MTES-beta catalyst as well as preparation method and application thereof

Abstract

The invention relates to an MTES-beta catalyst as well as a preparation method and application thereof, and belongs to the field of materials. According to the preparation method, part of MTES is used as a silicon source, coordination of aluminum atoms in the catalyst is affected by the silicification reaction of MTES in the preparation process, and a relatively high number of Lewis acid sites are generated, so that the catalytic cracking reaction performance of the crosslinked polyethylene is regulated and controlled; and the prepared MTES-beta catalyst can realize higher liquid product yield and gaseous product yield under a relatively mild condition.

Description

Technical Field

[0001] The present invention relates to the technical field of materials, and in particular to an MTES-β catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] There are mainly three degradation methods for cross-linked polyethylene materials in waste high-voltage cable insulation materials: mechanical degradation, thermal cracking, and solvent degradation. Mechanical degradation mainly treats the material through mechanical force to reduce its cross-linking degree and achieve subsequent recycling. Through processes such as crushing, grinding, and classification screening, regranulation is carried out to achieve downgraded recycling. Thermal cracking is to heat and decompose cross-linked polyethylene through high temperature. However, since the product components obtained by breaking chemical bonds through heating are complex, the use of an appropriate catalyst during thermal cracking can effectively improve the reaction efficiency and regulate the product distribution. Solvent degradation is to dissolve and crack using an appropriate solvent at a relatively low temperature to break the cross-linked structure and form recyclable oligomers or monomers.

[0003] Although mechanical degradation can achieve the de-cross-linking and recycling of cross-linked polyethylene, its degree of de-cross-linking is relatively low, and the utilization value of the recycled product is not high. After using the solvent in solvent degradation, due to the low solubility of cross-linked polyethylene, the reaction conditions are restricted, and the treatment of the solvent recycled product is difficult. Existing catalysts for thermal cracking of cross-linked polyethylene materials have problems of low yields of liquid products and gaseous products. Therefore, seeking a way to improve the yields of liquid and gaseous products when thermally cracking cross-linked polyethylene in waste high-voltage cable insulation materials has become an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides an MTES-β catalyst, a preparation method thereof, and an application thereof. This catalyst can improve the yields of liquid and gaseous products when thermally cracking cross-linked polyethylene materials in waste high-voltage cable insulation materials.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] In the first aspect, the present invention provides a preparation method of an MTES-β catalyst, comprising the following steps:

[0007] (1) Mix a silicon source, an aluminum source, a templating agent, a pH regulator, and H2O evenly to obtain a mixture;

[0008] (2) Evaporate the solvent in the mixture to obtain a dry gel;

[0009] (3) Grind the dry gel, then add water, and place it in an environment of 180 °C for crystallization reaction to obtain a precipitate;

[0010] (4) Centrifuge the precipitate and then dry it, and grind the dried precipitate into powder;

[0011] (5) Calcinate the said powder to obtain MTES-β zeolite;

[0012] (6) Add the MTES-β zeolite into ammonium chloride solution for activation to obtain activated MTES-β zeolite;

[0013] (7) Calcinate the activated MTES-β zeolite to obtain the said MTES-β catalyst.

[0014] The β zeolite (Beta Zeolite) described in the present invention is a zeolite molecular sieve with a high silicon-aluminum ratio and medium pores, and its structure belongs to the BEA structure type (classified by the International Zeolite Association (IZA)); the said MTES-β zeolite is a β-type zeolite molecular sieve modified by methyltriethoxysilane (MTES).

[0015] The present invention selects to use part of methyltriethoxysilane (MTES) as the silicon source to modify the β zeolite. During the preparation process, the silicification reaction of MTES affects the coordination of aluminum atoms in the catalyst, resulting in a relatively high number of Lewis acid sites, so that the prepared MTES-β catalyst can catalytically crack cross-linked polyethylene in waste high-voltage cable insulation materials under relatively mild conditions.

[0016] Preferably, in the step (1), the molar ratio of the silicon source, aluminum source, template agent, pH regulator and H2O is 1:0.068:0.5:0.3:21.

[0017] Preferably, the template agent is tetrapropylammonium hydroxide; the silicon source is a mixture of methyltriethoxysilane and colloidal SiO2; the aluminum source is aluminum sulfate octadecahydrate.

