CN112679401B - A kind of potassium carbonate full cycle process for preparing D, L-methionine - Google Patents

Abstract

The invention relates to the technical field of methionine production processes, in particular to a potassium carbonate full-circulation process for preparing D, L-methionine. The process is simple and efficient, all the extracted potassium salt is recovered in the form of potassium carbonate and returned to the preparation step of the hydantoin hydrolysate, complete circulation of almost all the potassium carbonate in the whole process is realized, the advantages of the methionine production process are improved, additional supplement of the potassium carbonate is not needed, no waste byproduct potassium salt is generated, and the material cost and the environment-friendly treatment cost are saved.

Description

A kind of potassium carbonate full cycle process for preparing D, L-methionine

technical field

The invention relates to the technical field of methionine production technology, in particular to a potassium carbonate full cycle process for preparing D,L-methionine.

Background technique

In the industrial chemical synthesis production process of D,L-methionine, potassium carbonate, potassium bicarbonate, and potassium hydroxide are used as intermediate hydantoin for hydrolyzing methionine to generate an aqueous solution of methionine salt, which is separated after acidification of methionine salt solution by carbon dioxide The "potassium salt process", which circulates the potassium-containing salt crystallization mother liquor back to the hydantoin hydrolysis step after the production of amino acid, is one of the mainstream processes for chemically synthesizing D,L-methionine, but in actual industrial applications, this process only realizes part of the potassium In the salt cycle, part of the potassium salt is discharged based on the purpose of removing impurities, and due to the complexity of the potassium salt composition, it cannot be effectively recovered, so it is necessary to continuously supplement the lost potassium salt to the system.

The formation of impurities is mainly due to the existence of side reactions in the reaction process, such as the oxidation of residual hydrogen cyanide to formic acid, the polymerization and decomposition of cyanohydrin into sulfur-containing impurities, the polymerization of hydantoin into macromolecular pigments, the condensation of methionine products into methionine dipeptide and the inability of hydantoin Complete hydrolysis to obtain intermediates such as hydantoin acid, and various impurities continue to accumulate in the system with the circulation of the mother liquor, which will directly affect the crystallization yield and quality of methionine. Among the above various derived impurities, except for methionine dipeptide and incomplete hydantoin hydrolyzate, which can be partially eliminated and transformed into methionine through the regeneration of the mother liquor under high-pH, high-temperature and high-pressure conditions, other impurities basically accumulate in one direction. It also comes from the use of catalysts and stabilizers in the entire process. For example, the catalysts and stabilizers used in the synthesis and storage of 3-methylthiopropanal and cyanohydrin will accumulate in the system in one direction, which is also supported by the analysis results. Therefore, for the sake of process sustainability and product quality stability, it is necessary to extract a part of the crystallization mother liquor and discharge it and no longer return it to the circulation. By extracting the crystallization mother liquor to remove excessive harmful impurities, the overall circulation of the potassium salt mother liquor remains relatively healthy. Stable, and the potassium salt is also lost with the extracted mother liquor, so it needs to be added to the system through fresh potassium salt, which causes the absolute loss of potassium salt, so the actual circulation rate of potassium salt in the methionine process is actually between 80% and 90%. . At the same time, the extracted crystallization mother liquor contains potassium salt, methionine, dipeptide, hydantoin, hydantoin amide, formic acid and cyclic pigments and other components, among which potassium salt is composed of potassium carbonate, potassium bicarbonate, potassium methionine, formic Potassium, potassium propionate, potassium citrate, etc. exist in various forms, and the composition is complex, so it is difficult to directly recover, which makes it difficult to deal with the extracted crystallization mother liquor, and it is also difficult to effectively recover the extracted potassium salt and circulate it back to the methionine production step. .

The above problems are also applicable to the D,L-methionine derivative process with similar characteristics of the "potassium salt process" based on potassium carbonate hydrolysis hydantoin, carbon dioxide neutralization, and potassium carbonate mother liquor returning to the previous stage, such as:

