Glycine wastewater treatment method

Abstract

The invention discloses a glycine wastewater treatment method, and relates to the technical field of chemical engineering. The treatment method comprises the following steps: cooling ammoniation reaction liquid, separating out mixed crystals of glycine and ammonium chloride, and filtering to obtain the mixed crystals and filtrate; mixing the mixed crystal with water, heating for dissolving, cooling for the first time, sequentially mixing with three methanol aqueous solutions with different volumes, and then cooling for the second time to separate out a finished product glycine; performing membrane decoloration treatment on the filtrate, and performing nanofiltration membrane treatment on the decolorized permeate to obtain nanofiltration membrane trapped fluid and nanofiltration membrane permeate fluid; the nanofiltration membrane trapped fluid is subjected to alcohol precipitation to recover glycine, ammonium chloride is removed through electrodialysis, and a urotropine solution is obtained; carrying out electrodialysis on the nanofiltration membrane permeate to remove ammonium chloride, and mixing with zinc acetate and zinc oxide to react to obtain a zinc glycinate finished product. Through the post-treatment process of decoloration, nanofiltration, alcohol precipitation and electrolysis, impurities in ammoniation filtrate are removed, urotropine is enriched, and the utilization rate of raw materials is increased.

Description

Technical Field

[0001] The invention relates to the technical field of chemical industry, and in particular to a method for treating glycine wastewater. Background Art

[0002] The traditional domestic chloroacetic acid method for producing glycine is as follows: add a catalyst urotropine aqueous solution to the reactor, add chloroacetic acid solution dropwise while passing ammonia gas, and perform an amination reaction within a certain temperature and pH range. After the reaction is completed, slowly add methanol aqueous solution dropwise to the reaction liquid and cool it to a certain range before centrifuging it in a centrifuge to obtain crude glycine. The mother liquor is distilled to recover methanol through a rectification tower, and water is recovered through multi-effect evaporation. The remaining kettle residue is cooled, crystallized, and filtered to obtain by-product ammonium chloride, and a reddish-brown waste liquid containing urotropine, glycine, and other side reaction products is also obtained.

[0003] In this production process, the catalyst urotropine required for the amination reaction cannot be recovered, and the high temperature conditions in the process of recovering methanol and water will lead to side reactions and produce a large amount of impurities. The recycling will affect the glycine yield; the methanol consumption per unit area is high in the process of producing glycine, and the mother liquor needs to consume a large amount of steam to recover methanol; some glycine and ammonium chloride are difficult to recover, and the recovery process through the distillation tower and multi-effect evaporation will produce a large amount of reddish-brown wastewater, which cannot be discharged directly, increasing the treatment cost.

[0004] Chinese patent CN102167668A discloses an environmentally friendly alcohol-phase chloroacetic acid method for producing glycine, a glycine production process using methanol or methanol aqueous solution as solvent, chloroacetic acid and liquid ammonia as raw materials, and nanofiltration membrane separation technology is used to achieve continuous production of glycine, and the catalyst urotropine can be recycled. The method is characterized in that the method comprises the following steps: step 1, selecting a reactor suitable for continuous reaction, the reactor having the following characteristics: the glycine ammonolysis reactor is equipped with a condenser, which can recover the solvent methanol or methanol aqueous solution; the mixed crystals of glycine and ammonium chloride generated in the reactor can be separated out in time; step 2, adding methanol or methanol aqueous solution into the reactor; adding urotropine to prepare urotropine methanol solution or urotropine methanol aqueous solution; the urotropine solution concentration is 3%-20% by weight; step 3, passing chloroacetic acid methanol solution or chloroacetic acid methanol aqueous solution into the reactor, and simultaneously passing liquid ammonia to carry out ammonolysis reaction; step 4, the ammonolysis reaction temperature is maintained at the methanol solution or methanol aqueous solution near the boiling point of the alcohol aqueous solution; methanol or methanol aqueous solution evaporates and is condensed and recovered by a condenser; the amount of methanol or methanol aqueous solution brought into the reactor by the chloroacetic acid solution is the same as the amount of methanol or methanol aqueous solution evaporated, ensuring that the total amount of methanol or methanol aqueous solution in the reactor remains unchanged; step five, the mixed crystal solid of glycine and ammonium chloride generated by the reaction is separated from the reactor in time by a crystallization device; the urotropine solution after filtering and centrifuging the mixed crystals of glycine and ammonium chloride is returned to the reactor for recycling; step six, the urotropine methanol solution or urotropine methanol aqueous solution in the reactor stops the aminolysis reaction after the color turns yellow; the solution is cooled and the ammonium chloride solid is filtered out, and then treated with a nanofiltration device; the nanofiltration device selects a nanofiltration membrane with a molecular weight cutoff of less than 300; when the volume of the nanofiltration retentate is less than one-sixth of the volume of the permeate, the concentration is stopped; the nanofiltration permeate is returned to the reactor for recycling; step seven, after the mixed crystals of glycine and ammonium chloride are dissolved by heating with water, the glycine is recovered by alcohol precipitation. The production method does not generate high value-added glycine zinc and does not improve the recovery rate of glycine.