[0018] Preferably, the molar ratio of methyltriethoxysilane to colloidal SiO2 is 1:(10 - 50).

[0019] Exemplarily, the molar ratio of methyltriethoxysilane to SiO2 can be any point value or any two-point range value between 1:(5 - 50), such as 1:10, 1:11.5, 1:24, 1:30, 1:40, 1:49, 1:50.

[0020] Preferably, the molar ratio of methyltriethoxysilane to colloidal SiO2 is 1:24.

[0021] The present invention synthesizes β zeolite with a rich defect structure by regulating the molar ratio of methyltriethoxysilane to colloidal SiO2. The silylation of MTES affects the coordination of aluminum atoms, forming more extra-framework six-coordinated aluminum. At the same time, the Si-O-Si-C bond formed between MTES and silicate introduces silanol groups after calcination. This structural feature enhances the Lewis acidity of the MTES-β catalyst, thereby enhancing its catalytic cracking activity. The present invention discovers through experiments that when the molar ratio of methyltriethoxysilane to colloidal SiO2 is 1:(10 - 50), especially 1:24, the catalytic cracking activity of the formed MTES-β catalyst is optimal.

[0022] Preferably, in the calcination in step (5) to protonate the zeolite, the temperature is 550 °C and the time is 6 hours.

[0023] Preferably, the concentration of the ammonium chloride solution in step (6) is 1 mol / L.

[0024] Preferably, the temperature of the calcination in step (7) is 550 °C, and it is calcined for 6 hours at a heating rate of 5 °C / min.

[0025] In a second aspect, the present invention provides an MTES-β catalyst obtained by the described preparation method.

[0026] In a third aspect, the present invention provides the application of the MTES-β catalyst in catalytically cracking crosslinked polyethylene in waste high-voltage cable insulating materials.

[0027] The MTES-β catalyst prepared by the present invention can catalytically crack crosslinked polyethylene in waste high-voltage cable insulating materials at 400 °C under relatively mild conditions, with a conversion rate greater than 80%, a liquid product yield greater than 50%, and a gas product yield greater than 30%. This catalyst has high crosslinked polyethylene cracking performance and is an effective β catalyst with rich defects.

[0028] Preferably, the application includes the following steps:

[0029] (1) Uniformly mix crosslinked polyethylene with the described MTES-β catalyst to obtain a mixture;

[0030] (2) Place the mixture in a vertical tube furnace, introduce nitrogen, and heat it to 400 °C at a heating rate of 5 °C / min in the furnace and react for 30 min.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] (1) The method of the present invention uses partial MTES as a silicon source. During the preparation process, the silicification reaction of MTES affects the coordination of aluminum atoms in the catalyst, generating a relatively high number of Lewis acid sites, thereby realizing the regulation of the catalytic cracking reaction performance of cross-linked polyethylene. The prepared MTES-β catalyst can achieve a relatively high yield of liquid and gaseous products under relatively mild conditions, providing an efficient strategy for the catalytic cracking of cross-linked polyethylene in waste high-voltage cable insulation materials.

[0033] (2) The MTES-β catalyst of the present invention is prepared by the dry gel conversion method, which can largely retain the crystalline form of β zeolite.

[0034] (3) Through the performance test of the catalytic cracking of cross-linked polyethylene, it is confirmed that when the MTES-β catalyst is applied to the catalytic thermal cracking reaction of cross-linked polyethylene, the conversion rate is greater than 80%, the liquid product yield is greater than 50%, and the gaseous product yield is greater than 30%. This shows that the catalyst has high performance in the cracking of cross-linked polyethylene and is an effective defective β catalyst. Description of the Drawings

[0035] Figure 1 It is a schematic diagram of the yield comparison of the catalytic cracking of cross-linked polyethylene by catalysts H-β, MTES-β-0.02, MTES-β-0.04, and MTES-β-0.08. Detailed Embodiments

[0036] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0037] Example 1

[0038] This example provides a preparation method of an MTES-β catalyst, and the specific steps are as follows:

[0039] (1) Mix the silicon source, aluminum source, template agent, pH regulator, and H2O evenly to obtain a mixture. The specific operations are as follows:

