Catalyst for degrading organic pollutants as well as preparation method and application thereof

Abstract

The invention relates to the field of energy conservation and environmental protection, in particular to a catalyst for degrading organic pollutants and a preparation method and application thereof.The dual-modified MCM-49 zeolite nanocrystal is prepared through a one-step method by taking hexamethyleneimine and quaternary ammonium salt as dual templates, so that the prepared MCM-49 zeolite nanocrystal has amphipathy, and the molecular weight of the prepared MCM-49 zeolite nanocrystal is increased; the composite material has hydrophilic and oleophylic characteristics at the same time, has a synergistic effect with peroxymonosulfate or peroxydisulfate, can efficiently degrade organic pollutants such as antibiotics, dyes and endocrine disruptors in a wide pH range, and is suitable for treating wastewater containing the organic pollutants. The catalyst can be repeatedly used for more than or equal to 10 times, and the activity retention rate of the catalyst reaches 95% or above. The catalyst disclosed by the invention is simple in preparation process and low in cost, and has a good application prospect.

Description

Technical Field

[0001] The present invention relates to the field of energy conservation and environmental protection, and particularly relates to a catalyst for degrading organic pollutants, a preparation method thereof, and an application thereof. Background Art

[0002] With the acceleration of the global industrialization pace, a large amount of wastewater containing organic pollutants has been discharged into natural water bodies during the industrial production process. These organic pollutants have a wide range of sources and complex types. Among them, the chemical industry will generate wastewater containing complex organic substances such as aromatic compounds, halogenated hydrocarbons, and amine compounds during organic synthesis reactions. These substances often have high toxicity, poor degradability, and bioaccumulation; the textile printing and dyeing industry uses a large number of various dyes and auxiliaries, resulting in high chroma of wastewater and containing organic pollutants such as azo dyes and anthraquinone dyes that are difficult to degrade; the wastewater generated during the pulping and papermaking processes in the paper industry contains lignin, cellulose derivatives, and various chemical additives, with high chemical oxygen demand (COD) and biochemical oxygen demand (BOD), and some contain toxic and harmful organic chlorides; the wastewater generated during processes such as printed circuit board production and semiconductor manufacturing in the electronics industry contains heavy metal ions, organic solvents, photoresists and other organic pollutants. These organic pollutants have stable chemical properties and strong biological toxicity and are difficult to degrade by conventional methods. Domestic sewage cannot be ignored either. With the growth of the population and the acceleration of the urbanization process, its discharge volume is increasing continuously. In addition to containing conventional organic substances, it also contains various emerging organic pollutants, such as components in personal care products, drug residues, and endocrine disruptors. These emerging organic pollutants have potential ecotoxicological risks and pose threats to aquatic organisms and human health.

[0003] In the face of the severe situation of wastewater containing organic pollutants, traditional wastewater treatment technologies have many limitations. Biological treatment methods use the metabolic action of microorganisms to degrade organic pollutants. However, many organic pollutants have biological toxicity, which will inhibit the growth and metabolic activity of microorganisms, reducing the biological treatment efficiency or even making it ineffective. Moreover, some organic pollutants have complex structures and stable chemical properties, and it is difficult for microorganisms to completely degrade them; physical treatment methods remove organic pollutants in wastewater through physical actions, but they can only transfer organic pollutants from one phase to another phase and do not really achieve degradation. For example, the regeneration treatment of the adsorbent after adsorption may cause secondary pollution, and the precipitation and filtration methods have limited removal effects on dissolved organic pollutants; chemical treatment methods convert organic pollutants into harmless substances through chemical reactions. However, traditional chemical oxidation-reduction methods and chemical precipitation methods have limited treatment effects and may cause secondary pollution. Although advanced oxidation methods are efficient and fast, they have high costs and strict requirements for equipment and operating conditions, restricting large-scale applications; physical-chemical combined processes and biological-physical-chemical combined processes have improved the wastewater treatment efficiency to a certain extent, but they have complex processes, high costs, large floor areas, and poor adaptability to different types and concentrations of organic pollutants.

