Method for treating glycine production wastewater

Abstract

The present application relates to the field of water treatment, and particularly relates to a treatment method of glycine production wastewater, comprising the following steps: S1, rectification: removing and recycling part of methanol in the wastewater; S2, catalytic hydrolysis: adding an acid agent into the wastewater to perform catalytic hydrolysis, decomposing urotropin in the water into ammonia and formaldehyde; S3, catalytic condensation: adding condensation agents urea, a promoter and a curing agent into the catalytic hydrolysis water, condensing the formaldehyde generated by the catalytic hydrolysis water into urea-formaldehyde resin to remove it from the system; S4, concentration: evaporating and crystallizing the condensation water in step S3 to obtain by-product glycine ammonium salt solid organic fertilizer, and the mother liquor is used as liquid organic fertilizer. The treatment method solves the toxicity problem of urotropin in the wastewater, and solves the inhibition of organic components such as chloroacetic acid and hydroxyacetic acid on the catalytic condensation process, and effectively recycles ammonium salt and glycine resources in the wastewater, and realizes hazardous waste reduction.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment, specifically to a method for treating wastewater from glycine production. Background Technology

[0002] Glycine (abbreviated Gly), also known as aminoacetic acid, is a non-essential amino acid with the chemical formula C2H5NO2. Glycine is an important intermediate in fine chemical production, widely used in pharmaceuticals, food processing, animal feed, daily chemicals, biochemical experiments, and organic chemical synthesis, with its application being particularly prominent in pesticides. In bioengineering, glycine is an important raw material for the synthesis of peptides and proteins, and also serves as a coenzyme and regulator for many biological enzymes. Industrially, glycine also has wide applications, such as as a solvent, electroplating solution, and lubricant. Currently, glycine is prepared using chloroacetic acid and liquid ammonia as raw materials, with hexamethylenetetramine as a catalyst, in a methanol solvent environment through alcohol precipitation, filtration, refining, and drying. The glycine production process generates a large amount of waste, including wastewater characterized by high color, high COD, and low B / C ratio, which is difficult to treat.

[0003] Currently, commonly used methods for treating glycine production wastewater include evaporation concentration, wet oxidation, high-temperature oxidation, and catalytic oxidation. Patent CN108218089A discloses a method for treating glycine wastewater. This application targets glycine wastewater, firstly using a deammoniation method to remove and recover ammonia nitrogen from the wastewater, and finally using a high-temperature oxidation method to decompose large molecular organic matter in the wastewater into smaller molecular organic matter for better removal. However, because glycine wastewater has an extremely high ammonium chloride content, a large amount of liquid alkali needs to be added during deammoniation, leading to increased treatment costs. Secondly, the advanced oxidation method completely decomposes large molecular organic matter, resulting in a large amount of glycine in the wastewater not being recovered and reused, leading to low economic efficiency. Finally, the high-temperature oxidation requires temperatures above 400℃, making the equipment highly hazardous and unsuitable for chemical operations.

[0004] Furthermore, patent CN110683695A discloses a resource recovery method for glycine wastewater. This application targets glycine wastewater, firstly by nanofiltration concentration, then by catalytic wet oxidation to convert macromolecular organic matter into smaller organic and inorganic molecules, followed by evaporation and concentration to obtain ammonium chloride. The mother liquor is then recycled. While this process thoroughly decomposes macromolecular substances and effectively decomposes toxic organic compounds such as hexamethylenetetramine, the high concentration of glycine in the wastewater is also decomposed and cannot be recovered, resulting in low economic efficiency. Secondly, the catalytic wet oxidation method requires high temperature and pressure operation, leading to high equipment risk, high operating costs, and significantly increased treatment costs.

[0005] Patent CN101544513A also discloses a method for spray drying glycine wastewater. This application targets glycine wastewater and uses spray drying to produce organic-inorganic compound fertilizer. However, spray drying cannot effectively decompose the toxic organic pollutant hexamethylenetetramine in the wastewater. Therefore, the produced organic-inorganic compound fertilizer still contains hexamethylenetetramine and some free formaldehyde, which can cause soil and water pollution when applied to the fertilizer industry. Furthermore, due to the high salt and organic matter content of glycine wastewater, viscous, coked salt lumps often form during spray drying, leading to equipment blockage, difficulty in equipment processing, and a significant reduction in equipment lifespan.

[0006] Patent CN119797393A discloses a method for the resource utilization of mother liquor in the production of glycine. The method involves first catalytically hydrolyzing hexamethylenetetramine by passing HCl gas through it, then adding urea for catalytic condensation to obtain urea-formaldehyde resin. Finally, methanol is removed from the filtrate, and chloromethane is recovered. However, the drawback is that if methanol is not removed in advance, methanol and formaldehyde will undergo a side reaction in an acidic environment to produce methylal, which reduces the quality and strength of the precipitated urea-formaldehyde resin. Furthermore, methylal has high biotoxicity, which greatly increases the difficulty of subsequent deep treatment of the evaporation liquid.

