Pt-loaded hierarchical pore HY molecular sieve double-effect catalyst as well as preparation method and application thereof

Abstract

The invention discloses a Pt-loaded hierarchical pore HY molecular sieve double-effect catalyst and a preparation method and application thereof.The preparation method comprises the steps that firstly, an acid solution and an HY molecular sieve are mixed, heated and stirred, and the hierarchical pore HY molecular sieve is obtained; then, Pt salt is loaded on the hierarchical pore HY molecular sieve through an impregnation method, and the hierarchical pore HY molecular sieve is dried, calcined and then reduced. The concentration of the acid solution is not higher than 0.1 mol / L; the catalyst is used for hydrocracking of polyethylene or polypropylene. According to the Pt-loaded hierarchical pore HY molecular sieve double-effect catalyst disclosed by the invention, Pt atoms have excellent C-H bond activation capability, meanwhile, the hierarchical pore HY molecular sieve carrier has an open connection mesoporous structure and an acid site, and the mesoporous structure constructed by acid pickling and dealumination is beneficial to diffusion of a reaction intermediate and improvement of the yield of a liquid product; more orifice acid can be exposed by surface erosion, so that the initial cracking of reaction raw materials is facilitated, and the catalytic performance is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of polyolefin (polyethylene and polypropylene) hydrocracking, and specifically relates to a Pt-loaded multi-level pore HY molecular sieve dual-effect catalyst, a preparation method thereof, and application in polyethylene or polypropylene hydrocracking to produce fuel oil. Background Art

[0002] In recent years, with the gradual depletion of fossil resources and the increasing severity of global environmental pollution, research on alternative resources as a supplement to traditional fossil resources has attracted more and more attention. The biggest difference between plastic (organic polymers such as polyethylene, etc.) resources and fossil resources is that the carbon chain is long, the molecular weight is large, and it is difficult to degrade, making it much more difficult to prepare alternative fuels and chemicals from plastics than fossil resources. How to regulate the degradation of organic polymers in plastics to produce sustainable energy is a scientific problem that needs to be solved urgently.

[0003] Polyethylene is one of the main components of plastics. It is a thermoplastic resin obtained by polymerization of ethylene. In industry, it also includes copolymers of ethylene and a small amount of α-olefins. The total annual output of plastics in the world is 380 megatons (80% of which becomes garbage), which is about 7% of the total production of crude oil and natural gas. Polyethylene has excellent chemical stability, can withstand the corrosion of most acids and alkalis, is very difficult to degrade, and is insoluble in general solvents at room temperature. On October 27, 2017, the World Health Organization's International Agency for Research on Cancer listed polyethylene in the list of Class 3 carcinogens. Polyethylene is mainly composed of carbon chains (C) and hydrogen (H), with a molecular weight between 8000-158,000. It can be used as a raw material to produce long-chain alkanes, aromatics and platform compounds. Unlike other polymers such as polyethylene terephthalate (PET), it is more difficult to prepare alternative energy using polyethylene as a raw material. The chemical methods are mainly hydrocracking and catalytic thermal cracking. Catalytic thermal cracking is a reaction path that has been studied more in the early years. The main catalyst is molecular sieve, and the product is mainly aromatics. Using polyethylene as raw material and molecular sieve (ZSM-5, MCM-41, Y, etc.) as catalyst, polyethylene is catalytically cracked to produce aromatic hydrocarbons and small molecular organic compounds.

[0004] Although catalytic thermal cracking technology can produce aromatics and small molecular organic compounds, the carbon content of aromatics in its products varies, and the separation cost is high; the reactions need to be carried out at high temperature and in an inert atmosphere, and the collapse of the catalyst skeleton and a large amount of carbon deposition make the catalyst unstable, which will hinder its industrial production. Compared with the catalytic thermal cracking route, the precious metal catalyst + hydroisomerization / cracking route can produce straight-chain alkanes and isoalkanes. By regulating the catalyst structure and reaction conditions, polyethylene can be selectively hydrogenated and cracked to obtain alkanes with different carbon chain ranges, which can be directly used for fuel blending.

