Method for treating glycine production wastewater

Abstract

The application relates to the technical field of wastewater treatment, and discloses a treatment method for glycine production wastewater. The treatment method for the glycine production wastewater comprises the following steps: (1) after methanol in the glycine production wastewater is recovered through rectification, dilute sulfuric acid is added to adjust the pH to 2.5-3.0, and then stirring and standing are carried out; (2) supernatant is transferred to another container, ZIF-8 modified material is added, stirring and standing are carried out, and then filter residue and filtrate are collected after filtration, and the filter residue is washed by ether to recover urotropin; and (3) the filtrate is concentrated by evaporation under the condition of a vacuum of-0.08 MPa and a temperature of 50-60 DEG C, and high-purity ammonium chloride crystals are separated. The treatment method for the glycine production wastewater is prepared, the problem that the existing treatment method has poor urotropin removal effect on the glycine production wastewater is solved, and the glycine production wastewater after treatment meets the discharge standard.

Description

Technical Field

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

[0002] Glycine, an important amino acid, is widely used in medicine, food, feed, and chemical industries. With the continuous expansion of glycine production, the amount of wastewater generated during its production process is also increasing. Glycine production wastewater is characterized by its complex composition, high concentration of organic matter, high salt content, and poor biodegradability. If discharged directly without effective treatment, it will cause serious harm to the aquatic environment and ecosystem.

[0003] Glycine production methods mainly include the ammonolysis of chloroacetic acid, the Strecker process, and the Hein process. The wastewater composition varies depending on the method, but generally contains large 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 a large amount of recalcitrant organic matter, such as chloroacetic acid and hexamethylenetetramine. Existing treatment methods are ineffective at removing these recalcitrant organic compounds, resulting in wastewater still containing high concentrations of organic matter after treatment, making it difficult to meet stringent discharge standards. Therefore, this invention proposes a method for treating glycine production wastewater. Summary of the Invention

[0004] This invention proposes a method for treating glycine production wastewater, which improves upon the problem of poor removal efficiency of hexamethylenetetramine from glycine production wastewater by existing treatment methods, enabling the treated glycine production wastewater to meet discharge standards.

[0005] The technical solution of the present invention is as follows:

[0006] This invention proposes a method for treating glycine production wastewater, comprising the following steps:

[0007] (1) After recovering methanol from glycine wastewater by distillation, add dilute sulfuric acid to adjust the pH to 2.5-3.0, stir and let stand;

[0008] (2) Transfer the supernatant to another container, add ZIF-8 modified material, stir and let stand, filter and collect the filter residue and filtrate, and recover hexamethylenetetramine by washing the filter residue with ether.

[0009] (3) The filtrate was evaporated and concentrated under -0.08 MPa vacuum and 50-60℃ to separate high-purity ammonium chloride crystals.

[0010] As a further technical solution, the ratio of the ZIF-8 modified material to the supernatant is (1.2-1.6) g / L.

[0011] As a further technical solution, the preparation method of the ZIF-8 modified material includes: soaking activated carbon that has undergone impurity removal pretreatment in PDA dispersion, stirring and mixing at 55-65℃ and 150-200rpm for 10-12h to obtain AC@PDA; dissolving zinc nitrate and 2-methylimidazole in methanol respectively, mixing them, adding AC@PDA, ultrasonically dispersing, allowing the mixture to stand for reaction, centrifuging, washing, and drying to obtain the final product.

[0012] As a further technical solution, the impurity removal pretreatment step includes: cleaning the activated carbon with hydrochloric acid and hydrofluoric acid in sequence to remove impurities, and then drying it.

[0013] As a further technical solution, the PDA dispersion is prepared by dissolving dopamine hydrochloride in a 10 mM Tris-HCl buffer solution at pH 8.5 to obtain a PDA dispersion with a concentration of 0.1-0.5 mg / mL.

[0014] As a further technical solution, the ratio of the amount of pretreated activated carbon to PDA dispersion is 1g:15-20mL.

[0015] As a further technical solution, the ratio of 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.

[0016] As a further technical solution, the static reaction temperature is 25±2℃ and the time is 22-26h.

