Polyvinyl alcohol production wastewater treatment process

Abstract

The invention belongs to the field of sewage treatment, and particularly relates to a polyvinyl alcohol production wastewater treatment process. The outer surface of the porous cordierite is coated with a polymer to form a protective film, and then a manganese-cobalt composite oxide is loaded in pores; removing the protective film on the outer surface of the porous cordierite, and coating the outer surface of the porous cordierite loaded with the manganese-cobalt composite oxide with titanium dioxide to obtain composite cordierite; modifying the composite cordierite by using a silane coupling agent containing a sulfydryl group, and oxidizing to obtain a catalytic treatment agent; the catalytic treatment agent is placed in the wastewater, and illumination reaction is carried out in an oxygen-containing atmosphere. According to the process, high cost and complexity of medicament treatment are avoided, the requirement on equipment is low, the treatment conditions are easy to achieve, refractory organic matters are degraded firstly, the viscosity of the system is reduced, and the subsequent treatment difficulty for inorganic matters is reduced.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment, specifically relating to a process for treating wastewater from polyvinyl alcohol production. Background Technology

[0002] The production of polyvinyl alcohol (PVA) involves complex polymerization and alcoholysis processes, requiring the input of various raw materials and generating numerous byproducts. This results in a large volume of wastewater containing polymers, PVA, and hydrolysates. This wastewater has a high chemical oxygen demand (COD) and is considered difficult to degrade, exhibiting poor biodegradability. Once released into the natural environment, it not only affects the self-purification cycle of water bodies but also accumulates continuously, leading to serious environmental problems. Therefore, it requires water treatment to meet standards before discharge. Furthermore, the alcoholysis process of PVA consumes a large amount of alkaline media, resulting in highly alkaline wastewater that is difficult for conventional biodegrading organisms to survive and reproduce. Therefore, direct biological treatment of this wastewater has significant limitations. In addition, due to the presence of PVA molecules and hydrolysates, PVA wastewater typically has a certain viscosity, leading to rapid flux decline and low filtration efficiency in methods such as membrane filtration. How to treat highly alkaline, high-viscosity PVA production wastewater while considering the economics of the treatment project has become a challenge for the industry. Summary of the Invention

[0003] To address the problems of high alkalinity, high viscosity, easy foaming, and high chemical oxygen demand in polyvinyl alcohol (PVA) production wastewater in existing technologies, this invention provides a process that can alleviate strong alkalinity, operate in a relatively alkaline environment, and specifically treat key pollutants in PVA production wastewater. The technical solution is as follows: A process for treating wastewater from polyvinyl alcohol production includes the following steps: coating the outer surface of porous cordierite with a polymer to form a protective film, and then loading manganese-cobalt composite oxides into the pores; removing the protective film from the outer surface of the porous cordierite, and coating the outer surface of the porous cordierite loaded with manganese-cobalt composite oxides with titanium dioxide to obtain composite cordierite; modifying the composite cordierite with a silane coupling agent containing mercapto groups, and oxidizing it to obtain a catalytic treatment agent; placing the catalytic treatment agent in wastewater and reacting it under light in an oxygen-containing atmosphere.

[0004] Furthermore, the polymer includes one or more of polyvinyl butyral, ethyl cellulose, or cellulose acetate; the silane coupling agent containing a thiol group includes one or more of 3-mercaptopropyltriethoxysilane or 3-mercaptopropyltrimethoxysilane.

[0005] Furthermore, the cordierite has a pore size of 2~5µm; the solid-liquid ratio of the catalyst to the wastewater is 1~10g / L.

[0006] Furthermore, this includes the following steps: a. After dissolving the polymer, a film is formed on the surface of porous cordierite; b. Prepare a mixed solution of manganese and cobalt salts containing citric acid. Place porous cordierite coated with a protective film into the mixed solution, mix thoroughly, and then remove the air under vacuum. Then, remove the cordierite and gel it at 60-90℃ and 75-95% humidity for 1-2 hours, and then dry it. After drying, calcine it at 300-450℃ for 2-4 hours to complete the loading. c. Dissolve tetrabutyl titanate in ethanol, add nitric acid to adjust the pH of the system to 2-3, and stir until a transparent sol is formed; wash the porous cordierite loaded with manganese-cobalt composite oxide with water and then immerse it in ethanol, wash it thoroughly with ethanol, and dry it; after drying, immerse it in the sol, pull it at a speed of 3-8 mm / s, and then calcine it at 450-550℃ for 1.5-3 h to obtain composite cordierite; d. Place the silane coupling agent containing mercapto groups in an aqueous solution of ethanol, then add ammonia, mix thoroughly at 60-75°C, then mix with composite cordierite, and stir and react for 4-6 hours under a protective atmosphere. After washing and drying the product, mercapto-modified composite cordierite is obtained. e. The mercapto-modified cordierite was fully dispersed in hydrogen peroxide, and sulfuric acid was added to adjust the pH of the system to 2-4. The mixture was stirred for 20-30 hours. After the product was thoroughly washed, the catalyst was obtained.

