Treatment method of glycine production wastewater

Abstract

The invention relates to the technical field of wastewater treatment, and provides a treatment method of glycine production wastewater. The treatment method of glycine production wastewater comprises the following steps: (1) rectifying glycine wastewater to recover methanol, adding dilute sulphuric acid to adjust the pH value to 2.5-3.0, stirring, and standing; (2) transferring the supernate into another container, adding a ZIF-8 modified material, stirring, standing, filtering, collecting filter residues and filtrate, washing the filter residues with diethyl ether, and recovering urotropine; and (3) evaporating and concentrating the filtrate under the vacuum condition of-0.08 MPa and the temperature of 50-60 DEG C, and separating out high-purity ammonium chloride crystals. According to the treatment method for the glycine production wastewater, the problem that an existing treatment method is poor in removal effect on urotropin in the glycine production wastewater is solved; and the treated glycine production wastewater reaches the discharge standard.

Description

Technical Field

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

[0002] Glycine, a key amino acid, is widely used in medicine, food, feed, and chemical industries. As glycine production continues to expand, the amount of wastewater generated during the process is also increasing. Glycine production wastewater is characterized by complex composition, high organic matter concentration, high salinity, and poor biodegradability. If discharged without effective treatment, it will cause serious harm to the aquatic environment and ecosystems.

[0003] The main glycine production methods include the chloroacetic acid ammonolysis method, the Streeck process, and the Hein process. While the wastewater produced by these methods varies in composition, they generally contain significant amounts of organic matter, such as glycine, chloroacetic acid, hexamethylenetetramine, and methanol; inorganic salts, such as ammonium chloride and ammonium sulfate; and other impurities. Glycine production wastewater contains significant amounts of recalcitrant organic matter, such as chloroacetic acid and hexamethylenetetramine. Existing treatment methods are ineffective in removing these recalcitrant organics, resulting in relatively high concentrations of organic matter in the treated wastewater, making it difficult to meet stringent emission standards. Therefore, the present invention proposes a method for treating glycine production wastewater. Summary of the Invention

[0004] The present invention provides a method for treating glycine production wastewater, which improves the problem that the existing treatment method has poor removal effect of hexamethylenetetramine in glycine production wastewater; and ensures that the treated glycine production wastewater meets the discharge standard.

[0005] The technical solutions of the present invention are as follows: The present invention provides a method for treating glycine production wastewater, comprising the following steps: (1) After distilling glycine wastewater to recover methanol, dilute sulfuric acid was added to adjust the pH to 2.5-3.0, stirred, and then allowed to stand; (2) The supernatant was transferred to another container, and the ZIF-8 modified material was added. After stirring, the mixture was allowed to stand. After filtering, the residue and filtrate were collected. The residue was washed with ether to recover the urotropine. (3) The filtrate was evaporated and concentrated under -0.08 MPa vacuum and 50-60°C to separate high-purity ammonium chloride crystals.

[0006] As a further technical solution, the usage ratio of the ZIF-8 modified material and the supernatant is (1.2-1.6) g / L.

[0007] As a further technical solution, the preparation method of the ZIF-8 modified material includes: immersing the activated carbon that has been pretreated for impurity removal in a PDA dispersion, stirring and mixing at 55-65°C and 150-200 rpm for 10-12 hours to obtain AC@PDA; dissolving zinc nitrate and 2-methylimidazole in methanol respectively, adding AC@PDA after mixing, ultrasonically dispersing and then standing for reaction, centrifuging, washing, and drying to obtain the material.

[0008] As a further technical solution, the impurity removal pretreatment step includes: washing the activated carbon with hydrochloric acid and hydrofluoric acid in sequence to remove impurities and then drying.

[0009] As a further technical solution, the PDA dispersion is prepared by dissolving dopamine hydrochloride in a Tris-HCl buffer solution with a pH of 8.5 and a concentration of 10 mM to obtain a PDA dispersion solution with a concentration of 0.1-0.5 mg / mL.

[0010] As a further technical solution, the usage ratio of the pretreated activated carbon and the PDA dispersion is 1 g:15-20 mL.

