Method for waste plastic hydrocracking and its application
By using ZSM-5 molecular sieve-supported transition metal catalysts to treat waste plastics in a hydrogen atmosphere, the problems of environmental pollution, high temperature and high cost in waste plastic treatment have been solved, achieving efficient and low-cost fuel conversion.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- BEIJING UNIV OF TECH
- Filing Date
- 2024-05-06
- Publication Date
- 2026-06-05
AI Technical Summary
In existing technologies, waste plastic treatment methods mainly rely on landfill and incineration, which pose environmental pollution risks and have low recycling rates. High-temperature pyrolysis methods require precious metal catalysts, which are costly and make it difficult to achieve highly selective conversion into fuel under mild conditions.
Using ZSM-5 molecular sieve as a support, catalysts loaded with transition metals chromium or zirconium as active centers are subjected to high-temperature static cracking in a hydrogen atmosphere. The reaction temperature is below 300℃, the catalyst loading is low, and the products are mainly saturated alkanes in the gasoline range.
It achieves efficient conversion of polyethylene into saturated alkanes within a highly selective gasoline range under low temperature and low pressure conditions. The catalyst is low-cost, the reaction energy consumption is low, the yield is as high as 70% or more, and it is safe and environmentally friendly.
Smart Images
Figure CN118460234B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of waste plastic treatment technology, specifically relating to a method and application of waste plastic hydrogenation catalytic cracking oil refining technology. Background Technology
[0002] In recent years, the large-scale production of plastic materials has resulted in significant waste. Currently, the most common types of plastics are resins and fibers, including: high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), polyethylene terephthalate (PET), PUR resin, and polyester (polyester), polyamide (nylon), and acrylic (acrylic) fibers (PP&A). Among these materials, polyethylene accounts for the largest share of total production.
[0003] The increasing trend of waste plastics and their associated negative environmental impacts have attracted much attention, leading to various solutions for their disposal, recycling, and reuse. Plastics are made from non-renewable resources (petroleum), and their biodegradation process is relatively slow; some plastics are even non-biodegradable. For most plastic applications, products have a lifespan of only a few months. Aside from a small portion that is recycled and reused, the vast majority is disposed of through open incineration and unsanitary waste landfills. Landfilling or incineration is relatively suitable, but its facilities are expensive, and incineration emits a range of harmful gases such as NOx, SOx, and COx, as well as some carcinogens (polycyclic aromatic hydrocarbons (PAHs), which, due to their low volatility and biodegradability, can bioaccumulate once ingested), posing public and environmental health risks. Landfilling, on the other hand, shortens the design life of waste treatment facilities such as landfills.
[0004] Pyrolysis, as an emerging and promising treatment method, is gaining popularity among most researchers. It is an effective way to extract fuel from plastic waste and the best way to manage waste plastics and achieve environmental sustainability. Ideally, the high-temperature pyrolysis process can transform waste plastics into commercially available oil products, which can be used as alternative fuels for internal combustion engines to reduce fossil fuel consumption.
[0005] Unfortunately, pyrolysis is still in the research and development stage and has not yet been widely adopted. Currently, the main methods for treating plastic waste are landfill and incineration, which recover less than 50% of the plastic. Many researchers have proposed a series of methods for plastic pyrolysis, but these methods require high temperatures and have poor product selectivity. A few researchers have added catalysts to pyrolysis to improve the reaction efficiency, but the active centers are mostly precious metals, which are expensive and impractical for industrial application. In summary, existing technologies require further exploration to treat waste plastics in a relatively gentle manner and achieve high product selectivity. Summary of the Invention
[0006] In view of the current shortcomings in plastic processing, the purpose of this invention is to provide a method and application of hydrogenation catalytic cracking refining technology for waste plastics. The method can convert plastics into crude oil in a relatively safe and environmentally friendly manner, with a low reaction temperature and significant catalyst effect.
[0007] To achieve the above objectives, the present invention adopts the following technical solution:
[0008] This invention provides a method for hydrogenation catalytic cracking of waste plastics for oil refining, comprising two steps: catalyst synthesis and reaction process.
[0009] The catalyst is supported by ZSM-5 molecular sieve, and the active center is one or two transition metals.
