneficial resources, which is environmentally friendly, economical and safe, and has broad market value. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a process flow chart of the present invention;

[0042] Figure 2 It is a structural schematic diagram of the sodium sulfate washing equipment. DETAILED DESCRIPTION

[0043] The present invention is described in detail below by specific examples. It is pointed out that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above invention content. Unless otherwise specified, the parts described in the present invention are all weight parts, the percentages described are all mass percentages, and the concentrations described are mass percentage concentrations.

[0044] Example 1 Sodium sulfate washing equipment

[0045] like Figure 2 As shown in the figure, the sodium sulfate washing equipment includes a washing tank 1, a settling tank 2, a thickening tank 3 and a centrifuge 4 which are connected in sequence by pipelines; the upper part of the washing tank 1 is connected to the lower pipeline of the settling tank 2, and the lower part of the washing tank 1 is connected to the upper overflow pipe of the settling tank 2; a reflux pipeline 5 is provided between the upper and lower parts of the settling tank 2, and a water supply pipe 6 and a precision filter 7 are provided on the reflux pipeline 5, and the water outlet of the water supply pipe 6 is located at the water inlet of the precision filter 7; the thickening tank 3 is located directly below the settling tank 2, and the filtrate outlet of the centrifuge 4 is connected to the liquid outlet pipe 8, and one outlet of the liquid outlet pipe 8 is connected to the upper part of the settling tank 2.

[0046] Example 2 Optimized preparation method of methionine based on direct sulfuric acid acidification method

[0047] S1. The sodium hydrolyzate of 5-(2-methylthioethyl)-hydantoin is adjusted to pH 5-8 with sulfuric acid, kept at 25-40°C for 10-100 minutes, and centrifuged to separate crude methionine and crystallization mother liquor;

[0048] S2. The crude methionine is pulped with water and then separated and dried, and the pulping water is returned to S1 and combined with the crystallization mother liquor; the sodium sulfate embedded deep in the methionine is washed out by means of pulping, and the methionine content is greater than 99wt% is obtained by separation and drying again; the sodium sulfate is washed using a sodium sulfate washing device, and the washing water is returned to S1 and combined with the crystallization mother liquor;

[0049] S3. Using the hydrolyzate to adjust the pH of the crystallization mother liquor to >8.5, at 60-120°C, concentrate to a methionine content of >7%wt, and centrifuge to separate into sodium sulfate and concentrated mother liquor; since the ammonia in the hydrolyzate will not be completely removed, it will react with sulfuric acid to form ammonium sulfate, resulting in subsequent enrichment. When the pH is adjusted to above 8, ammonia will evaporate with water, and the evaporated water will be used to prepare an ammonium / ammonia solution or to prepare ammonium sulfate using a hydrogen-type sulfonic acid or carboxylic acid resin for adsorption. Moreover, since the hydrolysis of 5-(2-methylmercaptoethyl)-hydantoin is not thorough, hydantoin will be used as an intermediate to generate a variety of derivatives such as methionine urea, methionine amide, methionine urea amide and methionylmethionine, which will continue to decompose into methionine under alkaline conditions, and these derivatives are decomposed as much as possible while the crystallization mother liquor is concentrated; in the production of methionine, formic acid is inevitably produced. When the crystallization mother liquor pH is >8.5, formic acid is not evaporated and is collected after enrichment;

[0050] S4. Control the pH of the concentrated mother liquor to 6-10, keep warm at 25-40° C. for 10-100 min, and separate into secondary methionine and impurity-enriched solution; as the crystallization mother liquor is concentrated, the 5-(2-methylthioethyl)-hydantoin derivative will continue to decompose, which may cause the pH of the concentrated solution to be greater than 10. Controlling the pH of the concentrated mother liquor is beneficial to the extraction of secondary methionine; in actual operation, the pH of the concentrated mother liquor is controlled to 6-10, more preferably 6-9, and further preferably 6-8.5;

