Environment-friendly composite catalyst for preparing gasoline through plastic catalytic pyrolysis and application of environment-friendly composite catalyst

Abstract

The invention discloses an environment-friendly composite catalyst for preparing gasoline through plastic catalytic pyrolysis and application of the environment-friendly composite catalyst, relates to the technical field of catalysts for preparing gasoline through polyethylene pyrolysis, and aims to improve the yield of gasoline prepared through plastic catalytic pyrolysis. The composite catalyst is composed of a metal oxide and an HZSM-5 zeolite molecular sieve, the mass ratio of the metal oxide to the HZSM-5 zeolite molecular sieve is 1: (2-10), the metal element of the metal oxide is one of Ce, Zr, Al and Ti, the molar ratio range of Si to Al in the HZSM-5 zeolite molecular sieve is (10-300): 1, the composite catalyst is used for catalytic pyrolysis of low-density polyethylene, the gasoline yield can reach 61.89%, the composite catalyst is regenerated and repeatedly used for catalytic pyrolysis of low-density polyethylene, and the gasoline yield can reach 61.89%. The reduction value of the gasoline yield in the fourth time can be lower than 2.5% compared with the gasoline yield in the first time; the composite catalyst disclosed by the invention is simple in component, only two materials are mixed, the plastic pyrolysis catalysis efficiency is high, the gasoline yield is high, and the composite catalyst has a relatively high recycling value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polyethylene pyrolysis gasoline catalyst, in particular to an environment-friendly composite catalyst for preparing gasoline by catalytic pyrolysis of plastics and application thereof. BACKGROUND

[0002] Polyethylene (PE) is one of the synthetic plastics with the largest global production and the most widely application, which is widely used in packaging, agriculture, electronics, construction and other fields. However, its chemical structure is stable and difficult to degrade naturally, so a large amount of waste polyethylene products remain in the environment for a long time, becoming the main source of "white pollution". In addition, traditional landfill and incineration treatment methods not only occupy a large amount of land resources, but also may release toxic and harmful substances, causing secondary environmental pollution. Therefore, how to realize efficient recovery and resource utilization of polyethylene waste has become a global focus and an urgent environmental problem to be solved.

[0003] In recent years, converting polyethylene into liquid fuel through pyrolysis as a way to deal with polyethylene waste has received extensive attention. The traditional pyrolysis method is to directly heat polyethylene under anaerobic conditions, so that it decomposes into a mixture of gas, liquid (such as fuel oil), and solid products (such as wax and coke). However, this method usually requires high temperature of 400 ℃ to 600 ℃, and has poor product selectivity and low conversion rate. In order to improve the conversion efficiency and product selectivity, catalytic pyrolysis technology has been widely studied. By introducing catalysts, the product distribution can be improved to some extent, the yield and quality of liquid fuel can be improved, and the generation of coke can be reduced. In this process, hydrogen is often introduced to enhance the catalytic effect, but the preparation, storage and transportation cost of hydrogen is high, and due to its highly flammable and explosive characteristics, there are certain safety hazards. In addition, external solvents are often added in catalytic pyrolysis. The introduction of solvents not only can reduce the pyrolysis temperature, but also can improve the yield of liquid products, and some solvents also have good hydrogen supply capacity, which helps to inhibit the generation of coke. However, most solvents are expensive, and after reaction, they need to be recovered and fractionated, which increases the complexity and cost of the process. Therefore, it is of great significance to develop a polyethylene pyrolysis catalyst without the need for external hydrogen and solvents, which can not only realize the efficient conversion of polyethylene into high value-added chemicals or fuels, but also simplify the process flow and reduce the operation cost, and has broad application prospects.

[0004] In the process of polyethylene catalytic pyrolysis, the type of catalyst plays a crucial role in product distribution and reaction efficiency, with acid catalysts and metal-based catalysts each having their own characteristics. Acid catalysts, such as HZSM-5, can effectively promote the cracking of macromolecular chains due to their abundant acid sites, which are particularly beneficial for the production of light olefins and aromatics. The catalytic performance of acid catalysts is highly dependent on the strength and distribution of their acid sites. Metal-based catalysts, on the other hand, can flexibly regulate product composition and improve the selectivity and quality of liquid fuels through the participation of metal active centers in cracking, dehydrogenation, hydrogenation, and other reactions. How to organically combine the advantages of these two types of catalysts, both to take advantage of the high efficiency of acid sites in cracking reactions and to utilize the regulatory ability of metal centers in hydrogenation and dehydrogenation processes, has become an important challenge and research focus in current catalytic pyrolysis research.