[0005] At present, the research on the hydrogenation treatment of polyethylene to prepare short-chain alkanes (C4-C18) is relatively scarce and all at the laboratory research stage. It mainly uses noble metal-supported catalysts. Pt-based catalysts are used for the catalytic conversion of polyethylene in H 2 environment and N 2 environment. In H 2 environment, polyethylene is hydrocracked under the action of a Pt-based catalyst to obtain liquid oil products with a molecular weight of about 1000, while in N 2 environment, polyethylene aromatizes to obtain aromatics of graft polymers. However, the short-chain oil products obtained from the hydrogenation treatment of polyethylene face the following two problems: (1) The reaction needs to react at 300 °C for a long time of 24-96 h. The noble metal exposed to high temperature for a long time will easily cause sintering or loss due to low Tamman temperature and high surface energy; (2) Since the main components of polyethylene are C and H, and its molecular weight is between Mn = 8000-158,000, the molecular chain is extremely long and insoluble in conventional solvents, so the mass transfer problem in the reaction is very serious, and long-term high-temperature reaction is prone to carbon deposition covering the active metal. Summary of the Invention

[0006] In order to solve the above technical problems, the purpose of the present invention is to provide a Pt-loaded hierarchical pore HY zeolite dual-functional catalyst, its preparation method and application. By simply pickling the HY zeolite and then loading Pt, a Pt / HY metal-acid dual-functional catalyst is obtained, which is used for the hydrocracking of polyethylene or polypropylene and has excellent catalytic performance.

[0007] In order to achieve the above technical purpose, the present invention adopts the following technical solutions:

[0008] A preparation method of a Pt-loaded hierarchical pore HY zeolite dual-functional catalyst. First, an acidic solution and HY zeolite are mixed and heated with stirring to obtain hierarchical pore HY zeolite; then a Pt salt is loaded on the hierarchical pore HY zeolite by an impregnation method, dried, calcined and then reduced; the concentration of the hydrochloric acid is not higher than 0.1 mol / L.

[0009] Preferably, the acid in the acidic solution is selected from hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, hydrofluoric acid, acetic acid, oxalic acid, citric acid, ammonium chloride, etc.

[0010] Preferably, the temperature of heating and stirring is 60-90 °C and the time is 1-2 h.

[0011] Preferably, the Pt salt is selected from H 2 PtCl 6 、H 2 PtCl 4 、Pt(NO 3 ) 4 、Pt(CH 3 COO)2 , [Pt(NH 3 ) 4 Cl 2 , Pt(S 2 O 3 ) 2 2- etc., and the mass of the Pt salt accounts for 2-8 wt% of the hierarchical pore HY molecular sieve.

[0012] Preferably, the calcination temperature is 500-600 °C and the time is 1-3 h.

[0013] Preferably, the reducing atmosphere is 5% H 2 / 95% Ar atmosphere, the reduction temperature is 200-300 °C and the time is 1-3 h.

[0014] The present invention also provides a dual-functional catalyst of Pt-loaded hierarchical pore HY molecular sieve prepared by the above preparation method.

[0015] In the present invention, after the HY molecular sieve is mixed and treated with hydrochloric acid, obvious connected pit-shaped mesopores appear and more pore mouth acids can be exposed.

[0016] The present invention also provides the application of the above dual-functional catalyst of Pt-loaded hierarchical pore HY molecular sieve, which is used for the hydrocracking of polyethylene or polypropylene.

[0017] The beneficial effects of the present invention are embodied in:

[0018] For the dual-functional catalyst of Pt-loaded hierarchical pore HY molecular sieve of the present invention, Pt atoms have excellent C-H bond activation ability. At the same time, the hierarchical pore HY molecular sieve carrier has an open-connected mesoporous structure and acidic sites. The mesoporous structure constructed by acid elution and dealumination is beneficial to the diffusion of reaction intermediates and the improvement of the liquid product yield. Surface erosion can expose more pore mouth acids, which is beneficial to the preliminary cracking of reaction raw materials, helps to improve the catalytic performance and enhance the reaction conversion rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is the XRD spectrum of Pt-HY-0.1 prepared in Example 1.

[0020] Figure 2 It is the TEM (a) and SEM (b) spectra of Pt-HY-0.1 prepared in Example 1.