[0051] S5. The secondary methionine is returned to S1 and washed with crystallization mother liquor to form secondary mother liquor. The leaf filter extracts 10-30%wt of the total secondary mother liquor and returns it to S1 to be combined with the methionine solution. This part of the secondary mother liquor contains all solids. The crystallization mother liquor is used to dissolve and dilute the secondary methionine impurities for cleaning to reduce the impurity concentration and avoid the secondary methionine directly returning to the methionine solution to cause the reflux of impurities, which may lead to unqualified methionine quality. In actual operation, the extracted secondary mother liquor can be 10%wt, 20%wt, or 30%wt of the total secondary mother liquor.

[0052] S6. The impurity-enriched liquid is divided into two parts, the first part of the impurity-enriched liquid is returned to S1 and combined with the crystallization mother liquor, the second part of the impurity-enriched liquid is adjusted to pH <3 with sulfuric acid, and then steam / carbon dioxide is used for stripping / gas stripping, the gas containing formic acid is absorbed with alkali solution and then returned for stripping / gas stripping, and the alkali solution is concentrated to prepare formate; the impurity-enriched liquid with formic acid is separated into oil phase and water phase by layering or organic solvent extraction, the oil phase is adjusted to pH > 10 with calcium oxide, and can be solidified for use as a soil conditioner; the organic solvent is alcohol with a carbon chain > 5, the water phase is returned to S1 for acidification of the hydrolyzate or returned to S4 for adjusting the pH of the impurity-enriched liquid; the system is kept in normal operation by controlling the split impurity removal ratio, and there is no obvious decrease in the hydrolysis yield of hydantoin and the quality of methionine. In actual operation, the mass ratio of the first part of the crystallization mother liquor to the second part of the crystallization mother liquor can be 3:1, 4:1, 5:1, 6:1, 7:1.

[0053] The following provides a specific embodiment of production practice using the technical solution provided by the present invention, and the practical operations are performed in sequence to simulate the process of industrial continuous production using the present invention.

[0054] Example 2-1

[0055] Take 100kg of hydantoin hydrolyzate (wherein the methionine content is 14.7wt% and the basic sodium content is 4.8wt%) of 5-(β-methylthioethyl)hydantoin solution hydrolyzed with sodium hydroxide, use 10.8kg of 95wt% sulfuric acid to adjust the pH to 6.1, keep warm at 34°C for 40min, centrifuge to obtain 13.4kg of methionine and 94.1kg of crystallization mother liquor (, 13.4kg of methionine and 20kg of water are stirred at 35°C for 10min, methionine and 21kg of beating water are separated again, methionine is dried to be a white powder with a mass fraction of 99.6wt%, and the beating water is incorporated into the next crystallization mother liquor; 94.1kg of crystallization mother liquor is adjusted to pH 8.6 with 9kg of hydrolyzate, the mixed solution is concentrated at 90°C to a methionine content of 9.8wt%, and 9.3kg of sodium sulfate and 35kg of concentrated solution (pH=10.3) are separated by centrifugation, and the sodium sulfate is washed with the sodium sulfate washing device of Example 1 Washing and separation are performed, and the content after drying is greater than 99.9wt%, and the single sodium sulfate extraction rate is 63.7%. When the sodium sulfate content is lower than 99.9wt%, the sodium sulfate washing water is transferred to the crystallization mother liquor, and the concentrated water is used for the preparation of ammonia / ammonium solution or the enrichment of ammonia using hydrogen carboxylic acid / sulfonic acid resin; 35kg of the concentrated solution is added with 0.9kg of 95wt% sulfuric acid, the pH is adjusted to 7.9, and after being kept at 35℃ for 50min, it is separated into 2.4kg of secondary methionine and 30kg of impurity-enriched liquid; 10kg of the impurity-enriched liquid is split, and the pH is adjusted to 2.4 with 95wt% sulfuric acid, and formic acid is removed with carbon dioxide at 60-100℃. When the pH is stabilized at 2.7, the formic acid removal is completed, and the split impurity-enriched liquid after formic acid removal is left standing at 40℃ for 30min, separated into an oil phase and a water phase, and the oil phase is solidified after adjusting the pH to 10.3 with calcium oxide; the remaining 20kg of impurity-enriched liquid is returned to the concentration of the crystallization mother liquor.