[0011] As a further technical solution, the usage ratio of the zinc nitrate, 2-methylimidazole, AC@PDA and methanol is (1.49-2.38) g: (1.96-3.14) g: (10-12) g: (200-220) mL.

[0012] As a further technical solution, the static reaction temperature is 25±2°C and the time is 22-26h.

[0013] As a further technical solution, the step of standing after stirring in step (1) is stirring at 100-120 rpm for 45-60 minutes, and standing for 100-120 minutes after stirring.

[0014] As a further technical solution, the step of standing after stirring in step (2) is stirring at 80-100 rpm for 120-140 minutes and standing for 50-60 minutes.

[0015] The working principle and beneficial effects of the present invention are: The present invention organically combines three steps: acid adjustment, adsorption by a ZIF-8 modified material, and evaporation crystallization to form a complete wastewater treatment process. This process effectively addresses the poor removal of hexamine by existing treatment methods, ensuring that the treated wastewater meets discharge standards. First, after distilling the glycine wastewater to recover methanol, dilute sulfuric acid is added to adjust the pH to 2.5-3.0. This acidic environment facilitates the subsequent removal of pollutants such as hexamine, as some pollutants may undergo chemical form transformations within this pH range, making them more easily captured in subsequent treatment steps. Next, a ZIF-8 modified material is added for adsorption. The ZIF-8 modified material has a unique metal-organic framework structure. Its pore structure and surface properties enable selective adsorption of pollutants (such as hexamine and heavy metals) in the wastewater, effectively removing target pollutants. Finally, the filtrate is evaporated and concentrated under a vacuum of -0.08 MPa at 50-60°C to separate high-purity ammonium chloride crystals. This step not only recycles the ammonium chloride but also further concentrates the pollutants in the wastewater, facilitating subsequent treatment or achieving standard discharge. Through this combined process, the advantages of each step are fully utilized, and the efficient removal of various pollutants in glycine production wastewater is achieved.

[0016] This invention uses activated carbon as a substrate and modifies it with a PDA coating to achieve stable loading of ZIF-8. This results in a ZIF-8-modified material with high adsorption properties for use in treating glycine production wastewater. Activated carbon has a large specific surface area and a rich pore structure, making it an excellent carrier for loading ZIF-8. The activated carbon is first pretreated to remove impurities. This cleaning process involves washing with hydrochloric acid and then hydrofluoric acid to remove impurities, followed by drying. This removes impurities from the activated carbon surface, increases the number of surface active sites, and improves its adsorption performance and binding capacity with ZIF-8. The pretreated activated carbon is then immersed in a PDA dispersion and stirred at 55-65°C and 150-200 rpm for 10-12 hours to produce AC@PDA. The PDA (polydopamine) coating enhances the binding between ZIF-8 and the activated carbon through π-π stacking and hydrogen bonding, enabling more stable loading of ZIF-8 on the activated carbon surface, thus forming the ZIF-8-modified material. This modified material combines the adsorption properties of activated carbon and the selective adsorption ability of ZIF-8, improving the adsorption capacity and stability of pollutants in wastewater. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present invention. It should be noted that the zinc nitrate raw material used in the present invention is hydrated zinc nitrate.

[0018] Example 1 This embodiment provides a method for treating glycine production wastewater, comprising the following steps: (1) After distilling glycine wastewater to recover methanol, dilute sulfuric acid was added to adjust the pH to 2.5, stirred at 110 rpm for 50 min, and then allowed to stand for 110 min; (2) The supernatant was transferred to another container, and 1.4 g / L of ZIF-8 modified material was added relative to the supernatant. The mixture was stirred at 90 rpm for 130 min, allowed to stand for 55 min, and filtered to collect the residue and filtrate. The residue was washed with ether to recover the urotropine. (3) The filtrate was evaporated and concentrated under -0.08 MPa vacuum and 55°C to separate high-purity ammonium chloride crystals.