[0007] Furthermore, in step b, the molar ratio of cobalt salt to manganese salt is 0.1~2:1; the molar ratio of citric acid to the sum of cobalt salt and manganese salt is 1~1.5:1; and the concentration of cobalt salt and manganese salt in the mixed solution is 0.15~0.5 mol / L.

[0008] Furthermore, the mass concentration of tetrabutyl titanate in the sol in step c is 5-10%.

[0009] Furthermore, in step d, the molar ratio of the mercapto-containing silane coupling agent to ammonia is 1:1.5~2.5; the concentration of the mercapto-containing silane coupling agent in the aqueous ethanol solution is 0.02~0.05 mol / L; the volume concentration of the aqueous ethanol solution is 60~90%; and the mass concentration of the hydrogen peroxide in step e is 20~30%.

[0010] Furthermore, the polymer is dissolved in ethanol to prepare a polymer solution with a mass fraction of 8-20%; porous cordierite is immersed in the polymer solution and allowed to stand for 10-40 minutes; then it is dried at 60-80°C to form a protective film on the outer surface of the cordierite.

[0011] Furthermore, the composite cordierite is placed in water and hydrothermally heated at 100~120℃ for 1~3 hours before modification.

[0012] Furthermore, the step of regenerating the catalyst includes: thoroughly washing the catalyst with water and then neutralizing it by aeration with carbon dioxide.

[0013] By adopting the above scheme, the method of the present invention has the following advantages: 1. The process of the present invention degrades polyvinyl alcohol-related organic matter through photocatalysis without the need to add chemical agents such as oxidants and reducing agents, thus avoiding the introduction of new pollutants. Moreover, during the degradation process, polyvinyl alcohol-related organic matter is decomposed into environmentally friendly carbon dioxide and water, which is highly controllable, has no secondary pollution, and the treated wastewater has better biodegradability and is more suitable for biological treatment, and the wastewater can quickly meet the discharge standards.

[0014] 2. The water treatment agent of this invention is synthesized in situ by loading a manganese-cobalt composite oxide as a photocatalyst within the pores of porous cordierite, coating the outer surface with titanium dioxide, and then grafting sulfonic acid groups onto the surface. This creates a lower alkalinity environment around the water treatment agent, ensuring catalytic activity and achieving catalytic degradation under a highly alkaline environment. This avoids the increase of uncontrollable products caused by conventional pH adjustment and the influence of introduced anions on the water treatment agent, and the products are not easily detached. This solves the problem of conventional treatment methods requiring pH adjustment before separate treatment of organic and inorganic substances, which is multi-step and inefficient. Organic degradation is performed first, and pH adjustment can be carried out simultaneously during inorganic substance treatment, avoiding the reduced controllability of pH adjustment and the difficulty of mixing caused by high viscosity and foaming defects.

[0015] 3. The pores and surface of the water treatment agent of the present invention are filled with hydroxyl groups, which is conducive to the full combination of wastewater and catalyst. In addition, the residual polyvinyl alcohol therein has good affinity with the water treatment agent, and the grafted sulfonic acid groups can help capture polyvinyl alcohol organic matter and improve catalytic efficiency.

[0016] 4. The sulfonic acid modified layer on the outer surface of the present invention and the hydroxylated titanium dioxide can form a synergistic protection to resist the corrosion of strong alkali, reduce the risk of graft layer hydrolysis and titanium dioxide dissolution, further protect the stability and activity of the oxide catalyst in the pores, and the titanium dioxide and oxide can synergistically catalyze, resulting in high degradation efficiency.

[0017] 5. This invention loads different substances on the surface and within the pores of the carrier through polymer protection, which provides stronger protection for the oxide catalyst. The titanium dioxide with stronger surface stability can improve the service life of the water treatment agent and is also more conducive to the grafting of coupling agents.

[0018] 6. The process of the present invention avoids the high cost and complexity of chemical treatment, has low requirements for equipment, and the treatment conditions are easy to meet. It first degrades the difficult-to-degrade organic matter, reduces the viscosity of the system, and reduces the difficulty of subsequent treatment of inorganic matter.