[0007] In summary, current glycine wastewater treatment technologies are generally ineffective and extremely costly. They either fail to fully recover glycine from the wastewater or result in incomplete decomposition of urotropine, leaving toxic organic matter still present in the system. Therefore, targeted pretreatment of glycine wastewater to address the toxicity of urotropine while simultaneously recovering ammonium salts and glycine resources is crucial for wastewater treatment. Summary of the Invention

[0008] The main objective of this invention is to provide a method for treating glycine production wastewater. This method solves the toxicity problem of hexamethylenetetramine in the wastewater, while also mitigating the inhibitory effects of organic components such as chloroacetic acid and glycolic acid on the catalytic condensation process. Furthermore, it effectively recovers ammonium salts and glycine resources from the wastewater, achieving hazardous waste reduction. The treatment process includes distillation, catalytic hydrolysis, catalytic condensation, and concentration.

[0009] A method for treating glycine production wastewater, characterized by comprising the following steps:

[0010] S1, Distillation: At a certain temperature, distillation removes and recovers part of the methanol in the glycine production wastewater, and the effluent is used for reuse;

[0011] S2, Catalytic hydrolysis: Add an acidic agent to the distillate from step S1 to adjust the pH value. At a certain temperature and for a certain time, decompose hexamethylenetetramine in the glycine production wastewater and convert it into ammonia and formaldehyde. The effluent is then used for further processing.

[0012] S3, Catalytic condensation: Add condensation agent urea, accelerator and curing agent to the water catalytically hydrolyzed in step S2, react at a certain temperature for a certain time, and condense the formaldehyde into a macromolecular organic compound urea-formaldehyde resin, thereby separating it from the water in solid form. After the reaction is completed, filter to obtain filtrate for later use, and filter residue is condensation product.

[0013] S4, Concentration: Add an alkaline agent to the filtrate from step S3, adjust the pH, evaporate and crystallize to obtain glycine ammonium salt solid organic fertilizer as a by-product, and use the mother liquor as liquid organic fertilizer.

[0014] In step S3, the promoter is selected from one or more of glutamic acid, ascorbic acid, and citric acid.

[0015] In step S3, the curing agent is selected from one or more of triethanolamine, ammonium dihydrogen phosphate, and ammonium polyphosphate.

[0016] The inventors discovered that, since glycine wastewater mainly contains organic components such as methanol and hexamethylenetetramine, in step S2, during the catalytic hydrolysis of hexamethylenetetramine into formaldehyde and ammonia by an acidic agent, excessively high methanol concentration in the wastewater can lead to a side reaction between methanol and formaldehyde under acidic conditions, generating methylal. This results in a decrease in the quality and strength of the urea-formaldehyde resin precipitated in step S3, and the presence of methylal also increases the difficulty of subsequent wastewater treatment. Therefore, before decomposing hexamethylenetetramine in glycine production wastewater, this application first removes and recovers methanol from the glycine production wastewater through distillation. However, the inventors further discovered that the hydroxyl groups in methanol molecules can form a stable hydrogen bond network with hydrogen bond acceptors in hydrogen chloride through hydrogen bonds, maintaining acidic reaction conditions through dissolution, thereby accelerating the decomposition of hexamethylenetetramine. When the methanol concentration is too low, the decomposition efficiency of hexamethylenetetramine decreases. Therefore, this invention chooses to first remove some methanol through distillation, preferably with 0.1%-0.3% methanol remaining in the wastewater by mass, before catalytic hydrolysis.

[0017] Preferably, in step S1, the reflux temperature of the distillation treatment is 64-70℃. If the reflux temperature is too high, the methanol will be completely extracted, which will not promote the decomposition of hexamethylenetetramine in the catalytic hydrolysis and will reduce the purity of the extracted methanol. If the reflux temperature is too low, some methanol will not be extracted in time, resulting in an increase in the residual methanol concentration in the wastewater, an increase in the by-products in the catalytic hydrolysis, and an increase in the toxicity of the wastewater. The reflux ratio of the distillation treatment is 2-4. If the reflux ratio is too low, it will increase the treatment cost and pose a risk of flooding. If the reflux ratio is too high, it will reduce the residual methanol concentration in the wastewater and affect the catalytic hydrolysis process.

[0018] Preferably, in step S2, the acidic agent is a hydrochloric acid solution with a mass fraction of 10%-35%. If the mass fraction is too low, the hydrogen ion concentration in the catalytic hydrolysis will not meet the requirements, and the amount of hydrochloric acid solution added will increase dramatically, leading to an increase in wastewater treatment volume and cost.

[0019] Preferably, in step S2, the pH value is adjusted to maintain the hydrogen ion concentration in the wastewater at 0.01-1 mol / L. Excessive hydrogen ion concentration leads to increased hydrochloric acid solution addition, increasing costs, and inhibits catalytic condensation. Insufficient hydrogen ion concentration results in incomplete decomposition of hexamethylenetetramine in the wastewater, leaving it with biological toxicity. The reaction temperature is 80-100℃. Excessive temperature leads to the decomposition of organic components such as glycine in the wastewater, increasing the COD of the distillate and affecting the quality of the glycine-ammonium chloride compound organic fertilizer. Chloroacetic acid in the water oxidizes at excessively high temperatures, darkening the wastewater color and affecting the appearance of the urea-formaldehyde resin. Insufficient temperature leads to incomplete decomposition of hexamethylenetetramine, increasing wastewater toxicity and prolonging the reaction time. The reaction time is 0.5-2 hours. Excessive reaction time leads to the self-polymerization of the decomposition product formaldehyde, affecting catalytic condensation efficiency. Insufficient reaction time leads to incomplete decomposition of hexamethylenetetramine, increasing wastewater toxicity.