[0004] Among many emerging advanced oxidation technologies, the oxidation systems based on peroxymonosulfate (PMS) and persulfate (PDS) have attracted attention due to their strong oxidation ability, wide application range, environmental friendliness and other advantages. The sulfate radicals (SO4 - ·) generated by the decomposition of PMS and PDS in water have an oxidation ability close to that of hydroxyl radicals and can effectively oxidize a variety of organic pollutants. However, the decomposition of PMS and PDS is easily affected by the water environment, and when used alone, the activation efficiency is low and the cost is high. Therefore, developing a highly efficient, stable and low-cost catalyst to act synergistically with them, improving the generation and utilization efficiency of sulfate radicals, and achieving efficient degradation of organic pollutants have become the key to solving the problem of treating wastewater containing organic pollutants. The double-modified MCM-49 catalyst came into being. The MCM-49 zeolite material provides a carrier for the adsorption and catalytic reaction of organic pollutants due to its large specific surface area, regular pore structure, good thermal stability and other advantages. After double modification, the adsorption selectivity and catalytic activity for organic pollutants are enhanced, and the synergistic effect with PMS or PDS is improved, which is expected to play an important role in the field of wastewater treatment. Summary of the Invention

[0005] The purpose of the present invention is to provide a catalyst for degrading organic pollutants and its preparation method. By using hexamethyleneimine and quaternary ammonium salt as double templates, double-modified MCM-49 zeolite nanocrystals are prepared in one step. This makes the prepared MCM-49 zeolite nanocrystals amphiphilic, that is, they have both hydrophilic and lipophilic characteristics, which plays an extremely important role in the field of treating wastewater containing organic pollutants. It can significantly improve the activation efficiency of peroxymonosulfate (PMS) and persulfate (PDS), and accelerate the generation of strongly oxidizing sulfate radicals (SO4 - ·), thereby realizing the efficient degradation of organic pollutants. In practical applications, the catalyst can effectively treat various types of organic pollutants, including antibiotics, dyes, and endocrine disruptors, decompose them into harmless carbon dioxide, water and inorganic ions, significantly reduce the chemical oxygen demand (COD) and toxicity of the wastewater, and ensure that the treated wastewater can meet strict environmental emission standards, which is of great significance for protecting the ecological environment and human health.

[0006] To solve the above technical problems, the present invention provides a catalyst for degrading organic pollutants, its preparation method and application.

[0007] To achieve the above purpose, the present invention provides the following technical solutions: A catalyst for degrading organic pollutants and its preparation method, including the following steps: S1: Dissolve sodium aluminate and sodium hydroxide in deionized water, then add silica sol, stir at 800 r / min for 1 h. After the solution is dissolved to clarity, add hexamethyleneimine and continue stirring for 15 min, then add quaternary ammonium salt and continue stirring for 30 min. Load the above mixture into a reaction kettle with a polytetrafluoroethylene kettle liner, age at 40 - 50 °C for 24 h to obtain a mixture. Among the above raw materials, by mass ratio, silica sol:sodium aluminate:sodium hydroxide:hexamethyleneimine:quaternary ammonium salt:deionized water = 1:0.01 - 0.03:0.15 - 0.35:0.2 - 0.45:0.15 - 0.35:5 - 25; S2. Dry the above mixture at 40 °C for 0.5 - 4 h until the mass is reduced to within the range of 35% - 70% of the original mixture mass, and the sample presents a dry gel state; S3: Place the dry gel-like mixture in an open glassware, put the glassware into the reaction kettle liner, add deionized water outside the glassware, and the addition amount is 1 / 3 - 2 / 3 of the volume between the glassware and the reaction kettle liner, so that the deionized water in the liquid state cannot enter the glassware to provide a water vapor environment for the reaction. Crystallize at 150 °C for 1 - 3 days under the condition of steam assistance. After washing and drying, a crystalline product is obtained; S4: Calcinate the crystalline product at 300 - 400 °C for 4 - 8 h to obtain a double-modified MCM-49 nanocrystal catalyst for degrading organic pollutant D.