[0010] The reaction process is a high-temperature static pyrolysis process in a hydrogen atmosphere, where plastic and catalyst are mixed.
[0011] As a further preferred embodiment of the technical solution of the present invention, the active center of the catalyst, in terms of mass fraction loading, has a content of only one transition metal between 1% and 8%; when two transition metals are loaded, the sum of their contents is between 1% and 8%.
[0012] As a further preferred embodiment of the technical solution of the present invention, the catalyst support ZSM-5 molecular sieve has a silicon-to-aluminum ratio of 10 to 100.
[0013] As a further preferred embodiment of the technical solution of the present invention, the active center of the catalyst is one or a combination of two of the transition metal elements chromium or zirconium.
[0014] As a further preferred embodiment of the technical solution of the present invention, the transition metal element chromium is obtained by dissolving chromium nitrate nonahydrate in water and decomposing it; the transition metal element zirconium is obtained by dissolving zirconium nitrate pentahydrate in water and decomposing it.
[0015] This invention provides a method for preparing the above-mentioned catalyst, comprising the following steps:
[0016] ZSM-5 molecular sieve was added to deionized water and stirred until homogeneous; then metal salt loaded with transition metal was added and stirred again until homogeneous to obtain solution 1.
[0017] Solution 1 was heated in a water bath for a period of time while being stirred at a constant speed. After heating was completed, solution 2 was obtained.
[0018] Solution 2 was dried and calcined to obtain the finished catalyst;
[0019] The specific steps of the drying and calcination process are as follows: the obtained solution 2 is placed on a rotary evaporator equipped with a water bath, the temperature of the water bath is raised to 50-80 degrees Celsius, and the solution 2 is simultaneously evaporated by rotation for 10-120 minutes; then the obtained solid is dried at 60-120 degrees Celsius for 2-6 hours, and after drying, it is calcined at 400-600 degrees Celsius for 2-8 hours to obtain the finished catalyst.
[0020] This invention provides a specific application of the above-mentioned catalyst mixed with plastic in a catalytic cracking reaction process, wherein the plastic component is polyethylene.
[0021] As a further preferred embodiment of the technical solution of the present invention, the reaction process is carried out in a high-pressure reactor equipped with a quartz liner. The pressure of the hydrogen atmosphere during the reaction is between 0.5 MPa and 2 MPa; the temperature during the reaction is between 250 and 300°C.
[0022] The product oil is separated from the catalyst by dissolving it in an organic solvent.
[0023] The product oil is separated from the catalyst by dissolving it in an organic solvent. The mixture of product oil and organic solvent is then dried in an oil bath at 10–50 degrees Celsius for 2–6 hours to obtain the product oil.
[0024] Compared with the prior art, the present invention has the following beneficial effects:
[0025] (1) The catalyst in this invention can directly catalytically crack polyethylene to produce saturated alkanes in the gasoline range.
[0026] (2) The catalyst in this invention directly catalytically cracks polyethylene into liquid products with high yield, and the highest yield can reach 70%+.
[0027] (3) The catalyst in this invention directly catalytically cracks polyethylene into liquid products, and the yield of saturated alkanes in the gasoline range is the highest, all of which are 80%+.
[0028] (4) The active center on the catalyst in this invention is a transition metal, which effectively reduces the cost of the catalyst compared to the active center of noble metal.
[0029] (5) In the catalytic cracking process of polyethylene in this invention, the catalyst accounts for a low proportion in the reaction mixture. A small amount of catalyst can achieve good results. By mass fraction, the proportion of transition metals loaded on the catalyst relative to polyethylene is less than 0.3%.
[0030] (6) The reaction process temperature in this invention is below 300 degrees, which is much lower than the decomposition temperature of polyethylene itself of 450 degrees, and the energy consumption of the reaction process is low.
[0031] (7) The hydrogen pressure in the reaction process of this invention is lower than 2 MPa, which is lower than the pressure of other current hydrogenation catalytic cracking methods and is safer. Attached Figure Description
[0032] Figure 1 The state of the mixture after the reaction is complete in the absence of a catalyst
[0033] Figure 2 The state of the mixture after the reaction is complete in the presence of a catalyst. Detailed implementation method:
[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0035] This invention provides a method for hydrogenating and catalytically cracking waste plastics to refine oil, comprising two steps: catalyst synthesis and reaction process.