[0005] In the invention patent with the publication number CN119529874A and the title of a method for producing high-value products by catalytic cracking of waste plastics and heavy oil mixture, it is disclosed that after the waste plastic fragments are liquefied by heating with a solvent, they are contacted with a fluidized catalyst for catalytic cracking reaction to obtain an oil gas mixture. The catalyst is one or a combination of molecular sieve, silicon-aluminum material catalyst, waste FCC catalyst, quartz sand, and alumina. The advantage of this "oil-plastic co-refining" scheme is that the conversion rate of plastics can reach more than 98%. Although it is beneficial for plastic treatment, the product types are relatively scattered. The catalyst used in the examples includes 35% alumina, 20% kaolin, 10% silicon-aluminum sol, and 35% ZSM-5 molecular sieve. The gasoline yield is only about 47%, which requires more effort in product fractionation to achieve better economic value. In summary, how to control the product distribution of polyethylene catalytic pyrolysis is of great significance for plastic recycling. SUMMARY

[0006] The present application aims to provide an environmentally friendly composite catalyst for plastic catalytic pyrolysis to prepare gasoline and its application, in order to improve the yield of plastic catalytic pyrolysis to prepare gasoline.

[0007] To achieve the above-mentioned purpose, the present application provides the following technical solution: an environmentally friendly composite catalyst for plastic catalytic pyrolysis to prepare gasoline, which is composed of metal oxides and HZSM-5 zeolite molecular sieve, and is used for converting low-density polyethylene catalytic pyrolysis into gasoline. The mass ratio of metal oxides to HZSM-5 zeolite molecular sieve is 1:(2-10), the metal element of the metal oxide is one of Ce, Zr, Al, and Ti, and the molar ratio of Si to Al in the HZSM-5 zeolite molecular sieve ranges from 10 to 300:1.

[0008] Preferably, the metal oxide is synthesized by a precipitation method, and the synthesis steps comprise: dissolving a certain amount of metal nitrate in deionized water to obtain solution A, preparing an alkaline solution for coprecipitation, denoted as solution B, under stirring conditions, simultaneously dropping the two aqueous solutions A and B into a beaker, controlling the temperature and pH value of the reaction, and preparing flocculent precipitate by coprecipitation and aging; washing, filtering and drying the flocculent precipitate, and grinding and calcining the dried product to obtain the metal oxide.

[0009] Preferably, the alkaline solution is one or more of ammonium carbonate, ammonia water and ammonium nitrate; the reaction temperature, pH and aging time of the coprecipitation are 50-100 DEG C, 7.0-10.0 and 1-5 h respectively; the drying time and temperature are 8-15 h and 50-100 DEG C respectively; and the calcining time and temperature are 9-16 h and 350-500 DEG C respectively.

[0010] Preferably, the reaction temperature, pH and aging time of the coprecipitation are 70-80 DEG C, 8.0-9.0 and 2-3 h respectively.

[0011] Preferably, the HZSM-5 zeolite molecular sieve is synthesized by a hydrothermal method, and the synthesis steps comprise: dissolving the reactants tetraethoxysilane, aluminum nitrate nonahydrate, tetrapropylammonium hydroxide and ethanol in distilled water, stirring the obtained clear solution, transferring the solution into a reaction kettle for reaction in a homogeneous reactor, washing and filtering the obtained solid, and drying and calcining the solid to obtain the HZSM-5 zeolite molecular sieve.

[0012] Preferably, after the tetraethoxysilane and the aluminum nitrate are converted into SiO2 and Al2O3 respectively, the molar ratio of the components in the reactants is SiO2: Al2O3: H2O: TPAOH: EtOH = 1: X: 50: 0.24: 4, wherein X is adjusted according to the silicon-aluminum ratio; the reactants are stirred for 3-7 h before being transferred into the reaction kettle; the reaction conditions are as follows: the reaction is carried out in a homogeneous reactor at 150-220 DEG C at a rotation speed of 2-10 r / min for 12-48 h; the drying time and temperature are 60-100 DEG C and 10-16 h respectively; and the calcining time and temperature are 3-6 h and 450-650 DEG C respectively.

[0013] The application further provides another technical scheme: application of the composite catalyst in the preparation of gasoline from low-density polyethylene by catalytic pyrolysis.

[0014] Preferably, the conversion rate of the low-density polyethylene is not less than 80%, and the gasoline yield is not less than 54%; the metal oxide is ZrO2; the mass ratio of the metal oxide to the HZSM-5 zeolite molecular sieve is 1:5; and when the molar ratio of Si to Al in the HZSM-5 zeolite molecular sieve is 200:1, the gasoline yield can reach 61.89%.

[0015] The application further provides another technical scheme: application of the composite catalyst after regeneration in catalytic pyrolysis of low-density polyethylene to prepare gasoline.