[0005] In view of this, in order to solve the deficiencies of the prior art, the present invention provides a method for treating glycine wastewater. Summary of the invention

[0006] The purpose of the invention is to provide a method for treating glycine wastewater, which greatly improves the yield and content of glycine.

[0007] To achieve the above-mentioned purpose of the invention, the technical solution of the present invention is as follows:

[0008] The present invention provides a method for treating glycine wastewater, comprising the following steps:

[0009] S1, after the amination reaction liquid is cooled, mixed crystals of glycine and ammonium chloride are precipitated, and the mixed crystals and filtrate are obtained by filtration;

[0010] S2, mixing the mixed crystals obtained in step S1 with water and heating them to dissolve them, cooling them for the first time and sequentially mixing them with three different volumes of methanol aqueous solutions, and then cooling them for a second time to precipitate finished glycine;

[0011] S3, subjecting the filtrate obtained in step S1 to membrane decolorization treatment, and subjecting the decolorized permeate to nanofiltration membrane treatment to obtain nanofiltration membrane retentate and nanofiltration membrane permeate;

[0012] S4, subjecting the nanofiltration membrane retentate obtained in step S3 to alcohol precipitation to recover glycine, and removing ammonium chloride through electrodialysis to obtain a urotropine solution;

[0013] S5. After the ammonium chloride is removed from the nanofiltration membrane permeate obtained in step S3 by electrodialysis, the permeate is mixed with zinc acetate and zinc oxide for reaction to obtain a finished zinc glycinate product.

[0014] Preferably, in step S1, the mixed crystals of glycine and ammonium chloride are precipitated after the temperature is lowered to 20-40°C.

[0015] Further preferably, in step S1, the mixed crystals of glycine and ammonium chloride are precipitated after the temperature is lowered to 30°C.

[0016] Preferably, in step S2, the mass ratio of the mixed crystal to water is 128:60-100.

[0017] Further preferably, in step S2, the mass ratio of the mixed crystal to water is 128:80.

[0018] Preferably, in step S2, the mixed crystals and water are mixed and then heated to 60-80° C. for dissolution.

[0019] Further preferably, in step S2, the mixed crystals and water are mixed and then heated to 70° C. for dissolution.

[0020] Preferably, in step S2, the first temperature reduction is to 50-70°C.

[0021] Further preferably, in step S2, the first temperature reduction is to 60°C.

[0022] Preferably, in step S2, the mass fraction of the methanol aqueous solution is 85%-97%.

[0023] Further preferably, in step S2, the mass fraction of the methanol aqueous solution is 92%.

[0024] Preferably, in step S2, the volume ratio of water to three different volumes of methanol aqueous solutions is 60-100:30-70:40-80:400-540.

[0025] Further preferably, in step S2, the volume ratio of water to three different volumes of methanol aqueous solutions is 80:50:60:470.

[0026] Preferably, in step S2, the secondary cooling is performed to 20-40°C.

[0027] Further preferably, in step S2, the secondary cooling is to 30°C.

