Method for treating amide reaction wastewater and device thereof

Abstract

The application discloses a treatment method and device for amide reaction wastewater. Carbon dioxide and methylamine in the wastewater are separated by a first rectifying device; methyl alcohol in the wastewater is separated by a second rectifying device; dimethyl carbonate in the wastewater is separated by a third rectifying device; acid is added into residual liquid obtained after rectification, so that residual methylamine in the residual liquid is converted into methylamine salt and residual dimethyl carbonate is hydrolyzed into carbon dioxide and methyl alcohol; the residual liquid is filtered, the filter cake is a crude product and is sent to a crude product treatment process; the obtained filtrate is separated into layers, the lower layer of the methylamine salt aqueous solution is subjected to decolorization and evaporation crystallization to obtain the methylamine salt; the upper layer of the methyl alcohol is subjected to decolorization and rectification to obtain the methyl alcohol; residual liquid after the filtered and rectified methyl alcohol is used to obtain the crude product again, and is sent to the crude product treatment process; and the secondary filtrate is returned to the layering treatment. The amide reaction wastewater is treated by the application, useful substances are all recycled, the treated water is used again, there is no secondary pollution, and all the unit operations are environmentally-friendly chemical unit operations, which meet the requirements of safety and environmental protection and the concept of sustainable development.

Description

Technical Field

[0001] This invention relates to the field of fine chemicals technology, specifically to a method and apparatus for treating wastewater generated during the amidation reaction of chlorantraniliprole intermediate 2-amino-5-chloro-N,3-dimethylbenzamide, i.e., a method and apparatus for treating amidation reaction wastewater. Background Technology

[0002] 2-Amino-5-chloro-N,3-dimethylbenzamide (also known as K-amine) is an important intermediate for chlorantraniliprole. It appears as a white powder, CAS number 890707-28-5, and its structural formula is:

[0003] .

[0004] The mainstream production process for K-amine is as follows: starting with 2-amino-3-methylbenzoic acid, K-amine is obtained through a three-step reaction involving chlorination, phosgenation, and amidation. Specifically, chlorination involves the reaction of 2-amino-3-methylbenzoic acid with sulfuryl chloride to produce 2-amino-3-methyl-5-chlorobenzoic acid; phosgenation involves the reaction of 2-amino-3-methyl-5-chlorobenzoic acid with triphosgene to produce 5-chloro-7-methylindorubicin anhydride; and amidation involves the reaction of 5-chloro-7-methylindorubicin anhydride with methylamine to obtain 2-amino-3-methyl-5-chloro-N-methylformamide (hereinafter referred to as the main product).

[0005] The reaction equations are as follows:

[0006] ;

[0007] 2-Amino-3-methylbenzoic acid and 2-amino-3-methyl-5-chlorobenzoic acid

[0008] ;

[0009] 2-Amino-3-methyl-5-chlorobenzoic acid and 5-chloro-7-methylindocyanine anhydride

[0010] .

[0011] 5-Chloro-7-methylindocyanine anhydride Kamine

[0012] The wastewater treated in this invention originates from dimethyl carbonate, which is typically used as the solvent in the chlorination, phosgenation, and amidation reactions. The methylamine used in the third step, amidation, is an aqueous solution containing 40% methylamine in excess (50-200%). After the reaction, the material is discharged, filtered, and the filter cake is washed with dimethyl carbonate and water until its content reaches 98%, then dried to obtain K-amine. The filtrate is separated into solvent and aqueous phases using a separator. The solvent phase is reused, while the aqueous phase constitutes the wastewater.

[0013] The wastewater is weakly alkaline and contains dissolved substances including methylamine, methanol, dimethyl carbonate, carbon dioxide, and the product K-amine. The sources of each component are as follows: methylamine is the unreacted methylamine; methanol and carbon dioxide are produced by the alkaline hydrolysis of dimethyl carbonate; and the product K-amine is the portion produced during the reaction that did not precipitate.