[0008] Furthermore, the preparation method of the quaternary ammonium salt includes the following steps: In a nitrogen atmosphere, drop a mixed solution of methyl acrylate and methanol into diethylenetriamine. After the reaction ends, a light yellow transparent liquid is obtained. After removing methanol, raise the temperature to 150 °C and continue the reaction under reduced pressure to generate a viscous, light yellow compound. Dissolve the compound in water and drop an aqueous solution of 2,3-epoxypropyltrimethylammonium chloride, the mass of which is 1 - 10 times the mass of the compound. After the reaction is completed, the product is separated and purified to obtain a light yellow solid quaternary ammonium salt. Among the above raw materials, by mass ratio, methyl acrylate:methanol:diethylenetriamine = 1:3 - 15:2 - 10, and the mass fraction of the aqueous solution of 2,3-epoxypropyltrimethylammonium chloride is 40% - 80%.

[0009] Furthermore, the method for removing methanol is the distillation method.

[0010] Furthermore, the degradation method of the double-modified MCM-49 nanocrystal catalyst for degrading organic pollutant D includes the following steps: Disperse the catalyst in the wastewater containing organic pollutants at a concentration of 0.2 - 1.5 g / L, adjust the pH to 3.0 - 9.0, add 0.5 - 5 mmol / L of peroxymonosulfate (PMS) or persulfate (PDS), and react at 20 - 50 °C for 10 - 120 minutes to achieve efficient degradation of organic pollutants.

[0011] Furthermore, the organic pollutants include at least one of antibiotics, dyes, or endocrine disruptors, such as tetracycline, rhodamine B, bisphenol A, etc.

[0012] Furthermore, the number of times the catalyst can be reused ≥ 10 times, and the catalytic activity of the catalyst can still be maintained above 95% of the initial catalytic performance.

[0013] A catalyst for degrading organic pollutants and its preparation method provided by the present invention. This catalyst synergistically reacts with peroxymonosulfate (PMS) or persulfate (PDS) through a unique double-modified structure to achieve efficient degradation of organic pollutants. The stacked pore structure between MCM-49 nanocrystals provides it with rich active sites and a large specific surface area, which is beneficial to the adsorption and enrichment of organic pollutant molecules. When in contact with PMS or PDS, the active sites on the catalyst can lower the activation energy, prompting PMS or PDS to rapidly decompose to generate sulfate radicals (SO4 - ·). These radicals have strong oxidation ability and can attack organic pollutant molecules without selectivity, break their chemical bonds, and decompose them into small organic molecules or even completely mineralize them into carbon dioxide and water. At the same time, the modified substances such as quaternary ammonium salts introduced during the double-modification process further enhance the adsorption selectivity and catalytic activity of the catalyst towards organic pollutants, improve the generation efficiency and utilization efficiency of sulfate radicals, and thus accelerate the degradation process of organic pollutants.

[0014] In addition, the catalyst of this invention patent has good stability and reusability, which has significant economic advantages in actual wastewater treatment applications. After multiple cycles of use, the structure and performance of the catalyst are relatively stable, and the catalytic activity of the catalyst can still be maintained above 95% of the initial catalytic performance. As shown in Example 1, the degradation rate of tetracycline reached 92% during the initial degradation. After multiple regeneration cycles, its degradation rate only slightly decreased to 89%, still maintaining 96.7% of the initial catalytic activity. Its excellent catalytic activity retention rate reduces the replacement frequency and treatment cost of the catalyst. This characteristic makes this catalyst highly feasible in large-scale industrial wastewater treatment, providing strong support for reducing wastewater treatment costs and improving treatment efficiency. At the same time, the preparation method of this catalyst is relatively simple, the conditions are mild, and it is easy to industrialize production, further promoting its wide application in the field of actual wastewater treatment and providing a solid technical guarantee for achieving the goal of green and efficient wastewater purification. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 XRD patterns of a catalyst for degrading organic pollutants prepared in Example 1 of the present invention and a catalyst of model NZ-HM49-001 purchased in Comparative Example 1 DETAILED DESCRIPTION OF THE INVENTION

