A method for catalytic conversion of waste plastics to produce fuel oil and liquefied petroleum gas

Abstract

This invention discloses a method for the catalytic hydrogenolysis of waste plastics to produce fuel oil and liquefied petroleum gas (LPG), belonging to the field of waste plastic upgrading and recycling. The catalyst preparation process is short and simple, suitable for industrial production. The catalyst has uniformly distributed active sites, exhibiting excellent activity and stability. It can efficiently catalyze the hydrogenolysis of waste plastics to produce liquid fuels under relatively low temperature, low pressure, and without the need for solvent addition. The liquid mass yield can reach 83.82%, with a small molecular weight, mainly composed of gasoline components; the gaseous product contains almost no methane or ethane and can be used to produce LPG. This method achieves high-value-added conversion of waste plastics and provides a solution for waste plastic upgrading and recycling.

Description

Technical Field

[0001] This invention belongs to the field of waste plastic upgrading and recycling, and relates to a method for catalytic conversion of waste plastics to produce fuel oil and liquefied petroleum gas. Background Technology

[0002] Since its invention, plastic has brought immense convenience to our lives thanks to its superior performance and low price. Now, we rely heavily on various plastic products in every aspect of our lives, from clothing and food to housing and transportation. 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, and 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, exhibiting strong stability and making them difficult to degrade in the natural environment. Coupled with short average lifespans, high consumption, and improper disposal, they accumulate in large quantities in nature, causing serious negative impacts on the ecological environment. It has been reported that in 2010 alone, an estimated 4 to 12 million tons of plastic waste entered the ocean, causing marine pollution. Furthermore, soil and freshwater pollution are rampant, ultimately threatening human life and health. In addition, as a petrochemical product, the production of plastics consumes a large amount of fossil fuels and contains abundant carbon resources. Improper disposal of waste plastics not only causes environmental pollution but also wastes valuable resources. Under the dual pressure of global environmental pollution and resource scarcity, finding a reasonable way to dispose of waste plastic products has become urgent.

[0003] It is estimated that from 1950 to 2015, the world accumulated 6.3 billion tons of plastic waste (production, use, and fate of all plastics ever made). Currently, the main methods for treating plastic waste include direct landfill, incineration, mechanical recycling, and chemical recycling. Most waste plastics are directly landfilled, easily causing soil and groundwater pollution. A small portion is incinerated to generate low-quality heat energy, producing large amounts of carbon dioxide and toxic gases during the process. Mechanical recycling requires high-quality waste plastics, is time-consuming, labor-intensive, and inefficient; the heat and mechanical effects during recycling can lead to a decline in the performance of recycled plastics. Chemical recycling methods are diverse and highly designable; the recycled products can be controlled according to reaction conditions and catalysts to improve product quality and performance, fully utilize carbon resources, and achieve high-value-added recycling of plastic waste.

[0004] Among numerous plastic products, polyolefin plastics (mainly including polyethylene (PE) and polypropylene (PP) account for over 60% of total plastic production, making them the most widely used and largest category of waste plastics. Upgrading and recycling waste polyolefin plastics is of great significance to global environmental protection and resource utilization. However, due to their composition of carbon dioxide (CC), they are stable and difficult to degrade. Traditional pyrolysis generally requires high temperatures of 400–600°C and typically produces large amounts of low-value-added components such as light hydrocarbons, tar, and coke. Catalytic hydrogenolysis of waste plastics, on the other hand, can significantly lower the reaction temperature and improve the selectivity of high-value products under the action of a catalyst, achieving high-value utilization of waste plastics.