[0017] As a further technical solution, the step of stirring and then standing in step (1) is to stir for 45-60 minutes at 100-120 rpm and then stand for 100-120 minutes.

[0018] As a further technical solution, the step (2) of stirring and then standing is to stir at 80-100 rpm for 120-140 min and then stand for 50-60 min.

[0019] The working principle and beneficial effects of this invention are as follows:

[0020] This invention organically combines three steps—acidity adjustment, ZIF-8 modified material adsorption, and evaporation crystallization—to form a complete wastewater treatment process. This effectively solves the problem of poor removal of hexamethylenetetramine by existing methods, ensuring the treated wastewater meets discharge standards. First, glycine wastewater is distilled to recover methanol, and then dilute sulfuric acid is added to adjust the pH to 2.5-3.0. An acidic environment is beneficial for the subsequent removal of pollutants such as hexamethylenetetramine because some pollutants may undergo chemical transformation within this pH range, making them more easily captured by subsequent treatment steps. Next, ZIF-8 modified material is added for adsorption. ZIF-8 has a unique metal-organic framework structure; its pore structure and surface properties give it selective adsorption capacity for pollutants in wastewater (such as hexamethylenetetramine and heavy metals), effectively removing target pollutants. Finally, the filtrate is evaporated and concentrated under -0.08 MPa vacuum and 50-60℃ to separate high-purity ammonium chloride crystals. This step not only achieves the recovery and utilization of ammonium chloride but also further concentrates the pollutants in the wastewater, facilitating subsequent treatment or achieving discharge standards. This combined process fully leverages the advantages of each step, achieving highly efficient removal of various pollutants from glycine production wastewater.

[0021] This invention uses activated carbon as a substrate and modifies it with a PDA coating to achieve stable loading of ZIF-8, preparing a ZIF-8 modified material with high adsorption performance for the treatment of glycine production wastewater. Activated carbon has a large specific surface area and abundant pore structure, providing a good carrier for ZIF-8 loading. First, the activated carbon undergoes a pretreatment to remove impurities, sequentially washing with hydrochloric acid and 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 the adsorption performance and binding capacity with ZIF-8. Then, the pretreated activated carbon is immersed in a PDA dispersion and stirred at 55-65℃ and 150-200 rpm for 10-12 hours to obtain AC@PDA. The PDA (polydopamine) coating enhances the binding force between ZIF-8 and activated carbon through π-π stacking and hydrogen bonding, enabling ZIF-8 to be more stably loaded on the activated carbon surface, forming the ZIF-8 modified material. This modified material combines the adsorption properties of activated carbon with the selective adsorption capacity of ZIF-8, thereby improving the adsorption capacity and stability of pollutants in wastewater. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort 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.

[0023] Example 1

[0024] This embodiment provides a method for treating glycine production wastewater, the steps of which include:

[0025] (1) After recovering methanol from glycine wastewater by distillation, add dilute sulfuric acid to adjust the pH to 2.5, stir at 110 rpm for 50 min, and let stand for 110 min after stirring.

[0026] (2) Transfer the supernatant to another container, add ZIF-8 modified material at a ratio of 1.4 g / L relative to the supernatant, stir at 90 rpm for 130 min, let stand for 55 min, filter and collect the filter residue and filtrate, and recover hexamethylenetetramine by washing the filter residue with ether.

[0027] (3) The filtrate was evaporated and concentrated under -0.08 MPa vacuum and 55℃ to separate high-purity ammonium chloride crystals.

[0028] 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℃ 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℃ for 12 hours to obtain pretreated activated carbon; dissolving dopamine hydrochloride in 10 mM Tris-HCl buffer solution at pH 8.5 to obtain a PDA dispersion with a concentration of 0.3 mg / mL; soaking 1 g of pretreated activated carbon in 15 mL of PDA dispersion, stirring and mixing at 55℃ and 180 rpm for 11 hours, centrifuging at 8000 rpm for 10 min after the reaction to separate the solid, washing three times with deionized water to remove unadsorbed PDA, and vacuum drying at 60℃ 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, mixed, and then 11 g of AC@PDA was added. The mixture was ultrasonically dispersed at 300 W and 40 kHz for 30 min, and then allowed to stand at 25 °C for 24 h. After centrifugation, washing with deionized water, and drying at 60 °C for 24 h, the product was obtained.