[0014] How to recover substances from the wastewater produced during the amidation reaction process and how to reuse the treated wastewater are urgent problems that need to be solved. Summary of the Invention

[0015] The technical problem this invention aims to solve is the urgent need to recover relevant substances from wastewater generated during the amidation reaction of K-amine and to enable the reuse of the treated wastewater. This invention provides an effective method and apparatus for treating wastewater generated during the amidation reaction, specifically a method and apparatus for treating amidation reaction wastewater. Through this method and apparatus, all useful substances in the amidation reaction wastewater are recovered, the treated water can be reused, there is no secondary pollution, and all operations are environmentally friendly chemical unit operations, meeting safety and environmental protection requirements and the concept of sustainable development.

[0016] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0017] This invention provides a method for treating amidation reaction wastewater, the method comprising the following steps:

[0018] 1) The amidation reaction wastewater is subjected to a first distillation treatment to separate carbon dioxide and most of the methylamine gas from the wastewater; the separated carbon dioxide is absorbed and treated to prepare sodium carbonate aqueous solution, and the separated methylamine is absorbed and treated to prepare methylamine aqueous solution.

[0019] 2) The distillation residue after step 1) is subjected to a second distillation to separate methanol;

[0020] 3) The distillation residue after step 2) is subjected to a third distillation to separate dimethyl carbonate;

[0021] 4) Add acid to the distillation residue after three distillation processes to convert the residual methylamine into methylamine salt, and hydrolyze the residual dimethyl carbonate into carbon dioxide and methanol; the carbon dioxide generated by hydrolysis is absorbed to prepare an aqueous sodium carbonate solution; filter the acid-added residue (i.e., neutralized liquid), and the filter cake is the crude product, which is sent to the crude product processing step; the obtained filtrate is subjected to a layering process to separate the lower layer of methylamine salt aqueous solution and the upper layer of methanol (this methanol is produced by the hydrolysis of dimethyl carbonate);

[0022] 5) The methylamine salt aqueous solution obtained from the lower layer of the layering treatment in step 4) is decolorized by activated carbon and evaporated and crystallized by evaporator to obtain methylamine salt; the methanol obtained from the upper layer of the layering treatment is decolorized by activated carbon and distilled to obtain colorless methanol. The residue is filtered to obtain the second batch of crude Kamine, which is sent to the crude product processing step. The secondary filtrate is returned to the layering treatment.

[0023] According to the above-mentioned method for treating wastewater from amidation reaction, in step 1), liquid alkali is used to absorb the separated carbon dioxide; the mass percentage concentration of the resulting sodium carbonate aqueous solution is 10-15%; water is used to absorb the separated methylamine gas; the mass percentage concentration of the resulting methylamine aqueous solution is 30-40%.

[0024] According to the above-mentioned treatment method for amidation reaction wastewater, the methanol separated in step 2) is transferred to a storage tank with a methanol content of ≥98% and sold as a by-product.

[0025] According to the above-mentioned method for treating wastewater from the amidation reaction, the dimethyl carbonate separated in step 3) has a purity of ≥98% and is used as a solvent in the amidation reaction process.

[0026] According to the above-mentioned method for treating wastewater from amidation reaction, the acid mentioned in step 4) is sulfuric acid, hydrochloric acid, benzenesulfonic acid, or methylbenzenesulfonic acid; the acid is added until the pH of the solution is neutral.

[0027] According to the above-mentioned method for treating wastewater from amidation reaction, activated carbon is used in the decolorization treatment described in step 5), and the amount of activated carbon added is 0.05 to 10% (preferably 0.2 to 1%) of the amount to be treated.

[0028] According to the above-mentioned method for treating wastewater from amidation reaction, the water generated during the evaporation and crystallization process in step 5) is used for the absorption and treatment of methylamine in step 1) or as washing water during production.

[0029] Additionally, an apparatus for treating wastewater from an amidation reaction is provided, the apparatus comprising:

[0030] The first distillation unit is used to separate carbon dioxide and most of the methylamine gas from the amidation reaction wastewater;

[0031] An absorption device is used to absorb the carbon dioxide and methylamine gas separated from the first distillation unit;

[0032] The second distillation unit is used to separate methanol from the distillation residue transferred from the first distillation unit;

[0033] The third distillation unit is used to separate dimethyl carbonate from the distillation residue transferred from the second distillation unit;

[0034] Neutralization vessel, used for neutralization reaction treatment of distillation residue transferred from the third distillation unit;

[0035] The first filter is used to filter and separate the neutralized liquid transferred from the neutralization vessel;

[0036] A stratification tank is used to process the filtrate transferred from the first filter in stages.