[0028] Preferably, in step S3, the operating pressure of the membrane decolorization treatment is 1.5MPa-3.0MPa, and the operating temperature is 15°C-40°C.

[0029] Further preferably, in step S3, the operating pressure of the membrane decolorization treatment is 2.0 MPa and the operating temperature is 20°C.

[0030] Preferably, in step S3, the operating pressure of the nanofiltration membrane treatment is 1.5 MPa-3.0 MPa; and the operating temperature is 20°C-30°C.

[0031] Further preferably, in step S3, the operating pressure of the nanofiltration membrane treatment is 2.0 MPa; and the operating temperature is 25°C.

[0032] Preferably, in step S4, the specific process of recovering glycine by alcohol precipitation is as follows: anhydrous methanol is added to the nanofiltration retentate to prepare a methanol aqueous solution, wherein the mass fraction of methanol in the methanol aqueous solution is 79%-81%.

[0033] Further preferably, in step S4, the specific process of recovering glycine by alcohol precipitation is as follows: anhydrous methanol is added to the nanofiltration retentate to prepare a methanol aqueous solution, wherein the mass fraction of methanol in the methanol aqueous solution is 80%.

[0034] Preferably, in step S4, the circulation flow rate of the concentrated and diluted chambers of the electrodialysis is 350 L / h-450 L / h; and the circulation pressure is 0.04 MPa-0.08 MPa.

[0035] Further preferably, in step S4, the circulation flow rate of the concentrated and dilute chambers of the electrodialysis is 400 L / h; and the circulation pressure is 0.06 MPa.

[0036] Preferably, in step S4, anhydrous methanol is added to the nanofiltration membrane retentate so that the methanol content in the methanol aqueous solution is 79%-81%, and then the temperature is reduced and crystallized to recover glycine, and then the remaining methanol aqueous solution after recovering the glycine is distilled at -0.1MPa and 50°C-60°C to recover the methanol fraction, and the kettle residue after recovering the methanol is added to the "dilute chamber" of the electrodialysis equipment to recover ammonium chloride, and the circulation flow rate of the concentrated and dilute chambers is 350L / h-450L / h, and the circulation pressure is 0.04MPa-0.08MPa.

[0037] Preferably, in step S5, the circulation flow rate of the concentrated and diluted chambers of the electrodialysis is 250 L / h-350 L / h; and the circulation pressure is 0.03 MPa-0.07 MPa.

[0038] Further preferably, in step S5, the circulation flow rate of the concentrated and diluted chambers of the electrodialysis is 300 L / h; and the circulation pressure is 0.05 MPa.

[0039] Preferably, in step S5, the ratio of the nanofiltration membrane permeate, zinc acetate and zinc oxide is 6.0-7.0 L: 0.76-0.78 mol: 3.87-3.89 mol.

[0040] Further preferably, in step S5, the ratio of the nanofiltration membrane permeate, zinc acetate and zinc oxide is 6.5L:0.77mol:3.88mol.

[0041] Preferably, in step S5, the reaction temperature is 80-100° C., and the reaction time is 1-3 h.

[0042] Further preferably, in step S5, the reaction temperature is 90° C. and the reaction time is 2 h.

[0043] The beneficial effects of the present invention are:

[0044] (1) The present invention discloses a method for treating glycine wastewater, which directly cools the amination reaction liquid to precipitate mixed crystals to obtain glycine and by-product ammonium chloride, thereby reducing the amount of methanol used.

[0045] (2) The present invention discloses a method for treating glycine wastewater, which removes impurities in the filtrate of ammoniated liquid and enriches hexamethylenetetramine through a post-treatment process of "decolorization-nanofiltration-alcohol analysis-electrodialysis", thereby increasing the utilization rate of raw materials.

[0046] (3) The present invention discloses a method for treating glycine wastewater. The treated glycine wastewater can be directly used as a raw material to synthesize high-value-added glycine zinc, thereby increasing the utilization rate of raw materials and reducing wastewater discharge. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a process flow chart of Example 1 of the present invention. DETAILED DESCRIPTION

[0048] The following non-limiting examples can enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way. The following content is merely an exemplary description of the scope of the present invention, and those skilled in the art can make various changes and modifications to the present invention based on the disclosed content, which should also fall within the scope of the present invention.