[0029] Example 2

[0030] This embodiment provides a method for treating glycine production wastewater, the steps of which include:

[0031] (1) After recovering methanol from glycine wastewater by distillation, add dilute sulfuric acid to adjust the pH to 2.5, stir at 100 rpm for 45 min, and let stand for 100 min after stirring.

[0032] (2) Transfer the supernatant to another container, add ZIF-8 modified material at a ratio of 1.2 g / L relative to the supernatant, stir at 80 rpm for 120 min, let stand for 50 min, filter and collect the filter residue and filtrate, and recover hexamethylenetetramine by washing the filter residue with ether.

[0033] (3) The filtrate was evaporated and concentrated under -0.08 MPa vacuum and 50℃ to separate high-purity ammonium chloride crystals.

[0034] 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 10 mM Tris-HCl buffer solution at pH 8.5 to obtain a PDA dispersion with a concentration of 0.1 mg / mL; soaking 1 g of pretreated activated carbon in 15 mL of PDA dispersion, stirring and mixing at 55°C and 150 rpm for 10 hours, centrifuging at 8000 rpm for 10 min after the reaction to separate the solid, washing three times with deionized water 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, 1.96 g of... 2-Methylimidazole was dissolved in 100 mL of methanol, mixed, and then 10 g of AC@PDA was added. The mixture was ultrasonically dispersed at 300 W and 40 kHz for 30 min, and then allowed to stand at 25 °C for 22 h. After centrifugation, washing with deionized water, and drying at 60 °C for 24 h, the product was obtained.

[0035] Example 3

[0036] This embodiment provides a method for treating glycine production wastewater, the steps of which include:

[0037] (1) After recovering methanol from glycine wastewater by distillation, add dilute sulfuric acid to adjust the pH to 3.0, stir at 120 rpm for 60 min, and let stand for 120 min after stirring.

[0038] (2) Transfer the supernatant to another container, add ZIF-8 modified material at a ratio of 1.6 g / L relative to the supernatant, stir at 100 rpm for 140 min, let stand for 60 min, filter and collect the filter residue and filtrate, and recover hexamethylenetetramine by washing the filter residue with ether.

[0039] (3) The filtrate was evaporated and concentrated under -0.08 MPa vacuum and 60℃ to separate high-purity ammonium chloride crystals.

[0040] 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℃ 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℃ for 12 hours to obtain pretreated activated carbon; dissolving dopamine hydrochloride in 10 mM Tris-HCl buffer solution at pH 8.5 to obtain a PDA dispersion with a concentration of 0.5 mg / mL; soaking 1 g of pretreated activated carbon in 20 mL of PDA dispersion, stirring and mixing at 65℃ and 200 rpm for 12 hours, centrifuging at 8000 rpm for 10 min after the reaction to separate the solid, washing three times with deionized water to remove unadsorbed PDA, and vacuum drying at 60℃ for 6 hours to obtain AC@PDA; dissolving 2.38 g of zinc nitrate in 110 mL of methanol, 3.14 g... 2-Methylimidazole was dissolved in 110 mL of methanol, mixed, and then 12 g of AC@PDA was added. The mixture was ultrasonically dispersed at 300 W and 40 kHz for 30 min, and then allowed to stand at 25 °C for 26 h. After centrifugation, washing with deionized water, and drying at 60 °C for 24 h, the product was obtained.

[0041] Example 4

[0042] This embodiment provides a method for treating glycine production wastewater, the steps of which include:

[0043] (1) After recovering methanol from glycine wastewater by distillation, add dilute sulfuric acid to adjust the pH to 2.5, stir at 120 rpm for 45 min, and let stand for 120 min after stirring.

[0044] (2) Transfer the supernatant to another container, add ZIF-8 modified material at a ratio of 1.2 g / L relative to the supernatant, stir at 100 rpm for 120 min, let stand for 60 min, filter and collect the filter residue and filtrate, and recover hexamethylenetetramine by washing the filter residue with ether.