[0037] Aqueous phase decolorization kettle, used for decolorizing the methylamine salt aqueous solution transferred from the lower layer of the layered tank;

[0038] The evaporator is used to evaporate the decolorized methylamine salt aqueous solution that has been filtered by the second filter in the aqueous phase decolorization kettle (the water produced during the evaporation process can be returned to the absorption unit for recycling).

[0039] A crude methanol decolorization kettle is used to decolorize crude methanol solutions transferred from the upper layer of a layering tank.

[0040] The fourth distillation unit is used to distill and separate the methanol material that has been decolorized in the crude methanol decolorization kettle and then filtered by the third filter.

[0041] According to the apparatus used in the above-mentioned amidation reaction wastewater treatment method, the absorption device consists of a first absorption device, a second absorption device, a third absorption device, and a fourth absorption device; the first distillation device, the second distillation device, the third distillation device, and the fourth distillation device are all packed towers, and the packing used in the packed towers is ceramic rectangular saddle ring packing or ceramic corrugated packing.

[0042] According to the apparatus used in the above-mentioned amidation reaction wastewater treatment method, the separated carbon dioxide and methylamine gas enter the absorption unit through the first induced draft fan; the methanol separated by the second distillation unit is transferred to the storage tank; the distillation residue in the third distillation unit is transferred to the neutralization kettle; during the neutralization kettle treatment of the distillation residue transferred from the third distillation unit, the carbon dioxide generated by the hydrolysis of dimethyl carbonate enters the absorption unit through the second induced draft fan; the neutralization kettle is equipped with a reflux condenser and a gas-liquid separator; the distillation residue after separation and treatment by the fourth distillation unit is transferred to the fourth filter for filtration.

[0043] In the technical solution of this invention, the filters used are integrated filter washing machine, titanium rod filter, centrifuge, vacuum filter tank, bag filter or plate and frame filter press.

[0044] All the equipment used in the technical solution of this invention is made of non-metallic materials, because metallic materials (such as stainless steel) can catalyze the oxidation of materials and turn them dark, affecting their appearance.

[0045] The distillation apparatus used in this invention is a glass-lined packed tower because the content of wastewater varies significantly between different batches, requiring greater operational flexibility from the distillation tower, which the glass-lined packed tower can meet. The packing used in the tower is either ceramic rectangular saddle ring packing or ceramic corrugated packing. These two types of packing provide a higher number of trays and higher separation efficiency. The layered tank used is a conical-bottom glass-lined stirred tank.

[0046] The positive and beneficial effects of this invention are:

[0047] This invention enables the primary recovery of over 99% of carbon dioxide, over 80% of methylamine, over 80% of dimethyl carbonate, and over 99% of methanol from K-amine amidation reaction wastewater. Unrecovered methylamine is converted to methylamine salt with over 99% conversion rate, and unrecovered dimethyl carbonate is hydrolyzed to carbon dioxide and methanol with over 99% conversion rate, which are then recovered a second time with a 99% recovery rate. Therefore, through this method and apparatus, all useful substances in the amidation reaction wastewater are recovered, the treated water can be reused, there is no secondary pollution, and all operations are environmentally friendly chemical unit operations, meeting safety and environmental protection requirements and the concept of sustainable development. It has significant economic and social benefits. Attached Figure Description

[0048] Figure 1 A schematic diagram of the apparatus used in the amide reaction wastewater treatment method of the present invention;