[0016] Preferably, the regeneration is to wash away the residual organic matter with a solvent, and then dry and calcine to completely remove the coke; the composite catalyst is used in catalytic pyrolysis of low-density polyethylene, and then regenerated and used again in catalytic pyrolysis of low-density polyethylene; after three rounds of regeneration, the yield reduction of gasoline in the fourth catalytic pyrolysis of low-density polyethylene is not more than 5% compared with the first time; the metal oxide is ZrO2, the mass ratio of the metal oxide to the HZSM-5 zeolite molecular sieve is 1:5, and when the molar ratio of Si to Al in the HZSM-5 zeolite molecular sieve is 200:1, the yield reduction of gasoline in the fourth time compared with the first time is not more than 2.5%.

[0017] Compared with the prior art, the application has the following beneficial effects:

[0018] 1. The environment-friendly composite catalyst for preparing gasoline by catalytic pyrolysis of plastics and the application thereof, which is composed of a metal oxide and a HZSM-5 zeolite molecular sieve, can play the advantages of the two components through a suitable mixing ratio, so that a catalyst suitable for catalytic pyrolysis of plastics is obtained, a high conversion rate and liquid yield are obtained, and the C5-C9 product selectivity is significantly higher than that of the existing catalyst. 11

[0019] 2. Under the composite ratio in the application, the HZSM-5 zeolite molecular sieve can effectively promote the cracking reaction of long-chain hydrocarbons such as polyethylene by using abundant acid sites and a regular pore structure, the strong acidic environment helps to improve the cracking efficiency and product selectivity, and is especially beneficial to the generation of aromatic hydrocarbons and high-octane components; the metal oxide can adjust the reaction path in the pyrolysis process, promote the further conversion of intermediate products, inhibit the generation of coke, and at the same time help to stabilize the liquid products and improve the yield and quality of gasoline.

[0020] 3. The environment-friendly composite catalyst for preparing gasoline by catalytic pyrolysis of plastics can be repeatedly used after regeneration, and the effect changes little compared with the initial use, the catalytic performance is relatively stable, and has high use value. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The XRD image of ZrO2 obtained in Example 1;

[0022] Figure 2 The XRD image of HZSM-5 obtained in Example 4;

[0023] Figure 3 The SEM image of HZSM-5 obtained in Example 4; ​

[0024] Figure 4 NH3-TPD profile of HZSM-5 obtained in Example 4;

[0025] Figure 5 SEM image of the composite catalyst obtained by physically grinding ZrO2 and HZSM-5 in a mass ratio of 1:5 in Example 7. DETAILED DESCRIPTION

[0026] In the present application, gasoline refers to hydrocarbons distributed in the range of C5-C 11 If C4 and / or C 12 are also counted as gasoline, the gasoline yield described in the present application will also be improved. In order to show the advantages of the present application, the present application is calculated in the minimum range.

[0027] The present application provides an environmentally friendly composite catalyst composed of a metal oxide and HZSM-5 zeolite molecular sieve, which is used for converting low-density polyethylene into gasoline by catalytic pyrolysis; the mass ratio of the metal oxide and the HZSM-5 zeolite molecular sieve is 1:(2-10), the metal element of the metal oxide is one of Ce, Zr, Al, and Ti, and the molar ratio of Si to Al in the HZSM-5 zeolite molecular sieve ranges from 10:1 to 300:1.

[0028] When the composite catalyst is applied to the preparation of gasoline by catalytic pyrolysis of low-density polyethylene, the conversion rate of low-density polyethylene is not less than 80%, and the gasoline yield is not less than 54%; after catalysis, the catalyst is recovered, residual organic matter is washed away with a solvent, specifically deionized water and ethanol are used for washing in turn, and after drying, calcination is performed to completely remove coke, thereby realizing catalyst regeneration; after regeneration, the catalyst is used again for catalytic pyrolysis of low-density polyethylene; after three rounds of regeneration, the gasoline yield of the fourth catalytic pyrolysis of low-density polyethylene is reduced by no more than 5% compared with the yield of the first time;

[0029] In a more preferred embodiment, the metal oxide is ZrO2, the mass ratio of the metal oxide and the HZSM-5 zeolite molecular sieve is 1:5, and the molar ratio of Si to Al in the HZSM-5 zeolite molecular sieve is 200:1, and the gasoline yield can reach 61.89%; in addition, after three rounds of regeneration, the gasoline yield of the fourth time is reduced by no more than 2.5% compared with the first time.

[0030] The content of the present application will be further described below through several preparation examples and embodiments, but the following is not all the embodiments of the present application, but only part, and therefore should not be considered as an absolute limitation on the scheme of the present application.

