Method for producing fuel oil and liquefied petroleum gas through catalytic conversion of waste plastics

Abstract

A method for producing fuel oil and liquefied petroleum gas through catalytic conversion of waste plastics, relating to the field of upgrading and recycling of waste plastics. The preparation process of a catalyst involves a short procedure and a simple process, and is suitable for industrial production. The catalyst has characteristics of uniform active site distribution, and good activity and stability, and can efficiently catalyze hydrogenolysis of the waste plastics to produce liquid fuel at a low temperature under low pressure without adding a solvent, wherein the liquid fuel has a liquid mass yield of 83.82%, has a small molecular weight, and is mainly composed of a gasoline component; and a gas product almost contains no methane or ethane, and can be used as liquefied petroleum gas. The method implements high value-added conversion of the waste plastics, and provides a solution for upgrading and recycling of the waste plastics.

Description

Method for producing fuel oil and liquefied petroleum gas by catalytic conversion of waste plastics Technical Field

[0001] The invention belongs to the field of waste plastics upgrading and recycling, and relates to a method for producing fuel oil and liquefied petroleum gas by catalytic conversion of waste plastics. Background Art

[0002] Since its invention, plastics have brought immense convenience to our lives thanks to their excellent properties and low price. Now, a wide variety of plastic products are indispensable to our daily lives. With increasing demand for plastic products and advancements in production technology, annual plastic production has grown almost exponentially, from less than 2 million tons in 1950 to 380 million tons in 2015. Production is projected to double to a staggering 780 million tons by 2035 (Polyethylene upcycling to long-chain alkylaromatics by tandem hydrogenolysis / aromatization). However, most plastic products are acid-, alkali-, and oxidation-resistant, offering strong stability and resistance to degradation in the natural environment. Coupled with their short average lifespan, high consumption, and improper disposal, plastics have accumulated in large quantities, resulting in significant negative impacts on the environment. According to reports, in 2010 alone, an estimated 4 to 12 million tons of plastic waste entered the oceans, contributing to marine pollution. Furthermore, soil and freshwater pollution are becoming increasingly common, ultimately threatening human life and health. Furthermore, as petrochemical products, the production of plastics consumes significant amounts of fossil energy and contains abundant carbon resources. Improper disposal of waste plastics not only pollutes the environment but also wastes precious resources. Faced with the dual pressures of global environmental pollution and resource shortages, finding a suitable disposal method for waste plastics is urgent.

[0003] It is estimated that between 1950 and 2015, the world generated a cumulative 6.3 billion tons of plastic waste (production, use, and fate of all plastics ever made). Currently, the main methods for disposing of plastic waste include direct landfill, incineration, mechanical recycling, and chemical recycling. Most discarded plastics are directly landfilled, which can easily cause soil and groundwater contamination. A small portion is incinerated to generate low-quality heat, which also produces large amounts of carbon dioxide and toxic gases during the incineration process. Mechanical recycling, on the other hand, requires high quality of discarded plastics, is time-consuming, labor-intensive, and inefficient. Thermal and mechanical effects during the recycling process can degrade the properties of the recycled plastics. Chemical recycling methods are diverse and highly designable. Recycled products can be controlled based on reaction conditions and catalysts, improving product quality and performance, fully utilizing carbon resources, and achieving high-value-added upcycling of plastic waste.

[0004] Among the many plastic products, polyolefin plastics (primarily polyethylene (PE) and polypropylene (PP)) account for over 60% of total plastic production, making them the most widely used and waste-heavy category. Upcycling polyolefin plastic waste is crucial for global environmental protection and resource utilization. However, due to its stable composition of carbon monoxide (CC), it is difficult to degrade. Traditional pyrolysis typically requires high temperatures of 400-600°C and produces large amounts of low-value-added components such as light hydrocarbons, tar, and coke. Catalytic hydrogenolysis of waste plastics, using a catalyst, significantly reduces the reaction temperature, improves the selectivity of high-value products, and enables high-value-added utilization of waste plastics.