[0005] Chinese patent CN116137834A discloses a method for recycling waste plastics, which 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℃ to 900℃ to pyrolyze the plastics into monomers, consuming a large amount of energy, and the products are mainly gaseous, making them inconvenient to use and transport. In a hydrogen atmosphere, a catalyst can significantly reduce the temperature of plastic degradation and regulate the product distribution, achieving high-value utilization of waste plastics. Summary of the Invention

[0006] This invention provides a method for the catalytic conversion of waste plastics into fuel oil and liquefied petroleum gas (LPG). Under the action of a catalyst, this method can efficiently catalyze the conversion of waste plastics into fuel oil and LPG at relatively low temperatures and pressures without the need for solvents. The gasoline component exhibits high selectivity. The gaseous products are mainly propane and isobutane, with almost no methane or ethane, and can be readily converted into LPG after simple processing. The conversion rate is high, with almost no solid products, and the catalyst exhibits good stability. The catalyst preparation, reaction, and product extraction processes are simple and convenient to operate, achieving high-value-added conversion of waste plastics and providing a solution for the upgrading and recycling of waste plastics.

[0007] The technical solution of the present invention:

[0008] To achieve the objectives of this invention, a method for preparing a highly active catalyst for this reaction system has been developed. This method is concise, simple to operate, and suitable for mass production. Specifically, metal active centers are supported on metal oxides using a hard template method to form a supported catalyst for the catalytic conversion of waste plastics into fuel oil and liquefied petroleum gas. This method facilitates the uniform distribution of metal active centers on the support, increases the number of active sites, and improves reaction activity. During the reaction, non-terminal carbon-carbon bonds in the polyolefin backbone are selectively adsorbed, leading to their gradual breakage and shortening of chain length, thus limiting the production of low-value-added light alkanes.

[0009] A method for preparing a catalyst for the catalytic conversion of waste plastics into fuel oil and liquefied petroleum gas includes the following steps:

[0010] (1) After dispersing the carrier metal salt in deionized water, the metal salt precursor is added to obtain a mixed intermediate solution A;

[0011] 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.

[0012] The carrier metal salt includes one or more of the following: zirconium nitrate, zirconium chloride, cerium nitrate, cerium ammonium nitrate, aluminum nitrate, and lanthanum nitrate hydrates;

[0013] The metal salt precursor is one of ruthenium chloride, ruthenium nitrite nitrite, platinum nitrate, cobalt nitrate, nickel nitrate, and ammonium molybdate;

[0014] (2) The template agent is added to the mixed intermediate solution A to obtain intermediate substance B, wherein the mass ratio of the template agent to the mixed intermediate solution is 1:(4~15);

[0015] The stencil agent is one of silicon dioxide, carbon black, C3N4, and graphite;

[0016] (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℃ and the calcination time is 5 hours.

[0017] (4) The calcined intermediate C is reduced under a reducing atmosphere to obtain the catalyst; wherein the reduction temperature is 20 to 500°C and the reduction time is 1 to 4 hours.

[0018] The waste plastic is one or a mixture of two or more of polyethylene, polypropylene, and polyvinyl chloride.

[0019] (5) After mixing the catalyst and waste plastic at a mass ratio of 0.05 to 0.5, the mixture is loaded into a high-pressure reactor. The reaction temperature is 200–300°C, and hydrogen gas is introduced at room temperature at 0–5 MPa. The reaction time is 2–24 hours. No additional solvent is needed to decompose the waste plastic into fuel oil. After the reaction, the gaseous products are collected, and the fuel oil and catalyst are separated by centrifugation to obtain pure fuel oil, in which the gasoline component mass fraction can reach 77%–95%. The catalyst has good stability and can maintain the same activity in cyclic reactions.

[0020] The beneficial effects of this invention are as follows: This innovative method utilizes a hard template method to prepare catalysts for the catalytic conversion of waste plastics. The catalyst prepared by this method has a high specific surface area, which avoids the aggregation of active centers, promotes their uniform distribution, and improves catalyst activity. It effectively achieves the efficient conversion of waste plastics into fuel oil, significantly reduces the generation of low-value-added light alkanes such as methane and ethane, and increases the yield of gasoline components. This provides an excellent solution for addressing waste plastic pollution, upgrading and recycling plastic waste, integrating carbon resources, and realizing carbon cycling. Attached Figure Description

[0021] Figure 1 The image shows the X-ray diffraction patterns of the Ru / ZrO2 catalyst and ZrO2.