[0049] The present invention is further described below by way of specific examples. The various chemical reagents used in the examples of the present invention are obtained through conventional commercial channels unless otherwise specified. Unless otherwise specified, the contents described below are all weight contents. Unless otherwise specified, it is understood that the process is carried out at room temperature.

[0050] Example 1

[0051] Step S1, take 35L of amination reaction solution (4% urotropine, 32% glycine, 22% ammonium chloride, 0.6% ammonium acetate, 2.5% iminodiacetic acid), stir, cool naturally to 30°C and filter, obtain about 19.75kg of mixed crystals of glycine and ammonium chloride, and obtain 17kg of filtrate, about 16.5L, then take 128g of mixed crystals, add 80g of pure water, heat to 70°C and dissolve completely, then wait for it to slowly cool to 60°C, start dripping methanol aqueous solution with a mass fraction of 92%, drip in three steps, the volume of methanol aqueous solution dripped in each step is 50mL, 60mL, 470mL respectively, control each step of dripping alcohol temperature to 5°C, then slowly cool to 30°C and filter, drip 80mL of 92% methanol to wash the solid during the filtration process, dry the wet product to obtain 68.28g of finished glycine, and detect its content of 99.3%.

[0052] Step S2, taking all the filtrate (about 16.5L) obtained by suction filtration of the amination reaction liquid, and performing membrane decolorization treatment (the membrane material is modified polytetrafluoroethylene, the membrane pore size can divert molecules below 300 Daltons, the operating pressure is 2.0MPa, and the operating temperature is 20°C), and the decolorization membrane permeate is collected about 14L, and then the decolorized permeate is treated with a nanofiltration membrane, a nanofiltration membrane with a molecular weight cutoff of more than 200 Daltons, an operating pressure of 2.0MPa, and a temperature of 25°C to obtain a nanofiltration retentate of about 7L; anhydrous methanol is added to the retentate to prepare an 80% methanol aqueous solution, and then the temperature is lowered to 20°C for crystallization to recover glycine, and the filtrate after recovering glycine is The solution temperature is ≤85°C, and the fraction is recovered by vacuum distillation at -0.1MPa. The residual liquid left in the kettle after vacuum distillation is added to the "light chamber" of the electrodialysis device, pure water is added to the "concentrate chamber", and the polar liquid (sulfuric acid solution with a mass fraction of 1%) is added to the "polar chamber", and then the circulation pump is turned on. The circulation flow rates of the concentrated and light chambers are both 400L / h, the circulation pressure is about 0.06MPa, and the polar liquid circulation flow rate is 40L / h. Then direct current is applied to the membrane assembly, and the applied current is selected to circulate at 7.5A. During the circulation process, the solutions of the concentrated and light chambers are taken every ten minutes to detect chloride until the chloride of the solution in the "light chamber" is ≤0.03%, and then the power is turned off and the circulation is stopped. The mass fraction of urotropine in the "light chamber" is taken out and tested to be about 24%; the urotropine solution is directly applied to the amination reaction, and the glycine yield is 88% and the content is 99.1%.

[0053] Step S3, about 6.5L of nanofiltration membrane permeate is added to the "dilute chamber" of the electrodialysis device, pure water is added to the "concentrate chamber", and the pole liquid (sulfuric acid solution with a mass fraction of 1%) is added to the "pole chamber", and then the circulation pump is turned on. The circulation flow rates of the concentrate and dilute chambers are both 300L / h, the circulation pressure is about 0.05MPa, and the pole liquid circulation flow rate is 35L / h. Then direct current is applied to the membrane assembly, and the applied current selects "steady flow" and circulates at 6A. During the circulation process, the solutions of the concentrate and dilute chambers are taken every ten minutes to detect chloride until the chloride content of the solution in the "dilute chamber" is ≤0.03%, and then the power is turned off and the circulation is stopped. The solution in the "light room" was taken out and the glycine content was detected to be about 10%. Then, 142.65g of zinc acetate and 316.37g of zinc oxide were added and the temperature was raised to 90°C and condensed and refluxed for 2 hours. Then, vacuum distillation was performed to concentrate the solution to 1 / 3 of the original nanofiltration permeate volume. The solution was then filtered while hot. The filtrate was slowly cooled to room temperature under stirring and then filtered to obtain a solid wet product. The solid was dried at 60°C to obtain 537.8g of finished zinc glycinate product. The zinc glycinate content was detected to be 93.47%.