[0021] Figure 3 It is the N 2 adsorption and desorption isotherm (a) and the mesopore size distribution diagram (b) determined by the NLDFT model of Pt-HY-0.1 prepared in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments cited do not limit the present invention.

[0023] Example 1

[0024] The preparation process of the hierarchical pore molecular sieve HY is as follows: 5 g of commercial molecular sieve HY (silicon-aluminum ratio of 5.3) is stirred in 50 mL of 0.1 mol / L HCl solution at 70 °C for 1 h, and then filtered, washed, and dried to obtain a white sample, namely the HY-0.1 hierarchical pore molecular sieve. Subsequently, the precious metal salt (H 2 PtCl 6 : 5% by mass of the support) is dissolved in 15 mL of absolute ethanol and impregnated onto the hierarchical pore molecular sieve HY-0.1 in the form of a salt. After impregnation, the sample is stirred and volatilized to a dry state at 65 °C. The dried powder sample is taken out, ground evenly, placed in a muffle furnace and treated at 550 °C for 2 h, and then placed in a tubular furnace and reduced at 250 °C for 2 h in an atmosphere of 5% H 2 / 95% Ar. The catalyst is labeled as Pt-HY-0.1.

[0025] As can be seen from the XRD pattern shown in Figure 1 , the characteristic peaks belonging to the HY molecular sieve are observed, and the diffraction peaks of Pt metal particles appear, proving that the basic structure of the HY molecular sieve after acid treatment is maintained and the Pt metal is successfully loaded, which is consistent with the results of the metal particles shown in Figure 2 (a) and Figure 2 (b). For the scanning electron microscope analysis of Pt-HY-0.1, the results are as shown in Figure 2 (a), and obvious connected pit-shaped mesopores appear. After N 2 adsorption and desorption tests, the hysteresis loop in Figure 3 (a) is related to the open mesopores in the structure, and the mesopore distribution in Figure 3 (b) is significantly changed after acid treatment and has a tendency to expand the pores.

[0026] The catalytic performance of the Pt-HY-0.1 catalyst in the hydrocracking reaction of polyethylene was evaluated in a high-pressure autoclave reactor. 3 g of LDPE (Mw = 335,000) and 0.1 g of the Pt-HY-0.1 catalyst were ball-milled and mixed, and placed in a reaction kettle made of stainless steel metal. The reaction conditions are as follows: 3 MPa H 2, reaction temperature of 250 °C, reaction time of 4 h. After the liquid product was dissolved in acetone, n-hexadecane was used as the internal standard, and it was separated and detected online by a gas chromatograph (Agilent 8860). This chromatograph was equipped with an alumina-packed column and a flame ionization detector (FID). Analysis showed that for the hydrocracking catalytic reaction catalyzed by Pt-HY-0.1, the conversion rate was 97.5%, and its liquid yield was 90.2%.

[0027] Example 2

[0028] The preparation process of the hierarchical pore molecular sieve HY is as follows: 5 g of commercial molecular sieve HY (silica-alumina ratio of 5.3) was stirred in 50 mL of 0.1 mol / L HCl solution at 70 °C for 1 h, and then filtered, washed, and dried to obtain a white sample, namely the HY-0.1 hierarchical pore molecular sieve. Subsequently, the precious metal salt (H 2 PtCl 6 : 5% by mass of the support) was dissolved in 15 mL of absolute ethanol and impregnated onto the hierarchical pore molecular sieve HY-0.1 in the form of a salt. After impregnation, the sample was stirred and volatilized to a dry state at 65 °C. The dried powder sample was taken out, ground evenly, placed in a muffle furnace and treated at 550 °C for 2 h, and then placed in a tube furnace and reduced at 250 °C for 2 h in an atmosphere of 5% H 2 / 95% Ar. The catalyst was labeled Pt-HY-0.1.