[0019] The preparation method of the ZIF-8 modified material includes: immersing 10 g of activated carbon in 1 M HCl solution (solid-liquid ratio 1:10), stirring at 80°C for 4 hours, filtering and washing with water until neutral; transferring to 40% HF solution (solid-liquid ratio 1:5), immersing at room temperature for 12 hours, filtering and washing with water until neutral; vacuum drying at 100°C for 12 hours to obtain pretreated activated carbon; dissolving dopamine hydrochloride in Tris-HCl buffer with a pH of 8.5 and a concentration of 10 mM to obtain a PDA dispersion with a concentration of 0.3 mg / mL; immersing 1 g of activated carbon after impurity removal pretreatment in 15 mL of PDA dispersion, stirring and mixing at 55°C and 180 rpm for 11 hours, centrifuging at 8000 rpm for 10 minutes after the reaction to separate the solid, washing with deionized water three times to remove unadsorbed PDA, and vacuum drying at 60°C for 6 hours to obtain AC@PDA; dissolving 2 g of zinc nitrate in 105 mL of methanol, 2.5 g 2-Methylimidazole was dissolved in 105 mL of methanol, and 11 g of AC@PDA was added after mixing. Ultrasonic dispersion was performed at a power of 300 W and a frequency of 40 kHz for 30 min, and then the mixture was allowed to react at a temperature of 25°C for 24 h. The mixture was then centrifuged, washed with deionized water, and dried at 60°C for 24 h to obtain the product.

[0020] Example 2 This embodiment provides a method for treating glycine production wastewater, comprising the following steps: (1) After distilling glycine wastewater to recover methanol, dilute sulfuric acid was added to adjust the pH to 2.5, stirred at 100 rpm for 45 minutes, and then allowed to stand for 100 minutes; (2) The supernatant was transferred to another container, and 1.2 g / L of ZIF-8 modified material was added relative to the supernatant. The mixture was stirred at 80 rpm for 120 min, allowed to stand for 50 min, and filtered to collect the residue and filtrate. The residue was washed with ether to recover the urotropine. (3) The filtrate was evaporated and concentrated under -0.08 MPa vacuum and 50°C to separate high-purity ammonium chloride crystals.

[0021] The preparation method of the ZIF-8 modified material includes: immersing 10 g of activated carbon in 1 M HCl solution (solid-liquid ratio 1:10), stirring at 80°C for 4 hours, filtering and washing with water until neutral; transferring to 40% HF solution (solid-liquid ratio 1:5), immersing at room temperature for 12 hours, filtering and washing with water until neutral; vacuum drying at 100°C for 12 hours to obtain pretreated activated carbon; dissolving dopamine hydrochloride in Tris-HCl buffer with a pH of 8.5 and a concentration of 10 mM to obtain a PDA dispersion with a concentration of 0.1 mg / mL; immersing 1 g of activated carbon after impurity removal pretreatment in 15 mL of PDA dispersion, stirring and mixing at 55°C and 150 rpm for 10 hours, centrifuging at 8000 rpm for 10 minutes after the reaction to separate the solid, washing with deionized water three times to remove unadsorbed PDA, and vacuum drying at 60°C for 6 hours to obtain AC@PDA; dissolving 1.49 g of zinc nitrate in 100 mL of methanol, and 1.96 g of 2-Methylimidazole was dissolved in 100 mL of methanol, and 10 g of AC@PDA was added after mixing. Ultrasonic dispersion was performed at a power of 300 W and a frequency of 40 kHz for 30 min, and then the mixture was allowed to react at a temperature of 25°C for 22 h. The mixture was then centrifuged, washed with deionized water, and dried at 60°C for 24 h to obtain the product.

[0022] Example 3 This embodiment provides a method for treating glycine production wastewater, comprising the following steps: (1) After distilling glycine wastewater to recover methanol, dilute sulfuric acid was added to adjust the pH to 3.0, stirred at 120 rpm for 60 min, and then allowed to stand for 120 min; (2) The supernatant was transferred to another container, and a ZIF-8 modified material was added at a ratio of 1.6 g / L relative to the supernatant, stirred at 100 rpm for 140 min, allowed to stand for 60 min, filtered, and the residue and filtrate were collected. The residue was washed with ether and then the urotropine was recovered; (3) The filtrate was evaporated and concentrated under -0.08 MPa vacuum and 60°C to separate high-purity ammonium chloride crystals.