[0020] In step S3, the inventors discovered that because the wastewater from glycine production contains organic components such as chloroacetic acid and glycolic acid at high concentrations, these components inhibit the catalytic condensation of urea-formaldehyde resin, resulting in a significant reduction in the amount of urea-formaldehyde resin released from the system. By adding glutamic acid, ascorbic acid, and citric acid as promoters, not only can the dehydration condensation of hydroxymethylurea be promoted, but the balance of the acidic environment within the system can also be controlled, thereby allowing the urea-formaldehyde resin to solidify and be released.

[0021] Regarding curing agents, the inventors discovered that triethanolamine, ammonium dihydrogen phosphate, and ammonium polyphosphate are stable on their own and cannot produce side reactions with organic components in wastewater under acidic conditions. They can also participate in cross-linking reactions, improving the toughness, water resistance, and storage stability of urea-formaldehyde resin and avoiding brittle defects caused by rapid curing.

[0022] Preferably, in step S3, the mass of urea accounts for 5%-20% of the mass of wastewater. If the amount of urea added is too high, it will lead to insufficient hydroxymethylation, low crosslinking degree, decreased product viscosity and poor water resistance. If the amount added is too low, it will lead to excessive formaldehyde, violent polycondensation reaction and easy gelation. After curing, the resin will be brittle and the amount of free formaldehyde residue will increase, while reducing storage stability.

[0023] Preferably, in step S3, the mass of the accelerator accounts for 2%-5% of the mass of the wastewater. If the amount of accelerator added is too high, the polycondensation reaction will run out of control, the product will become more brittle and the free formaldehyde residue will increase. If the amount added is too low, the reaction rate will be too slow, the polycondensation will be incomplete, the resin will be difficult to cure and have poor water resistance, which will also increase the risk of formaldehyde release.

[0024] Preferably, in step S3, the curing agent accounts for 1%-3% of the wastewater mass. If the amount of curing agent added is too high, it will accelerate the polycondensation reaction, causing the resin to gel rapidly, increase its brittleness and cause uneven internal stress, while releasing excessive free formaldehyde. If the amount added is too low, the reaction rate will be too slow, the curing will be incomplete, the resin strength and water resistance will decrease, and the formaldehyde residue will also increase.

[0025] Preferably, in step S3, the reaction temperature is 80-100℃. Excessive reaction temperature leads to increased side reactions, accelerated condensation reaction, excessive cross-linking of the product, and even gelation. Furthermore, components such as glycine in the glycine production wastewater will decompose, increasing the COD of the distilled water and affecting the quality of the organic fertilizer. At excessively high temperatures, chloroacetic acid in the water oxidizes, darkening the wastewater color and affecting the appearance of the urea-formaldehyde resin. Conversely, excessively low temperatures result in a slow reaction rate, accumulation of hydroxymethylurea intermediates, potentially leading to uneven molecular weight distribution or incomplete condensation of the product, affecting resin performance. The reaction time is 0.5-2.5 hours. Excessively long reaction times lead to excessive condensation, resin aging, and reduced product performance. Insufficient reaction times result in incomplete condensation, leaving residual free formaldehyde, affecting the resin's curing effect and stability.

[0026] Preferably, in step S4, the pH range of the wastewater is adjusted to 3-5. Since the mother liquor in the evaporation and concentration process is a complex mother liquor of glycine, chloroacetic acid, and ammonium chloride, and the distilled salt is a glycine-ammonium chloride complex organic fertilizer, in order to meet the requirements for preparing the complex fertilizer, ensure the quality of the distilled salt and mother liquor, and prevent the decomposition of ammonium chloride and glycine during the evaporation process, it is required to adjust the pH range of the wastewater to 3-5 before evaporation. If the pH is too high, it will cause ammonium chloride to decompose, generate ammonia gas, and reduce the yield of salt from evaporation, while increasing the ammonia nitrogen in the distilled water. If the pH is too low, it will lead to an increase in free formaldehyde in the effluent and an increase in COD.

[0027] Preferably, in step S4, the evaporation and crystallization temperature is 100-110℃. If the temperature is too low, the water will not be able to evaporate and the evaporation and crystallization process cannot proceed; if the temperature is too high, the glycine in the wastewater will decompose and the glycolic acid will be oxidized, affecting the quality of the mother liquor and increasing the COD of the distilled water, which will affect subsequent deep treatment.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] 1. This invention utilizes a combined process of distillation, catalytic decomposition, catalytic condensation, and evaporation concentration to treat glycine production wastewater. This process effectively decomposes and removes hexamethylenetetramine from the wastewater. Furthermore, the decomposition product, formaldehyde, is removed and recovered via catalytic condensation, converting it into urea-formaldehyde resin. This condensation product has wide applications in the fertilizer and resin industries. The decomposition product, ammonia, is also converted into ammonium chloride, which, along with the ammonium chloride in the original system, is separated from the system via evaporation concentration and recovered as ammonium chloride fertilizer. Therefore, this invention solves the hexamethylenetetramine toxicity problem, has low treatment costs, stable removal efficiency, and significant economic benefits.