[0036] The catalyst is supported by ZSM-5 molecular sieve, and the active center is one or two transition metals.
[0037] The reaction process is a high-temperature static pyrolysis process in a hydrogen atmosphere, where plastic and catalyst are mixed.
[0038] In the above technical solution, the catalyst is a ZSM-5 molecular sieve supported on transition metals. The reaction of polyethylene on the ZSM-5 molecular sieve catalyst supported on transition metals follows the carbon ion theory and free radical catalytic pyrolysis.
[0039] ZSM-5 molecular sieves provide protons for the reaction, which combine with polyethylene and subsequently generate short-chain olefins via the carbocation theory. However, due to the large molecular size, polyethylene cannot directly enter the pores of the ZSM-5 molecular sieve. Therefore, molten polyethylene first undergoes a reaction catalyzed by the active centers on the surface, depolymerizing into products with smaller molecular weights, which then enter the pores for further reaction. Once inside the pores, secondary reactions such as β-fracture, isomerization, and aromatic cyclization occur.
[0040] In the absence of hydrogen, the reaction, due to secondary reactions such as β-cleavage, isomerization, and aromatic cyclization, will ultimately produce unsaturated hydrocarbons such as alkenes and aromatics, which is undesirable. However, under hydrogen pressure, hydrogen will react with the double bonds, greatly reducing the number of unsaturated bonds in the product and thus producing saturated alkane products.
[0041] In some embodiments, the supporting component is selected from one or a combination of two of chromium and zirconium; preferably, the content of the supported monometallic chromium is 1-5%, the content of the supported monometallic zirconium is 1-5%, and the combined content of the supported bimetallic chromium and zirconium is 1-5%.
[0042] In some embodiments, the source of the metallic chromium is chromium ions obtained by dissolving chromium nitrate in water, and the source of the metallic zirconium is zirconium ions obtained by dissolving zirconium nitrate in water.
[0043] In some embodiments, the silicon-to-aluminum ratio of the ZSM-5 molecular sieve is 10 to 100; preferably, the silicon-to-aluminum ratio is 20 to 40.
[0044] This invention provides a method for synthesizing a catalyst for the hydrogenation catalytic cracking of polyethylene, comprising the following steps:
[0045] Add ZSM-5 molecular sieve to deionized water and stir until homogeneous;
[0046] Add the metal salt of the transition metal and stir again until homogeneous to obtain solution 1;
[0047] Solution 1 was heated in a water bath for a period of time while being stirred at a constant speed. After heating was completed, solution 2 was obtained.
[0048] Solution 2 was dried and calcined to obtain the finished catalyst.
[0049] The specific steps of the drying and calcination process are as follows: the obtained solution 2 is placed on a rotary evaporator equipped with a water bath, the temperature of the water bath is raised to 50-80 degrees Celsius, and the solution 2 is simultaneously evaporated by rotation for 10-120 minutes; then the obtained solid is dried at 60-120 degrees Celsius for 2-6 hours, and after drying, it is calcined at 400-600 degrees Celsius for 2-8 hours to obtain the finished catalyst.
[0050] This invention provides a reaction process for the hydrogenation catalytic cracking of polyethylene, in which the above-mentioned catalyst is mixed with plastic for catalytic cracking, wherein the plastic component is polyethylene, and the reaction process is carried out in a high-pressure reactor equipped with a quartz liner.
[0051] In some embodiments, the ratio of plastic to catalyst in the reaction mixture is 10:1 to 50:1, and the transition metal on the catalyst accounts for only 0.01 to 0.1% of the mass of the plastic.
[0052] In some embodiments, the temperature range during the reaction process is between 250 and 300 degrees Celsius, with a preferred reaction temperature of 280 degrees Celsius; the pressure range is between 0.5 MPa and 2 MPa, with a preferred pressure range of between 0.5 MPa and 1 MPa; and the duration is between 6 hours and 24 hours, with a preferred duration of 8 hours and 12 hours.
[0053] In some embodiments, the selected organic solvent is a polar organic solvent with a low boiling point, and dichloromethane is a preferred organic solvent.