[0049] Figure 1 In the diagram, 1 is the first distillation unit, 2 is the first induced draft fan, 3 is the first absorption unit, 4 is the second absorption unit, 5 is the third absorption unit, 6 is the fourth absorption unit, 7 is the second distillation unit, 8 is the third distillation unit, 9 is the second induced draft fan, 10 is the neutralization vessel, 11 is the first filter, 12 is the layering tank, 13 is the aqueous phase decolorization vessel, 14 is the second filter, 15 is the evaporator, 16 is the crude methanol decolorization vessel, 17 is the third filter, 18 is the fourth distillation unit, and 19 is the fourth filter. Detailed Implementation

[0050] The present invention is further illustrated below with reference to embodiments, but this does not limit the scope of protection of the technical solutions of the present invention. The technical solutions in the embodiments of the present invention are clearly described below with reference to the accompanying drawings. The embodiments described below are only a part of the embodiments of the present invention. Based on the embodiments described in the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the technical solutions of the present invention. For example, if the chlorination reaction is placed as the last step, the product of the amidation reaction is 2-amino-N,3-dimethylformamide, and the wastewater treatment method and apparatus for the amidation reaction are almost exactly the same as those for K-amine, and are therefore also within the scope of protection. Furthermore, if the distillation method and process of the present invention are operated intermittently, and then changed to a continuous process, they are also within the scope of protection. Moreover, if the carbon dioxide and methylamine distilled by the apparatus of the present invention are purified and compressed into commercially available gases in steel cylinders, this process is also within the scope of protection of the technical solutions of the present invention.

[0051] Example 1:

[0052] like Figure 1 As shown, the apparatus used in the amidation reaction wastewater treatment method of the present invention includes:

[0053] The first distillation unit 1 is used to separate carbon dioxide and most of the methylamine gas from the amidation reaction wastewater;

[0054] An absorption device is used to absorb and process the carbon dioxide and methylamine gas separated from the first distillation unit 1.

[0055] The second distillation unit 7 is used to separate methanol from the distillation residue transferred from the first distillation unit 1;

[0056] The third distillation unit 8 is used to separate dimethyl carbonate from the distillation residue transferred from the second distillation unit 7.

[0057] Neutralization vessel 10 is used for neutralization reaction treatment of distillation residue transferred from the third distillation unit 8;

[0058] The first filter 11 is used to filter and separate the neutralized liquid transferred into the neutralization vessel 10;

[0059] The stratification tank 12 is used for stratified treatment of the filtrate transferred from the first filter 11;

[0060] Aqueous phase decolorizing kettle 13 is used to decolorize the methylamine salt aqueous solution transferred into the lower layer of the layered tank 12;

[0061] Evaporator 15 is used to evaporate the decolorized methylamine salt aqueous solution transferred into the aqueous phase decolorization kettle 13 after filtration by the second filter 14 (the water generated during the evaporation process can be returned to the absorption device for recycling).

[0062] Crude methanol decolorizing kettle 16 is used to decolorize the crude methanol solution transferred from the upper layer of the layering tank 12;

[0063] The fourth distillation unit 18 is used to distill and separate the methanol material that has been decolorized by the crude methanol decolorizing kettle 16 and filtered by the third filter 17.

[0064] Furthermore, the absorption device is composed of a first absorption device 3, a second absorption device 4, a third absorption device 5, and a fourth absorption device 6.

[0065] Furthermore, the first distillation unit 1, the second distillation unit 7, the third distillation unit 8, and the fourth distillation unit 18 are all glass-lined packed towers, and the packing used in the packed towers is ceramic rectangular saddle ring packing or ceramic corrugated packing.

[0066] Furthermore, the carbon dioxide and methylamine gas separated from the first distillation unit 1 enter the absorption unit through the first induced draft fan 2; the methanol separated from the second distillation unit 7 is transferred to the storage tank; the distillation residue in the third distillation unit 8 is pumped into the neutralization vessel. During the process of treating the distillation residue transferred from the third distillation unit in the neutralization vessel, the dimethyl carbonate hydrolyzes to generate carbon dioxide, which then enters the first absorption unit 3 and the second absorption unit 2 in sequence through the second induced draft fan 9; the neutralization vessel 10 is equipped with a reflux condenser and a gas-liquid separator; the distillation residue after separation and treatment by the fourth distillation unit 18 is transferred to the fourth filter 19 for filtration.