[0030] 2. The evaporation mother liquor of the present invention is a composite mother liquor of glycine, chloroacetic acid and ammonium chloride. Therefore, there are no toxic organic pollutants in the mother liquor. It can be output as liquid fertilizer. It can also be concentrated, dried and frozen into slices to form a good glycine-ammonium chloride composite organic fertilizer, effectively recovering glycine from wastewater and perfectly realizing the resource utilization of wastewater.

[0031] 3. Before catalytically decomposing hexamethylenetetramine in wastewater, this invention first removes and recovers some methanol from the glycine production wastewater by distillation, leaving 0.1%-0.3% methanol by mass of the wastewater, and then performs catalytic hydrolysis, effectively ensuring the decomposition efficiency of hexamethylenetetramine and the quality of the produced urea-formaldehyde resin. Attached image description:

[0032] Figure 1 Here is a flow chart of a glycine wastewater treatment process according to the present invention: Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0035] <Example 1>

[0036] The wastewater was taken from the glycine production workshop of a chemical plant in Shaanxi Province. The water quality was as follows: pH=6, COD: 145927 mg / L, ammonia nitrogen: 39541 mg / L, formaldehyde: 4746 mg / L, and the color was orange-yellow. The wastewater contained 4.12 wt% methanol and 1.83 wt% hexamethylenetetramine.

[0037] (1) Distillation: 620 ml of wastewater was distilled at a reflux ratio of 3 and a reflux temperature of 64 °C. After distillation, the methanol content in the wastewater was 0.15 wt%.

[0038] (2) Catalytic hydrolysis: Take 600 ml of distilled wastewater, add 15% of the wastewater volume of 35 wt% hydrochloric acid, adjust the hydrogen ion concentration to 0.1 mol / L, the reaction temperature is 90℃, and the reaction time is 0.5 h;

[0039] Specifically, the decomposition principle of hexamethylenetetramine under acidic conditions is as follows:

[0040] (CH2)6N4+4HCl+6H2O→6CH2O+4NH4Cl

[0041] After catalytic decomposition, the COD removal rate reached 17.5%, producing formaldehyde at 23085 mg / L, and the hexamethylenetetramine content after catalytic decomposition was 0.042 wt%.

[0042] (3) Catalytic condensation: Add 13% solid urea, 3% solid citric acid, and 2% liquid triethanolamine by mass of the wastewater to the hydrolyzed water to carry out a catalytic condensation reaction. The reaction temperature is 90℃ and the reaction time is 1.5h. After the reaction is completed, cool to room temperature and filter to obtain urea-formaldehyde resin. The filtrate is used for later use.

[0043] Specifically, the principle of catalytic condensation is as follows:

[0044] nH2N-CO-NH2+ nHCHO —H-[NH-CO-NH-CH2]-OH + (n-1) H2O

[0045] After catalytic condensation, the COD removal rate can reach 58.3%, with the remaining COD provided by chloroacetic acid and glycine in the water; the formaldehyde removal rate can reach 90.8%, producing 133.0g of urea-formaldehyde resin wet weight, which is 71.3g after drying.

[0046] (4) Concentration: Add 27% ammonia solution to the condensation filtrate, adjust pH=4, and evaporate the filtrate at 100℃ to obtain ammonium salt-glycine solid organic fertilizer, distillate, and mother liquor.

[0047] After evaporation and concentration, the catalytic condensation filtrate yielded 154.9 g of ammonium chloride-glycine complex salt, which was then dried to obtain 140.0 g. The COD of the distillate was 2292 mg / L, with a removal rate of 98.4%, and the formaldehyde in the distillate was 216 mg / L, with a removal rate of 99.1%. After subsequent deep biochemical treatment, the distillate met the Class III standard of the Integrated Wastewater Discharge Standard (GB8978-96).

[0048] The following are the indicators of urea-formaldehyde resin after drying, all of which are higher than the standard values.

[0049]

[0050] In addition, crop growth experiments were conducted on the distilled ammonium chloride-glycine complex salt, and the crop growth was compared with that of ordinary ammonium chloride salt. The experiments showed that the complex salt had a better effect on crops than ordinary ammonium chloride.

[0051] <Example 2>

[0052] The wastewater was taken from the glycine production workshop of a pharmaceutical factory in Inner Mongolia. The water quality was as follows: pH=6, COD: 587264 mg / L, ammonia nitrogen: 34020 mg / L, formaldehyde: 8629 mg / L, and the color was orange-yellow. The wastewater contained 20.97 wt% methanol and 5.32 wt% hexamethylenetetramine.

[0053] (1) Distillation: Take 800ml of wastewater for distillation, with a reflux ratio of 4 and a reflux temperature of 64℃.

[0054] After distillation, the methanol content is 0.11 wt%.

[0055] (2) Catalytic hydrolysis: Take 600 ml of distilled wastewater and add 30% of the wastewater volume of 35wt% hydrochloric acid to adjust the hydrogen ion concentration to 0.25 mol / L. The reaction temperature is 95℃ and the reaction time is 1 h.