[0023] The preparation method of the ZIF-8 modified material includes: immersing 10 g of activated carbon in 1 M HCl solution (solid-liquid ratio 1:10), stirring at 80°C for 4 hours, filtering and washing with water until neutral; transferring to 40% HF solution (solid-liquid ratio 1:5), immersing at room temperature for 12 hours, filtering and washing with water until neutral; vacuum drying at 100°C for 12 hours to obtain pretreated activated carbon; dissolving dopamine hydrochloride in Tris-HCl buffer with a pH of 8.5 and a concentration of 10 mM to obtain a PDA dispersion with a concentration of 0.5 mg / mL; immersing 1 g of activated carbon after impurity removal pretreatment in 20 mL of PDA dispersion, stirring and mixing at 65°C and 200 rpm for 12 hours, centrifuging at 8000 rpm for 10 minutes after the reaction to separate the solid, washing with deionized water three times to remove unadsorbed PDA, and vacuum drying at 60°C for 6 hours to obtain AC@PDA; dissolving 2.38 g of zinc nitrate in 110 mL of methanol, and 3.14 g of 2-Methylimidazole was dissolved in 110 mL of methanol, and 12 g of AC@PDA was added after mixing. Ultrasonic dispersion was carried out at a power of 300 W and a frequency of 40 kHz for 30 min, and then the mixture was allowed to react at a temperature of 25°C for 26 h. The mixture was then centrifuged, washed with deionized water, and dried at 60°C for 24 h to obtain the product.

[0024] Example 4 This embodiment provides a method for treating glycine production wastewater, comprising the following steps: (1) After distilling glycine wastewater to recover methanol, dilute sulfuric acid was added to adjust the pH to 2.5, stirred at 120 rpm for 45 minutes, and then allowed to stand for 120 minutes; (2) The supernatant was transferred to another container, and a ZIF-8 modified material was added at a ratio of 1.2 g / L relative to the supernatant. The mixture was stirred at 100 rpm for 120 min, allowed to stand for 60 min, and filtered to collect the residue and filtrate. The residue was washed with ether and the urotropine was recovered. (3) The filtrate was evaporated and concentrated under -0.08 MPa vacuum and 50°C to separate high-purity ammonium chloride crystals.

[0025] The preparation method of the ZIF-8 modified material includes: soaking 10 g of activated carbon in 1 M HCl solution (solid-liquid ratio 1:10), stirring at 80°C for 4 hours, filtering and washing with water until neutral; transferring to 40% HF solution (solid-liquid ratio 1:5), soaking at room temperature for 12 hours, filtering and washing with water until neutral; vacuum drying at 100°C for 12 hours to obtain pretreated activated carbon; dissolving dopamine hydrochloride in Tris-HCl buffer with a pH of 8.5 and a concentration of 10 mM to obtain a PDA dispersion with a concentration of 0.5 mg / mL; soaking 1 g of activated carbon after impurity removal pretreatment in 15 mL of PDA dispersion, stirring and mixing at 65°C and 150 rpm for 12 hours, centrifuging at 8000 rpm for 10 minutes after the reaction to separate the solid, washing with deionized water three times to remove unadsorbed PDA, and vacuum drying at 60°C for 6 hours to obtain AC@PDA; dissolving 1.49 g of zinc nitrate in 110 mL of methanol, and 1.96 g of 2-Methylimidazole was dissolved in 110 mL of methanol, and 10 g of AC@PDA was added after mixing. Ultrasonic dispersion was performed at a power of 300 W and a frequency of 40 kHz for 30 min, and then the mixture was allowed to react at a temperature of 25°C for 26 h. The mixture was then centrifuged, washed with deionized water, and dried at 60°C for 24 h to obtain the product.

[0026] Comparative Example 1 This comparative example provides a method for treating glycine production wastewater. The activated carbon is not pretreated, and the rest is the same as in Example 1.