[0040] (1-1) Weigh 10.2 g of tetrapropylammonium hydroxide using an analytical balance, and then measure 37.5 mL of deionized water with a measuring cylinder and transfer it to a beaker. Add the weighed reagents and stir at room temperature until completely dissolved to obtain a template agent solution;

[0041] (1-2) Weigh 6.47 g of the total silicon source, 1.2 g of NaOH, and 0.51 g of Al2(SO4)3·18H2O respectively, and add them to the above template agent solution. Stir at room temperature for 2 hours to obtain a mixture;

[0042] At this time, the molar ratio of the silicon source, aluminum source, template agent, pH regulator and H2O in the mixture is 1:0.068:0.5:0.3:21;

[0043] The silicon source includes: 0.71 g of methyltriethoxysilane (MTES) and 5.76 g of colloidal SiO2; the molar ratio of methyltriethoxysilane to colloidal SiO2 in the silicon source is 1:24;

[0044] (2) After sufficient stirring, the solvent of the mixture is evaporated to obtain a dry gel;

[0045] (3) The dry gel is ground and transferred to a high-pressure reactor, and 2 mL of deionized water is measured and added. The crystallization reaction is carried out at a constant temperature in an oven at 180 °C for 48 hours to obtain a precipitate;

[0046] (4) The precipitate is centrifuged and washed with deionized water, and the precipitate is transferred to an oven at 80 °C for drying; the dried product is ground into powder;

[0047] (5) The powder is calcined in an air atmosphere at 550 °C for 6 hours to obtain MTES-β zeolite;

[0048] (6) Weigh 1.5 g of MTES-β zeolite and add it to 30 mL of 1 mol / L ammonium chloride solution for activation. Stir at room temperature for 2 hours, centrifuge and wash the precipitate to obtain activated MTES-β zeolite;

[0049] (7) The activated MTES-β zeolite is calcined in an air atmosphere at 550 °C at a heating rate of 5 °C / min for 6 hours to obtain the catalyst of the present invention, which is named MTES-β-0.04.

[0050] The β zeolite described in this example is a zeolite molecular sieve with a high silicon-aluminum ratio and medium pores, and its structure belongs to the BEA structure type (classified by the International Zeolite Association (IZA)). The MTES-β zeolite described in this example is a β-type zeolite molecular sieve modified by methyltriethoxysilane (MTES).

[0051] Example 2

[0052] The difference between Example 2 and Example 1 is the molar ratio of MTE to colloidal SiO2. Specifically, it is: 0.36 g of MTES and 5.88 g of colloidal SiO2, and the molar ratio of MTES to colloidal SiO2 is 1:49. The catalyst prepared in Example 2 is named: MTES-β-0.02.

[0053] Example 3

[0054] Example 3 is different from Example 1 in that the molar ratio of MTES to colloidal SiO2 is different. Specifically: 1.43 g of MTES, 5.52 g of colloidal SiO2, and the molar ratio of MTES to colloidal SiO2 is 1:11.5. The catalyst prepared in Example 3 was named: MTES-β-0.08.

[0055] Comparative Example 1

[0056] Comparative Example 1 is different from Example 1 in that MTES is not added. The operation in step (1-2) is as follows: Weigh 6.0 g of colloidal SiO2, 1.2 g of NaOH, and 0.51 g of Al2(SO4)3·18H2O respectively, add them to the template agent solution, and stir at room temperature for 2 hours to obtain a mixture; The catalyst prepared in Comparative Example 1 was named: H-β.

[0057] Comparative Example 2

[0058] Comparative Example 2 is different from Example 1 in that methyltriethoxysilane is replaced by sodium silicate, and the molar ratio of sodium silicate to colloidal SiO2 is 1:24. It was named: nSiO2-β.

[0059] Comparative Example 3

[0060] Comparative Example 3 is different from Example 1 in that methyltriethoxysilane is replaced by polydimethylsiloxane, and the molar ratio of polydimethylsiloxane to colloidal SiO2 is 1:24. It was named: PDMS-β.