Patent CN1680311 discloses a method of dividing the crystallization mother liquor into the first circulation part and the second treatment part. By heating the second part of the mother liquor at a high temperature of 200-280 ° C, the methionine dipeptide is hydrolyzed into monomer methionine at high temperature, and carbon dioxide is introduced Precipitate the methionine and potassium bicarbonate in it, and obtain the precipitation of methionine and potassium hydrogenate and the second crystallization mother liquor after separation, and the second crystallization mother liquor continues to circulate or extract according to the state; patent CN1017351125 discloses a similar method, which divides the crystallization mother liquor For the first circulation part and the second treatment part, the second treatment part is still concentrated and thermally regenerated. The difference is that when recovering the methionine in the mother liquor of the second treatment part, lower alcohols are introduced to increase the ability to recover methionine; patent CN109485589 published A method for preparing zinc methionine chelate from methionine mother liquor containing potassium carbonate or potassium bicarbonate is disclosed. The concentrated methionine mother liquor is treated by bipolar membrane electrodialysis until the molar ratio of methionine to potassium ion is 1:0.8～1.1, and the acid chamber obtains Methionine desalting mother liquor and 0.5 methionine molar equivalent zinc salt react at 70-90°C for 30-90 minutes, then cool down and separate to prepare methionine zinc chelate, and the recovered potassium hydroxide dilute alkali in the alkali chamber is recycled to methionine production; patent CN106748932 discloses A mother liquor post-treatment method including filtration, acidification, gas-liquid separation, separation of methionine, regeneration of saturated acidification column and other steps. In this method, the crystallization mother liquor is first filtered through a microporous membrane to remove methionine and intermediate macromolecular polymerization Then let the filtrate be acidified by acidic resin to absorb the metal cations in it, and then separate the carbon dioxide by steam stripping to obtain a mixed solution whose main components are methionine and potassium formate, and then separate by electrodialysis to obtain methionine concentrated solution and potassium formate concentrated solution Enter recovery and biochemical treatment respectively, and finally acidify and regenerate the ion exchange resin to obtain potassium sulfate as a by-product.

In summary, the common problems in the current technology are: first, the potassium salt in the crystallization mother liquor is not completely recovered for return to the process cycle, and new potassium carbonate or potassium hydroxide needs to be continuously added to the methionine synthesis system; second, The main focus is on the recovery of beneficial methionine from the mined crystallization mother liquor, while the recovery of potassium salt and the environmental protection disposal measures of harmful components such as formic acid are less, which not only causes waste of resources, but also increases the pressure on subsequent environmental protection. The third is that it has not overcome the shortcomings that it is difficult to completely separate organic matter such as potassium salt and methionine in the extracted crystallization mother liquor, and that potassium salts (potassium bicarbonate, potassium formate, potassium butyrate, potassium citrate, etc.) that exist in various forms are difficult to be uniformly recovered; The fourth is to use advanced equipment such as chromatography, separation resin, electrodialysis, bipolar membrane, etc. to classify and process step by step. The process is complex, the investment in facilities is large, and the large dilution concentration consumes a lot of water and steam; the fifth is for methionine and dipeptide. The components undergo general and repeated physical concentration, neutralization and precipitation or organic solvent extraction and precipitation. The methionine recovered in the later stage contains more dipeptides and pigment impurities, which will cause secondary accumulation when returned to the system. The use of organic solvents to extract methionine not only faces separation, solvent recovery and disposal. , the organic solvent will also extract organic impurities, which may also cause secondary accumulation and pollution of the system. Generally speaking, the existing main technical problem is that the treatment after the mother liquor is extracted does not increase the advantages of the main process system of methionine, but may cause the secondary accumulation of impurities, and the complexity is reflected in the back end of the mother liquor treatment. Potassium Salt recovery measures have also been less studied.

Contents of the invention

In view of this, the purpose of the present invention is to provide a kind of potassium carbonate full-circulation process for preparing D, L-methionine, the process is simple and efficient, and the potassium salt produced is all recovered in the form of potassium carbonate and returned to hydantoin hydrolyzate for preparation In the first step, almost all potassium carbonate in the whole process is completely recycled, which improves the advantages of the methionine production process, and does not require additional potassium carbonate supplementation, and no waste by-product potassium salt is produced, saving material costs and environmental protection treatment costs.

The present invention solves the above technical problems by the following technical means:

A kind of potassium carbonate full cycle process for preparing D, L-methionine, comprising the following steps:

Obtaining methionine and crystallization mother liquor: the hydantoin feed solution from the front end is mixed with the potassium carbonate liquid flow and then reacted at 160-200°C and 0.2-2.0MPa to obtain the hydrolyzate of potassium methionine. The hydrolyzate is stripped and then carbon dioxide is introduced Acidification and crystallization to obtain methionine solid product and crystallization mother liquor containing potassium bicarbonate;

Transformation and circulation of potassium carbonate in the crystallization mother liquor: the crystallization mother liquor is divided into two parts, namely the circulating crystallization mother liquor part and the mining crystallization mother liquor part, and the circulating crystallization mother liquor is returned to the potassium carbonate liquid flow used in the methionine obtaining step after being regenerated at high temperature, The crystallization mother liquor is taken out and entered into a purification system for conversion and removal of organic impurities to obtain purified potassium carbonate, which is recovered to adjust the concentration of the potassium carbonate liquid flow.

Preferably, the extracted crystallization mother liquor entering the purification system is the extracted crystallization mother liquor one and/or the extracted crystallization mother liquor two, the extracted crystallization mother liquor one is the extracted crystallization mother liquor directly entering the purification system, and the extracted crystallization mother liquor The crystallization mother liquor 2 is the extracted crystallization mother liquor that undergoes secondary crystallization treatment and then enters the purification system before entering the purification system; The secondary crystallization methionine product and the secondary crystallization mother liquor enter the purification system to obtain potassium carbonate.