[0056] After catalytic decomposition, the COD removal rate can reach 73%, and the formaldehyde content is 48893 mg / L. The hexamethylenetetramine content after catalytic decomposition is 0.152 wt%.

[0057] (3) Catalytic condensation: Add 18.9% urea solid, 3% citric acid solid and 3% triethanolamine liquid by mass of the wastewater to the hydrolyzed water to carry out catalytic condensation reaction. The reaction temperature is 95℃ and the reaction time is 2.5h. After the reaction is completed, cool to room temperature and filter to obtain urea-formaldehyde resin. The filtrate is used for later use.

[0058] After catalytic condensation, the COD removal rate can reach 81.3%, with the remaining COD provided by chloroacetic acid and glycine in the water; the formaldehyde removal rate can reach 92.3%, and the wet weight of the urea-formaldehyde resin produced is 111.7g.

[0059] (4) Concentration: Add 27% ammonia solution to the condensation filtrate, adjust pH=4, and evaporate the filtrate at 100℃ to obtain ammonium salt-glycine solid organic fertilizer, distillate, and mother liquor.

[0060] After evaporation and concentration, the catalytic condensation filtrate produces 150.8g of ammonium chloride-glycine complex salt, with a COD of 1238mg / L (removal rate of 99.8%) and formaldehyde of 223mg / L (removal rate of 97.4%). After subsequent deep biochemical treatment, the distillate meets the Class III standard of the Integrated Wastewater Discharge Standard (GB8978-96).

[0061] <Example 3>

[0062] The wastewater source is the same as in Example 1.

[0063] (1) Distillation: 620 ml of wastewater was distilled at a reflux ratio of 2 and a reflux temperature of 70 °C. After distillation, the methanol content in the wastewater was 0.3 wt%.

[0064] (2) Catalytic hydrolysis: Take 600 ml of distilled wastewater, add 35% of the wastewater volume of 10 wt% hydrochloric acid, adjust the hydrogen ion concentration to 0.06 mol / L, react at 80℃, and react for 2 h.

[0065] After catalytic decomposition, the COD removal rate reached 15.4%, producing formaldehyde at 21844 mg / L, and hexamethylenetetramine content at 0.082 wt%.

[0066] (3) Catalytic condensation: Add 20% solid urea, 5% solid ascorbic acid, and 3% liquid ammonium dihydrogen phosphate by mass of the wastewater to the hydrolyzed water to carry out catalytic condensation reaction. The reaction temperature is 100℃ and the reaction time is 0.5h. After the reaction is completed, cool to room temperature and filter to obtain urea-formaldehyde resin. The filtrate is used for later use.

[0067] After catalytic condensation, the COD removal rate can reach 54.7%, with the remaining COD provided by chloroacetic acid and glycine in the water; the formaldehyde removal rate can reach 87.7%, producing urea-formaldehyde resin with a wet weight of 121.4g, which is 65.8g after drying.

[0068] (4) Concentration: Add 25% sodium hydroxide solution to the condensation filtrate, adjust pH=5, and evaporate the filtrate at 110℃ to obtain ammonium salt-glycine solid organic fertilizer, distillate, and mother liquor.

[0069] After evaporation and concentration, the catalytic condensation filtrate yielded 166.4g of ammonium chloride-glycine complex salt, which was then dried to obtain 143.7g. The COD of the distillate was 2553mg / L, with a removal rate of 98.3%, and the formaldehyde in the distillate was 311mg / L, with a removal rate of 98.6%. After subsequent deep biochemical treatment, the distillate met the Class III standard of the Integrated Wastewater Discharge Standard (GB8978-96).

[0070] <Example 4>

[0071] The wastewater source is the same as in Example 1.

[0072] (1) Distillation: 620 ml of wastewater was distilled at a reflux ratio of 4 and a reflux temperature of 64 °C. After distillation, the methanol content in the wastewater was 0.1 wt%.

[0073] (2) Catalytic hydrolysis: Take 600 ml of distilled wastewater, add 25% of the wastewater volume of 20 wt% hydrochloric acid, adjust the hydrogen ion concentration to 0.24 mol / L, the reaction temperature is 100℃, and the reaction time is 1 h;

[0074] After catalytic decomposition, the COD removal rate reached 18.0%, producing formaldehyde at 22589 mg / L, and hexamethylenetetramine content at 0.044 wt%.

[0075] (3) Catalytic condensation: Add 5% solid urea, 2% solid glutamic acid and 1% liquid ammonium polyphosphate by mass of the wastewater to the hydrolyzed water to carry out catalytic condensation reaction. The reaction temperature is 80℃ and the reaction time is 2.5h. After the reaction is completed, cool to room temperature and filter to obtain urea-formaldehyde resin. The filtrate is used for later use.

[0076] After catalytic condensation, the COD removal rate can reach 54.1%, with the remaining COD provided by chloroacetic acid and glycine in the water; the formaldehyde removal rate can reach 84.3%, producing urea-formaldehyde resin with a wet weight of 118.1g, which is 64.9g after drying.