[0027] Comparative Example 2 This comparative example provides a method for treating glycine production wastewater. The preparation method of the ZIF-8 modified material is different, and the rest is the same as Example 1.

[0028] The preparation method of the ZIF-8 modified material in this comparative example is as follows: 10 g of activated carbon is immersed in 1 M HCl solution (solid-liquid ratio 1:10), stirred at 80°C for 4 hours, filtered and washed with water until neutral; transferred to a 40% HF solution (solid-liquid ratio 1:5) with a mass concentration of 40%, immersed at room temperature for 12 hours, filtered and washed with water until neutral; vacuum dried at 100°C for 12 hours to obtain pretreated activated carbon; 1.49 g of zinc nitrate is dissolved in 110 mL of methanol, and 1.96 g of 2-methylimidazole is dissolved in 110 mL of methanol, mixed and added with 10 g of pretreated activated carbon, ultrasonically dispersed at a power of 300 W and a frequency of 40 kHz for 30 minutes, and then allowed to react at a temperature of 25°C for 26 hours, centrifuged, washed with deionized water, and dried at 60°C for 24 hours.

[0029] Comparative Example 3 This comparative example provides a method for treating glycine production wastewater, wherein the amount of ZIF-8 modified material used is halved (0.7 g / L), and the rest is the same as in Example 1.

[0030] Comparative Example 4 This comparative example provides a method for treating glycine production wastewater, without using ZIF-8 modified material, and the rest is the same as Example 1.

[0031] Comparative Example 5 This comparative example provides a method for treating glycine production wastewater, wherein the concentration of the PDA dispersion is changed to 0.1 mg / mL (originally 0.3 mg / mL), and the rest is the same as in Example 1.

[0032] Comparative Example 6 This comparative example provides a method for treating glycine production wastewater. 2.5 g of 2-methylimidazole is adjusted to 1.25 g of 2-methylimidazole, and the rest is the same as in Example 1.

[0033] Test Example 1: The pollutant contents of the glycine production wastewater before and after treatment in the above Examples 1-4 and Comparative Examples 1-6 were measured: Chemical oxygen demand (COD): determined according to the dichromate method (HJ 828-2017); Ammonia nitrogen (NH3-N): Nessler's reagent spectrophotometric method (HJ 535-2009); Hexamethylenetetramine: High performance liquid chromatography (HPLC), test conditions: C18 column, mobile phase: methanol-water (60:40), flow rate: 1.0 mL / min, detection wavelength: 254 nm; Heavy metals: inductively coupled plasma mass spectrometry (ICP-MS, HJ 700-2014); The test results are shown in Table 1 below: Table 1

[0034] Combined with the above data, it can be seen that Examples 1-4 achieved efficient treatment results with COD removal rates of 89.7%-92.5%, ammonia nitrogen removal rates of 97.5%-98.3%, and hexamethylenetetramine recovery rates of 92.8%-95.6% through the "acidity adjustment + ZIF-8 modified material adsorption + evaporation crystallization" process combination, and the heavy metal residual levels were significantly lower than those in the raw water (Zn / Fe were both <5 μg / L).

[0035] In Comparative Example 1, the COD removal rate (75.3%) and hexamethylenetetramine recovery (70.1%) of the unpretreated activated carbon decreased significantly, while the residual Zn / Fe concentrations increased to 25 / 15 μg / L. HCl / HF pretreatment of activated carbon is crucial for removing impurities and increasing the number of surface active sites; untreated activated carbon is unable to effectively load functional materials.

[0036] In Comparative Example 2, ZIF-8 was directly loaded without a PDA coating. Although pretreated activated carbon was retained, the COD removal rate (82.4%), ammonia nitrogen removal rate (91.6%), and hexamethylenetetramine recovery rate (81.5%) were all lower than those in Example 1. The PDA coating enhances the binding force between ZIF-8 and activated carbon through π-π stacking and hydrogen bonding. Its absence leads to a decrease in the material's adsorption capacity and stability.