[0067] Example 2:

[0068] See appendix Figure 1 The detailed steps of the method for treating amidation reaction wastewater of the present invention are as follows:

[0069] 1) 2000 kg of amidation reaction wastewater is pumped into the first distillation unit 1 for distillation separation under total reflux (only carbon dioxide and methylamine gas are distilled off under total reflux). The mixture is heated to a slight boil, and carbon dioxide gas is distilled off first. The distilled carbon dioxide gas is then passed through the first induced draft fan 2 and sequentially enters the first absorption unit 3 and the second absorption unit 4 to be absorbed by liquid alkali to form a sodium carbonate aqueous solution with a mass percentage concentration of 13%. The methylamine gas that is then evaporated is passed through the first induced draft fan 2 and sequentially enters the first absorption unit 3 and the second absorption unit 4 to be absorbed by liquid alkali to remove the small amount of carbon dioxide mixed in with the methylamine gas. Then it sequentially enters the third absorption unit 5 and the fourth absorption unit 6 to be absorbed by water to form a methylamine aqueous solution with a mass percentage concentration of 38%. The resulting methylamine aqueous solution is then transferred to the amidation reaction process.

[0070] 2) When there is basically no methylamine gas escaping, the distillation residue after treatment in the first distillation unit 1 in step 1) is pumped into the second distillation unit 7, the reflux ratio is adjusted within 0.2 to 5, and methanol is heated to distill off; the methanol content is ≥98%; the distilled methanol is condensed by a condenser and cooled to room temperature by a cooler, and then transferred to a storage tank for sale as a by-product.

[0071] 3) When almost no methanol is distilled off, the distillation residue from the second distillation unit 7 in step 2) is pumped into the third distillation unit 8. The reflux ratio is adjusted to within 0.2 to 5, and dimethyl carbonate is heated to distill off. The dimethyl carbonate content collected is ≥98%. After the distilled dimethyl carbonate is condensed in a condenser and cooled to room temperature in a cooler, it is transferred to the amidation reaction process as a solvent (if the methanol content in the fore fraction exceeds 2%, the fore fraction is transferred to the second distillation unit for processing, and the collection of the fore fraction ends when the methanol content in the collected liquid is less than 2%).

[0072] 4) When almost no dimethyl carbonate is distilled off, the distillation residue from the third distillation unit 8 in step 3) is pumped into a neutralization vessel 10 equipped with a condenser and a gas-liquid separator. Sulfuric acid is slowly added dropwise to convert the residual methylamine into methylamine salt. The reaction temperature is controlled to maintain a slight reflux. The remaining small amount of dimethyl carbonate undergoes hydrolysis to produce carbon dioxide and methanol. This carbon dioxide enters the first absorption unit 3 through the second induced draft fan 9 and is absorbed by liquid alkali to form an aqueous sodium carbonate solution. When the pH of the distillation residue drops to 6-7, the addition of sulfuric acid is stopped, the temperature is lowered to room temperature, and the product is discharged. It is then transferred to the first filter 11 for filtration. The resulting filter cake is crude 2-amino-5-chloro-N,3-dimethylbenzamide (K amine). After washing twice with water, it is transferred to the crude product processing step. The resulting filtrate and washing liquid are transferred to a 2000L layering tank 12 and allowed to stand for 2 hours to separate. After separation, a methanol layer is obtained at the top and an aqueous methylamine salt layer is obtained at the bottom.

[0073] 5) Transfer the lower layer of methylamine salt aqueous solution obtained from the separation to the aqueous phase decolorization kettle 13, add activated carbon accounting for 0.2% of the weight of the methylamine salt aqueous solution to be decolorized, heat to 50-60℃ and keep it at the temperature for 2 hours for decolorization treatment, cool to room temperature, discharge, and transfer to the second filter 14 for treatment to remove activated carbon; the filtrate after removing activated carbon is transferred to the MVR evaporator 15 with crystallizer to evaporate water, cool and crystallize, filter to obtain methylamine sulfate, and sell it as a by-product; the evaporated water is transferred to the third absorption device 5, the fourth absorption device 6 or the washing process after the amidation reaction;