[0054] In some embodiments, the product oil is further separated from the organic solvent by evaporating the organic solvent in an oil bath at 10–50 degrees Celsius for 2–6 hours, with a preferred temperature of 45 degrees Celsius, to finally obtain the product oil.
[0055] The following specific embodiments further illustrate the catalyst for catalytic cracking of waste plastics to produce olefins, its preparation method, and its application.
[0056] Example 1
[0057] A method for synthesizing a catalyst for the hydrogenation catalytic cracking of polyethylene, comprising:
[0058] 1g of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 26, 0.312g of Cr(NO3)3·9H2O, and 0.047g of Zr(NO3)4·5H2O were added to 100ml of deionized water and stirred until homogeneous to obtain solution 1. Solution 1 was placed in an 80°C water bath for 6 hours while being stirred at a constant speed of 500rpm to obtain solution 2. After stirring, solution 2 was placed on a rotary evaporator equipped with a water bath. The temperature of the water bath was raised to 70°C and maintained for 30 minutes to evaporate the deionized water in the solution. Then, it was placed in an oven to dry for 2 hours. After drying, it was calcined in a muffle furnace at 500°C for 5 hours to obtain the finished 4%Cr-1%Zr / ZSM-5 catalyst.
[0059] 0.05g of the synthesized 4%Cr-1%Zr / ZSM-5 catalyst and 1g of polyethylene wax were placed in a quartz liner and stirred. The quartz liner containing the catalyst and polyethylene wax mixture was placed in a high-pressure reactor with a stirrer. The reactor was purged with hydrogen ten times to create a hydrogen atmosphere, and then 0.5MPa hydrogen gas was introduced. The reactor was heated to 280 degrees Celsius and subjected to a static reaction for 12 hours. After the reaction was completed, 40ml of dichloromethane was added to the reactor, and the reactor was heated to 80 degrees Celsius again and stirred for 10 minutes at a rate of 400rpm. After the reaction was completed, the mixture was filtered, and the filtrate was placed in an oil bath at 47 degrees Celsius for 3 hours. The final filter cake was a solid product, and the filtrate residue was a liquid product.
[0060] Example 2
[0061] A method for synthesizing a catalyst for the hydrogenation catalytic cracking of polyethylene, comprising:
[0062] 1g of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 26, 0.234g of Cr(NO3)3·9H2O, and 0.094g of Zr(NO3)4·5H2O were added to 100ml of deionized water and stirred until homogeneous to obtain solution 1. Solution 1 was placed in an 80°C water bath for 6 hours while being stirred at a constant speed of 500rpm to obtain solution 2. After stirring, solution 2 was placed on a rotary evaporator equipped with a water bath. The temperature of the water bath was raised to 70°C and maintained for 30 minutes to evaporate the deionized water in the solution. Then, it was placed in an oven to dry for 2 hours. After drying, it was calcined in a muffle furnace at 500°C for 5 hours to obtain the finished 3%Cr-2%Zr / ZSM-5 catalyst.
[0063] 0.05g of the synthesized 3%Cr-2%Zr / ZSM-5 catalyst and 1g of polyethylene wax were placed in a quartz liner and stirred. The quartz liner containing the catalyst and polyethylene wax mixture was placed in a high-pressure reactor with a stirrer. The reactor was purged with hydrogen ten times to create a hydrogen atmosphere, and then 0.5MPa hydrogen gas was introduced. The reactor was heated to 280 degrees Celsius and subjected to a static reaction for 12 hours. After the reaction was completed, 40ml of dichloromethane was added to the reactor, and the reactor was heated to 80 degrees Celsius again and stirred for 10 minutes at a rate of 400rpm. After the reaction was completed, the mixture was filtered, and the filtrate was placed in an oil bath at 47 degrees Celsius for 3 hours. The final filter cake was a solid product, and the filtrate residue was a liquid product.
[0064] Example 3
[0065] 1g of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 26, 0.234g of Cr(NO3)3·9H2O, and 0.094g of Zr(NO3)4·5H2O were added to 100ml of deionized water and stirred until homogeneous to obtain solution 1. Solution 1 was placed in an 80°C water bath for 6 hours while being stirred at a constant speed of 500rpm to obtain solution 2. After stirring, solution 2 was placed on a rotary evaporator equipped with a water bath. The temperature of the water bath was raised to 70°C and maintained for 30 minutes to evaporate the deionized water in the solution. Then, it was placed in an oven to dry for 2 hours. After drying, it was calcined in a muffle furnace at 500°C for 5 hours to obtain the finished 3%Cr-2%Zr / ZSM-5 catalyst.