Preferably, the circulating crystallization mother liquor accounts for 70-97% of the total volume of the crystallization mother liquor; the total volume of the withdrawn crystallization mother liquor 1 and the withdrawn crystallization mother liquor 2 accounts for 3-30% of the total volume of the crystallization mother liquor.

Preferably, the purification system includes a feed unit, an incineration unit, a desulfurization and denitrification unit, a compression condensation unit, a carbon dioxide recovery unit and a carbon storehouse connected in sequence, and also includes an intake air preheating unit, a tail gas heat exchange unit, a crude potassium carbonate The collection unit, the decolorization and impurity removal unit, the intake air preheating unit and the crude potassium carbonate collection unit are all connected to the incineration unit, and the decolorization and impurity removal unit is connected to the crude potassium carbonate collection unit.

Preferably, the incineration unit includes a main incinerator and a secondary combustion chamber, and the residual gas of the main incinerator is separated by a high-temperature cyclone to remove a small amount of solids and enters the secondary combustion chamber for decomposition. The temperature of the main incinerator is The temperature of the secondary combustion chamber is controlled at 1100-1300° C. at 700-800° C.

Preferably, the hydantoin concentration of the hydantoin feed solution is 15-25w%, and the molar ratio of potassium carbonate to hydantoin is 1-1.5:1.

As preferably, the crude potassium carbonate obtained in the purification system is dissolved and then reclaimed for adjusting the concentration of potassium carbonate solution after activated carbon or membrane decolorization treatment, and the added amount of the activated carbon is 0.05～0.5% of the quality of potassium carbonate, The temperature of the decolorization treatment is 40-80° C., and the decolorization time is 10-30 minutes.

The process of the present invention is simple and efficient, all the recovered potassium salt is recovered in the form of potassium carbonate and returned to the preparation step of hydantoin hydrolyzate, and almost all potassium carbonate in the whole process is completely circulated, so that the advantages of the methionine production process are improved; the present invention The process does not require additional supplementation of potassium carbonate, and no waste by-product potassium salt is generated, which saves material costs and environmental protection treatment costs; in the process of the present invention, the extracted crystallization mother liquor is directly incinerated to convert the main organic matter into oxidizing gas, potassium formate and potassium acetate , Potassium citrate and other organic potassium salts are all converted into recyclable high-purity potassium carbonate, which simplifies the classification and treatment steps of each component of the extracted crystallization mother liquor, and obtains good treatment effect again; Before incineration, high-temperature hydrolysis and secondary crystallization are carried out on the extracted crystallization mother liquor, which further reduces the methionine content in the mother liquor, not only obtains additional products, but also reduces the energy consumed by excess methionine incineration and the nitrogen and oxygen in the flue gas The formation of compounds and sulfur dioxide reduces the pressure of subsequent treatment.

Description of drawings

Fig. 1 is a kind of potassium carbonate full cycle technological process schematic diagram for preparing D, L-methionine of the present invention;

Figure 2 is a schematic diagram of the purification system.

detailed description

The following will clearly and completely describe the technical solutions in the embodiments of the present invention in combination with the specific implementation manners of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

The present invention is used to prepare D, the potassium carbonate full-cycle process of L-methionine, as shown in Figure 1, with 3-methylthiopropionaldehyde, hydrogen cyanide (or potassium cyanide), carbon dioxide and ammonia (or ammonium bicarbonate) solution) as raw material to prepare hydantoin feed liquid, hydantoin feed liquid is hydrolyzed into hydantoin hydrolyzate at 160-200°C under the action of potassium carbonate of 1 to 1.5 times the molar amount of hydantoin after stripping and deamination, hydantoin The hydrolyzate is further stripped to remove excess ammonia, neutralized under the action of carbon dioxide to obtain a suspension containing D,L-methionine solids, and then separated to obtain D,L-methionine solids and potassium salts (potassium carbonate, potassium bicarbonate) Crystallization mother liquor 1, the crystallization mother liquor is divided into circulating crystallization mother liquor and mining crystallization mother liquor, and circulating crystallization mother liquor (70～97% crystallization mother liquor one volume) is recycled and used for hydantoin hydrolyzate preparation step, and mining crystallization mother liquor is extracted into The purification system (the schematic diagram of the purification system as shown in Figure 2) obtains potassium carbonate and tail gas, and the recovery of potassium carbonate is used to adjust the concentration of potassium carbonate solution. After heat exchange, the tail gas is further recovered through steps such as desulfurization and denitrification, compression and condensation, and stored in the carbon bin for methionine production, and the remaining inert tail gas is evacuated.