[0031] 1) Preparation of metal oxide:

[0032] A certain amount of metal nitrate is dissolved in deionized water to obtain solution A, and a basic solution for co-precipitation is prepared and marked as solution B, and one or more of the following solutions can be selected: ammonium carbonate, ammonia, ammonium nitrate, etc. Under stirring conditions, solutions A and B are simultaneously added to a beaker, and the reaction temperature and pH value are controlled. The flocculent precipitate is prepared by co-precipitation and aging. For reference, the reaction temperature, pH, and aging time can be controlled at 50-100 ℃, 7.0-10.0, and 1-5 h, respectively, and more preferably at 70-80 ℃, 8.0-9.0, and 2-3 h, respectively. The flocculent precipitate is washed, filtered, and dried. For reference, the drying time and temperature can be controlled at 8-15 h and 50-100 ℃, respectively. After drying, it is ground and calcined. For reference, the calcination time and temperature can be controlled at 9-16 h and 350-500 ℃, respectively. The final product is a corresponding metal oxide.

[0033] 2) Preparation of HZSM-5 zeolite molecular sieve:

[0034] Prepare the reactants, i.e., dissolve tetraethoxysilane (TEOS), aluminum nitrate nonahydrate, tetrapropylammonium hydroxide (TPAOH), and ethanol (EtOH) in distilled water. After stirring, the obtained clear solution is transferred to a reaction kettle for reaction in a homogeneous reactor. The reaction produces HZSM-5 zeolite. For reference, after the tetraethoxysilane and aluminum nitrate are converted into SiO2 and Al2O3, respectively, the molar ratio of the components in the reactants is SiO2: Al2O3: H2O: TPAOH: EtOH = 1: X: 50: 0.24: 4, where X is adjusted according to the silicon-aluminum ratio. The reactants are stirred for 3-7 h before being transferred to the reaction kettle. The reaction conditions can be controlled as follows: the homogeneous reactor is at 150-220 ℃, the rotation speed is 2-10 r / min, and the reaction time is 12-48 h. The obtained solid is washed, filtered, and dried. For reference, the drying time and temperature can be controlled at 60-100 ℃ and 10-16 h, respectively. After drying, it is calcined. For reference, the calcination time and temperature are controlled at 3-6 h and 450-650 ℃, respectively. The final product is a HZSM-5 zeolite molecular sieve.

[0035] Mix the metal oxide and HZSM-5 zeolite molecular sieve in a certain proportion to obtain the target catalyst product. The mass ratio of the two is preferably 1:(2-10), and the mixing method is preferably physical mixing, which can be mixing followed by grinding for 5 minutes.

[0036] The catalyst can be applied to convert polyethylene into gasoline in one step under the condition of no hydrogen source and no solvent. Specifically, after grinding the catalyst with a certain amount of polyethylene, the catalyst can complete the pyrolysis of polyethylene to obtain gasoline in one step under the reaction condition. The principle is that the metal oxide in the catalyst activates the C-H bond in the polyethylene molecule through the metal active site, promotes the generation of unsaturated C=C intermediate, and thus effectively shortens the length of the polyethylene chain. This change in chain structure optimizes the interaction between the polyethylene and the HZSM-5 molecular sieve. HZSM-5 has strong and extensive Brønsted and Lewis acid sites, which exhibits excellent catalytic activity for the further conversion of unsaturated C=C intermediates. In addition, HZSM-5 has a rich microporous structure, which helps to promote the β- cleavage, isomerization and aromatization reaction paths, and ultimately obtain gasoline grade hydrocarbons mainly distributed in the C5-C 11 range.

[0037] As described in the background art for CN119529874A patent, although it uses alumina and ZSM-5 molecular sieve in the composite catalyst at the same time, the ideal effect is not obtained. The catalyst prepared in the present application has a conversion rate of more than 80%, mostly more than 85% in the polyethylene pyrolysis reaction, and more importantly, the gasoline yield can reach more than 54%, and under the more optimal conditions, it can reach more than 60%. The following examples further illustrate the present application.

[0038] Example 1:

[0039] ZrO2 was prepared by the precipitation method: a certain amount of ZrO(NO3)2·xH2O was dissolved in deionized water, and ultrasonic treatment was performed to disperse it sufficiently to obtain precursor solution A1; another 1M ammonia solution was prepared as a precipitant, denoted as solution B1. Under the conditions of continuous stirring and heating, solutions A1 and B1 were simultaneously and slowly added to the reaction beaker, and the reaction temperature was controlled at 70-80 ℃, and the pH value was maintained at 8-9, generating a large amount of flocculent precipitate. The precipitate was aged in the original solution for 3-4 h, then centrifuged and washed repeatedly with deionized water until the washing liquid was neutral. The obtained solid product was placed in a programmed oven and dried at 60-70 ℃ for 12-14 h. After grinding, the dried sample was calcined at a temperature of 400-450 ℃ for 12-14 h, and finally a white powder of ZrO2 product was obtained. The XRD pattern of the synthesized ZrO2 is shown in Figure 1 The crystal phase is composed of monoclinic phase and tetragonal phase, showing a mixed crystal phase structure.