[0022] Figure 2 The effect of different reaction pressures on the conversion of polypropylene plastics catalyzed by Ru / ZrO2 catalyst.

[0023] Figure 3 The effect of different reaction times on the conversion of polypropylene plastics catalyzed by Ru / ZrO2 catalyst.

[0024] Figure 4 This is a diagram of the products from the catalytic conversion of waste plastics into fuel oil.

[0025] Figure 5 The distribution of gaseous products after 8 hours of reaction with 1.5 MPa hydrogen under Ru / ZrO2. Detailed Implementation

[0026] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions, but the present invention is not limited thereto.

[0027] Example 1: Preparation of Ru / ZrO2 catalyst

[0028] 3.484 g of zirconium nitrate pentahydrate was weighed, added to 10 ml of deionized water, and heated and stirred until the zirconium nitrate was completely dissolved. Then, 1.710 ml of nitrosyl ruthenium nitrate solution was added and stirred evenly. 1 g of carbon black was then weighed and added to the above mixture. The mixture was then dried at 60 °C for 12 hours to ensure complete removal of moisture. Subsequently, the dried catalyst precursor powder was calcined at 500 °C in air for 5 hours to burn off the template agent. The catalyst was then reduced at 350 °C in a hydrogen atmosphere for 2 hours. The theoretical metal loading of the obtained catalyst was 2.5 wt%, and the specific surface area was approximately 130 m² / g. The XRD pattern comparison between the catalyst and ZrO₂ is shown below. Figure 1 .

[0029] Similarly, without adding carbon black during catalyst preparation and with other conditions kept the same, the resulting catalyst had a specific surface area of ​​only 58 m² / g, a reduction of 2.24 times.

[0030] Example 2: The effect of metallic Ru on the reaction was investigated by using ZrO2 and Ru / ZrO2 catalysts under the same reaction conditions.

[0031] 0.4 g of ZrO2 and Ru / ZrO2 catalyst were weighed and mixed with 4.0 g of polypropylene plastic, respectively, and loaded into a high-pressure reactor. The reaction was carried out under the same conditions (1.5 MPa H2, 300 °C) for 8 hours. After cooling to room temperature, the gaseous product was collected using a gas 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 that the conversion rate of polypropylene plastic under Ru / ZrO2 catalysis was 95.13%, the fuel oil yield was 62.29%, with a selectivity of 77.06% for gasoline components (C5-C12), and a selectivity of 98.56% for propane and higher components (C3-C6) in the gaseous product. The product with only ZrO2 added had almost no liquid product.

[0032] Example 3: Investigating the effect of different supports on catalyst performance

[0033] Weigh out 3.484 g of zirconium nitrate pentahydrate, 2.526 g of cerium nitrate hexahydrate, 7.358 g of aluminum nitrate nonahydrate, and 2.658 g and 2.526 g of lanthanum nitrate hexahydrate, respectively. Add 10 ml of deionized water and heat and stir until the zirconium nitrate is completely dissolved. Then add 1.710 ml of nitrosyl ruthenium nitrate solution and stir well. Weigh out 1 g of carbon black and add it to the above mixture. Then dry at 60 °C for 12 hours to ensure complete removal of moisture. Subsequently, calcine the dried mixture in air at 500 °C for 5 hours. Then reduce the catalyst in hydrogen atmosphere at 350 °C for 2 hours.

[0034] 0.4 g of the catalyst with different supports was weighed and mixed with 4.0 g of polypropylene plastic, and then placed in a high-pressure reactor. 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 gaseous product was collected using a gas 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 that the fuel oil yields were 72.44%, 65.30%, 67.52%, and 62.45%, respectively.