[0077] (4) Concentration: Add 15% potassium hydroxide solution to the condensation filtrate, adjust pH=3, and evaporate the filtrate at 100℃ to obtain ammonium salt-glycine solid organic fertilizer, distillate, and mother liquor.

[0078] After evaporation and concentration, the catalytic condensation filtrate yielded 152.8g of ammonium chloride-glycine complex salt, which was then dried to obtain 133.7g. The COD of the distillate was 2684mg / L, with a removal rate of 98.2%, and the formaldehyde in the distillate was 411mg / L, with a removal rate of 98.2%. After subsequent deep biochemical treatment, the distillate met the Class III standard of the Integrated Wastewater Discharge Standard (GB8978-96).

[0079] <Example 5>

[0080] The wastewater source is the same as in Example 1. The difference from Example 1 is that after distillation, the reflux ratio is 1, the reflux temperature is 64°C, and the methanol content in the wastewater is 0.4 wt%.

[0081] Tests revealed that after catalytic hydrolysis, the formaldehyde concentration decreased to 18055 mg / L; the amount of urea-formaldehyde resin produced by catalytic condensation decreased to 99.2 g wet weight; and the COD of the distilled water increased to 4457 mg / L.

[0082] The reason is that the reflux ratio is too low, which leads to an increase in methanol residue in the water, resulting in an increase in the amount of methyl acetal formed by condensation with formaldehyde, thus affecting the yield of urea-formaldehyde resin; methyl acetal enters the distillate during the evaporation process, affecting the COD of the distillate and increasing the difficulty of deep treatment of the distillate.

[0083] <Example 6>

[0084] The wastewater source is the same as in Example 1. The difference from Example 1 is that in step S1, the reflux ratio is 5, the reflux temperature is 76°C, and after distillation, the methanol content in the wastewater is 0.05 wt%.

[0085] The test results showed that after catalytic hydrolysis, the formaldehyde concentration decreased to 19145 mg / L, and the hexamethylenetetramine content increased to 0.164 wt% after catalytic decomposition; correspondingly, the amount of urea-formaldehyde resin produced by catalytic condensation decreased to 101.3 g wet weight.

[0086] The reason is that the reflux ratio was too high, resulting in a decrease in methanol residue in the water and a reflux temperature higher than normal. During catalytic hydrolysis, the catalytic effect of methanol on the decomposition of hexamethylenetetramine was reduced, leading to incomplete decomposition of hexamethylenetetramine and a decrease in the formaldehyde concentration in the effluent.

[0087] <Example 7>

[0088] The wastewater source is the same as in Example 1. The difference from Example 1 is that in step S2, the hydrogen ion concentration is adjusted to 1.5 mol / L.

[0089] Tests revealed that after catalytic hydrolysis, the formaldehyde concentration was normal at 22764 mg / L, and the hexamethylenetetramine content after catalytic decomposition was 0.051 wt%. After catalytic condensation, the formaldehyde removal rate decreased to 78.8%, and the amount of urea-formaldehyde resin produced decreased to 98.5 g wet weight.

[0090] The reason is that excessively high hydrogen ion concentration inhibits the condensation of urea-formaldehyde resin, resulting in reduced yield.

[0091] <Example 8>

[0092] The wastewater source is the same as in Example 1. The difference from Example 1 is that the reaction temperature in step S2 is 70°C.

[0093] The test results showed that the formaldehyde concentration produced after catalytic hydrolysis decreased to 15264 mg / L, while the hexamethylenetetramine content increased to 0.658 wt% after catalytic decomposition; correspondingly, the amount of urea-formaldehyde resin produced by catalytic condensation decreased to 64.8 g wet weight.

[0094] The reason is that the reaction temperature was too low, which prevented hexamethylenetetramine from completely decomposing, resulting in a decrease in the amount of formaldehyde produced and an increase in the residual hexamethylenetetramine content in the water.

[0095] <Example 9>

[0096] The wastewater source is the same as in Example 1. The difference from Example 1 is that the reaction temperature in step S2 is 105°C.

[0097] Tests revealed that the formaldehyde concentration produced after catalytic hydrolysis was normal at 23104 mg / L, and the hexamethylenetetramine content after catalytic decomposition was 0.039 wt%. The COD of the distilled water increased to 4457 mg / L, and the color of the catalytic decomposition effluent darkened, with the urea-formaldehyde resin turning yellow and becoming even darker.

[0098] The reason is that the reaction temperature is too high, which causes a small amount of glycine in the water to decompose into small molecule organic matter, resulting in an increase in COD of the distilled water. Correspondingly, the proportion of glycine in the glycine-ammonium chloride compound organic fertilizer decreases. Chloroacetic acid is oxidized at high temperature, which darkens the color of the wastewater and affects the color of the precipitated urea-formaldehyde resin.

[0099] <Example 10>

[0100] The wastewater source is the same as in Example 1. The difference from Example 1 is that in step S3, 23% of the mass of urea solids is added to the hydrolyzed water.

[0101] The test results showed that the wet weight of the urea-formaldehyde resin produced by catalytic condensation was normal, at 132.5g, but the COD removal rate decreased to 44.5%. The produced urea-formaldehyde resin was relatively dry and had poor water solubility.