[0056] Example 2-2

[0057] 100 kg of hydantoin hydrolyzate obtained by hydrolyzing 5-(β-methylthioethyl)hydantoin solution with sodium hydroxide (wherein the methionine content is 14.7 wt % and the basic sodium content is 4.8 wt %) was taken, and the pH value was adjusted to 6.1 using 10.8 kg of 95 wt % sulfuric acid, and the mixture was kept at 34° C. for 40 min, and centrifuged to obtain 14 kg of methionine and 90 kg of crystallization mother liquor; 14 kg of methionine and 20 kg of water were stirred at 35° C. for 10 min, and methionine and 22 kg of beating water were separated again, and the methionine was dried. The mass fraction of the white powder is 99.6wt%, and the beating water is incorporated into the next crystallization mother liquor; 90kg of the crystallization mother liquor is mixed with 2.4kg of secondary methionine in Example 2-1, and 88kg of the crystallization mother liquor is extracted for pH adjustment and concentration treatment (the 4.4kg mixed system not extracted is transferred to the acidification of the next hydrolyzate), and 21kg of the beating water in Example 2-1 and 20kg of the impurity enriched liquid in Example 2-1 are added to the 88kg of the crystallization mother liquor, and then 10.6kg of the hydrolyzate is used to adjust the pH to 8.6. The mixed solution was concentrated at 100° C. to a methionine content of 11 wt %, and centrifuged to obtain 13.6 kg of sodium sulfate and 42 kg of concentrated solution. The sodium sulfate was washed and separated using the sodium sulfate washing equipment of Example 1. After drying, the content of the sodium sulfate was greater than 99.9 wt %, and the single sodium sulfate extraction rate was 66.9%. When the sodium sulfate content was lower than 99.9 wt %, the sodium sulfate washing water was transferred to the crystallization mother liquor, and the concentrated water was used for the preparation of ammonium carbonate solution or the enrichment of ammonia using hydrogen carboxylic acid / sulfonic acid resin. 1.2 kg of 95 wt % sulfuric acid was added to 42 kg of the concentrated solution, and the pH was adjusted to 7.7. , after being kept at 35°C for 50 minutes, it is separated into 3.3kg of secondary methionine and 38kg of impurity-enriched liquid; 11kg of impurity-enriched liquid is taken for diversion, and the pH is adjusted to 2.2 with 95wt% sulfuric acid, and formic acid is removed with carbon dioxide at 60-100°C. When the pH is stabilized at 2.8, the formic acid removal is completed. The impurity-enriched liquid after formic acid removal is allowed to stand at 25°C for 30 minutes and separated into an oil phase and an aqueous phase. The oil phase is adjusted to pH 10.7 with calcium oxide and then solidified, and the aqueous phase is used for acidification of the subsequent hydrolyzate; the remaining 27kg of impurity-enriched liquid mother liquor is returned to the concentration of the crystallization mother liquor.