[0045] (3) The filtrate was evaporated and concentrated under -0.08 MPa vacuum and 50℃ to separate high-purity ammonium chloride crystals.

[0046] 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 10 mM Tris-HCl buffer solution at pH 8.5 to obtain a PDA dispersion with a concentration of 0.5 mg / mL; soaking 1 g of pretreated activated carbon in 15 mL of PDA dispersion, stirring and mixing at 65°C and 150 rpm for 12 hours, centrifuging at 8000 rpm for 10 min after the reaction to separate the solid, washing three times with deionized water 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, 1.96 g of... 2-Methylimidazole was dissolved in 110 mL of methanol, mixed, and then 10 g of AC@PDA was added. The mixture was ultrasonically dispersed at 300 W and 40 kHz for 30 min, and then allowed to stand at 25 °C for 26 h. After centrifugation, washing with deionized water, and drying at 60 °C for 24 h, the product was obtained.

[0047] Comparative Example 1

[0048] This comparative example provides a method for treating glycine production wastewater. The activated carbon was not pretreated, and the rest was the same as in Example 1.

[0049] Comparative Example 2

[0050] This comparative example provides a method for treating glycine production wastewater. The preparation method of the ZIF-8 modified material is different, but the rest is the same as in Example 1.

[0051] The preparation method of the ZIF-8 modified material in this comparative example is as follows: 10 g of activated carbon was soaked in 1 M HCl solution (solid-liquid ratio 1:10), stirred at 80℃ for 4 hours, filtered, and washed with water until neutral; transferred to 40% HF solution (solid-liquid ratio 1:5), soaked at room temperature for 12 hours, filtered, and washed with water until neutral; vacuum dried at 100℃ for 12 hours to obtain pretreated activated carbon; 1.49 g of zinc nitrate was dissolved in 110 mL of methanol, 1.96 g of 2-methylimidazole was dissolved in 110 mL of methanol, mixed, and 10 g of pretreated activated carbon was added. The mixture was ultrasonically dispersed at 300 W and 40 kHz for 30 min, and then allowed to stand at 25℃ for 26 h. After centrifugation, washing with deionized water, and drying at 60℃ for 24 h, the product was obtained.

[0052] Comparative Example 3

[0053] This comparative example provides a method for treating glycine production wastewater, with the amount of ZIF-8 modified material reduced by half (0.7 g / L), and the rest being the same as in Example 1.

[0054] Comparative Example 4

[0055] This comparative example provides a method for treating glycine production wastewater, without using ZIF-8 modified material; otherwise, it is the same as in Example 1.

[0056] Comparative Example 5

[0057] 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.

[0058] Comparative Example 6

[0059] This comparative example provides a method for treating glycine production wastewater, wherein 2.5g of 2-methylimidazole is adjusted to 1.25g of 2-methylimidazole, and the rest is the same as in Example 1.

[0060] Experimental Example 1: The contents of various pollutants in the glycine production wastewater before and after treatment in Examples 1-4 and Comparative Examples 1-6 were determined:

[0061] Chemical oxygen demand (COD): determined according to the dichromate method (HJ 828-2017);

[0062] Ammonia nitrogen (NH3-N): Nessler's reagent spectrophotometric method (HJ 535-2009);

[0063] Urotropin: 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;

[0064] Heavy metals: Inductively coupled plasma mass spectrometry (ICP-MS, HJ 700-2014).

[0065] The test results are shown in Table 1 below:

[0066] Table 1

[0067]

[0068] Based on the above data, it can be seen that Examples 1-4, through the combination of "acidic adjustment + ZIF-8 modified material adsorption + evaporation crystallization", achieved a high-efficiency treatment effect with COD removal rate of 89.7%-92.5%, ammonia nitrogen removal rate of 97.5%-98.3%, and hexamethylenetetramine recovery rate of 92.8%-95.6%, and the heavy metal residue was significantly lower than that of the raw water (Zn / Fe both <5μg / L).