[0019] 7. The water treatment agent of the present invention has high mechanical strength, can adapt to various working conditions, has a long service life, is simple to operate, can be adapted to intermittent or continuous processes, is easy to scale up and apply, and is easy to regenerate. Attached Figure Description

[0020] Figure 1 This is a comparison chart of COD removal rates between the various embodiments and the comparative examples; Figure 2 This is a comparison chart of the polyvinyl alcohol removal rates of each embodiment and the comparative example. Detailed Implementation

[0021] 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. Example 1: (1) Polyvinyl butyral was dissolved in ethanol to prepare a 15% mass fraction polyvinyl butyral solution; porous cordierite with a pore size of 3µm was immersed in the polyvinyl butyral solution and left to stand for 20min; then dried at 70℃ to form a protective film on the outer surface of the cordierite. (2) Dissolve 0.1 mol manganese nitrate and 0.08 mol cobalt nitrate in 800 mL of water, add 0.2 mol citric acid to obtain a mixed solution; place porous cordierite coated with a protective film into the mixed solution, stir evenly and then vacuum exhaust; then take out the cordierite, gel at 80℃ and 90% humidity for 1.5 h, and then dry it at 60℃; after drying, calcine at 400℃ for 3 h to complete the loading; (3) Tetrabutyl titanate was dissolved in ethanol to prepare a solution with a mass fraction of 8%. Nitric acid was added to adjust the pH of the system to 2.5. The mixture was stirred until a transparent sol was formed. The porous cordierite loaded with manganese cobalt composite oxide was washed with water and then immersed in ethanol. The mixture was stirred at 200 rpm for 30 min. The cordierite was removed and the ethanol was replaced. The operation was repeated three times and then dried. The dried porous cordierite loaded with manganese cobalt composite oxide was immersed in the sol and pulled at a speed of 5 mm / s. Then it was calcined at 500℃ for 2.5 h to obtain composite cordierite. (4) Place the composite cordierite in water and hydrothermally heat it at 110°C for 2 hours; take 7g of 3-mercaptopropyltriethoxysilane and place it in 1L of 75% v / v ethanol, then add 6mL of ammonia water, mix it evenly at 65°C, mix it with the composite cordierite, and stir and react it under a protective atmosphere for 5 hours. After washing and drying the product, the mercapto-modified composite cordierite is obtained. (5) The mercapto-modified cordierite was fully dispersed in 25% hydrogen peroxide, and the pH of the system was adjusted to 3 by adding sulfuric acid. The reaction was stirred for 24 hours. After the product was fully washed, the catalyst was obtained.

[0022] Example 2: The difference from Example 1 is as follows: (1) Dissolve polyvinyl butyral in ethanol to prepare an 8% polyvinyl butyral solution; immerse porous cordierite in the polyvinyl butyral solution and let it stand for 20 minutes; then dry it at 70°C to form a protective film on the outer surface of the cordierite.

[0023] Example 3: The difference from Example 1 is as follows: (2) Dissolve 0.15 mol manganese nitrate and 0.02 mol cobalt nitrate in 800 mL of water, add 0.2 mol citric acid to obtain a mixed solution; place porous cordierite coated with a protective film into the mixed solution, stir evenly and then vacuum exhaust; then take out the cordierite, gel at 80℃ and 90% humidity for 1.5 h, and then dry it at 60℃; after drying, calcine at 400℃ for 3 h to complete the loading.

[0024] Example 4: The difference from Example 1 is as follows: (2) Dissolve 0.6 mol manganese nitrate and 0.12 mol cobalt nitrate in 800 mL of water, add 0.2 mol citric acid to obtain a mixed solution; place porous cordierite coated with a protective film in the mixed solution, stir evenly and then vacuum exhaust; then take out the cordierite, gel at 80℃ and 90% humidity for 1.5 h, and then dry it at 60℃; after drying, calcine at 400℃ for 3 h to complete the loading.

[0025] Example 5: The difference from Example 1 is as follows: (3) Tetrabutyl titanate was dissolved in ethanol to prepare a 5% solution by mass. Nitric acid was added to adjust the pH of the system to 2.5. The mixture was stirred until a transparent sol was formed. The porous cordierite loaded with manganese cobalt composite oxide was washed with water and then immersed in ethanol. The mixture was stirred at 200 rpm for 30 min. The cordierite was removed and the ethanol was replaced. The operation was repeated three times and then dried. The dried porous cordierite loaded with manganese cobalt composite oxide was immersed in the sol and pulled at a speed of 8 mm / s. Then it was calcined at 500℃ for 2.5 h to obtain composite cordierite.