[0016] In order to make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions 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 a part rather than all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the scope of protection of the present invention.

[0017] The following specifically describes a catalyst for degrading organic pollutants and a preparation method thereof provided by the present invention through examples.

[0018] Example 1: Catalyst preparation: Step S1: Weigh 10 g of silica sol (mass fraction 30%), 0.2 g of sodium aluminate, and 2 g of sodium hydroxide, add them to deionized water, and stir at 800 r / min for 1 h until dissolved and clarified. Add 2 g of hexamethyleneimine, continue stirring for 15 min, then add 2 g of quaternary ammonium salt, and stir for 30 min. Put the mixture into a reaction kettle lined with polytetrafluoroethylene, and age at 45 °C for 24 h. The preparation method of the quaternary ammonium salt is as follows: In a nitrogen atmosphere, a mixed solution of 5 g of methyl acrylate and 30 g of methanol is dropped into 10 g of diethylenetriamine. After the reaction is completed, a light yellow transparent liquid is obtained. Methanol is removed by distillation, the temperature is raised to 150 °C, and the reaction continues under reduced pressure for 5 h to form a viscous, light yellow compound. The compound is dissolved in water, and 80 g of an aqueous solution of 2,3-epoxypropyltrimethylammonium chloride with a mass fraction of 60% (8 times the mass of the compound) is dropped. After the reaction is completed, through separation and purification, a light yellow solid quaternary ammonium salt is obtained.

[0019] S2: Dry the above mixture at 40 °C for 2 h until the mass is reduced to 50% of the original mixture mass, and the sample presents a dry gel state.

[0020] S3: Place the dry gel-like mixture in an open glassware, put it into the inner lining of the reaction kettle, add 10 g of deionized water outside the glassware, and crystallize at 150 °C for 2 days under steam assistance. After washing and drying, a crystalline product is obtained.

[0021] S4: Calcinate the crystalline product at 350 °C for 6 h to obtain a D double-modified MCM-49 nanocrystal catalyst for degrading organic pollutants.

[0022] Catalyst degradation of wastewater test: Prepare simulated wastewater containing tetracycline (concentration 100 mg / L). Take 500 ml of the simulated wastewater, add the catalyst to make its concentration 0.5 g / L, adjust the pH to 7.0, add 2 mmol / L of peroxymonosulfate PMS, and react at 30 °C for 60 minutes. The degradation rate of tetracycline reaches 92%. After completing the first tetracycline degradation reaction, the catalyst is separated by filtration and washed with deionized water until there are no obvious impurities in the filtrate. Subsequently, the recovered catalyst is dried in a vacuum oven at 240 °C for 2 hours, and then redispersed in fresh simulated wastewater containing tetracycline (100 mg / L), keeping the catalyst concentration at 0.5 g / L. The remaining reaction conditions (pH = 7.0, PMS concentration 2 mmol / L, reaction at 30 °C for 60 minutes) are the same as those in the initial use. Repeat the above process 10 times. After 10 consecutive cycles of use tests, that is, the 11th tetracycline degradation test, the degradation rate of tetracycline still reaches 89%.