[0058] Example 2-3

[0059] Take 100kg of hydantoin hydrolyzate (methionine content is 14.7wt% and basic sodium content is 4.8wt%) obtained by hydrolyzing 5-(β-methylthioethyl)hydantoin solution with sodium hydroxide, add 5.4kg of the aqueous phase removed from Example 2-2, adjust the pH to 6.7 with 95wt% sulfuric acid, add 4.4kg of the mixture not extracted from Example 2-2 and mix for 20min, then keep warm at 36°C for 40min, centrifuge to obtain 17.2kg of methionine and 91kg of crystallization mother liquor, stir 17.2kg of methionine with 20kg of water at 35°C for 10min, separate methionine and 23kg of beating water again, the mass fraction of methionine after drying is 99.6wt%, and the beating water is incorporated into the next crystallization mother liquor; 91kg of crystallization mother liquor is mixed with 3.3kg of secondary methionine of Example 2-2, extract 90kg of crystallization mother liquor for pH adjustment and concentration treatment (the 4.3kg mixed system not extracted is converted into The mixture was concentrated at 100°C to a methionine content of 10.5wt%, and then centrifuged to obtain 16kg of sodium sulfate and 44.7kg of concentrated solution. The sodium sulfate was washed and separated using the sodium sulfate washing equipment of Example 1. The content of the sodium sulfate was greater than 99.9wt% after drying. The single sodium sulfate extraction rate was 70.2%. When the sodium sulfate content was less than 99.9wt%, the sodium sulfate washing water was transferred to the crystallization mother liquor. The concentrated water was used for the preparation of ammonium carbonate solution or for the enrichment of ammonia using hydrogen carboxylic acid / sulfonic acid resin. 1.5kg of 95wt% sulfuric acid was added to 44.7kg of concentrated solution to adjust the pH to 6.1. After being kept at 35°C for 50min, the solution was separated into 3.8kg of secondary methionine and 41kg of impurity-enriched solution.

[0060] 12 kg of impurity-enriched liquid is added with 95 wt % sulfuric acid to adjust the pH to 2.2, and carbon dioxide is used to remove formic acid at 60-100° C. When the pH is stabilized at 2.6, the formic acid removal is completed. The impurity-enriched liquid after the removal of formic acid is allowed to stand at 25° C. for 30 minutes and separated into an oil phase and an aqueous phase. The oil phase is adjusted to a pH of 11 using calcium oxide and then solidified, and the aqueous phase is used for the subsequent acidification of the hydrolyzate; the remaining 28 kg of impurity-enriched liquid mother liquor is returned to the concentration of the crystallization mother liquor.

[0061] Embodiment 2-4

[0062] Take 100 kg of hydantoin hydrolyzate (methionine content is 14.7 wt %, basic sodium content is 4.8 wt %) obtained by hydrolyzing 5-(β-methylthioethyl)hydantoin solution with sodium hydroxide, add 5.8 kg of the aqueous phase removed from Example 2-3, adjust the pH to 6.7 with 95 wt % sulfuric acid, add 4.3 kg of the mixture not extracted from Example 2-3 and mix for 20 min, then keep warm at 36 ° C for 40 min, centrifuge to obtain 16.6 kg of methionine and 100 kg of crystallization mother liquor, stir 16.6 kg of methionine with 20 kg of water at 35 ° C for 10 min, separate methionine and 19 kg of beating water again, the mass fraction of methionine after drying is 99.8 wt %, and the beating water is incorporated into the next crystallization mother liquor; 100 kg of crystallization mother liquor is mixed with 3.8 kg of secondary methionine in Example 2-3, and 97 kg of crystallization mother liquor is extracted for pH adjustment and concentration treatment (6.8 kg of mixed system not extracted) Transfer to the next acidification of the hydrolyzate), add 23kg of beating water in Example 2-3 and 28kg of impurity-enriched liquid in Example 2-3 to 97kg of crystallization mother liquor, and then adjust the pH to 8.6 with 9.7kg of hydrolyzate; concentrate the mixed solution at 100°C to a methionine content of 9.6wt%, and centrifuge to obtain 15.2kg of sodium sulfate and 47kg of concentrated liquid. The sodium sulfate is washed and separated using the sodium sulfate washing equipment of Example 1, and the content after drying is greater than 99.9wt%, and the single sodium sulfate extraction rate is 62.3%. When the sodium sulfate content is lower than 99.9wt%, the sodium sulfate washing water is transferred to the crystallization mother liquor, and the concentrated water is used for the preparation of ammonium carbonate solution or the enrichment of ammonia using hydrogen carboxylic acid / sulfonic acid resin; add 0.9kg of 95wt% sulfuric acid to 47kg of concentrated liquid, adjust the pH to 6.7, and separate into 3.5kg of secondary methionine and 44.5kg of impurity-enriched liquid after keeping warm at 40°C for 50min;