[0026] Example 6: The difference from Example 1 is as follows: (4) Take 7g of 3-mercaptopropyltriethoxysilane and place it in 1L of 75% v / v ethanol. Then add 6mL of ammonia water, mix evenly at 65℃, mix with composite cordierite, and stir the reaction under nitrogen atmosphere for 5h. After washing and drying the product, obtain mercapto-modified composite cordierite.

[0027] Comparative Example 1: The difference from Example 1 is that 3-mercaptopropyltriethoxysilane grafting modification was not performed.

[0028] Comparative Example 2: 0.1 mol manganese nitrate and 0.08 mol cobalt nitrate were dissolved in 800 mL of water, and 0.2 mol citric acid was added to obtain a mixed solution. Clean porous cordierite was placed in the mixed solution, stirred evenly, and then the air was vented under vacuum. The cordierite was then removed and gelled at 80 °C and 90% humidity for 1.5 h, and then dried by blowing air at 60 °C. After drying, it was calcined at 400 °C for 3 h to complete the loading and obtain the water treatment agent.

[0029] Comparative Example 3: Porous cordierite with a pore size of 1 micrometer was used.

[0030] Process Example: Wastewater discharged from polyvinyl alcohol production is used. The water quality indicators of this wastewater are: COD Cr =6200mg / L, BOD5=660mg / L, polyvinyl alcohol=693.4mg / L, pH=11.2; at a solid-liquid ratio of 5g / L, the water treatment agent of each embodiment and wastewater were placed in a reactor, and air was introduced at a rate of 80mL / min for photocatalytic reaction for 4h.

[0031] Process comparison example: Take the above wastewater, adjust the pH to neutral, use ferric chloride as a coagulant, add 0.5 g / L, and carry out flocculation and sedimentation at 300 rpm.

[0032] Example Sample Testing: The water treatment agents from each embodiment were taken and subjected to photocatalytic treatment according to the process embodiments. The COD and polyvinyl alcohol content of the treated wastewater were measured, and the results are shown in Table 1. The COD and polyvinyl alcohol removal rates were calculated as the ratios of the changes in COD and polyvinyl alcohol to their initial values. The results are as follows: Figure 1 and Figure 2 As shown.

[0033] Table 1: The data in Table 1 show that, compared to the comparative process that requires prior neutralization before flocculation and sedimentation, the process of this invention can rapidly reduce the concentration of polyvinyl alcohol and COD in wastewater. The process of this invention has significant advantages in terms of cost and speed.

[0034] Combined with Table 1 and Figure 1 and Figure 2It can be seen that during polymer coating, the polymer concentration in Example 2 was significantly lower than that in Example 1. The COD and polyvinyl alcohol removal rates in Example 2 were both lower than those in Example 1, indicating that polymer coating can affect the catalytic degradation performance of the water treatment agent. Too low a concentration may lead to incomplete coating, resulting in excessive formation of composite polymers on the cordierite surface, reducing the formation sites for titanium dioxide. The cobalt and manganese contents in Examples 3 and 4 differed significantly, and the COD and polyvinyl alcohol removal effects in both were significantly worse than in Example 1, indicating that the cobalt and manganese contents need to be controlled at an appropriate ratio; too much or too little of any element will affect the catalytic effect. In Example 5, the pulling speed was faster, and the photocatalytic ability of the water treatment agent decreased, with both the COD and polyvinyl alcohol removal rates significantly decreasing. This indicates that an excessively fast pulling speed affects the catalytic process of the composite oxide within the pores. It is possible that a faster pulling speed results in a thicker film and a smaller pore size, affecting the contact efficiency between the composite oxide and the degradation raw materials. Comparative Example 1 demonstrates the importance of grafted sulfonic acid groups; without sulfonic acid groups, the water treatment agent cannot successfully degrade organic matter. In Comparative Example 2, the carrier contained only a simple manganese-cobalt composite oxide, resulting in a poorer catalytic effect. In Comparative Example 3, the pore size was too small, making it difficult for highly viscous wastewater to fully penetrate most of the pores, thus hindering the water treatment agent's ability to exert its catalytic effect.

[0035] For those skilled in the art, various other corresponding changes and modifications can be made based on the technical solutions and concepts described above, and all such changes and modifications should fall within the protection scope of the claims of this invention.