[0005] Chinese patent CN116137834A discloses a method for recycling waste plastics. This method uses high-temperature pyrolysis to convert waste plastics into ethylene, propylene, and other low-carbon olefins, achieving resource utilization of plastic waste. However, this method requires high temperatures of 600°C to 900°C to decompose the plastics into monomers, which consumes a large amount of energy. Furthermore, the products are primarily gaseous, making them inconvenient to use and transport. In a hydrogen atmosphere, the use of a catalyst can significantly reduce the degradation temperature of the plastics and regulate the product distribution, achieving high-value-added utilization of waste plastics. Technical issues

[0006] The present invention provides a method for catalytically converting waste plastics into fuel oil and liquefied petroleum gas. Under the action of a catalyst, this method can efficiently catalyze the conversion of waste plastics into fuel oil and liquefied petroleum gas at relatively low temperatures and pressures, without the addition of solvents. The method features high selectivity for the gasoline component, with the gaseous products primarily consisting of propane and isobutane, with virtually no methane and ethane, and can be converted into liquefied petroleum gas after simple treatment. The method also features high conversion rates, virtually no solid products, and excellent catalyst stability. The catalyst preparation, reaction, and product extraction processes are simple and easy to operate, achieving high-value-added conversion of waste plastics and providing a solution for the upcycling of waste plastics. Technical Solutions

[0007] To achieve the objectives of the present invention, a method for preparing a catalyst with high activity for this reaction system has been invented. This method features a short process, simple operation, and is suitable for large-scale production. Specifically, metal active centers are supported on a metal oxide via a hard template method to form a supported catalyst for catalytic conversion of waste plastics into fuel oil and liquefied petroleum gas. This method facilitates uniform distribution of the metal active centers on the support, increases the number of active sites, and enhances reaction activity. During the reaction, the catalyst selectively adsorbs non-terminal carbon-carbon bonds in the polyolefin backbone, causing them to gradually break, resulting in a gradual shortening of the chain length and limiting the production of low-value-added light alkanes.

[0008] A method for preparing a catalyst for catalytic conversion of waste plastics to produce fuel oil and liquefied petroleum gas, comprising the following steps:

[0009] (1) After dispersing the carrier metal salt in deionized water, the metal salt precursor is added to obtain a mixed intermediate solution A;

[0010] The molar ratio of the metal salt precursor to the carrier metal salt is 1:(5-35), and the concentration of the metal component in the metal salt precursor in the mixed intermediate solution A is 0.1-20 g / L;

[0011] The carrier metal salt includes one or a mixture of two or more of the corresponding hydrates of zirconium nitrate, zirconium chloride, cerium nitrate, cerium ammonium nitrate, aluminum nitrate, and lanthanum nitrate;

[0012] The metal salt precursor is one of ruthenium chloride, ruthenium nitrosyl nitrate, platinum nitrate, cobalt nitrate, nickel nitrate, and ammonium molybdate;

[0013] (2) adding the template to the mixed intermediate solution A to obtain the intermediate substance B, wherein the mass ratio of the template to the mixed intermediate solution is 1:(4-15);

[0014] The template agent is one of silicon dioxide, carbon black, C3N4, and graphite;

[0015] (3) After the intermediate substance B is completely dried, it is calcined in air to obtain the calcined intermediate C, wherein the calcination temperature is 300-600°C and the calcination time is 5 hours;

[0016] (4) The calcined intermediate C is subjected to reduction treatment in a reducing atmosphere to obtain a catalyst; wherein the reduction temperature is 20-500°C and the reduction treatment time is 1-4 hours.

[0017] The waste plastic is one of polyethylene, polypropylene, and polyvinyl chloride, or a mixture of two or more thereof.