[0054] Example 2

[0055] Step S1, take 35L of amination reaction solution (4% urotropine, 32% glycine, 22% ammonium chloride, 0.6% ammonium acetate, 2.5% iminodiacetic acid), stir, cool naturally to 30°C and filter, obtain about 19.5kg of mixed crystals of glycine and ammonium chloride, and obtain 17kg of filtrate, about 16.5L, then take 128g of mixed crystals, add 76g of pure water, heat to 70°C and dissolve completely, then wait for it to slowly cool to 60°C, start dripping methanol aqueous solution with a mass fraction of 92%, drip in three steps, the volume of methanol aqueous solution dripped in each step is 50mL, 60mL, 470mL respectively, control each step of dripping alcohol temperature to 5°C, then slowly cool to 30°C and filter, drip 80mL of 92% methanol to wash the solid during the filtration process, dry the wet product to obtain 69.20g of finished glycine, and detect its content of 98.4%.

[0056] Step S2, taking all the filtrate (about 16.5L) obtained by suction filtration of the amination reaction liquid, and performing membrane decolorization treatment (the membrane material is modified polytetrafluoroethylene, the membrane pore size is 0.25μm, the operating pressure is 3.0MPa, and the operating temperature is 40°C), and about 14L of the decolorized membrane permeate is collected, and then the decolorized permeate is treated with a nanofiltration membrane, a nanofiltration membrane with a molecular weight cutoff of more than 200 Daltons, an operating pressure of 2.0MPa, and a temperature of 25°C to obtain a nanofiltration retentate of about 7L; anhydrous methanol is added to the retentate to prepare an 80% methanol aqueous solution, and then the temperature is lowered to 20°C for crystallization to recover glycine, and the filtrate after recovering glycine is heated to a temperature of 20°C. ≤85℃, -0.1MPa vacuum distillation to recover fractions, vacuum distillation remaining still residue added to the "light chamber" of the electrodialysis device, pure water added to the "concentrate chamber", polar liquid (sulfuric acid solution with a mass fraction of 1%) added to the "polar chamber", then start the circulation pump, the circulation flow of the concentrate and dilute chambers are both 400L / h, the circulation pressure is about 0.06MPa, the polar liquid circulation flow is 40L / h, then apply direct current to the membrane assembly, select "steady flow" for current application and circulate at 7.5A, take the solution of the concentrate and dilute chambers every ten minutes to detect chloride during the circulation process, until the chloride in the solution in the "light chamber" is ≤0.03%, then turn off the power and stop the circulation. Take out the solution in the "light chamber" and test it for the mass fraction of urotropine, which is about 24%; the urotropine solution is directly applied to the amination reaction, the glycine yield is 87%, and the content is 99.2%.

[0057] Step S3, about 6.5L of nanofiltration membrane permeate is added to the "dilute chamber" of the electrodialysis device, pure water is added to the "concentrate chamber", and the pole liquid (sulfuric acid solution with a mass fraction of 1%) is added to the "pole chamber", and then the circulation pump is turned on. The circulation flow rates of the concentrate and dilute chambers are both 300L / h, the circulation pressure is about 0.05MPa, and the pole liquid circulation flow rate is 35L / h. Then direct current is applied to the membrane assembly, and the applied current selects "steady flow" and circulates at 6A. During the circulation process, the solutions of the concentrate and dilute chambers are taken every ten minutes to detect chloride until the chloride content of the solution in the "dilute chamber" is ≤0.03%, and then the power is turned off and the circulation is stopped. The solution in the "light room" was taken out and the glycine content was detected to be about 10%. Then, 95.04g of zinc acetate and 210.99g of zinc oxide were added and the temperature was raised to 90°C and condensed and refluxed for 2 hours. Then, vacuum distillation was performed to concentrate the solution to 1 / 3 of the original nanofiltration permeate volume. The solution was then filtered while hot. The filtrate was slowly cooled to room temperature under stirring and then filtered to obtain a solid wet product. The solid was dried at 60°C to obtain 302.76g of finished zinc glycinate product. The zinc glycinate content was detected to be 92.11%.