[0035] Example 4: Investigating the effects of different metals on catalyst performance

[0036] 3.484 g of zirconium nitrate pentahydrate was weighed, added to 10 ml of deionized water, and heated and stirred until the zirconium nitrate was completely dissolved. Then, 1.710 ml of solutions of 1.5% nitrosyl ruthenium nitrate, platinum nitrate, cobalt nitrate, nickel nitrate, and ammonium molybdate were added and stirred until homogeneous. 1 g of carbon black was then weighed and added to the mixture. 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 air for 5 hours. The catalyst was then reduced at 350 °C in a hydrogen atmosphere for 2 hours. The theoretical metal loading of the obtained catalyst was 2.5 wt%.

[0037] 0.4 g of the catalyst loaded with different metals was weighed and mixed with 4.0 g of polypropylene plastic, and then placed in a high-pressure reactor. 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 gaseous product was collected using a gas 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 that the fuel oil yields were 72.44%, 79.22%, 10.05%, 40.26%, and 30.50%, respectively.

[0038] Example 5: Investigating the effect of different loading rates on catalyst performance

[0039] 3.484 g of zirconium nitrate pentahydrate was weighed, added to 10 ml of deionized water, and heated and stirred until the zirconium nitrate was completely dissolved. Then, 0.685 ml, 1.710 ml, 7.407 ml, and 16.667 ml of a 1.5% nickel nitrate solution were added respectively, and stirred evenly. 1 g of carbon black was then weighed and added to the above mixture. 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 air for 5 hours. The catalyst was then reduced at 350 °C in a hydrogen atmosphere for 2 hours. The theoretical metal loadings of the obtained catalysts were 1 wt%, 2.5 wt%, 10 wt%, and 20 wt%.

[0040] 0.4 g of the catalyst with different loadings was weighed and mixed with 4.0 g of polypropylene plastic, and then placed in a high-pressure reactor. 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 gaseous product was collected using a gas 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 that the fuel oil yields were 8.62%, 40.26%, 50.28%, and 30.98%, respectively.

[0041] Example 6: Investigating the effect of different calcination temperatures on catalyst performance

[0042] Weigh 3.484 g of zirconium nitrate pentahydrate, add 10 ml of deionized water, and heat and stir until the zirconium nitrate is completely dissolved. Then add 1.710 ml of nitrosyl ruthenium nitrate solution, stir well, and then weigh 1 g of carbon black and add it to the above mixture. Dry at 60 °C for 12 hours to ensure complete removal of moisture. Subsequently, calcine the dried mixture in air at 300 °C, 500 °C, and 600 °C for 5 hours each. Finally, treat the catalyst in a hydrogen atmosphere at 350 °C for 2 hours.

[0043] 0.4 g of the catalyst at different calcination temperatures was weighed and mixed with 4.0 g of polypropylene plastic, then placed in a high-pressure reactor and reacted for 8 hours at 1.5 MPa and 300 °C. After the reaction was completed and cooled to room temperature, the gaseous product was collected using a gas 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 that the fuel oil yields were 0%, 72.44%, and 42.36%, respectively.

[0044] Example 7: Investigating the effect of different reduction temperatures on catalyst performance

[0045] Weigh 3.484 g of zirconium nitrate pentahydrate, add 10 ml of deionized water, and heat and stir until the zirconium nitrate is completely dissolved. Then add 1.710 ml of nitrosyl ruthenium nitrate solution, stir well, and then weigh 1 g of carbon black and add it to the above mixture. Dry at 60 °C for 12 hours to ensure complete removal of moisture. Subsequently, calcine the dried mixture in air at 500 °C for 5 hours. Then, treat the catalyst in a non-reducing atmosphere, at 350 °C, and at 500 °C for 2 hours each.

[0046] 0.4 g of the catalyst treated under different reduction conditions was weighed and mixed with 4.0 g of polypropylene plastic, then loaded into a high-pressure reactor and reacted for 8 hours at 1.5 MPa and 300 °C. After the reaction was completed and cooled to room temperature, the gaseous product was collected using a gas 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 that the fuel oil yields were 72.44%, 70.68%, and 0%, respectively.