[0018] (5) The mass ratio of the catalyst to the waste plastic is controlled at 0.05-0.5, and the mixture is then evenly mixed and loaded into a high-pressure reactor. The reaction temperature is 200-300°C, and hydrogen gas of 0-5 MPa is injected at room temperature for 2-24 hours. No additional solvent is required to decompose the waste plastic into fuel oil. After the reaction is completed, the gaseous products are collected and the fuel oil and catalyst are separated by centrifugation to obtain pure fuel oil, in which the mass fraction of the gasoline component can reach 77%-95%. The catalyst has good stability and can maintain the same activity after the cyclic reaction. Beneficial effects

[0019] This method innovatively utilizes a hard template method to prepare catalysts for the catalytic conversion of waste plastics. The catalysts prepared using this method possess a high specific surface area, which prevents the aggregation of active centers, promotes their uniform distribution, and enhances catalytic activity. This method effectively achieves the efficient conversion of waste plastics into fuel oil, significantly reducing the production of low-value-added light alkanes such as methane and ethane, and increasing the yield of gasoline components. This provides a promising solution for addressing waste plastic pollution, promoting the upcycling of plastic waste, integrating carbon resources, and achieving carbon recycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is the X-ray diffraction pattern of Ru / ZrO2 catalyst and ZrO2.

[0021] Figure 2 shows the effect of different reaction pressures on the conversion of polypropylene plastics catalyzed by Ru / ZrO2 catalyst.

[0022] Figure 3 shows the effect of different reaction times on the conversion of polypropylene plastics catalyzed by Ru / ZrO2 catalyst.

[0023] FIG4 is a diagram of the products of catalytic conversion of waste plastics into fuel oil.

[0024] Figure 5 shows the distribution of gaseous products after 8 hours of reaction at 1.5 MPa of hydrogen under the action of Ru / ZrO2. Modes for Carrying Out the Invention

[0025] The following further illustrates specific implementations of the present invention in conjunction with the accompanying drawings and technical solutions, but the present invention is not limited thereto.

[0026] Example 1: Preparation of Ru / ZrO2 catalyst

[0027] Weigh 3.484g of zirconium nitrate pentahydrate, add 10ml of deionized water and heat and stir until the zirconium nitrate is completely dissolved. Then add 1.710ml of nitrosyl ruthenium nitrate solution and stir evenly. Then weigh 1g of carbon black and add it to the mixed solution. Then dry it at 60°C for 12 hours to ensure that the water is completely removed. Subsequently, the dried mixed catalyst precursor powder is calcined at 500°C in an air atmosphere for 5h to burn off the template. The catalyst is then reduced at 350°C in a hydrogen atmosphere for 2 hours. The theoretical metal loading of the obtained catalyst is 2.5wt% and the specific surface area is about 130㎡ / g. The XRD ray comparison diagram of it and ZrO2 is shown in Figure 1.

[0028] Similarly, when no carbon black is added during the catalyst preparation process and other conditions remain the same, the specific surface area of ​​the obtained catalyst is only 58 ㎡ / g, which is 2.24 times smaller.

[0029] Example 2: ZrO2 and Ru / ZrO2 catalysts were used to carry out reactions under the same reaction conditions to explore the effect of metal Ru on the reaction.

[0030] 0.4g of ZrO2 and Ru / ZrO2 catalysts, respectively, were mixed with 4.0g of polypropylene plastic in an autoclave and reacted under the same reaction conditions (1.5 MPa H2, 300°C) for 8 hours. After cooling to room temperature, the vapor product was collected using an air bag, and the fuel oil and catalyst were separated by centrifugation. The vapor and liquid products were further analyzed by gas chromatography. The results showed that under the Ru / ZrO2 catalysis, the conversion of polypropylene plastic was 95.13%, the fuel oil yield was 62.29%, the selectivity for gasoline components (C5-C12) reached 77.06%, and the selectivity for propane and higher components (C3-C6) in the vapor product was 98.56%. In contrast, almost no liquid product was produced when only ZrO2 was added.