In addition, more specifically, the mined crystallization mother liquor can be divided into the mined crystallization mother liquor 1 and the mined crystallization mother liquor 2, the mined crystallization mother liquor 1 directly enters the purification system for incineration to obtain potassium carbonate, and the mined crystallization mother liquor 2 enters the purification system , first carry out the secondary crystallization treatment, the secondary crystallization treatment is to pass carbon dioxide into the extracted crystallization mother liquor 2 again for neutralization, separate and obtain the secondary crystallization product and the crystallization mother liquor 2, and return the obtained secondary crystallization product methionine to the hydrolysis step for crystallization The second mother liquor enters the purification system for treatment to obtain purified potassium carbonate.

The main components of the crystallization mother liquor of the present invention and its circulating part or mining part are potassium carbonate, potassium bicarbonate, methionine, potassium formate, potassium propionate, methionine dipeptide, hyinic acid, diketopiperazine, acrolein and 3- Methionaldehyde polymer and potassium acetate, potassium citrate, triethylamine, pyridine, polyvinyl alcohol, hydroxypropyl methylcellulose, etc. that may exist depending on specific process conditions.

The purification system of the present invention includes a feed unit, an incineration unit, a desulfurization and denitrification unit, a compression condensation unit, a carbon dioxide recovery unit and a carbon storehouse connected in sequence, and also includes an intake air preheating unit, a tail gas heat exchange unit, a crude potassium carbonate collection unit, Decolorization and impurity removal unit, the outlet end of the intake air preheating unit is connected to the incineration unit, the outlet end of the incineration unit is divided into two routes, one is connected to the crude potassium carbonate collection unit, the other is connected to the desulfurization and denitrification unit, the crude potassium carbonate collection unit is connected to the decolorization unit Cleaning unit connection. The feed unit is used to import the extracted crystallization mother liquor into the purification system. The following examples illustrate with compressed air sprayer as the feed unit; the incineration unit includes a main incinerator and a secondary combustion chamber, and the temperature of the main incinerator is controlled at 700- 800°C, during the high-temperature combustion process, the organic potassium salt is decomposed into potassium carbonate and falls to the bottom of the main incinerator, and the organic impurities are incinerated and oxidized into gas oxides and enter the tail gas. In the crude potassium carbonate collection unit, decolorization and impurity removal treatment is carried out through the decolorization and impurity removal unit to obtain purified potassium carbonate; the residual gas (water vapor, flue gas and a small amount of solids) of the main incinerator is separated by high-temperature cyclone to remove a small amount of solids and then enters the secondary The secondary combustion chamber is decomposed, and the temperature of the secondary combustion chamber is controlled at 1100-1300°C. The waste gas in the secondary combustion chamber enters the waste heat boiler and the heat exchanger of the tail gas heat exchange unit for waste heat recovery and utilization, and is used for circulating crystallization mother liquor respectively. The regeneration and purification system of the incineration unit preheats the intake air, and the exhaust gas after heat exchange is further purified by the desulfurization and denitrification device of the desulfurization and denitrification unit to purify the acid gas, and then condensed and compressed by the compression condensation unit to recover the carbon dioxide in it. The recovered carbon dioxide It is stored in a low-temperature carbon warehouse for the preparation of methionine, and the remaining exhaust gas is finally discharged through the chimney.

Different forms of potassium salts such as potassium bicarbonate, potassium formate, potassium citrate, potassium acrylate, and potassium methionine in the crystallization mother liquor produced in the purification system are converted into potassium carbonate, while methionine dipeptide, diketopiperazine, acrylic acid polymer, Organic impurities such as pyridine are converted into gaseous oxides and water is removed.

Specifically, the process of the present invention will be described in detail through the following specific examples.

Example 1

Step 1: Obtaining methionine and crystallization mother liquor

According to the existing conventional method, the hydantoin feed liquid is prepared from 3-methylthiopropionaldehyde, hydrogen cyanide, carbon dioxide and ammonia as raw materials. After the hydantoin feed liquid is stripped and deaminated, the hydantoin concentration is detected to be 15w%. .

The regenerated crystallization mother liquor (potassium carbonate: 35.6%; Potassium formate: 6.7%; Methionine: 9.86%; Methionine dipeptide: 1.45%) supplemented with fresh potassium carbonate is a 50w% potassium carbonate (potassium ion meter) solution from the regenerated crystallization mother liquor after multiple cycles flow.

The hydantoin feed liquid is mixed at 686kg/h and 50w% potassium carbonate liquid flow at 166Kg/h through a static device, and then enters the first-stage tubular reactor made of 316 material, and enters the second-stage tubular reactor after staying at 180°C for 5 minutes. The reaction pressure in the first-stage tubular reactor varies from 0.2 to 1.5 MPa, the temperature of the second-stage tubular reactor is 150°C, the reaction pressure varies from 0.8 to 2.0 MPa, and the residence time is 5 minutes. The outlet of the type reactor is pumped into the stripper, and after stripping to remove carbon dioxide and ammonia, the hydantoin hydrolyzate with potassium methionine and potassium carbonate as the main body is obtained at the bottom of the stripper, and methionine MET: 19.88w%, K ⁺ : 10.41w%.