[0063] 15 kg of impurity-enriched liquid is added with 95 wt % sulfuric acid to adjust the pH to 2.1, and formic acid is removed by using carbon dioxide at 60-100° C. When the pH is stabilized at 2.4, the formic acid removal is completed. The impurity-enriched liquid after the removal of formic acid is allowed to stand at 35° C. for 30 minutes and separated into an oil phase and an aqueous phase. The oil phase is adjusted to a pH of 9.9 by using calcium oxide and then solidified, and the aqueous phase is used for the subsequent acidification of the hydrolyzate; the remaining 30 kg of impurity-enriched liquid mother liquor is returned to the concentration of the crystallization mother liquor.

[0064] Embodiment 2-5

[0065] Take 100kg of hydantoin hydrolyzate (methionine content is 14.7wt% and basic sodium content is 4.8wt%) obtained by hydrolyzing 5-(β-methylmercaptoethyl)hydantoin solution with sodium hydroxide, add 6.7kg of the aqueous phase removed from Example 2-4, adjust the pH to 6.7 with 95wt% sulfuric acid, add 6.8kg of the mixture not extracted from Example 2-4 and mix for 20min, then keep warm at 36°C for 40min, centrifuge to obtain 18kg of methionine and 103kg of crystallization mother liquor, stir 18kg of methionine with 20kg of water at 35°C for 10min, separate methionine and 21.7kg of beating water again, the mass fraction of methionine after drying is 99.8wt%, and the beating water is incorporated into the next crystallization mother liquor; 103kg of crystallization mother liquor is mixed with 3.5kg of secondary methionine from Example 2-4, extract 100kg of crystallization mother liquor for pH adjustment and concentration treatment (6.5kg of mixed solution not extracted is used for pH concentration treatment). The system is transferred to the next acidification of the hydrolyzate), 100kg of the crystallization mother liquor is added with 19kg of the beating water in Example 2-4 and 30kg of the impurity-enriched liquid in Example 2-4, and then 11kg of the hydrolyzate is used to adjust the pH to 8.6; the mixed solution is concentrated at 100°C to a methionine content of 10.7wt%, and centrifuged to separate into 19kg of sodium sulfate and 45kg of concentrated liquid. The sodium sulfate is washed and separated using the sodium sulfate washing equipment of Example 1, and the content after drying is greater than 99.9.wt%, and the single sodium sulfate extraction rate is 80%. When the sodium sulfate content is lower than 99.9wt%, the sodium sulfate washing water is transferred to the crystallization mother liquor, and the concentrated water is used for the preparation of ammonium carbonate solution or the use of hydrogen carboxylic acid / sulfonic acid resin to enrich ammonia; 45kg of the concentrated liquid is added with 1.2kg of 95wt% sulfuric acid, the pH is adjusted to 7.7, and separated into 4.4kg of secondary methionine and 42kg of impurity-enriched liquid after being kept at 35°C for 50min;