[0031] Example 3: Exploring the effects of different supports on catalyst performance

[0032] 3.484g of zirconium nitrate pentahydrate, 2.526g of cerium nitrate hexahydrate, 7.358g of aluminum nitrate nonahydrate, and 2.658g and 2.526g of lanthanum nitrate hexahydrate were weighed, added to 10ml of deionized water, and heated with stirring until the zirconium nitrate was completely dissolved. 1.710ml of ruthenium nitrosyl nitrate solution was then added, stirred evenly, and 1g of carbon black was added to the mixed solution. The mixture was then dried at 60°C for 12 hours to ensure complete removal of moisture. Subsequently, the dried mixture was calcined at 500°C in an air atmosphere for 5 hours. The catalyst was then reduced at 350°C in a hydrogen atmosphere for 2 hours.

[0033] 0.4g of each of the above catalysts with different supports was weighed and mixed with 4.0g of polypropylene plastic in an autoclave. The mixture was reacted at 1.5 MPa and 300°C for 8 hours. After the reaction was completed and cooled to room temperature, the vapor product was collected using an air bag, and the fuel oil and catalyst were separated by centrifugation. The vapor and liquid products were further analyzed by gas chromatography. The results showed fuel oil yields of 72.44%, 65.30%, 67.52%, and 62.45%, respectively.

[0034] Example 4: Exploring the effects of different metals on catalyst performance

[0035] 3.484g of zirconium nitrate pentahydrate was weighed, 10ml of deionized water was added, and the mixture was heated and stirred until the zirconium nitrate was completely dissolved. 1.710ml of a 1.5% metal mass fraction of ruthenium nitrate solution, platinum nitrate, cobalt nitrate, nickel nitrate, and ammonium molybdate solution were then added, stirred evenly, and 1g of carbon black was added to the mixed solution. The mixture was then dried at 60°C for 12 hours to ensure complete removal of moisture. The dried mixture was then calcined at 500°C in air for 5 hours. The catalyst was then reduced at 350°C in a hydrogen atmosphere for 2 hours. The resulting catalyst had a theoretical metal loading of 2.5wt%.

[0036] 0.4g of each of the above metal-loaded catalysts was weighed and mixed with 4.0g of polypropylene plastic in an autoclave. The mixture was reacted at 1.5 MPa and 300°C for 8 hours. After cooling to room temperature, the vapor product was collected using an air bag, and the fuel oil and catalyst were separated by centrifugation. The vapor and liquid products were further analyzed by gas chromatography. The results showed fuel oil yields of 72.44%, 79.22%, 10.05%, 40.26%, and 30.50%, respectively.

[0037] Example 5: Exploring the effects of different loadings on catalyst performance

[0038] 3.484g of zirconium nitrate pentahydrate was weighed, 10ml of deionized water was added, and the mixture was heated and stirred until the zirconium nitrate was completely dissolved. Then, 0.685ml, 1.710ml, 7.407ml, and 16.667ml of nickel nitrate solution with a metal content of 1.5% were added, respectively, and stirred thoroughly. After that, 1g of carbon black was added to the mixed solution. The mixture was then dried at 60°C for 12 hours to ensure complete removal of moisture. The dried mixture was then calcined at 500°C in air for 5 hours. The catalyst was then reduced at 350°C in a hydrogen atmosphere for 2 hours. The resulting catalysts had theoretical metal loadings of 1wt%, 2.5wt%, 10wt%, and 20wt%.

[0039] 0.4g of each catalyst with varying loadings was weighed and mixed with 4.0g of polypropylene plastic in an autoclave. The mixture was reacted at 1.5 MPa and 300°C for 8 hours. After cooling to room temperature, the vapor product was collected using an air bag, and the fuel oil and catalyst were separated by centrifugation. The vapor and liquid products were further analyzed by gas chromatography. The results showed fuel oil yields of 8.62%, 40.26%, 50.28%, and 30.98%, respectively.