Claims

1. A process for treating wastewater from polyvinyl alcohol production, characterized in that, Includes the following steps: A protective film is formed by coating the outer surface of porous cordierite with a polymer, and then a manganese-cobalt composite oxide is loaded into the pores. The protective film on the outer surface of the porous cordierite is removed, and titanium dioxide is coated on the outer surface of the porous cordierite loaded with manganese-cobalt composite oxide to obtain composite cordierite. The composite cordierite is modified with a silane coupling agent containing mercapto groups, and after oxidation, a catalyst is obtained. The catalyst is placed in wastewater and reacted under light in an oxygen-containing atmosphere.

2. The polyvinyl alcohol production wastewater treatment process according to claim 1, characterized in that, The polymer includes one or more of polyvinyl butyral, ethyl cellulose, or cellulose acetate; the silane coupling agent containing thiol groups includes one or more of 3-mercaptopropyltriethoxysilane or 3-mercaptopropyltrimethoxysilane.

3. The polyvinyl alcohol production wastewater treatment process according to claim 1, characterized in that, The cordierite has a pore size of 2~5µm; the solid-liquid ratio of the catalyst to the wastewater is 1~10g / L.

4. The polyvinyl alcohol production wastewater treatment process according to claim 1, characterized in that, Includes the following steps: a. After dissolving the polymer, a film is formed on the surface of porous cordierite; b. Prepare a mixed solution of manganese and cobalt salts containing citric acid. Place porous cordierite coated with a protective film into the mixed solution, mix thoroughly, and then remove the air under vacuum. Then, remove the cordierite and gel it at 60-90℃ and 75-95% humidity for 1-2 hours, and then dry it. After drying, calcine it at 300-450℃ for 2-4 hours to complete the loading. c. Dissolve tetrabutyl titanate in ethanol, add nitric acid to adjust the pH of the system to 2-3, and stir until a transparent sol is formed; wash the porous cordierite loaded with manganese-cobalt composite oxide with water and then immerse it in ethanol, wash it thoroughly with ethanol, and dry it; after drying, immerse it in the sol, pull it at a speed of 3-8 mm / s, and then calcine it at 450-550℃ for 1.5-3 h to obtain composite cordierite; d. Place the silane coupling agent containing mercapto groups in an aqueous solution of ethanol, then add ammonia, mix thoroughly at 60-75°C, then mix with composite cordierite, and stir and react for 4-6 hours under a protective atmosphere. After washing and drying the product, mercapto-modified composite cordierite is obtained. e. The mercapto-modified cordierite was fully dispersed in hydrogen peroxide, and sulfuric acid was added to adjust the pH of the system to 2-4. The mixture was stirred for 20-30 hours. After the product was thoroughly washed, the catalyst was obtained.

5. The polyvinyl alcohol production wastewater treatment process according to claim 4, characterized in that, The molar ratio of cobalt salt to manganese salt in step b is 0.1~2:1; the molar ratio of citric acid to the sum of cobalt salt and manganese salt is 1~1.5:1; and the concentration of cobalt salt and manganese salt in the mixed solution is 0.15~0.5mol / L.

6. The polyvinyl alcohol production wastewater treatment process according to claim 4, characterized in that, The mass concentration of tetrabutyl titanate in the sol in step c is 5-10%.

7. The polyvinyl alcohol production wastewater treatment process according to claim 4, characterized in that, The molar ratio of the mercapto-containing silane coupling agent to ammonia in step d is 1:1.5~2.5; the concentration of the mercapto-containing silane coupling agent in the aqueous ethanol solution is 0.02~0.05 mol / L; the volume concentration of the aqueous ethanol solution is 60~90%; and the mass concentration of hydrogen peroxide in step e is 20~30%.

8. The polyvinyl alcohol production wastewater treatment process according to claim 1 or 4, characterized in that, The polymer is dissolved in ethanol to prepare a polymer solution with a mass fraction of 8-20%; porous cordierite is immersed in the polymer solution and allowed to stand for 10-40 minutes; then it is dried at 60-80℃ to form a protective film on the outer surface of the cordierite.

9. The polyvinyl alcohol production wastewater treatment process according to claim 1 or 4, characterized in that, The composite cordierite is placed in water and hydrothermally heated at 100-120℃ for 1-3 hours, and then modified.

10. The polyvinyl alcohol production wastewater treatment process according to claim 1 or 4, characterized in that, The steps for regenerating the catalyst include: thoroughly washing the catalyst with water and then neutralizing it by aeration with carbon dioxide.

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