[0069] In Comparative Example 1, the COD removal rate (75.3%) and hexamethylenetetramine recovery rate (70.1%) of the untreated activated carbon decreased significantly, while the Zn / Fe residue 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 cannot effectively load functional materials.

[0070] 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 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 adsorption capacity and stability of the material.

[0071] In Comparative Example 3, the COD removal rate (79.8%) and hexamethylenetetramine recovery rate (76.3%) were significantly reduced when the ZIF-8 dosage was halved, while the heavy metal residue doubled. The ZIF-8 modified material needs to reach a critical dosage (≥1.2 g / L) to provide sufficient adsorption sites; insufficient dosage leads to incomplete removal of pollutants.

[0072] Comparative Example 4, which did not use ZIF-8 material, showed a significant deterioration in all indicators (COD removal rate of 62.1%, and heavy metal residue close to that of raw water). ZIF-8 material is the core of the system, and its metal-organic framework structure plays a leading role in the selective adsorption and catalytic degradation of pollutants (especially heavy metals).

[0073] Comparative Example 5, using a low-concentration PDA dispersion, resulted in a lower COD removal rate (78.5%) and hexamethylenetetramine recovery rate (73.8%) compared to Example 1, with a Zn residue of 22 μg / L. The excessively low PDA concentration led to incomplete coating of the activated carbon surface and uneven ZIF-8 loading, weakening the synergistic effect of the composite material.

[0074] In Comparative Example 6, a reduction in 2-methylimidazole resulted in a comprehensive deterioration in performance, with a COD removal rate of 68.2% and a Zn residue of 45 μg / L, even weaker than the pure activated carbon system. The molar imbalance between 2-methylimidazole and zinc nitrate disrupted the formation of the ZIF-8 crystal structure, causing the material to lose its pore adsorption capacity and release free Zn. 2+ .

[0075] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for treating glycine production wastewater, characterized in that the steps include... include: (1) After recovering methanol from glycine wastewater by distillation, add dilute sulfuric acid to adjust the pH to 2.5-3.0, stir and let stand; (2) The supernatant was transferred to another container, ZIF-8 modified material was added, stirred and allowed to stand, filtered and the filter residue and filtrate were collected. The filter residue was washed with ether and hexamethylenetetramine was recovered. The ratio of ZIF-8 modified material to supernatant was 1.2-1.6 g / L. The preparation method of the ZIF-8 modified material includes: cleaning activated carbon with hydrochloric acid and hydrofluoric acid in sequence to remove impurities and then drying it to obtain activated carbon after impurity removal pretreatment; immersing the activated carbon after impurity removal pretreatment in PDA dispersion and stirring and mixing at 55-65℃ and 150-200rpm for 10-12h to obtain AC@PDA; dissolving zinc nitrate and 2-methylimidazole in methanol respectively, mixing them, adding AC@PDA, ultrasonically dispersing, allowing the reaction to stand, centrifuging, washing, and drying to obtain the final product. (3) The filtrate was evaporated and concentrated under -0.08MPa vacuum and 50-60℃ to separate high-purity ammonium chloride crystals.

2. The method for treating glycine production wastewater according to claim 1, characterized in that, The PDA dispersion is prepared by dissolving dopamine hydrochloride in a 10 mM Tris-HCl buffer solution at pH 8.5 to obtain a PDA dispersion with a concentration of 0.1-0.5 mg / mL.

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

4. The method for treating glycine production wastewater according to claim 1, characterized in that, The ratio of zinc nitrate, 2-methylimidazole, AC@PDA and methanol is 1.49-2.38g: 1.96-3.14g: 10-12g: 200-220mL.

5. The method for treating glycine production wastewater according to claim 1, characterized in that, The static reaction temperature is 25±2℃, and the time is 22-26h.

6. The method for treating glycine production wastewater according to claim 1, characterized in that, The step (1) of stirring and then letting stand involves stirring at 100-120 rpm for 45-60 minutes and then letting stand for 100-120 minutes.

7. The method for treating glycine production wastewater according to claim 1, characterized in that, The step (2) of stirring and then letting stand involves stirring at 80-100 rpm for 120-140 minutes and then letting stand for 50-60 minutes.

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