[0058] Example 3

[0059] Step S1, take 35L of amination reaction solution (4% urotropine, 32% glycine, 22% ammonium chloride, 0.6% ammonium acetate, 2.5% iminodiacetic acid), stir, cool naturally to 30°C and filter, obtain about 19.5kg of mixed crystals of glycine and ammonium chloride, and obtain 17kg (about 16.5L) of filtrate, then take 128g of mixed crystals, add 83g of pure water and heat to 70°C to dissolve all, then wait for it to slowly cool to 60°C, start dripping a methanol aqueous solution with a mass fraction of 92%, drip in three steps, the volume of methanol aqueous solution dripped in each step is 50mL, 60mL, 470mL, respectively, control each step of dripping alcohol temperature to 5°C, then slowly cool to 30°C and filter, drip 80mL of 92% methanol to wash the solid during the filtration process, dry the wet product to obtain 67.32g of finished glycine, and detect its content of 99.1%.

[0060] Step S2, taking all the filtrate (about 16.5L) obtained by suction filtration of the amination reaction liquid, and performing membrane decolorization treatment (the membrane material is modified polytetrafluoroethylene, the membrane pore size can divert molecules below 300 Daltons, the operating pressure is 1.5MPa, and the operating temperature is 15°C), and the decolorization membrane permeate is collected about 14L, and then the decolorized permeate is treated with a nanofiltration membrane, a nanofiltration membrane with a molecular weight cutoff of more than 200 Daltons, an operating pressure of 2.0MPa, and a temperature of 25°C to obtain a nanofiltration retentate of about 7L; anhydrous methanol is added to the retentate to prepare an 80% methanol aqueous solution, and then the temperature is lowered to 20°C for crystallization to recover glycine, and the filtrate after recovering glycine is The solution temperature is ≤85°C, and the fraction is recovered by vacuum distillation at -0.1MPa. The residual liquid left in the kettle after vacuum distillation is added to the "light chamber" of the electrodialysis device, pure water is added to the "concentrate chamber", and the polar liquid (sulfuric acid solution with a mass fraction of 1%) is added to the "polar chamber", and then the circulation pump is turned on. The circulation flow rates of the concentrated and light chambers are both 400L / h, the circulation pressure is about 0.06MPa, and the polar liquid circulation flow rate is 40L / h. Then direct current is applied to the membrane assembly, and the applied current is selected to circulate at 7.5A. During the circulation process, the solutions of the concentrated and light chambers are taken every ten minutes to detect chloride until the chloride of the solution in the "light chamber" is ≤0.03%, and then the power is turned off and the circulation is stopped. The mass fraction of urotropine in the "light chamber" is taken out and tested to be about 24%; the urotropine solution is directly applied to the amination reaction, and the glycine yield is 88% and the content is 99.1%.

[0061] Step S3, about 6.5L of nanofiltration membrane permeate is added to the "dilute chamber" of the electrodialysis device, pure water is added to the "concentrate chamber", and the pole liquid (sulfuric acid solution with a mass fraction of 1%) is added to the "pole chamber", and then the circulation pump is turned on. The circulation flow rates of the concentrate and dilute chambers are both 300L / h, the circulation pressure is about 0.05MPa, and the pole liquid circulation flow rate is 35L / h. Then direct current is applied to the membrane assembly, and the applied current selects "steady flow" and circulates at 6A. During the circulation process, the solutions of the concentrate and dilute chambers are taken every ten minutes to detect chloride until the chloride content of the solution in the "dilute chamber" is ≤0.03%, and then the power is turned off and the circulation is stopped. The solution in the "light room" was taken out and the glycine content was detected to be about 10%. Then, 285.31 g of zinc acetate and 632.88 g of zinc oxide were added and the temperature was raised to 90°C and condensed and refluxed for 2 hours. Then, vacuum distillation was performed to concentrate the solution to 1 / 3 of the original nanofiltration permeate volume. The solution was then filtered while hot. The filtrate was slowly cooled to room temperature under stirring and then filtered to obtain a solid wet product. The solid was dried at 60°C to obtain 599.86 g of finished zinc glycinate product. The zinc glycinate content was detected to be 92.58%.