[0102] The reason is that the amount of urea added is too high, which leads to an imbalance in the ratio of urea to formaldehyde, insufficient hydroxymethylation, low crosslinking degree of urea-formaldehyde resin, decreased viscosity and poor water resistance; a large amount of unreacted urea remains in the wastewater, affecting the COD of the effluent.

[0103] <Example 11>

[0104] The wastewater source is the same as in Example 1. The difference from Example 1 is that in step S3, 3% of the wastewater mass of solid urea is added to the hydrolyzed water.

[0105] The test revealed that the amount of urea-formaldehyde resin produced by catalytic condensation decreased, with a wet weight of 60.3g. The COD removal rate decreased to 28.3%, and the formaldehyde removal rate decreased significantly to 43.1%. The produced urea-formaldehyde resin was relatively viscous.

[0106] The reason is that the amount of urea added is too low, which leads to an imbalance in the ratio of urea to formaldehyde, resulting in excessive formaldehyde, increased free formaldehyde residue, decreased COD in the effluent, and reduced urea-formaldehyde resin production.

[0107] <Example 12>

[0108] The wastewater source is the same as in Example 1. The difference from Example 1 is that the reaction temperature in step S3 is 70°C.

[0109] The tests revealed a decrease in the amount of urea-formaldehyde resin produced by catalytic condensation, with a wet weight of 72.5g. The COD removal rate also decreased to 34.5%, and the formaldehyde removal rate decreased to 64.7%.

[0110] The reason is that if the temperature is too low, the reaction rate will be too slow, and the incomplete reaction will result in too much unreacted formaldehyde, which will affect the formaldehyde removal rate and the yield of urea-formaldehyde resin.

[0111] <Example 13>

[0112] The wastewater source is the same as in Example 1. The difference from Example 1 is that the reaction temperature in step S3 is 106°C.

[0113] The tests revealed that after catalytic condensation, the COD removal rate was 55.4%, the formaldehyde removal rate was 88.7%, and the wet weight of urea-formaldehyde resin produced was 127.5g, all within normal limits. However, the COD of the distilled water increased to 5213mg / L, and the color of the catalytic decomposition effluent darkened, while the urea-formaldehyde resin turned yellow and became more viscous.

[0114] The reasons are: the reaction temperature is too high, which causes a small amount of glycine in the water to decompose into small molecule organic matter, resulting in an increase in COD of the distilled water and a corresponding decrease in the proportion of glycine in the glycine-ammonium chloride compound organic fertilizer; chloroacetic acid is oxidized at high temperature, which darkens the color of the wastewater and affects the darkening of the color of the precipitated urea-formaldehyde resin; the reaction temperature is too high, which leads to a violent reaction, an increase in side reactions, and excessive cross-linking of the resin, making it more viscous and gel-like.

[0115] <Example 14>

[0116] The wastewater source is the same as in Example 1. The difference from Example 1 is that in step S4, before concentration, the pH is adjusted to 5.5.

[0117] The test revealed a decrease in salt yield from evaporation to 120.6g; the COD of the distilled water was 2446mg / L, which is normal; however, the ammonia nitrogen concentration in the distilled water increased to 4145mg / L.

[0118] The reason is that the pH of the evaporation is too high, which causes ammonium chloride to decompose, generating ammonia gas that overflows, reducing the salt yield from evaporation and increasing the ammonia nitrogen in the distillate.

[0119] <Example 15>

[0120] The wastewater source is the same as in Example 1. The difference from Example 1 is that in step S4, before concentration, the pH is adjusted to 1.5.

[0121] The test revealed that the COD of the distilled water was increased to 3881 mg / L, and the formaldehyde concentration in the distilled water was also increased to 1128 mg / L.

[0122] The reason is that the pH of the evaporation is too low, which leads to an increase in free formaldehyde in the distilled water and an increase in COD.

[0123] <Comparative Example 1>

[0124] The wastewater source is the same as in Example 1.

[0125] (1) Catalytic hydrolysis: Take 600ml of wastewater and add 15% of the wastewater volume of 35% hydrochloric acid to adjust the pH to <0.5. The reaction temperature is 90℃ and the reaction time is 0.5h.

[0126] (2) Catalytic condensation: Add 13% urea solid, 3% citric acid solid and 2% triethanolamine liquid (by volume of the wastewater) to the hydrolyzed water to carry out catalytic condensation reaction. The reaction temperature is 90℃ and the reaction time is 1.5h. After the reaction is completed, cool to room temperature and filter to obtain urea-formaldehyde resin. The filtrate is used for later use.

[0127] (3) Concentration: Add 27% ammonia solution to the condensation filtrate, adjust the pH to 4, and evaporate the filtrate at 100℃ to obtain ammonium salt-glycine solid organic fertilizer, distillate, and mother liquor.

[0128] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 did not undergo distillation; it directly proceeded to catalytic hydrolysis, catalytic condensation, and concentration. During the catalytic hydrolysis process, methanol and formaldehyde in the wastewater reacted to generate methylal, leading to a sharp decrease in the formaldehyde concentration in the hydrolysate. Comparison shows that after catalytic hydrolysis, the formaldehyde concentration in Comparative Example 1 was only 3385 mg / L. Therefore, in the subsequent catalytic condensation, the wet weight of urea-formaldehyde resin produced was 7.8 g, far lower than the resin production in Example 1. The presence of a large amount of methylal in the water affected the advanced treatment of the distillate.