[0029] The catalytic performance of the Pt-HY-0.1 catalyst in the hydrocracking of polyethylene was evaluated in a high-pressure autoclave reactor. 3 g of PP (Mw = 5000) and 0.1 g of the Pt-HY-0.1 catalyst were ball-milled and mixed, and placed in a reaction kettle made of stainless steel. The reaction conditions were as follows: 3 MPa H 2 , reaction temperature of 250 °C, reaction time of 4 h. After the liquid product was dissolved in acetone, n-hexadecane was used as the internal standard, and it was separated and detected online by a gas chromatograph (Agilent 8860). This chromatograph was equipped with an alumina-packed column and a flame ionization detector (FID). Analysis showed that for the hydrocracking catalytic reaction catalyzed by Pt-HY-0.1, the conversion rate was 100%, and its liquid yield was 75.2%.

[0030] Comparative Example 1

[0031] The precious metal salt (H 2 PtCl 6 : 5% by mass of the support) was dissolved in 15 mL of absolute ethanol and impregnated onto the commercial molecular sieve HY in the form of a salt. After impregnation, the sample was stirred and volatilized to a dry state at 65 °C. The dried powder sample was taken out, ground evenly, placed in a muffle furnace and treated at 550 °C for 2 h, and then placed in a tube furnace and in 5% H 2Reduction was carried out at 250 °C for 2 h under a 95% Ar atmosphere. The catalyst was labeled Pt-HY-0.

[0032] The catalytic performance of the Pt-HY-0 catalyst in the hydrocracking reaction of polyethylene was evaluated in a high-pressure autoclave reactor. 3 g of LDPE (Mw = 335,000) and 0.1 g of the Pt-HY-0 catalyst were ball-milled and mixed, and placed in a reaction kettle made of stainless steel. The reaction conditions were as follows: 3 MPa H 2 , reaction temperature of 250 °C, and reaction time of 4 h. After the liquid product was dissolved in acetone, n-hexadecane was used as an internal standard, and it was separated and detected online by a gas chromatograph (Agilent 8860). This chromatograph was equipped with an alumina-packed column and a flame ionization detector (FID). Analysis showed that for the hydrocracking catalytic reaction catalyzed by Pt-HY-0, the conversion rate was 72.3%, and its liquid yield was 29.7%.

[0033] Comparative Example 2

[0034] The preparation process of the hierarchical pore molecular sieve HY was as follows: 5 g of commercial molecular sieve HY (silica-alumina ratio of 5.3) was stirred in 50 mL of 0.2 mol / L HCl solution at 70 °C for 1 h, and then filtered, washed, and dried to obtain a white sample, namely the HY-0.2 hierarchical pore molecular sieve. Subsequently, the precious metal salt (H 2 PtCl 6 : 5% by mass of the carrier) was dissolved in 15 mL of absolute ethanol and impregnated onto the hierarchical pore molecular sieve HY-0.2 in the form of a salt. After impregnation, the sample was stirred and volatilized to a dry state at 65 °C. The dried powder sample was taken out, ground evenly, placed in a muffle furnace and treated at 550 °C for 2 h, and then placed in a tube furnace and reduced at 250 °C for 2 h under a 5% H 2 / 95% Ar atmosphere. The catalyst was labeled Pt-HY-0.2.

[0035] The catalytic performance of the Pt-HY-0.2 catalyst in the hydrocracking reaction of polyethylene was evaluated in a high-pressure autoclave reactor. 3 g of LDPE (Mw = 335,000) and 0.1 g of the Pt-HY-0.2 catalyst were ball-milled and mixed, and placed in a reaction kettle made of stainless steel. The reaction conditions were as follows: 3 MPa H 2 , reaction temperature of 250 °C, and reaction time of 4 h. After the liquid product was dissolved in acetone, n-hexadecane was used as an internal standard, and it was separated and detected online by a gas chromatograph (Agilent 8860). This chromatograph was equipped with an alumina-packed column and a flame ionization detector (FID). Analysis showed that for the hydrocracking catalytic reaction catalyzed by Pt-HY-0.2, the conversion rate was 84.5%, and its liquid yield was 42.0%.