Take 500 kg of the above-mentioned hydantoin hydrolyzate and transfer it to the crystallizer. Under the condition of 25°C, pass carbon dioxide from the carbon chamber into the crystallizer to carry out the neutralization reaction. D,L-methionine suspension was obtained, and the D,L-methionine suspension was filtered and separated, washed and dried to obtain 46.71Kg of solid D,L-methionine product, and the filtrate and washing liquid were combined to obtain 530kg of crystallization mother liquor, and the crystallization was detected Mother liquor composition: MET: 9.84%, K ⁺ : 9.66%, formic acid: 0.78%, dipeptide 1.12%.

Step 2: Conversion and circulation of potassium carbonate in crystallization mother liquor

The crystallization mother liquor obtained in step one is divided into two parts, and a part accounts for 70% of the total volume of the crystallization mother liquor as a circulating crystallization mother liquor. After the circulation crystallization mother liquor is maintained at 0.75MPa and 180°C for 10min for regeneration, potassium bicarbonate in the mother liquor is converted into potassium carbonate, and the system The pH is improved, and the corresponding part of methionine process derivatives such as methionine dipeptide and hydantoin acid are converted into methionine products under the action of high temperature, and the regenerated circulating crystallization mother liquor (MET: 9.98%, K ⁺ : 9.89%) is returned for use In the methionine acquisition step, it is used as a liquid stream of potassium carbonate; the other part accounts for 30% of the total volume of the crystallization mother liquor as the extraction crystallization mother liquor of impurities in the purification system.

About 160Kg of the extracted crystallization mother liquor (MET: 9.84%, K ⁺ : 9.66%) from the above operation enters the purification system, and is sprayed into the incinerator from the top spray gun of the main incinerator of the incineration unit by using a compressed air atomizer. Fully evaporative combustion under existing conditions, the main incinerator is set at a temperature of 700 ° C, during the high-temperature combustion process, the organic potassium salt is decomposed into potassium carbonate and falls to the bottom of the main incinerator, and the organic impurities are incinerated and oxidized into gas oxides and enter the tail gas, and the precipitated carbonic acid is burned and converted Potassium solid is transported and collected in the crude potassium carbonate bin through the scale conveying device, and the recovered crude potassium carbonate is 52.6Kg in total of light yellow powder and granules, and its purity is 98.5%. The residual gas (water vapor, flue gas and a small amount of solids) from the main incinerator is separated by a high-temperature cyclone to remove a small amount of solids, and then enters the secondary combustion chamber. The harmful components in the flue gas are completely decomposed at a high temperature of 1100°C, and the resulting high-temperature The secondary combustion waste gas enters the waste heat boiler and heat exchanger for waste heat recovery and utilization, and is used for the regeneration of the circulating crystallization mother liquor and the preheating of the intake air of the incineration unit of the purification system respectively. The tail gas after heat exchange is further purified by a desulfurization and denitrification device The acid gas is condensed and compressed to recover the carbon dioxide stored in the low-temperature carbon storage for the production of methionine, and the remaining tail gas is finally discharged through the chimney.

Step 3: recovery of potassium carbonate

The 52.6Kg crude potassium carbonate obtained by the above-mentioned purification system was dissolved to form a 50% potassium carbonate solution, and 0.05% activated carbon was added and stirred at 40° C. for 10 minutes for decolorization and purification, and 360 Kg of recycled crystallization mother liquor (MET: 9.98%, K ⁺ : 9.89%, fold potassium carbonate 35.2%), obtain potassium carbonate liquid flow 460Kg of potassium carbonate content 38.3% in the potassium carbonate 35.2%) and return to the methionine preparation step.

Compared with the 160Kg mining crystallization mother liquor (MET:9.84%, K+:9.66%) entering the purification system, the recovery rate of 52.6Kg content of 98.5% crude potassium carbonate is 94.72%.

Compared with the original potassium carbonate salt in the 530Kg crystallization mother liquor (MET: 9.84%, K ⁺ : 9.66%) in the operation, the 70% crystallization mother liquor is regenerated and used as potassium carbonate liquid flow and 30% crystallization mother liquor enters the purification system The purified potassium carbonate is purified and returned to the potassium carbonate liquid stream, and the overall potassium carbonate recovery rate is as high as 97.25%.

The loss of methionine in the methionine crystallization mother liquor during the purification process is: 30wt%.

Example 2

Step 1: Obtaining methionine and crystallization mother liquor

According to the existing conventional method, the hydantoin feed liquid is prepared from 3-methylthiopropionaldehyde, hydrogen cyanide, carbon dioxide and ammonia as raw materials. After the hydantoin feed liquid is stripped and deaminated, the hydantoin concentration is detected to be 20w%. ;

460 Kg from Example 1 was reused 38.3w% potassium carbonate liquid stream (MET: 7.81%, formic acid: 0.62%, dipeptide: 0.98%).