[0040] Example 2:

[0041] CeO2 was prepared by precipitation method: a certain amount of Ce(N03)3.6H2O was dissolved in deionized water, and was dispersed by ultrasonic treatment to obtain precursor solution A2; 1M ammonia solution was prepared as precipitant, and was recorded as solution B2. Under the conditions of continuous stirring and heating, solution A2 and B2 were simultaneously and slowly added into a reaction beaker, the reaction temperature was controlled at 70-80℃, and the pH value was maintained at 8-9, a large amount of flocculent precipitate was generated. The precipitate was continuously aged in the original solution for 3-4 h, then was separated by centrifugation and washed with deionized water repeatedly until the washing liquid was neutral. The obtained solid product was dried in a programmed oven at 60-70℃ for 12-14 h. After grinding, the dried sample was calcined, the calcination temperature was controlled at 400-450℃, and the temperature was maintained for 12-14 h, finally the light yellow CeO2 product was obtained.

[0042] Example 3:

[0043] Al2O3 was prepared by precipitation method: a certain amount of Al(N03)3.9H2O was dissolved in deionized water, and was dispersed by ultrasonic treatment to obtain precursor solution A3; 1M ammonia solution was prepared as precipitant, and was recorded as solution B3. Under the conditions of continuous stirring and heating, solution A3 and B3 were simultaneously and slowly added into a reaction beaker, the reaction temperature was controlled at 70-80℃, and the pH value was maintained at 8-9, a large amount of flocculent precipitate was generated. The precipitate was continuously aged in the original solution for 3-4 h, then was separated by centrifugation and washed with deionized water repeatedly until the washing liquid was neutral. The obtained solid product was dried in a programmed oven at 60-70℃ for 12-14 h. After grinding, the dried sample was calcined, the calcination temperature was controlled at 400-450℃, and the temperature was maintained for 12-14 h, finally the white powder Al2O3 product was obtained.

[0044] Example 4:

[0045] HZSM-5 zeolite molecular sieve with Si / Al ratio of 200 was prepared by hydrothermal method: tetraethoxysilane (TEOS), aluminum nitrate nonahydrate (Al(N03)3.9H2O), tetrapropylammonium hydroxide (TPAOH) and ethanol (EtOH) were dissolved in distilled water, wherein the molar ratio of SiO2 and Al2O3 converted from tetraethoxysilane and aluminum nitrate nonahydrate was SiO2:Al2O3:H2O:TPAOH:EtOH = 1:0.0025:50:0.24:4, the mixed solution was continuously stirred at room temperature for 3-5 h to ensure that the precursors were fully hydrolyzed and uniformly mixed. Then the homogeneous solution was transferred to a polytetrafluoroethylene-lined hydrothermal kettle, and was placed in a homogeneous reactor, and the crystallization reaction was carried out at a rotation speed of 3-5 r / min and a temperature of 160-190℃, and the reaction time was controlled at 12-48 h.

[0046] After the reaction, the obtained product was cooled to room temperature, filtered, washed with deionized water to remove residual templates and impurities, and then dried at 90 °C for 12 h. The dried sample was calcined in air at 550 °C for 4 h to completely remove the organic templates and form a porous structure, and finally obtain the HZSM-5 zeolite molecular sieve. The structure and acid characteristics of the synthesized HZSM-5 molecular sieve were shown by XRD, Figure 2 (XRD), Figure 3 (SEM), and Figure 4 (NH3-TPD). The XRD pattern confirmed that it had a typical MFI topology structure with good crystallinity; the SEM image showed that the particles were irregular polyhedrons with uniform size distribution, rough surface and rich pores, and the particles were tightly packed to form a three-dimensional network structure, which was beneficial to mass transfer and active site exposure. NH3-TPD analysis showed that the material had a double acid center distribution: the low-temperature desorption peak (~200 °C) corresponded to weak acid sites (such as silicon hydroxyl or physical adsorption sites), and the high-temperature peak (~400 °C) was attributed to strong Brønsted acid sites (derived from framework aluminum). The overall acid amount was moderate and the proportion of strong acid was high, indicating that it had excellent catalytic activity and selectivity in catalytic pyrolysis.