[0061] Comparative Examples 4-7 are common molecular sieves on the market:

[0062] Comparative Example 4: Molecular sieve HZSM-5, purchased from: Tianjin Yuanli Chemical Co., Ltd., product number: ZSM-5-35H;

[0063] Comparative Example 5: Molecular sieve HUSY, purchased from: Tianjin Yuanli Chemical Co., Ltd., product number: USY-7H;

[0064] Comparative Example 6: Molecular sieve Hβ, purchased from: Tianjin Yuanli Chemical Co., Ltd., product number: β-20H;

[0065] Comparative Example 7: Molecular sieve Al-MCM-41, purchased from: Tianjin Yuanli Chemical Co., Ltd., product number: Al-MCM-41-25H.

[0066] Test Example

[0067] The catalysts prepared in Examples 1-3 and Comparative Examples 1-7 were subjected to structural verification. The Si / Al of the catalysts was determined by energy-dispersive X-ray (EDX) analysis. By measuring the N2 adsorption of the samples and calculating the external surface area, the results are shown in Table 1:

[0068] Table 1: Structural verification results of the catalysts prepared in Examples 1-3 and Comparative Examples 1-7

[0069] Group Sample Si / Al <![CDATA[S ext [m 2 g -1 > Example 1 MTES-β-0.04 12.8 299 Example 2 MTES-β-0.02 12.5 290 Example 3 MTES-β-0.08 11.4 129 Comparative Example 1 H-β 12.0 283 Comparative Example 2 <![CDATA[nSiO2-β]]> 19.8 268 Comparative Example 3 PDMS-β 10.5 189 Comparative Example 4 HZSM-5 38 331 Comparative Example 5 HUSY 5.4 580 Comparative Example 6 Hβ 30 470 Comparative Example 7 Al-MCM-41 25 1010

[0070] Note: Comparative Examples 4-7 are common molecular sieves on the market.

[0071] Application Example

[0072] The catalysts prepared in Examples 1-3 and Comparative Examples 1-7 were used in the catalytic cracking reaction of crosslinked polyethylene. The process is as follows:

[0073] (1) 1.5 g of crosslinked polyethylene was uniformly mixed with 0.3 g of the catalysts prepared in Examples 1-3 and Comparative Examples 1-7, respectively, to obtain respective mixtures;

[0074] (2) The mixtures were placed in a reaction vessel and sealed. Nitrogen was introduced and the airtightness of the apparatus was checked. Nitrogen was passed for 30 min to ensure the evacuation of the air in the apparatus. Subsequently, the nitrogen flow rate was controlled at 35 mL / min, and the vertical tube furnace was heated to 400 °C at a heating rate of 5 °C / min and reacted for 30 min. The liquid products were collected by using an ice-water bath, and the gaseous products were collected by using a gas collection bag for chromatographic analysis; the remaining solid residues were weighed; the conversion efficiencies of different catalysts were analyzed.

[0075] Measurement method for the yield of gaseous products Yield(g): Yield(g) = (m1 - m0 - Q·t·ρ) / m × 100%

[0076] Measurement method for the yield of liquid products Yield(L): Yield(L) = m2 / m × 100%

[0077] Calculation method for the conversion rate C(%): C(%) = (m + m' - m") / m × 100%

[0078] Among them, m is the mass of crosslinked polyethylene; m' is the mass of the catalyst; m" is the mass of the solid residue; m1 is the total mass of the gas collection bag after the reaction; m2 is the mass of the liquid product; m0 is the original mass of the gas collection bag; Q is the nitrogen flow rate, with the unit of mL / min; t is the overall reaction time, with the unit of min; ρ is the density of nitrogen under standard conditions. The results are shown in Table 2:

[0079] Table 2: Conversion rates of different catalysts

[0080] Group Yield of gaseous product (%) Yield of liquid product (%) Conversion rate (%) Example 1 30.7％ 63.5％ 94.3％ Example 2 30.3％ 55.2％ 88.7％ Example 3 31.8％ 50.9％ 83.2％ Comparative Example 1 31.8％ 42.1％ 75.7％ Comparative Example 2 24.5％ 40.8％ 71.4％ Comparative Example 3 22.4％ 45.5％ 72.9％ Comparative Example 4 23.2％ 38.8％ 63.2％ Comparative Example 5 20.6％ 38.4％ 61.5％ Comparative Example 6 22.3％ 40.1％ 63.2％ Comparative Example 7 13.7％ 51.5％ 66.6％

[0081] As can be seen from Table 2, for the catalyst MTES-β-0.04 prepared by the method of Example 1, the yield of gaseous products reaches more than 30%, the yield of liquid products reaches more than 60%, and the conversion rate reaches more than 90%; for the catalyst MTES-β-0.02 prepared by the method of Example 2, the yield of gaseous products reaches more than 30%, the yield of liquid products reaches more than 50%, and the conversion rate reaches more than 85%; for the catalyst MTES-β-0.08 prepared by the method of Example 3, the yield of gaseous products reaches more than 30%, the yield of liquid products reaches more than 50%, and the conversion rate reaches more than 80%.