The Shanghai Yin material liquid is mixed with 400kg/h and 38.3w% potassium carbonate liquid at 169Kg/h through a static device, and then enters the first-stage tubular reactor made of 316 material, and enters the second-stage tubular reaction after staying at 180°C for 5 minutes device, the reaction pressure in the first-stage tubular reactor rises to 1.5MPa, the temperature of the second-stage tubular reactor is 150°C, the residence time is 5min, the reaction pressure rises to 2.0MPa, and then the feed liquid flows from the second-stage tubular reactor The outlet is pumped into the stripping tower, and after stripping to remove carbon dioxide and ammonia, hydantoin hydrolyzate mainly composed of potassium methionine and potassium carbonate is obtained at the bottom of the stripping tower. Methionine MET: 17.65w%, K ⁺ : 9.31 w%.

Take 500 kg of the above-mentioned hydantoin hydrolyzate and transfer it to the crystallizer. Under the condition of 25°C, pass carbon dioxide from the carbon chamber into the crystallizer to carry out the neutralization reaction. 8.65, D, L-methionine suspension was obtained, the D, L-methionine suspension was filtered and separated, washed and dried to obtain 45.89Kg of solid D, L-methionine product, the filtrate and washing liquid were combined to obtain 522 kg of crystallization mother liquor, and the crystallization was detected Mother liquor composition: MET: 8.25%, K ⁺ : 8.98%; formic acid: 0.62%; dipeptide: 1.02%;

Step 2: Conversion and circulation of potassium carbonate in crystallization mother liquor

The crystallization mother liquor obtained in step one is divided into two parts, and a part accounts for 80% of the total volume of the crystallization mother liquor as a circulating crystallization mother liquor. After the circulation crystallization mother liquor is maintained at 0.75MPa and 180°C for 10min for regeneration, potassium bicarbonate in the mother liquor is converted into potassium carbonate, and the system The pH is increased, and the corresponding part of methionine process derivatives such as methionine dipeptide and hydantoin acid are converted into methionine products under high temperature, and the recycled crystallization mother liquor after regeneration (MET: 8.88%, K ⁺ : 9.25%, formic acid: 0.69 %, dipeptide: 0.43%) is returned to be used as potassium carbonate liquid stream in the methionine obtaining step; Another part accounts for 20% of crystallization mother liquor total volume as the extraction crystallization mother liquor of purification system impurity.

About 104Kg of the crystallization mother liquor (MET: 8.25%, K+: 8.98%; formic acid: 0.62%; dipeptide: 1.02%) extracted from the above-mentioned extraction is sent into the crystallization kettle after being concentrated to a potassium ion concentration of 11%. The methionine in the mother liquor is recovered by carbon dioxide secondary crystallization, and the solid-liquid separation obtains 6Kg of the secondary crystallization mother liquor (Met: 66.7%, K ⁺ : 7.93%), and the secondary crystallization methionine product returns to the methionine crystallization step.

Dilute the secondary crystallization mother liquor (MET: 5.14%, K ⁺ : 9.85%) 90Kg, and the resulting secondary crystallization product returns to the hydantoin hydrolysis step, and the secondary crystallization mother liquor is atomized by compressed air and sprayed into the incineration system through the spray gun on the top of the main incinerator. Fully evaporative combustion in the presence of auxiliary fuel, the temperature of the main incinerator is 780°C, and the organic potassium salt is decomposed into potassium carbonate during the high-temperature combustion process, which falls to the bottom of the main incinerator, and is transported by a dry slag remover or a scale plate conveyor, and the recovered carbonic acid Potassium is in the form of white powder or light yellow granules, 31.4Kg, with a purity of 97.3%. The residual gas (water vapor, flue gas and a small amount of solids) from the main incinerator is separated by a high-temperature cyclone to remove a small amount of solids, and then enters the secondary combustion chamber. The harmful components in the flue gas are completely decomposed at a high temperature of 1200 ° C, and the resulting high-temperature The secondary combustion waste gas enters the waste heat boiler for waste heat recovery and utilization, so as to improve economic benefits and reduce operating costs. The flue gas discharged from the waste heat boiler further passes through the quenching device, dust removal device, and desulfurization device in turn to cool down and purify the soot and acid gas in it to meet the emission standards, and finally discharge through the chimney.

Step 3: recovery of potassium carbonate

The 31.4Kg crude product obtained in step 2 is recovered by adding water to dissolve potassium carbonate, and add 0.25% activated carbon of potassium carbonate quality, carry out decolorization treatment at a temperature of 80° C. for 30 minutes, filter and separate, and add the obtained potassium carbonate decolorization solution to the circulating crystallization mother liquor Used to prepare the potassium carbonate solution in the preparation step of hydantoin hydrolyzate.