[0062] Comparative Example 1

[0063] Compared with Example 1, the methanol solution in step S1 is added once, and the specific process is as follows:

[0064] Step S1, take 35L of amination reaction solution (4% urotropine, 32% glycine, 22% ammonium chloride, 0.6% ammonium acetate, 2.5% iminodiacetic acid), stir, cool naturally to 30°C and filter, obtain about 19.75kg of mixed crystals of glycine and ammonium chloride, and obtain 17kg of filtrate (about 16.5L), then take 128g of mixed crystals, add 80g of pure water, heat to 70°C and dissolve all of them, then wait for it to slowly cool to 60°C, start dripping methanol aqueous solution with a mass fraction of 92%, the volume of methanol aqueous solution added at one time is 580mL, control the dripping alcohol temperature to drop to 15°C, then slowly cool to 30°C and filter, during the filtration process, drip 80mL of 92% methanol to wash the solid, dry the wet product to obtain 67.32g of finished glycine, and detect its content of 85.89%.

[0065] Comparative Example 2

[0066] Compared with Example 1, step S2 omits the alcohol analysis and electrodialysis processes, and the specific process is as follows:

[0067] Step S1: Same as in Example 1.

[0068] Step S2, taking all the filtrate (about 16.5L) obtained by suction filtration of the amination reaction liquid, performing membrane decolorization treatment (the membrane material is modified polytetrafluoroethylene, the membrane pore size can divert molecules below 300 Daltons, the operating pressure is 2.0MPa, and the operating temperature is 20°C), collecting about 14L of the decolorized membrane permeate, and then performing nanofiltration membrane treatment on the decolorized permeate, with a nanofiltration membrane with a molecular weight cutoff of more than 200 Daltons, an operating pressure of 2.0MPa, and a temperature of 25°C, to obtain about 7L of nanofiltration retentate; the obtained retentate is directly applied to the amination reaction, and the glycine yield is 79.85% and the content is 89.7%.

[0069] Comparative Example 3

[0070] Step S1: Same as in Example 1.

[0071] Step S2: Same as in Example 1.

[0072] Step S3, about 6.5L of nanofiltration membrane permeate is added to the "dilute chamber" of the electrodialysis device, pure water is added to the "concentrate chamber", and the pole liquid (sulfuric acid solution with a mass fraction of 1%) is added to the "pole chamber", and then the circulation pump is turned on. The circulation flow rates of the concentrate and dilute chambers are both 300L / h, the circulation pressure is about 0.05MPa, and the pole liquid circulation flow rate is 35L / h. Then direct current is applied to the membrane assembly, and the applied current selects "steady flow" and circulates at 6A. During the circulation process, the solutions of the concentrate and dilute chambers are taken every ten minutes to detect chloride until the chloride content of the solution in the "dilute chamber" is ≤0.03%, and then the power is turned off and the circulation is stopped. The solution in the "light room" was taken out and the glycine content was detected to be about 10%; 7kg of the solution in the "light room" was evaporated and concentrated to 3kg, wherein glycine was about 700g, and the glycine content in the 3kg concentrated solution was about 23.33%, 316.44g of zinc oxide and 142.65g of zinc acetate were added to the concentrated solution, wherein the content of each component was 20.24% of glycine, 9.15% of zinc oxide, and 4.12% of zinc acetate; then, after heating and refluxing at 90°C for 2 hours, 480.66g of solid was obtained by hot filtration, and the glycine zinc content was detected to be 93.21%, and then the residual filtrate was concentrated under reduced pressure and its content was detected to be 81.55g of glycine zinc weight, and the calculated final yield was 53.17%; in low-concentration glycine-containing wastewater, no additional heating and extended reaction time were required, and the quality index and yield of the obtained glycine zinc remained basically unchanged.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for treating glycine wastewater, characterized in that: The following steps are involved: S1, after the amination reaction liquid is cooled, mixed crystals of glycine and ammonium chloride are precipitated, and the mixed crystals and filtrate are obtained by filtration; S2, mixing the mixed crystals obtained in step S1 with water and heating them to dissolve them, cooling them for the first time and sequentially mixing them with three different volumes of methanol aqueous solutions, and then cooling them for a second time to precipitate finished glycine; S3, subjecting the filtrate obtained in step S1 to membrane decolorization treatment, and subjecting the decolorized permeate to nanofiltration membrane treatment to obtain nanofiltration membrane retentate and nanofiltration membrane permeate; S4, subjecting the nanofiltration membrane retentate obtained in step S3 to alcohol precipitation to recover glycine, and removing ammonium chloride through electrodialysis to obtain a urotropine solution; S5. After the ammonium chloride is removed from the nanofiltration membrane permeate obtained in step S3 by electrodialysis, the permeate is mixed with zinc acetate and zinc oxide for reaction to obtain a finished zinc glycinate product.