[0023] Example 2: Catalyst preparation: Step S1: Weigh 10 g of silica sol (mass fraction 30%), 0.1 g of sodium aluminate, and 1.5 g of sodium hydroxide, add them to deionized water, and stir at 800 r / min for 1 h until dissolved and clear. Add 1 g of hexamethylenimine, continue stirring for 15 min, then add 1 g of quaternary ammonium salt, and stir for 30 min. Load the mixture into a reaction kettle lined with polytetrafluoroethylene, and age at 40 °C for 24 h. The preparation method of the quaternary ammonium salt is the same as that in Example 1, except that the raw material ratio is adjusted to 5 g of methyl acrylate, 15 g of methanol, 5 g of diethylenetriamine, and the mass fraction of the aqueous solution of 2,3-epoxypropyltrimethylammonium chloride dropped is 40% and its mass is 5 times the mass of this compound.

[0024] Step S2: Dry the above mixture at 40 °C for 3 h until the mass is reduced to 60% of the original mixture mass, presenting a dry gel-like sample.

[0025] Step S3: Place the dry gel-like mixture in an open glassware, put it into the reaction kettle liner, add 5 g of deionized water outside the glassware, and crystallize at 150 °C for 1 day under steam assistance. After washing and drying, a crystalline product is obtained.

[0026] Step S4: Calcinate the crystalline product at 300 °C for 8 h to obtain a D double-modified MCM-49 nanocrystal catalyst for degrading organic pollutants.

[0027] Catalyst degradation of wastewater test: Prepare simulated wastewater containing Rhodamine B (concentration 50 mg / L). Take 500 ml of the simulated wastewater, add the catalyst to make its concentration 1.0 g / L, adjust the pH to 5.0, add 3 mmol / L of persulfate PDS, and react at 25 °C for 90 minutes. The degradation rate of Rhodamine B reaches 89%.

[0028] Example 3: Catalyst preparation: Step S1: Weigh 10 g of silica sol (mass fraction 30%), 0.3 g of sodium aluminate, and 3 g of sodium hydroxide, add them to deionized water, and stir at 800 r / min for 1 h until dissolved and clarified. Add 3 g of hexamethyleneimine, continue stirring for 15 min, then add 3 g of quaternary ammonium salt, and stir for 30 min. Load the mixture into a reaction kettle with a polytetrafluoroethylene kettle liner, and age at 50 °C for 24 h. The preparation method of the quaternary ammonium salt is the same as that in Example 1, except that the raw material ratio is adjusted to 5 g of methyl acrylate, 20 g of methanol, 8 g of diethylenetriamine, and the mass fraction of the aqueous solution of 2,3-epoxypropyltrimethylammonium chloride dropped is 80% and its mass is 10 times that of this compound.

[0029] Step S2: Dry the above mixture at 40 °C for 4 h until the mass is reduced to 70% of the original mixture mass, and the sample presents a dry gel state.

[0030] Step S3: Place the dry gel-like mixture in an open glassware, put it into the reaction kettle liner, add 6 g of deionized water outside the glassware, and crystallize at 150 °C for 3 days under steam assistance. After washing and drying, a crystalline product is obtained.

[0031] Step S4: Calcinate the crystalline product at 400 °C for 4 h to obtain a D double-modified MCM-49 nanocrystal catalyst for degrading organic pollutants.

[0032] Catalyst degradation of wastewater test: Prepare simulated wastewater containing bisphenol A (concentration 80 mg / L). Take 500 ml of the simulated wastewater, add the catalyst to make its concentration 1.5 g / L, adjust the pH to 9.0, add 5 mmol / L of monopersulfate PMS, and react at 50 °C for 120 minutes. The degradation rate of bisphenol A reaches 95%.

[0033] Comparative Example 1: Prepare simulated wastewater containing tetracycline (concentration 100 mg / L). Take 500 ml of the simulated wastewater, add the purchased MCM-49 molecular sieve catalyst of model NZ-HM49-001 to make its concentration 0.5 g / L, adjust the pH to 7.0, add 2 mmol / L of monopersulfate PMS, and react at 30 °C for 60 minutes. The degradation rate of tetracycline is 72%.