[0129] <Comparative Example 2>

[0130] The wastewater source is the same as in Example 1. The difference from Example 1 is that in step S1, all methanol was recovered during the distillation process, and the residual methanol content in the wastewater is extremely low, at 0.002 wt%.

[0131] The test results showed that the formaldehyde concentration produced after catalytic hydrolysis was low, at 16423 mg / L, and the hexamethylenetetramine content after catalytic decomposition was 0.485 wt%; the yield of urea-formaldehyde resin produced by catalytic condensation was reduced to 78.6 g.

[0132] The reason is that the formaldehyde content is greatly reduced. During catalytic hydrolysis, the catalytic effect of methanol on the decomposition of hexamethylenetetramine is reduced, resulting in incomplete decomposition of hexamethylenetetramine and a decrease in the formaldehyde concentration in the effluent.

[0133] <Comparative Example 3>

[0134] The wastewater source is the same as in Example 1. The difference from Example 1 is that the accelerator used in step S3 is ethyl acetate.

[0135] The test revealed that the amount of urea-formaldehyde resin produced by catalytic condensation decreased, with a wet weight of 82.3g, and the urea-formaldehyde resin was relatively viscous, resembling a gel.

[0136] The reason is that the high concentrations of chloroacetic acid and glycolic acid in the wastewater from glycine production inhibited the catalytic condensation of urea-formaldehyde resin. Ethyl acetate could not promote the dehydration condensation of hydroxymethylurea, resulting in an imbalance of the acidic environment in the system and a significant reduction in the amount of urea-formaldehyde resin released from the system.

[0137] <Comparative Example 4>

[0138] The wastewater source is the same as in Example 1. The difference from Example 1 is that the curing agent used in step S3 is trisodium phosphate.

[0139] Tests revealed a decrease in the amount of urea-formaldehyde resin produced by catalytic condensation, with a wet weight of 103.8g, indicating poor properties, low toughness, and brittleness.

[0140] The reason is that trisodium phosphate is unstable under acidic conditions, which increases the hydrogen ion concentration, destroys the acidic environment, and reduces the amount of urea-formaldehyde resin produced; moreover, it cannot participate in the cross-linking reaction of urea-formaldehyde resin, resulting in poor properties of the produced urea-formaldehyde resin.

[0141] The above are merely specific embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for treating glycine production wastewater, characterized in that, Includes the following steps: S1, Distillation: At a certain temperature, distillation removes and recovers part of the methanol in the glycine production wastewater, and the effluent is used for reuse; S2, Catalytic hydrolysis: Add an acidic agent to the effluent from step S1 to adjust the pH value. At a certain temperature, react for a certain time to decompose the hexamethylenetetramine in the wastewater into ammonia and formaldehyde. The effluent is then used for further processing. S3, Catalytic condensation: Add condensation agent urea, accelerator and curing agent to the effluent in step S2, react at a certain temperature for a certain time, and condense the formaldehyde into a macromolecular organic compound urea-formaldehyde resin, thereby separating it from the water in solid form. After the reaction is completed, filter to obtain filtrate for later use, and filter residue is condensation product. S4, Concentration: Add an alkaline agent to the filtrate from step S3, adjust the pH, evaporate and crystallize to obtain glycine ammonium salt solid organic fertilizer as a by-product, and use the mother liquor as liquid organic fertilizer; In step S3, the promoter is selected from one or more of glutamic acid, ascorbic acid, and citric acid. In step S3, the curing agent is selected from one or more of triethanolamine, ammonium dihydrogen phosphate, and ammonium polyphosphate. In step S1, the mass of methanol in the wastewater after distillation accounts for 0.1%-0.3% of the wastewater mass; the reflux temperature of the distillation is 64-70℃, and the reflux ratio is 2-4.

2. The method for treating glycine production wastewater as described in claim 1, characterized in that, In step S2, the acidic agent is a hydrochloric acid solution with a mass fraction of 10%-35%.

3. The method for treating glycine production wastewater as described in claim 1, characterized in that, In step S2, the pH value is adjusted to make the hydrogen ion concentration in the wastewater between 0.01-1 mol / L, the reaction temperature is 80-100℃, and the reaction time is 0.5-2 hours.

4. The method for treating glycine production wastewater as described in claim 1, characterized in that, In step S3, the mass of urea accounts for 5%-20% of the mass of wastewater, the mass of accelerator accounts for 2%-5% of the mass of wastewater, and the mass of curing agent accounts for 1%-3% of the mass of wastewater.

5. The method for treating glycine production wastewater as described in claim 1, characterized in that, In step S3, the reaction temperature is 80-100℃ and the reaction time is 0.5-2.5 hours.

6. The method for treating glycine production wastewater as described in claim 1, characterized in that, In step S4, the alkaline agent is selected from ammonia, sodium hydroxide, and potassium hydroxide.

7. The method for treating glycine production wastewater as described in claim 1, characterized in that, In step S4, the pH range of the wastewater is adjusted to 3-5, and the temperature of the evaporation and crystallization is 100-110℃.

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