[0074] The upper methanol layer obtained from the stratification is transferred to the crude methanol decolorization kettle 16. Activated carbon accounting for 0.5% of the weight of the methanol to be decolorized is added to the crude methanol decolorization kettle, heated to reflux, and kept at this temperature for 2 hours for decolorization. Then, it is cooled to room temperature, discharged, and filtered through the third filter 17 to remove the activated carbon. The resulting filtrate is transferred to the fourth distillation unit 18, and the reflux ratio is adjusted within the range of 0.2 to 2 to ensure that the methanol content reaches ≥98%. The distilled methanol is filtered through the fourth filter 19, and the resulting methanol and the methanol obtained in step 2) are sold as by-products.

[0075] The amidation reaction wastewater, after treatment in this example, yielded 407 kg of methanol, 63 kg of dimethyl carbonate, 105 kg of a 13% sodium carbonate aqueous solution, 133 kg of a 38% methylamine aqueous solution, 120 kg of methylamine sulfate, and 116 kg of crude K-amine. The overall recovery rates of methanol, dimethyl carbonate, methylamine, carbon dioxide, and crude K-amine all exceeded 99%.

[0076] Example 3:

[0077] See appendix Figure 1 The detailed steps of the method for treating amidation reaction wastewater of the present invention are as follows:

[0078] 1) 4000 kg of amidation reaction wastewater is pumped into the first distillation unit 1 for distillation separation under total reflux (only carbon dioxide and methylamine gas are distilled off under total reflux). The mixture is heated to a slight boil, and carbon dioxide gas is distilled off first. The distilled carbon dioxide gas is then passed through the first induced draft fan 2 and sequentially into the first absorption unit 3 and the second absorption unit 4, where it is absorbed by liquid alkali to form a 12% sodium carbonate aqueous solution. The subsequently evaporated methylamine gas is then passed through the first induced draft fan 2 and sequentially into the first absorption unit 3 and the second absorption unit 4, where it is absorbed by liquid alkali to remove any small amount of carbon dioxide mixed in with the methylamine gas. It then sequentially enters the third absorption unit 5 and the fourth absorption unit 6, where it is absorbed by water to form a 40% methylamine aqueous solution. The resulting methylamine aqueous solution is then transferred to the amidation reaction process.

[0079] 2) When there is basically no methylamine gas escaping, the distillation residue after treatment in the first distillation unit 1 in step 1) is pumped into the second distillation unit 7, the reflux ratio is adjusted within 0.2 to 5, and methanol is heated to distill off; the methanol content is ≥98%; the distilled methanol is condensed by a condenser and cooled to room temperature by a cooler, and then transferred to a storage tank for sale as a by-product.

[0080] 3) When almost no methanol is distilled off, the distillation residue from the second distillation unit 7 in step 2) is pumped into the third distillation unit 8. The reflux ratio is adjusted to within 0.2 to 5, and dimethyl carbonate is heated to distill off. The dimethyl carbonate content collected is ≥98%. After the distilled dimethyl carbonate is condensed in a condenser and cooled to room temperature in a cooler, it is transferred to the amidation reaction process as a solvent (if the methanol content in the fore fraction exceeds 2%, the fore fraction is transferred to the second distillation unit 7 for processing, and the collection of the fore fraction ends when the methanol content in the collected liquid is less than 2%).

[0081] 4) When almost no dimethyl carbonate is distilled off, the distillation residue from the third distillation unit 8 in step 3) is pumped into a neutralization vessel 10 equipped with a condenser and a gas-liquid separator. Hydrochloric acid is slowly added dropwise to convert the residual methylamine into methylamine salt, and the reaction temperature is controlled to maintain a slight reflux. The remaining small amount of dimethyl carbonate is hydrolyzed to generate carbon dioxide and methanol. This carbon dioxide enters the first absorption unit 3 through the second induced draft fan 9 and is absorbed by liquid alkali to form a sodium carbonate aqueous solution. When the pH of the distillation residue drops to 6-7, the addition of hydrochloric acid is stopped, the temperature is lowered to room temperature, and the product is discharged. It is then transferred to the first filter 11 for filtration. The resulting filter cake is crude 2-amino-5-chloro-N,3-dimethylbenzamide (K amine). After washing twice with water, it is transferred to the crude product processing step. The resulting filtrate and washing liquid are transferred to a 2000L layering tank 12 and allowed to stand for 2 hours to separate. After separation, a methanol layer is obtained at the top and a methylamine salt aqueous solution is obtained at the bottom.