Compared with the 104Kg crystallization mother liquor (MET: 8.25%, K+: 8.98%; formic acid: 0.62%; dipeptide: 1.02%) entering the purification system, the 6Kg secondary crystallization solid (Met: 66.7 %, K+: 7.93%) and purification system incineration recovery to get 31.4Kg content is 97.3% crude potassium carbonate conversion, the rate of recovery of potassium ions is 98.5%;

Compared with the original potassium carbonate salt in the 522Kg crystallization mother liquor (MET: 8.25%, K+: 8.98%; formic acid: 0.62%; dipeptide: 1.02%;) in which the operation was carried out, the 80% crystallization mother liquor was regenerated and used as carbonic acid Potassium liquid flow and 20% crystallization mother liquor enter the purification system to purify and recover potassium carbonate after secondary crystallization, and the overall recovery rate of potassium carbonate is as high as 99.5%.

At the same time, the total loss of methionine in the crystallization mother liquor during the purification process is reduced to 10.7wt%.

Example 3

Step 1: Obtaining methionine and crystallization mother liquor

According to the existing conventional method, the hydantoin feed liquid is prepared from 3-methylthiopropionaldehyde, hydrogen cyanide, carbon dioxide and ammonia as raw materials. After the hydantoin feed liquid is stripped and deaminated, the hydantoin concentration is detected to be 25w%. , Hein material liquid is mixed at 686kg/h and 50w% new potassium carbonate solution at 276kg/h through a static device, then enters the first-stage tubular reactor made of 316 material, and enters the second-stage tubular reactor after staying at 200°C for 3 minutes , the reaction pressure in the first-stage tubular reactor rises to 1.6MPa, the temperature of the second-stage tubular reactor is 150°C, the reaction pressure rises to 1.6MPa, the residence time is 8min, and then the feed liquid flows from the outlet of the second-stage tubular reactor Pumped into the stripper, after stripping to remove carbon dioxide and ammonia, the hydantoin hydrolyzate with potassium methionine and potassium carbonate as the main body is obtained at the bottom of the stripper, and methionine (MET): 17.32w%, K ⁺ : 9.07w%, formic acid: 0.02%, dipeptide: 0.17%.

Take 500 kg of the above-mentioned hydantoin hydrolyzate and transfer it to the crystallizer. Under the condition of 25°C, pass carbon dioxide from the carbon chamber into the crystallizer to carry out the neutralization reaction. D,L-methionine suspension was obtained, and the D,L-methionine suspension was filtered and separated, washed and dried to obtain 49.89Kg of solid D,L-methionine product, and the filtrate and washing liquid were combined to obtain 510kg of crystallization mother liquor, and the crystallization was detected Mother liquor MET: 7.01%, K ⁺ : 8.16%.

Step 2: Conversion and circulation of potassium carbonate in crystallization mother liquor

The crystallization mother liquor is divided into two parts, one part accounts for 97% of the total volume of the crystallization mother liquor as a circulating crystallization mother liquor, and the circulating crystallization mother liquor is kept at 0.75MPa and 200°C for 10min for regeneration, and is recycled in the preparation step of hydantoin hydrolyzate for adjusting potassium carbonate The concentration of the solution; the other part accounts for 3% of the total volume of the crystallization mother liquor as the extraction crystallization mother liquor of impurities in the purification system.

15.3Kg of the extracted crystallization mother liquor (MET: 7.01%, K+: 8.16%) from step 2 is directly atomized by compressed air and sprayed into the incineration system through the top spray gun of the main incinerator, fully evaporated and burned in the presence of auxiliary fuel, and Set the temperature of the main incinerator to 800°C. During the high-temperature combustion process, organic potassium salts are decomposed into potassium carbonate, which falls to the bottom of the main incinerator, and is transported by a dry slag remover or scale conveyor. The recovered potassium carbonate is in the form of white powder, totaling 3.22 kg, its purity was detected to be greater than 99.5%, and it was directly used in the preparation of potassium carbonate solution in the hydantoin solution preparation step. The residual gas (water vapor, flue gas and a small amount of solids) from the main incinerator is separated by a high-temperature cyclone to remove a small amount of solids, and then enters the secondary combustion chamber. The harmful components in the flue gas are completely decomposed at a high temperature of 1300°C, and the resulting high-temperature The secondary combustion waste gas enters the waste heat boiler for waste heat recovery and utilization, so as to improve economic benefits and reduce operating costs. The flue gas discharged from the waste heat boiler further passes through the quenching device, dust removal device, and desulfurization device to cool down and purify the soot and acid gas in it. After meeting the emission standards, it is finally discharged through the chimney.

Step 3: recovery of potassium carbonate

The 3.22Kg crude potassium carbonate obtained by the above-mentioned purification system was dissolved to form a 50% potassium carbonate solution, and 0.5% activated carbon was added and stirred at 45° C. for 15 minutes for decolorization and purification, and flowed back as potassium carbonate solution for the methionine preparation step.