2. The method for treating glycine wastewater according to claim 1, wherein: In step S1, the temperature is lowered to 20-40° C. to precipitate mixed crystals of glycine and ammonium chloride.

3. The method for treating glycine wastewater according to claim 2, characterized in that: In step S2, the mass ratio of the mixed crystal to water is 128:60-100; the mixed crystal and water are mixed and then heated to 60-80°C for dissolution; the first temperature is lowered to 50-70°C; and the second temperature is lowered to 20-40°C.

4. The method for treating glycine wastewater according to claim 2, characterized in that: In step S2, the mass fraction of the methanol aqueous solution is 85%-97%; the volume ratio of the water to the three different volumes of methanol aqueous solutions is 60-100:30-70:40-80:400-540.

5. The method for treating glycine wastewater according to any one of claims 3 to 4, characterized in that: In step S3, the operating pressure of the membrane decolorization treatment is 1.5MPa-3.0MPa, and the operating temperature is 15°C-40°C; the operating pressure of the nanofiltration membrane treatment is 1.5MPa-3.0MPa; and the operating temperature is 20°C-30°C.

6. The method for treating glycine wastewater according to claim 5, characterized in that: In step S4, the specific process of recovering glycine by alcohol precipitation is as follows: anhydrous methanol is added to the nanofiltration retentate to prepare a methanol aqueous solution, wherein the mass fraction of methanol in the methanol aqueous solution is 79%-81%.

7. The method for treating glycine wastewater according to claim 5, characterized in that: In step S4, the circulation flow rate of the concentrated and dilute chambers of the electrodialysis is 350L / h-450L / h; the circulation pressure is 0.04MPa-0.08MPa.

8. The method for treating glycine wastewater according to claim 5, characterized in that: In step S4, anhydrous methanol is added to the nanofiltration membrane retentate so that the methanol content in the methanol aqueous solution is 79%-81%, and then the temperature is reduced to crystallize and recover glycine. The remaining methanol aqueous solution after recovering the glycine is distilled at -0.1MPa and 50°C-60°C to recover the methanol fraction. The kettle residue after recovering the methanol is added to the "dilute chamber" of the electrodialysis equipment to recover ammonium chloride. The circulation flow rate of the concentrated and dilute chambers is 350L / h-450L / h, and the circulation pressure is 0.04MPa-0.08MPa.

9. The method for treating glycine wastewater according to any one of claims 6 to 8, characterized in that: In step S5, the circulation flow rate of the concentrated and diluted chambers of the electrodialysis is 250L / h-350L / h; the circulation pressure is 0.03MPa-0.07MPa.

10. The method for treating glycine wastewater according to any one of claims 6 to 8, characterized in that: In step S5, the ratio of the nanofiltration membrane permeate, zinc acetate and zinc oxide is 6.0-7.0 L: 0.76-0.78 mol: 3.87-3.89 mol; the reaction temperature is 80-100° C., and the reaction time is 1-3 h.

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