[0047] Example 5:

[0048] The ZrO2 prepared in Example 1, CeO2 of Example 2, Al2O3 of Example 3, and commercially available TiO2 were physically mixed with the HZSM-5 zeolite molecular sieve synthesized in Example 4 at a mass ratio of 1:5, and were ground in a mortar for 5 minutes to prepare a series of composite catalysts (denoted as ZrO2-HZSM-5, CeO2-HZSM-5, Al2O3-HZSM-5, and TiO2-HZSM-5).

[0049] Before the catalytic performance test, 0.5 g of the above composite catalyst (denoted as M c ) and 2.0 g of low-density polyethylene (LDPE, denoted as M LDPE ) were accurately weighed, and were again ground together for 5 minutes to ensure sufficient contact. The uniformly mixed sample was transferred to a slurry bed reactor, and high-purity nitrogen was introduced for inert atmosphere replacement, and was repeatedly purged 8 times to remove the air in the reactor.

[0050] The reaction was carried out at a temperature of 200-300 °C, a stirring rate of 200-500 r / min, and a reaction time of 12 h. After the reaction, the gaseous product was collected by a gas bag and weighed, and the mass was denoted as M g . The liquid product was quantitatively analyzed using dichloromethane as the extraction solvent and n-hexadecane as the internal standard. The residual insoluble solid was washed with ethanol and dried in an oven at 80 °C for 12 h, and after cooling, the mass was weighed and denoted as M i.

[0051] According to the principle of material balance, insoluble solids usually contain three types of components: polyethylene residues that are not completely pyrolyzed, the catalyst itself, and possible solid products generated (such as waxes). Since the mass measurements of gas and solid residues are relatively accurate, while liquid products can have losses during extraction and handling, to improve the accuracy of the calculated liquid product yield, the mass conservation method is used to indirectly calculate the mass of liquid products:

[0052]

[0053] where M l is the mass of liquid products, and the liquid yield (Y l ) can be calculated by the following equation:

[0054]

[0055] The polyethylene conversion rate can be calculated by the following equation:

[0056]

[0057] The results of the catalytic performance of the four composite catalysts in the pyrolysis of polyethylene are shown in Table 1 below:

[0058] Table 1. Distribution of hydrocarbon products from the pyrolysis of polyethylene with catalysts

[0059]

[0060] Table 1 shows the distribution of hydrocarbon products produced during the catalytic pyrolysis of polyethylene with different catalysts. The results show that the ZrO2-HZSM-5 catalyst has the best performance in terms of LDPE conversion rate and liquid yield, reaching 86.25% and 72.32% respectively, indicating its significant advantage in promoting the decomposition of LDPE and the generation of liquid hydrocarbon products. In contrast, the conversion rate and liquid yield of Al2O3-HZSM-5 are lower, at 84.32% and 65.26% respectively. In terms of hydrocarbon distribution, TiO2-HZSM-5 has the highest selectivity for gasoline-range hydrocarbons (C5-C 11 ), reaching 88.2%, but its overall liquid product yield is lower, indicating that while it has good selectivity, its catalytic cracking activity is relatively insufficient. The above results show that the type of metal oxide significantly affects the activity and product distribution of the catalyst, and the rational selection of metal oxide components is crucial for achieving the synergistic optimization of high conversion rate and high selectivity.

[0061] Example 6:

[0062] This example is to explore the influence of HZSM-5 with different silicon aluminum ratios on the conversion rate of polyethylene, the liquid yield and the specific product distribution. On the basis of Example 4, the amount of aluminum nitrate nonahydrate is adjusted to prepare HZSM-5 with different silicon aluminum ratios, which are physically ground and mixed with ZrO2 prepared in Example 1, and the test method is the same as that in Example 5. The catalyst performance results are shown in Table 2 below:

[0063] Table 2. Product distribution of polyethylene pyrolysis hydrocarbons of catalysts

[0064]

[0065] Table 2 shows the influence of HZSM-5 molecular sieves with different silicon aluminum ratios (SiO2 / Al2O3) on the catalytic pyrolysis performance of polyethylene. As can be seen from the table, with the increase of the silicon aluminum ratio, the conversion rate of LDPE shows a gradually decreasing trend. The liquid product yield shows a "volcano-type" change rule, and reaches the highest value when the silicon aluminum ratio is 200.

[0066] A lower silicon aluminum ratio means a higher aluminum content in the molecular sieve, thereby introducing more acid sites and enhancing the overall acid strength. Overly strong acidity is easy to cause excessive cracking of polyethylene to generate a large amount of gas and other light hydrocarbon products, thereby reducing the liquid yield. When the silicon aluminum ratio is too high (such as 300), the number of acid sites and the acid strength are reduced, and the initial depolymerization ability of the catalyst to polyethylene is insufficient, which leads to insufficient cracking and generates more long-chain and heavy hydrocarbons (such as waxy substances), which is also not conducive to the yield of gasoline (C5-C 11 ).