[0066] 8 kg of concentrated liquid was added with 95 wt % sulfuric acid to adjust the pH to 2.1, and formic acid was removed by using carbon dioxide at 60-100° C. When the pH was stabilized at 2.4, the formic acid removal was completed. The impurity-enriched liquid after the removal of formic acid was allowed to stand at 30° C. for 30 min and separated into an oil phase and an aqueous phase. The oil phase was adjusted to pH 11 by using calcium oxide and then solidified, and the aqueous phase was used for the subsequent acidification of the hydrolyzate; the remaining 34 kg of impurity-enriched liquid mother liquor was returned to the concentration of the crystallization mother liquor.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. The optimized preparation method of methionine based on direct sulfuric acid acidification method is characterized in that The following steps are involved: S1. The sodium hydrolyzate of 5-(2-methylmercaptoethyl)-hydantoin is acidified with sulfuric acid and separated into crude methionine and crystallization mother liquor; S2. The crude methionine is mixed with water and beaten, separated and dried to obtain methionine, and the beating water is returned to S1 and combined with the crystallization mother liquor; S3. Adjust the crystallization mother liquor pH> 8.5, concentrate and separate into sodium sulfate and concentrated mother liquor, wash the sodium sulfate using a sodium sulfate washing device, and return the washing water to S1 and combine with the crystallization mother liquor; S4. Acidification and crystallization of the concentrated mother liquor to separate into secondary methionine and impurity-enriched liquid; S5. The secondary methionine is returned to S1 and washed with the crystallization mother liquor to form a secondary mother liquor. Part of the secondary mother liquor is extracted to perform S3 operation, and the remaining secondary mother liquor is returned to S1 for acidification of the hydrolyzate; S6. The impurity-enriched liquid is divided into two parts. The first part of the impurity-enriched liquid is returned to S3 and combined with the crystallization mother liquor. The second part of the impurity-enriched liquid is treated with impurities after acidification.

2. The method for optimizing the preparation of methionine based on direct sulfuric acid acidification according to claim 1, characterized in that S1 is specifically as follows: the sodium hydrolyzate of 5-(2-methylmercaptoethyl)-hydantoin is adjusted to pH 5-8 using sulfuric acid, kept at 25-40° C. for 10-100 minutes, and centrifuged to separate into crude methionine and crystallization mother liquor.

3. The method for optimizing the preparation of methionine based on direct sulfuric acid acidification according to claim 1, characterized in that S3 specifically comprises: using a hydrolyzate to adjust the pH of the crystallization mother liquor to be greater than 8.5, concentrating at 60-120° C. until the methionine content is greater than 7% wt, and centrifuging to separate into sodium sulfate and concentrated mother liquor.

4. The method for optimizing the preparation of methionine based on direct sulfuric acid acidification according to claim 1, characterized in that S4 specifically includes: controlling the pH of the concentrated mother liquor to be 6-10, keeping the concentrated mother liquor at 25-40° C. for 10-100 minutes, and separating the concentrated mother liquor into secondary methionine and impurity-enriched liquid.

5. The method for optimizing the preparation of methionine based on direct sulfuric acid acidification according to claim 1, characterized in that The secondary mother liquor extracted in S5 is 10-30%wt of the total secondary mother liquor. The extracted secondary mother liquor contains all methionine solids, and the remaining secondary mother liquor does not contain methionine solids.

6. The optimized preparation method of methionine based on direct sulfuric acid acidification method according to claim 1, characterized in that The mass ratio of the first part of the impurity-enriched solution to the second part of the impurity-enriched solution in S6 is 3:1-7:

1.

7. The method for optimizing the preparation of methionine based on direct sulfuric acid acidification according to claim 1, characterized in that In S6, sulfuric acid is used to adjust the pH of the second part of the impurity-enriched liquid to less than 3, and then an impurity removal treatment is performed.

8. The method for optimizing the preparation of methionine based on direct sulfuric acid acidification according to claim 1 or 7, characterized in that The impurity removal treatment in S6 is specifically as follows: steam / carbon dioxide is used for stripping / gas stripping, the formic acid-containing gas is absorbed by alkali solution and then returned to the stripping / gas stripping process, and the alkali solution is concentrated to prepare formate; the impurity-enriched liquid after formic acid removal is separated into an oil phase and an aqueous phase by stratification or organic solvent extraction, the oil phase is adjusted to pH>10 with calcium oxide, and can be solidified for use as a soil conditioner or used as a soil conditioner after fermentation; the aqueous phase is returned to S1 for acidification of the hydrolyzate or returned to S4 for adjusting the pH of the concentrate.

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