[0082] The conversion rates of Comparative Example 1 are all lower than those of Examples 1-3. This is because MTES was not added in Comparative Example 1. Compared with the catalysts with MTES added, the introduction of MTES increased the structural defects of the catalyst, further increasing the Lewis acidity on the surface of the catalyst, thus affecting the catalytic performance of the MTES-β catalyst for cross-linked polyethylene.

[0083] The conversion rates of Comparative Examples 2-3 are all lower than those of Examples 1-3. This is because methyltriethoxysilane was replaced by sodium silicate or dimethylsiloxane, affecting the defect structure of the catalyst, thus affecting the cracking reaction effect of its catalytic cross-linked polyethylene.

[0084] Comparative Examples 4-7 are common molecular sieves on the market (HZSM-5, HUSY, Hβ, HβMCM-41). Catalytic cracking experiments were carried out on cross-linked polyethylene with them, and it was found that the catalytic effects of the molecular sieves in Comparative Examples 4-7 were inferior to those of Examples 1-3. Therefore, the MTES-β catalyst prepared by the present invention has a better effect on catalyzing the cracking of cross-linked polyethylene than the commercially available molecular sieves.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred 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 essence and scope of the technical solutions of the present invention.

Claims

1. A preparation method of an MTES-β catalyst, characterized in that, It includes the following steps: (1) Mix a silicon source, an aluminum source, a template agent, a pH regulator, and H2O evenly to obtain a mixture; (2) Evaporate the solvent in the mixture to prepare a dry gel; (3) Grind the dry gel, then add water, and place it in an environment of 180 °C for crystallization reaction to obtain a precipitate; (4) Centrifuge and dry the precipitate, and grind the dried precipitate into powder; (5) Calcinate the powder to obtain MTES-β molecular sieve; (6) Add the MTES-β molecular sieve to an ammonium chloride solution for activation to obtain an activated MTES-β molecular sieve; (7) Calcinate the activated MTES-β molecular sieve to obtain the MTES-β catalyst; 2. The preparation method according to claim 1, characterized in that, In the step (1), the molar ratio of the silicon source, the aluminum source, the template agent, the pH regulator, and H2O is 1:0.068:0.5:0.3:

21.

3. The preparation method according to claim 1, characterized in that The template agent is tetrapropylammonium hydroxide; the silicon source is a mixture of methyltriethoxysilane and colloidal SiO2; the aluminum source is aluminum sulfate octadecahydrate.

4. The preparation method according to claim 3, characterized in that, The molar ratio of methyltriethoxysilane to colloidal SiO2 is: methyltriethoxysilane:colloidal SiO2 = 1:(10 - 50).

5. The preparation method according to claim 1, characterized in that, The calcination temperature in the step (5) is 550 °C and the time is 6 hours.

6. The preparation method according to claim 1, characterized in that, The concentration of the ammonium chloride solution in the step (6) is 1 mol / L.

7. The preparation method according to claim 1, wherein The calcination temperature in the step (7) is 550 °C, and it is calcined at a heating rate of 5 °C / min for 6 hours.

8. An MTES-β catalyst prepared by the preparation method according to any one of claims 1 - 7.

9. The application of the MTES-β catalyst according to claim 8 in catalytic cracking of cross-linked polyethylene, the waste high-voltage cable insulating material.

10. The application according to claim 9, wherein, It includes the following steps: (1) Uniformly mix cross-linked polyethylene with the MTES-β catalyst according to claim 8 to obtain a mixture; (2) Put the mixture into a vertical tubular furnace, introduce nitrogen, and heat the furnace to 400 °C at a heating rate of 5 °C / min, and react for 30 min.

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