[0067] Therefore, a moderate silicon aluminum ratio (such as 200) can achieve a good balance between acid density and acid strength, which promotes effective depolymerization of polyethylene and avoids excessive cracking or incomplete reaction, thereby obtaining the optimal liquid product yield.

[0068] Example 7:

[0069] This example aims to explore the influence of zirconium oxide (ZrO2) and HZSM-5 molecular sieves in different mass ratios on the catalytic pyrolysis performance of polyethylene. ZrO2 prepared in Example 1 and HZSM-5 prepared in Example 4 are physically ground and mixed in a set proportion, for example, Figure 5 Figure 1 is a scanning electron microscope (SEM) image of ZrO2 and HZSM-5 physically ground and mixed in a mass ratio of 1:5. The mixture shows an irregular agglomerated morphology, and the particle size and shape are more diverse. The catalytic performance of the catalyst is evaluated according to the test method of Example 5. To ensure the consistency of experimental conditions, even if ZrO2 or HZSM-5 is used alone, it is also first subjected to 5 minutes of pre-grinding treatment, then mixed and ground with polyethylene, and then subjected to pyrolysis reaction. The obtained catalytic performance data are shown in Table 3:

[0070] Table 3. Pyrolysis hydrocarbon product distribution of polyethylene over catalysts

[0071]

[0072] As shown in Table 3, different mass ratios of ZrO2to HZSM-5 catalysts exhibited different catalytic performances in the process of plastic pyrolysis to gasoline, which was mainly due to the functional complementation and synergistic effect of the two materials in the catalytic reaction. ZrO2had certain acidity and redox ability, which could promote the initial cracking reaction of plastics, but its pore structure was limited, and the ability to regulate product selectivity was weak; while HZSM-5 molecular sieve had strong acid sites and regular microporous structure, which could effectively catalyze the cracking intermediates and selectively generate gasoline fraction (especially C8–C 11 ), but when used alone, it was easy to be deactivated due to carbon deposition. When combined in a physical mixing manner, ZrO2may play a role in dispersing HZSM-5, improving heat and mass transfer, or moderately adjusting the acid density. At a mass ratio of 1:5, the content of HZSM-5 was high enough to provide sufficient acid sites and shape-selective catalytic ability, while the appropriate amount of ZrO2could assist the initial cracking and reduce the carbon deposition of the molecular sieve, thereby achieving the highest conversion, liquid yield and selectivity of target components.

[0073] Example 8:

[0074] This example aims to explore the recycling performance of the catalyst and its stability in multiple reactions. The ZrO2-HZSM-5 composite catalyst prepared in Example 5 was used for polyethylene catalytic pyrolysis experiment, after the reaction was completed, the used catalyst was recovered by centrifugation, and then washed with deionized water and ethanol in turn to remove the surface residual organic matter, then dried at 80 ℃ for 12 h, and calcined in air at 550 ℃ for 4 h to completely remove the carbon deposition, and realize the regeneration of the catalyst. The regenerated catalyst was reused for the next catalytic reaction, and the test conditions were consistent with Example 5 (the composite catalyst and low-density polyethylene were ground together before each reaction). Through three cycles of experiments, the change of polyethylene conversion and liquid product yield during the recycling process of the catalyst was investigated to evaluate its stability and reusability, and the results are shown in Table 4.

[0075] Table 4. Pyrolysis hydrocarbon product distribution of polyethylene over catalysts

[0076]

[0077] According to the data in Table 4, we can see that the ZrO2-HZSM-5 composite catalyst shows certain stability in catalytic performance during multiple cycles. Specifically, in the first run, the conversion rate of low-density polyethylene (LDPE) is 86.25%, and the liquid product yield is 72.32%. With repeated use of the catalyst, by the fourth run, the conversion rate of LDPE slightly decreases to 84.99%, and the liquid product yield decreases to 69.88%. This shows that after three regenerations and a total of four catalytic pyrolysis of polyethylene, the activity of the catalyst decreases, but it still maintains a high catalytic efficiency, and the gasoline (C5-C 11 ) yield is reduced by less than 2.5% compared to the first catalysis; in addition, using other composite catalysts in Example 5, after three regenerations, the gasoline (C5-C 11 ) yield in the fourth catalytic pyrolysis of polyethylene is reduced by no more than 5% compared to the first yield.

[0078] The above is only a preferred embodiment of the present application, but the protection scope of the present application is not limited thereto, and any changes or replacements that can be easily thought of by those skilled in the art within the technical scope disclosed by the present application should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be defined by the protection scope defined by the claims.

[0079] The details not described in the present application are well-known to those skilled in the art.