[0036] Comparative Example 3

[0037] The catalytic performance of commercial molecular sieve HY in the hydrocracking reaction of polyethylene was evaluated in a high-pressure autoclave reactor. 3 g of LDPE (Mw = 335,000) was ball-milled and mixed with 0.1 g of commercial molecular sieve HY, and placed in a reaction kettle made of stainless steel. The reaction conditions were as follows: 3 MPa H 2 , reaction temperature of 250 °C, and reaction time of 4 h. After the liquid product was dissolved in acetone, n-hexadecane was used as the internal standard, and it was separated and detected online by a gas chromatograph (Agilent 8860). This chromatograph was equipped with an alumina-packed column and a flame ionization detector (FID). The analysis showed that for the hydrocracking catalytic reaction catalyzed by commercial molecular sieve HY, the conversion rate was 17.6%, and its liquid yield was 0.3%.

[0038] Comparative Example 4

[0039] The preparation process of the hierarchical pore molecular sieve HY was as follows: 5 g of commercial molecular sieve HY (silica-alumina ratio of 5.3) was stirred in 50 mL of 0.1 mol / L HCl solution at 70 °C for 1 h, and then filtered, washed, and dried to obtain a white sample, namely the HY-0.1 hierarchical pore molecular sieve.

[0040] The catalytic performance of the HY-0.1 hierarchical pore molecular sieve catalyst in the hydrocracking reaction of polyethylene was evaluated in a high-pressure autoclave reactor. 3 g of LDPE (Mw = 335,000) was ball-milled and mixed with 0.1 g of HY-0.1 hierarchical pore molecular sieve, and placed in a reaction kettle made of stainless steel. The reaction conditions were as follows: 3 MPa H 2 , reaction temperature of 250 °C, and reaction time of 4 h. After the liquid product was dissolved in acetone, n-hexadecane was used as the internal standard, and it was separated and detected online by a gas chromatograph (Agilent 8860). This chromatograph was equipped with an alumina-packed column and a flame ionization detector (FID). The analysis showed that for the hydrocracking catalytic reaction catalyzed by HY-0.1, the conversion rate was 14.5%, and its liquid yield was 1.6%.

[0041] In the present invention, the Pt-HY-0.1 hydrocracking catalyst prepared by the impregnation method has the best conversion rate and liquid selectivity. Moreover, open-connected mesopores are constructed on the HY support during the acid treatment process, which improves the mass transfer and diffusion of reaction intermediates, exposes more pore mouth acid sites, and enhances the reaction activity. While the Pt-HY-0 catalyst has poor conversion rate and liquid selectivity. After the reaction intermediates enter the interior of the support, it is very difficult for them to escape through the micropores, and the intermediates are prone to carbon deposition and blockage inside the pores.

Claims

1. A method for preparing a Pt-loaded multi-level pore HY molecular sieve dual-effect catalyst, characterized in that: First, the acidic solution and HY molecular sieve are mixed, heated and stirred to obtain a multi-level pore HY molecular sieve; then, the Pt salt is loaded on the multi-level pore HY molecular sieve by an impregnation method, and then dried, calcined and reduced; the concentration of the acidic solution is not higher than 0.1 mol / L.

2. The preparation method according to claim 1, characterized in that: The acid in the acidic solution is selected from hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, hydrofluoric acid, acetic acid, oxalic acid, citric acid, and ammonium hydrochloride.

3. The preparation method according to claim 1, characterized in that: The heating and stirring temperature is 60-90°C and the time is 1-2h.

4. The preparation method according to claim 1, characterized in that: The Pt salt is selected from H2PtCl6, H2PtCl4, Pt(NO3)4, Pt(CH3COO)2, [Pt(NH3)4]Cl2, Pt(S2O3)22-, and the mass of the Pt salt accounts for 2 to 8 wt% of the multi-level pore HY molecular sieve.

5. The preparation method according to claim 1, characterized in that: The calcination temperature is 500-600° C. and the calcination time is 1-3 hours.

6. The preparation method according to claim 1, characterized in that: The reducing atmosphere is 5% H2 / 95% Ar atmosphere, the reducing temperature is 200-300°C, and the reducing time is 1-3h.

7. The Pt-loaded multi-level pore HY molecular sieve dual-effect catalyst prepared by the preparation method according to any one of claims 1 to 6.

8. The use of the Pt-loaded multi-level pore HY molecular sieve dual-effect catalyst according to claim 7, characterized in that: It is used for polyethylene or polypropylene hydrocracking.

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