[0040] Example 6: Investigating the effect of different calcination temperatures on catalyst performance

[0041] 3.484g of zirconium nitrate pentahydrate was weighed, 10ml of deionized water was added, and the mixture was heated and stirred until the zirconium nitrate was completely dissolved. 1.710ml of ruthenium nitrosyl nitrate solution was then added. After stirring, 1g of carbon black was weighed and added to the mixture. The mixture was then dried at 60°C for 12 hours to ensure complete removal of moisture. The dried mixture was then calcined in air at 300°C, 500°C, and 600°C for 5 hours. The catalyst was then treated in a hydrogen atmosphere at 350°C for 2 hours.

[0042] 0.4g of the catalysts calcined at different temperatures were weighed and mixed with 4.0g of polypropylene plastic in an autoclave. The mixture was reacted at 1.5 MPa and 300°C for 8 hours. After cooling to room temperature, the vapor product was collected using an air bag, and the fuel oil and catalyst were separated by centrifugation. The vapor and liquid products were further analyzed by gas chromatography. The results showed fuel oil yields of 0%, 72.44%, and 42.36%, respectively.

[0043] Example 7: Investigating the effect of different reduction temperatures on catalyst performance

[0044] 3.484g of zirconium nitrate pentahydrate was weighed, 10ml of deionized water was added, and the mixture was heated and stirred until the zirconium nitrate was completely dissolved. 1.710ml of ruthenium nitrosyl nitrate solution was then added. After stirring, 1g of carbon black was weighed and added to the mixture. The mixture was then dried at 60°C for 12 hours to ensure complete removal of moisture. The dried mixture was then calcined at 500°C in air for 5 hours. The catalyst was then treated in a hydrogen atmosphere for 2 hours at various temperatures, including non-reduction, 350°C, and 500°C.

[0045] 0.4g of the catalysts treated under different reduction conditions were weighed and mixed with 4.0g of polypropylene plastic in an autoclave. The mixture was reacted at 1.5 MPa and 300°C for 8 hours. After cooling to room temperature, the vapor product was collected using an air bag, and the fuel oil and catalyst were separated by centrifugation. The vapor and liquid products were further analyzed by gas chromatography. The results showed fuel oil yields of 72.44%, 70.68%, and 0%, respectively.

[0046] Example 8: Investigating the effect of different reaction pressures on the conversion of polypropylene waste plastics by catalysts

[0047] 0.4g of catalyst was weighed and mixed with 4.0g of polypropylene plastic in an autoclave. The mixture was then placed in a reactor at 300°C for 8 hours. The reaction pressure was varied to investigate the effects of 1 MPa, 1.5 MPa, 2 MPa, 3 MPa, and 4 MPa on the reaction. After the reaction was completed and cooled to room temperature, the gaseous product was collected using an air bag, and the fuel oil and catalyst were separated by centrifugation. The gaseous and liquid products were further analyzed by gas chromatography. The results showed fuel oil yields of 49.27%, 62.29%, 69.73%, 72.44%, and 73.13%, respectively. Detailed results are shown in Figure 2.

[0048] Example 9: Investigating the effect of different reaction times on the conversion of polypropylene waste plastics by catalysts

[0049] 0.4g of catalyst was weighed and mixed with 4.0g of polypropylene plastic in an autoclave. The mixture was then reacted at 300°C and 1.5 MPa. The reaction time was varied, primarily to investigate the effects of 3, 5, 8, and 10 hours. After cooling to room temperature, the gaseous products were collected using an air bag, and the fuel oil and catalyst were separated by centrifugation. The gaseous and liquid products were further analyzed by gas chromatography. The results showed fuel oil yields of 42.12%, 60.08%, 62.29%, and 73.68%, respectively. Detailed results are shown in Figure 3; more detailed information on the gaseous product distribution after 8 hours of reaction at 1.5 MPa is shown in Figure 5.