Compared with the 15.3Kg that enters the purifying system to extract crystallization mother liquor (MET:7.01%, K+:8.16%), reclaiming 3.22Kg content is the rate of recovery of potassium carbonate of 99.5% 72.49%;

Compared with the original potassium carbonate salt in the 510Kg crystallization mother liquor (MET: 7.01%, K+: 8.16%) for operation, the 97% crystallization mother liquor is regenerated and used as potassium carbonate liquid flow and 3% crystallization mother liquor enters the purification system for purification Purified potassium carbonate is obtained and returned to the potassium carbonate liquid flow, and the overall recovery rate of potassium carbonate is as high as 99.17%.

The above embodiments are only used to illustrate the technical solutions of the present invention without limitation. Although the present invention has been described in detail with reference to preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced. Without departing from the purpose and scope of the technical solutions of the present invention, all of them should be included in the scope of the claims of the present invention. The technologies, shapes and construction parts not described in detail in the present invention are all known technologies.

Claims (6)

1. a potassium carbonate full cycle process for preparing D, L-methionine, is characterized in that, may further comprise the steps: Obtaining methionine and crystallization mother liquor: the hydantoin feed solution from the front end is mixed with the potassium carbonate liquid flow and then reacted at 160-200°C and 0.2-2.0MPa to obtain the hydrolyzate of potassium methionine. The hydrolyzate is stripped and treated with carbon dioxide for acidification Crystallization obtains methionine solid product and crystallization mother liquor containing potassium bicarbonate; Transformation and circulation of potassium carbonate in the crystallization mother liquor: the crystallization mother liquor is divided into two parts, namely the circulating crystallization mother liquor part and the mining crystallization mother liquor part, and the circulating crystallization mother liquor is returned to the potassium carbonate liquid flow used in the methionine obtaining step after being regenerated at high temperature, Extract the crystallization mother liquor and enter the purification system to convert and remove organic impurities to obtain purified potassium carbonate, and the purified potassium carbonate is recovered to adjust the concentration of the potassium carbonate liquid flow; The purification system includes a feed unit, an incineration unit, a desulfurization and denitrification unit, a compression condensing unit, a carbon dioxide recovery unit and a carbon storehouse connected in sequence, and also includes an intake air preheating unit, an exhaust gas heat exchange unit, a crude potassium carbonate collection unit, a decolorization The impurity removal unit, the intake air preheating unit and the crude potassium carbonate collection unit are all connected to the incineration unit, and the decolorization and impurity removal unit is connected to the crude potassium carbonate collection unit. 2. A kind of potassium carbonate full-cycle process for preparing D, L-methionine according to claim 1, characterized in that, the extracted crystallization mother liquor entering the purification system is the extracted crystallization mother liquor one and/or the extracted crystallization mother liquor The crystallization mother liquor 2 is extracted crystallization mother liquor 1 is the extracted crystallization mother liquor that directly enters the purification system, and the extracted crystallization mother liquor 2 is the extraction that undergoes secondary crystallization treatment before entering the purification system and then enters the purification system. Crystallization mother liquor; the secondary crystallization treatment is to pass carbon dioxide into the extracted crystallization mother liquor again for neutralization, separate and obtain the secondary crystallization methionine product and the secondary crystallization mother liquor, and the secondary crystallization mother liquor enters the purification system to obtain potassium carbonate. 3. A kind of potassium carbonate full-circulation process for preparing D, L-methionine according to claim 2, characterized in that, the circulating crystallization mother liquor accounts for 70% to 97% of the total volume of the crystallization mother liquor; the crystallization mother liquor is extracted The total volume of one and the extracted crystallization mother liquor two accounts for 3-30% of the total volume of the crystallization mother liquor. 4. a kind of potassium carbonate full cycle process for preparing D, L-methionine according to claim 3, is characterized in that, described incineration unit comprises main incinerator and secondary combustion chamber, the main incinerator's After the residual gas is separated by a high-temperature cyclone to remove a small amount of solids, it enters the secondary combustion chamber for decomposition. The temperature of the main incinerator is controlled at 700-800°C, and the temperature of the secondary combustion chamber is controlled at 1100-1300°C. 5. A kind of potassium carbonate full cycle process for preparing D,L-methionine according to claim 1, characterized in that, the hydantoin concentration of the hydantoin feed liquid is 15～25w%, potassium carbonate and hydantoin Because the molar ratio is 1～1.5:1. 6. A kind of potassium carbonate full-circulation process for preparing D, L-methionine according to claim 1, characterized in that, the crude potassium carbonate obtained in the purification system is dissolved and then treated with activated carbon or membrane decolorization Recovery is used to adjust the concentration of potassium carbonate solution, the amount of the activated carbon added is 0.05-0.5% of the mass of potassium carbonate, the temperature of the decolorization treatment is 40-80°C, and the decolorization time is 10-30min.

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