[0037] In Comparative Example 3, halving the ZIF-8 dosage significantly reduced the COD removal rate (79.8%) and hexamethylenetetramine recovery rate (76.3%), while the heavy metal residues doubled. A critical dosage (≥1.2 g / L) of ZIF-8-modified material is required to provide sufficient adsorption sites; insufficient dosage results in incomplete pollutant removal.

[0038] Comparative Example 4, which did not use ZIF-8, showed significant degradation in all performance indicators (COD removal rate of 62.1%, heavy metal residues close to those in the raw water). ZIF-8 is the core of the system, with its metal-organic framework structure playing a leading role in the selective adsorption and catalytic degradation of pollutants, particularly heavy metals.

[0039] In Comparative Example 5, the use of a low-concentration PDA dispersion resulted in lower COD removal (78.5%) and hexamethylenetetramine recovery (73.8%) than in Example 1, with a residual Zn level of 22 μg / L. This low PDA concentration resulted in incomplete coating of the activated carbon surface and uneven ZIF-8 loading, weakening the composite's synergistic effect.

[0040] In Comparative Example 6, the amount of 2-methylimidazole was reduced, and the performance deteriorated overall, with a COD removal rate of 68.2% and Zn residue of 45 μg / L, which was even weaker than that of the pure activated carbon system. The imbalance in the molar ratio of 2-methylimidazole to zinc nitrate destroyed the ZIF-8 crystal structure, causing the material to lose its pore adsorption capacity and release free Zn. 2+ .

[0041] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for treating glycine production wastewater, characterized in that the steps include: (1) After distilling glycine wastewater to recover methanol, dilute sulfuric acid was added to adjust the pH to 2.5-3.0, stirred, and then allowed to stand; (2) The supernatant was transferred to another container, and the ZIF-8 modified material was added. After stirring, the mixture was allowed to stand. After filtering, the residue and filtrate were collected. The residue was washed with ether to recover the urotropine. (3) The filtrate is evaporated and concentrated under -0.08 MPa vacuum and 50-60°C to separate high-purity ammonium chloride crystals.

2. The method for treating glycine production wastewater according to claim 1, wherein: The usage ratio of the ZIF-8 modified material to the supernatant is 1.2-1.6 g / L.

3. The method for treating glycine production wastewater according to claim 1, wherein: The preparation method of the ZIF-8 modified material includes: immersing activated carbon that has undergone impurity removal pretreatment in a PDA dispersion, stirring and mixing at 55-65°C and 150-200 rpm for 10-12 hours to obtain AC@PDA; dissolving zinc nitrate and 2-methylimidazole in methanol respectively, adding AC@PDA after mixing, ultrasonically dispersing and then standing for reaction, centrifuging, washing, and drying to obtain the material.

4. The method for treating glycine production wastewater according to claim 3, wherein: The impurity removal pretreatment step includes: washing the activated carbon with hydrochloric acid and hydrofluoric acid in sequence to remove impurities and then drying.

5. The method for treating glycine production wastewater according to claim 3, wherein: The PDA dispersion is prepared by dissolving dopamine hydrochloride in a Tris-HCl buffer solution with a pH of 8.5 and a concentration of 10 mM to obtain a PDA dispersion solution with a concentration of 0.1-0.5 mg / mL.

6. The method for treating glycine production wastewater according to claim 3, wherein: The usage ratio of the pretreated activated carbon and the PDA dispersion is 1 g: 15-20 mL.

7. The method for treating glycine production wastewater according to claim 3, wherein: The usage ratio of the zinc nitrate, 2-methylimidazole, AC@PDA and methanol is 1.49-2.38 g: 1.96-3.14 g: 10-12 g: 200-220 mL.

8. The method for treating glycine production wastewater according to claim 3, wherein: The static reaction temperature is 25±2° C. and the reaction time is 22-26 hours.

9. The method for treating glycine production wastewater according to claim 1, wherein: The step of standing after stirring in step (1) is stirring at 100-120 rpm for 45-60 minutes, and standing for 100-120 minutes after stirring.

10. The method for treating glycine production wastewater according to claim 1, wherein: The step of standing after stirring in step (2) is stirring at 80-100 rpm for 120-140 minutes and standing for 50-60 minutes.