[0050] Example 10: Investigating the effect of catalysts on the conversion of different polypropylene waste plastics

[0051] 0.4g of catalyst was weighed, mixed with 4.0g each of polyethylene plastic and polypropylene plastic boxes, and loaded into an autoclave. The mixture was reacted under 1.5 MPa of H2 at 300°C for 8 hours. After cooling to room temperature, the vapor phase was collected using an air bag, and the fuel oil and catalyst were separated by centrifugation. The vapor and liquid phases were further analyzed by gas chromatography. The results showed that the conversion of polypropylene plastic under the catalytic conditions was 95.66%, with a fuel oil yield of 62.71%. The conversion of polypropylene plastic boxes was 96.40%, with a fuel oil yield of 68.79%.

Claims

1. A method for catalytic conversion of waste plastics to produce fuel oil and liquefied petroleum gas, characterized in that, the steps are as follows: (1) After dispersing the supported metal salt in deionized water, a metal salt precursor is added to obtain a mixed intermediate solution A; (2) A template agent is added to the mixed intermediate solution A to obtain an intermediate substance B; (3) After the intermediate substance B is completely dried, it is calcined in air to obtain a calcined intermediate C; (4) The calcined intermediate C is subjected to a reduction treatment in a reducing atmosphere to obtain a catalyst; (5) The mass ratio of the catalyst to the waste plastics is controlled at 0.05 - 0.

5. After mixing evenly, it is loaded into a high-pressure reactor and reacted under the conditions of a reaction temperature of 200 - 300 °C, charging hydrogen at room temperature to 0 - 5.0 MPa, and a reaction time of 2 - 24 hours. Without additional adding of solvents, the filled waste plastics are decomposed into fuel oil and liquefied petroleum gas.

2. The method for catalytic conversion of waste plastics to produce fuel oil and liquefied petroleum gas according to claim 1, characterized in that, in step (1), the molar ratio of the metal salt precursor to the supported metal salt is 1:(5 - 35), and the concentration of the metal component in the supported metal salt in the mixed intermediate solution A is 0.1 - 20 g / L.

3. The method for preparing a catalyst for catalytic conversion of waste plastics to produce fuel oil and liquefied petroleum gas according to claim 1, characterized in that, in step (1), the supported metal salt includes one or more mixtures of zirconium nitrate, zirconium chloride, cerium nitrate, ammonium cerium nitrate, aluminum nitrate, and lanthanum nitrate.

4. The method for catalytic conversion of waste plastics to produce fuel oil and liquefied petroleum gas according to claim 1, characterized in that, in step (1), the metal salt precursor is one of ruthenium chloride, ruthenium nitrosyl nitrate, platinum nitrate, cobalt nitrate, nickel nitrate, and ammonium molybdate.

5. The method for catalytic conversion of waste plastics to produce fuel oil and liquefied petroleum gas according to claim 1, characterized in that, in step (2), the template agent is one of silicon dioxide, carbon black, C3N4, and graphite.

6. The method for catalytic conversion of waste plastics to produce fuel oil and liquefied petroleum gas according to claim 1, characterized in that, in step (2), the mass ratio of the template agent to the mixed intermediate solution is 1:(4 - 15).

7. The method for catalytic conversion of waste plastics to produce fuel oil and liquefied petroleum gas according to claim 1, characterized in that, in step (3), the calcination temperature is 300 - 600 °C and the calcination time is 5 hours.

8. The method for catalytic conversion of waste plastics to produce fuel oil and liquefied petroleum gas according to claim 1, characterized in that, in step (4), the reduction temperature is 20 - 500 °C and the reduction treatment time is 1 - 4 hours.

9. The method for catalytic conversion of waste plastics to produce fuel oil and liquefied petroleum gas according to claim 1, characterized in that, the waste plastics are one or more mixtures of polyethylene, polypropylene, and polyvinyl chloride.

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