[0082] 5) Transfer the lower layer of methylamine salt aqueous solution obtained from the separation to the aqueous phase decolorization kettle 13, add activated carbon accounting for 0.5% of the weight of the methylamine salt aqueous solution to be decolorized, heat to 50-60℃ and keep it at the temperature for 2 hours for decolorization treatment, cool to room temperature, discharge, and transfer to the second filter 14 for treatment to remove activated carbon; the filtrate after removing activated carbon is transferred to the MVR evaporator 15 with crystallizer to evaporate water, cool and crystallize, filter to obtain methylamine sulfate, which is sold as a by-product; the evaporated water is transferred to the third absorption device 5, the fourth absorption device 6 or the washing process after the amidation reaction;

[0083] The upper methanol layer obtained from the separation process is transferred to the crude methanol decolorization kettle 16. Activated carbon accounting for 0.6% of the weight of the methanol to be decolorized is added to the crude methanol decolorization kettle, and the mixture is heated to reflux and kept at this temperature for 2 hours for decolorization. Then, the mixture is cooled to room temperature, discharged, and filtered through the third filter 17 to remove the activated carbon. The resulting filtrate is transferred to the fourth distillation unit 18, and the reflux ratio is adjusted within the range of 0.2 to 2 to ensure that the methanol content reaches ≥98%. The distilled methanol is filtered through the fourth filter 19, and the resulting methanol and the methanol obtained in step 2) are sold as by-products.

[0084] The amidation reaction wastewater, after treatment in this example, yielded 805 kg of methanol, 121 kg of dimethyl carbonate, 198 kg of a 12% sodium carbonate aqueous solution, 204 kg of a 40% methylamine aqueous solution, 110 kg of methylamine hydrochloride, and 196 kg of crude K-amine. The overall recovery rates of methanol, dimethyl carbonate, methylamine, carbon dioxide, and crude K-amine all exceeded 99%.

[0085] Comparative example:

[0086] 4000 kg of amidation reaction wastewater was pumped into an MVR evaporator for evaporation, cooling, and crystallization, yielding 3202 kg of distillate, 188 kg of crude K-amine, and 520 kg of dark brown filtrate. The crude K-amine was sent to the crude product treatment process. The COD of the distillate and the dark brown filtrate exceeded 100,000 mg / L, and the ammonia nitrogen content exceeded 30,000 mg / L, which could not be treated by conventional wastewater treatment equipment. Therefore, a qualified professional unit was commissioned to handle the wastewater for a fee.

Claims

1. A method for treating amidation reaction wastewater, characterized in that, The processing method includes the following steps: 1) The amidation reaction wastewater is subjected to a first distillation treatment to separate carbon dioxide and most of the methylamine gas from the wastewater; the separated carbon dioxide is absorbed and treated to prepare sodium carbonate aqueous solution, and the separated methylamine is absorbed and treated to prepare methylamine aqueous solution. 2) The distillation residue after step 1) is subjected to a second distillation to separate methanol; 3) The distillation residue after step 2) is subjected to a third distillation to separate dimethyl carbonate; 4) Add acid to the distillation residue after three distillation processes to convert the residual methylamine into methylamine salt and hydrolyze the residual dimethyl carbonate into carbon dioxide and methanol. The carbon dioxide generated by hydrolysis is absorbed to prepare an aqueous sodium carbonate solution. Filter the acid-added residue, and the filter cake is the crude product, which is sent to the crude product processing step. The obtained filtrate is subjected to a layering process to separate the lower layer of methylamine salt aqueous solution and the upper layer of methanol. 5) The methylamine salt aqueous solution obtained from the lower layer of the layering treatment in step 4) is successively decolorized and evaporated to crystallize, and then the methylamine salt is obtained. The methanol obtained from the upper layer of the layering treatment is successively decolorized and distilled to obtain colorless methanol. The residue is filtered to obtain the second batch of crude Kamine, which is sent to the crude product processing step. The secondary filtrate is returned to the layering treatment.