[0047] Example 8: Investigating the effect of different reaction pressures on the catalyst-catalyzed conversion of polypropylene waste plastics

[0048] 0.4 g of catalyst and 4.0 g of polypropylene plastic were weighed and mixed and placed in a high-pressure reactor. The reaction was carried out at 300 °C for 8 hours. The effects of reaction pressures of 1 MPa, 1.5 MPa, 2 MPa, 3 MPa, and 4 MPa on the reaction were investigated. After the reaction was completed and cooled to room temperature, the gaseous product was collected using a gas bag. Fuel oil and catalyst were separated by centrifugation. The gaseous and liquid products were further analyzed by gas chromatography. The results showed that the fuel oil yields were 49.27%, 62.29%, 69.73%, 72.44%, and 73.13%, respectively. Detailed results can be found in [link to detailed results]. Figure 2 .

[0049] Example 9: Investigating the effect of different reaction times on the catalyst-catalyzed conversion of polypropylene waste plastics

[0050] 0.4 g of catalyst and 4.0 g of polypropylene plastic were weighed and mixed in a high-pressure reactor. The reaction was carried out at 300 °C and 1.5 MPa. The reaction time was varied, mainly to investigate the effect of 3 hours, 5 hours, 8 hours, and 10 hours on the reaction. After the reaction was completed and cooled to room temperature, the gaseous product was collected using a gas bag. The fuel oil and catalyst were separated by centrifugation. The gaseous and liquid products were further analyzed by gas chromatography. The results showed that the fuel oil yields were 42.12%, 60.08%, 62.29%, and 73.68%, respectively. Detailed results are shown in [link to detailed results]. Figure 3 More specifically, the gaseous product distribution after 8 hours of reaction at 1.5 MPa is shown in [Figure number missing]. Figure 5 .

[0051] Example 10: Investigating the effect of catalysts on the catalytic conversion of different polypropylene waste plastics

[0052] 0.4 g of catalyst was weighed and mixed with 4.0 g each of polyethylene and polypropylene plastic containers, and then placed in a high-pressure reactor. The reaction was carried out at 1.5 MPa H2 and 300 °C for 8 hours. After cooling to room temperature, the gaseous product was collected using a gas 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 that under the catalysis of [catalyst name missing], the conversion rate of polypropylene plastic was 95.66%, and the fuel oil yield was 62.71%; the conversion rate of polypropylene plastic containers was 96.40%, and the fuel oil yield was 68.79%.

Claims

1. A method for the 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 carrier metal salt in deionized water, the metal salt precursor is added to obtain a mixed intermediate solution A; 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 carrier metal salt in the mixed intermediate solution A is 0.1-20 g / L; The carrier metal salt is one or a mixture of two or more of zirconium nitrate, zirconium chloride, cerium nitrate, cerium ammonium nitrate, aluminum nitrate, and lanthanum nitrate; The metal salt precursor is one of ruthenium chloride, ruthenium nitrite, or platinum nitrate; (2) Add the template agent to the mixed intermediate solution A to obtain intermediate substance B; the template agent is one of silicon dioxide, carbon black, C3N4, and graphite; (3) After the intermediate substance B is completely dried, it is calcined in air to obtain the calcined intermediate C; the calcination temperature is 500℃ and the calcination time is 5 hours. (4) The calcined intermediate C was reduced under a reducing atmosphere to obtain the catalyst; The reduction temperature is 350℃, and the reduction treatment time is 1~4 hours; (5) The mass ratio of catalyst to waste plastic is controlled at 0.05~0.

5. After mixing evenly, the mixture is loaded into a high-pressure reactor. Hydrogen gas is introduced at room temperature at 0~5.0 MPa. The reaction is carried out at a reaction temperature of 200-300℃ and a reaction time of 2~24 hours. No additional solvent is required. The waste plastic is 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 (2), the mass ratio of the template agent to the mixed intermediate solution is 1:(4~15).

3. 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 plastic is one or a mixture of two or more of polyethylene, polypropylene, and polyvinyl chloride.

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