Claims

1. An environmentally friendly composite catalyst for the catalytic pyrolysis of plastics to produce gasoline, characterized in that: Composed of metal oxides and HZSM-5 zeolite molecular sieves, it is used to catalytically pyrolyze low-density polyethylene into gasoline; the mass ratio of metal oxides to HZSM-5 zeolite molecular sieves is 1:(2~10), the metal element of the metal oxides is one of Ce, Zr, Al, Ti, and the molar ratio of Si to Al in HZSM-5 zeolite molecular sieves is (10~300):

1.

2. The environmentally friendly composite catalyst for producing gasoline by catalytic pyrolysis of plastics according to claim 1, characterized in that, The metal oxide is synthesized by precipitation method. The synthesis steps include: dissolving a certain amount of metal nitrate in deionized water to obtain solution A, preparing an alkaline solution for coprecipitation, denoted as solution B, and simultaneously adding the two aqueous solutions A and B to a beaker under stirring conditions, controlling the reaction temperature and pH value, coprecipitating to obtain flocculent precipitate and aging it; washing, filtering and drying the flocculent precipitate, grinding and calcining it after drying to obtain the metal oxide.

3. The environmentally friendly composite catalyst for producing gasoline by catalytic pyrolysis of plastics according to claim 2, characterized in that: The alkaline solution is one or more of ammonium carbonate, ammonia, and ammonium nitrate; the reaction temperature, pH, and aging time for co-precipitation are 50–100 °C, 7.0–10.0 °C, and 1–5 h, respectively; the drying time and temperature are 8–15 h and 50–100 °C, respectively; and the calcination time and temperature are 9–16 h and 350–500 °C, respectively.

4. The environmentally friendly composite catalyst for producing gasoline by catalytic pyrolysis of plastics according to claim 3, characterized in that: The reaction temperature, pH, and aging time for the co-precipitation were 70–80 °C, 8.0–9.0 °C, and 2–3 h, respectively.

5. The environmentally friendly composite catalyst for producing gasoline by catalytic pyrolysis of plastics according to claim 1, characterized in that, The HZSM-5 zeolite molecular sieve was synthesized by a hydrothermal method. The synthesis steps included: dissolving the reactants tetraethoxysilane, aluminum nitrate nonahydrate, tetrapropylammonium hydroxide and ethanol in distilled water, stirring and transferring the resulting clear solution to a reaction vessel for reaction in a homogeneous reactor, washing and filtering the resulting solid, drying it and calcining it to obtain the HZSM-5 zeolite molecular sieve.

6. The environmentally friendly composite catalyst for producing gasoline by catalytic pyrolysis of plastics according to claim 5, characterized in that: In the reactants, after converting tetraethoxysilane and aluminum nitrate to SiO2 and Al2O3 respectively, the molar ratio of each component is SiO2: Al2O3: H2O: TPAOH: EtOH = 1: X: 50: 0.24: 4, where X is adjusted according to the silicon-aluminum ratio; the reactants are stirred for 3-7 h and then transferred to a reaction vessel; the reaction conditions are as follows: reaction in a homogeneous reactor at 150-220 °C at a rotation speed of 2-10 r / min for 12-48 h; drying time and temperature are 60-100 °C and 10-16 h respectively; calcination time and temperature are 3-6 h and 450-650 °C respectively.

7. The application of the composite catalyst as described in any one of claims 1 to 6 in the catalytic pyrolysis of low-density polyethylene to produce gasoline.

8. The application according to claim 7, characterized in that: The conversion rate of low-density polyethylene is not less than 80%, and the gasoline yield is not less than 54%. The metal oxide is ZrO2, and the mass ratio of metal oxide to HZSM-5 zeolite molecular sieve is 1:

5. When the molar ratio of Si to Al in HZSM-5 zeolite molecular sieve is 200:1, the gasoline yield can reach 61.89%.

9. The application of the composite catalyst as described in any one of claims 1 to 6 for the catalytic pyrolysis of low-density polyethylene to produce gasoline after regeneration.

10. The application according to claim 9, characterized in that: The regeneration process involves solvent washing to remove residual organic matter, followed by drying and calcination to thoroughly remove carbon deposits. The composite catalyst is used for catalytic pyrolysis of low-density polyethylene and then regenerated for further catalytic pyrolysis of low-density polyethylene. After three rounds of regeneration, the gasoline yield from the fourth catalytic pyrolysis of low-density polyethylene is reduced by no more than 5% compared to the first regeneration. The metal oxide used is ZrO2, and the mass ratio of the metal oxide to HZSM-5 zeolite molecular sieve is 1:

5. When the molar ratio of Si to Al in the HZSM-5 zeolite molecular sieve is 200:1, the gasoline yield reduction from the fourth regeneration is no more than 2.5% compared to the first regeneration.

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