2. The method for treating amidation reaction wastewater according to claim 1, characterized in that: In step 1), the separated carbon dioxide is absorbed by liquid alkali; the resulting sodium carbonate aqueous solution has a mass percentage concentration of 10-15%; the separated methylamine gas is absorbed by water; the resulting methylamine aqueous solution has a mass percentage concentration of 30-40%.

3. The method for treating amidation reaction wastewater according to claim 1, characterized in that: Step 2) The separated methanol is transferred to a storage tank with a methanol content of ≥98% and sold as a by-product.

4. The method for treating amidation reaction wastewater according to claim 1, characterized in that: Step 3) The dimethyl carbonate separated has a purity of ≥98% and is used as a solvent in the amidation reaction process.

5. The method for treating amidation reaction wastewater according to claim 1, characterized in that: The acid mentioned in step 4) is sulfuric acid, hydrochloric acid, benzenesulfonic acid, or methylbenzenesulfonic acid; add acid until the pH of the solution is neutral.

6. The method for treating amidation reaction wastewater according to claim 1, characterized in that: In step 5), activated carbon is used for the decolorization process, and the amount of activated carbon added is 0.05 to 10% of the amount to be treated.

7. The method for treating amidation reaction wastewater according to claim 1, characterized in that: The water generated during the evaporation and crystallization process in step 5) is used for the absorption and treatment of methylamine in step 1) or as washing water during production.

8. An apparatus for treating wastewater from an amidation reaction, characterized in that, The device includes: The first distillation unit is used to separate carbon dioxide and most of the methylamine gas from the amidation reaction wastewater; An absorption device is used to absorb the carbon dioxide and methylamine gas separated from the first distillation unit; The second distillation unit is used to separate methanol from the distillation residue transferred from the first distillation unit; The third distillation unit is used to separate dimethyl carbonate from the distillation residue transferred from the second distillation unit; Neutralization vessel, used for neutralization reaction treatment of distillation residue transferred from the third distillation unit; The first filter is used to filter and separate the neutralized liquid transferred from the neutralization vessel; A stratification tank is used to process the filtrate transferred from the first filter in stages. Aqueous phase decolorization kettle, used for decolorizing methylamine salt aqueous solution transferred from the lower layer of a layered tank; Evaporator, used to evaporate the decolorized methylamine salt aqueous solution transferred into the aqueous phase decolorization kettle after filtration by the second filter; Crude methanol decolorization kettle, used for decolorizing crude methanol solution transferred from the upper layer of the layering tank; The fourth distillation unit is used to distill and separate the methanol material that has been decolorized in the crude methanol decolorization kettle and then filtered by the third filter.

9. The apparatus used in the amidation reaction wastewater treatment method according to claim 8, characterized in that: The absorption device consists of a first absorption device, a second absorption device, a third absorption device, and a fourth absorption device; the first distillation device, the second distillation device, the third distillation device, and the fourth distillation device are all packed towers, and the packing used in the packed towers is ceramic rectangular saddle ring packing or ceramic corrugated packing.

10. The apparatus used in the amidation reaction wastewater treatment method according to claim 8, characterized in that: The separated carbon dioxide and methylamine gas enter the absorption unit through the first induced draft fan; the methanol separated by the second distillation unit is transferred to the storage tank; the distillation residue in the third distillation unit is transferred to the neutralization vessel; during the neutralization vessel treatment of the distillation residue transferred from the third distillation unit, the carbon dioxide generated by the hydrolysis of dimethyl carbonate enters the absorption unit through the second induced draft fan; the neutralization vessel is equipped with a reflux condenser and a gas-liquid separator; the distillation residue after separation and treatment by the fourth distillation unit is transferred to the fourth filter for filtration.

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