[0034] Finally, it should be noted that the above specific implementation manners are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and all of them should be covered by the scope of the claims of the present invention.

Claims

1. A preparation method of a catalyst for degrading organic pollutants, characterized in that, It includes the following steps: S1: Dissolve sodium aluminate and sodium hydroxide in deionized water, then add silica sol, stir at 800 r / min for 1 h. After the solution is dissolved to clarity, add hexamethyleneimine and continue stirring for 15 min, then add quaternary ammonium salt and continue stirring for 30 min. Load the above mixture into a reaction kettle with a polytetrafluoroethylene kettle liner, age at 40 - 50 °C for 24 h to obtain a mixture, where the above raw materials are in a mass ratio of silica sol:sodium aluminate:sodium hydroxide:hexamethyleneimine:quaternary ammonium salt:deionized water = 1:0.01 - 0.03:0.15 - 0.35:0.2 - 0.45:0.15 - 0.35:5 - 25; S2: Dry the above mixture at 40 °C for 0.5 - 4 h until the mass is reduced to within the range of 35% - 70% of the original mixture mass, and the sample presents a dry gel state; S3: Place the dry gel-like mixture in an open glassware, put the glassware into the reaction kettle liner, add deionized water outside the glassware, and the addition amount is 1 / 3 - 2 / 3 of the volume between the glassware and the reaction kettle liner, so that the deionized water cannot enter the glassware to provide a water vapor environment for the reaction. Crystallize at 150 °C for 1 - 3 days under the condition of steam assistance, and after washing and drying, obtain a crystalline product; S4: Calcinate the crystalline product at 300 - 400 °C for 4 - 8 h to obtain a double-modified MCM-49 nanocrystal catalyst for degrading organic pollutants.

2. The preparation method of the catalyst for degrading organic pollutants according to claim 1, characterized in that, The preparation method of the quaternary ammonium salt includes the following steps: In a nitrogen atmosphere, drop a mixed solution of methyl acrylate and methanol into diethylenetriamine. After the reaction ends, a light yellow transparent liquid is obtained. After removing methanol, raise the temperature to 150 °C and continue the reaction under reduced pressure to generate a viscous, light yellow compound. Dissolve the compound in water and drop an aqueous solution of 2,3-epoxypropyltrimethylammonium chloride, whose mass is 1 - 10 times that of the compound. After the reaction is completed, the product is separated and purified to obtain a light yellow solid quaternary ammonium salt, where the above raw materials are in a mass ratio of methyl acrylate:methanol:diethylenetriamine = 1:3 - 15:2 - 10, and the mass fraction of the aqueous solution of 2,3-epoxypropyltrimethylammonium chloride is 40% - 80%.

3. The preparation method of the catalyst for degrading organic pollutants according to claim 2, wherein, The method for removing methanol is distillation.

4. The preparation method of the catalyst for degrading organic pollutants according to claim 3, wherein, The organic pollutants include at least one of antibiotics, dyes or endocrine disruptors, including tetracycline, rhodamine B, bisphenol A.

5. A catalyst for degrading organic pollutants, characterized in that, It is prepared by using the method described in any one of claims 1 - 4.

6. Use of a catalyst as described in claim 5 in the degradation of organic pollutants, characterized in that, The method for degrading organic pollutants using the catalyst includes the following steps: Disperse the catalyst in the wastewater containing organic pollutants at a concentration of 0.2 - 1.5 g / L, adjust the pH to 3.0 - 9.0, add 0.5 - 5 mmol / L of peroxymonosulfate PMS or persulfate PDS, and react at 20 - 50 °C for 10 - 120 minutes to achieve efficient degradation of organic pollutants.

7. Use of the catalyst according to claim 6 in degrading organic pollutants, characterized in that, The number of times the catalyst can be reused ≥ 10 times, and the catalytic activity of the catalyst can still be maintained above 95% of the initial catalytic performance.

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