[0066] 0.05g of the synthesized 3%Cr-2%Zr / ZSM-5 catalyst and 1g of polyethylene wax were placed in a quartz liner and stirred. The quartz liner containing the catalyst and polyethylene wax mixture was placed in a high-pressure reactor with a stirrer. The reactor was purged with hydrogen ten times to create a hydrogen atmosphere, and then 1MPa of hydrogen gas was introduced. The reactor was heated to 280 degrees Celsius and subjected to a static reaction for 12 hours. After the reaction was completed, 40ml of dichloromethane was added to the reactor, and the reactor was heated to 80 degrees Celsius again and stirred for 10 minutes at a rate of 400 rpm. After the reaction was completed, the mixture was filtered, and the filtrate was placed in an oil bath at 47 degrees Celsius for 3 hours. The final filter cake was a solid product, and the filtrate residue was a liquid product.
[0067] Comparative Example 1
[0068] 1g of polyethylene wax was placed in a quartz liner; the quartz liner containing polyethylene wax was placed in a high-pressure reactor equipped with a stirrer; the reactor was purged with hydrogen ten times to create a hydrogen atmosphere, and then 1MPa of hydrogen was introduced; the reactor was heated to 280 degrees Celsius and a static reaction was carried out for 12 hours; after the reaction was completed, 40ml of dichloromethane was added to the reactor, and the reactor was heated to 80 degrees Celsius again and held for 10 minutes, while stirring at a rate of 400rpm; after the reaction was completed, the mixture was filtered, and the filtrate was placed in an oil bath at 47 degrees Celsius for 3 hours; the final filter cake was a solid product, and the filtrate residue was a liquid product.
[0069] The test results are as follows:
[0070] Table 1 Catalytic cracking yield of the prepared catalyst, wt%
[0071]
[0072] Table 2 Distribution of catalytic cracking products from the prepared catalyst, wt%
[0073]
[0074] As shown in Tables 1 and 2, polyethylene undergoes virtually no cracking reaction in the absence of a catalyst at 280 degrees Celsius. With the addition of a catalyst, the polyethylene conversion rate can reach over 90% under optimal conditions, while the liquid yield is higher than 60%. In the liquid products, alkanes in the gasoline range account for as much as 90%. The results change slightly after altering the loading rate of the transition metal or some reaction conditions, but all of these changes contribute to the catalytic effect of the cracking process.
[0075] In summary, the dual-transition-metal-supported ZSM-5 catalyst of this invention is an excellent catalyst for the catalytic cracking of polyethylene into liquid products, especially achieving the highest yield of alkanes in the gasoline range. Under suitable conditions, this catalyst can catalytically crack polyethylene to produce more than 54% of alkanes in the gasoline range; at the same time, the use of transition metals as the active center in the dual-metal-supported ZSM-5 catalyst effectively reduces the cost of the catalyst.
[0076] The present invention has been illustrated through the above embodiments, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of individual raw materials in the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.
Claims
1. A method for refining oil through hydrogenation catalytic cracking of waste plastics, characterized in that, It includes two steps: catalyst synthesis and reaction process. The catalyst is supported by ZSM-5 molecular sieve, and the active centers are chromium and zirconium from transition metals; the molar ratio of SiO2 to Al2O3 in the ZSM-5 molecular sieve support is 10 to 100. ZSM-5 molecular sieve was added to deionized water and stirred until homogeneous; then metal salt loaded with transition metal was added and stirred again until homogeneous to obtain solution 1. Solution 1 was heated in a water bath for 4 to 10 hours with stirring. After heating, solution 2 was obtained. The obtained solution 2 is placed on a rotary evaporator equipped with a water bath. The temperature of the water bath is raised to 50-80 degrees Celsius, and solution 2 is evaporated by rotary evaporation. This process lasts for 10-120 minutes. Then, the obtained solid is dried at 60-120 degrees Celsius for 2-6 hours. After drying, it is calcined at 400-600 degrees Celsius for 2-8 hours to obtain the finished catalyst. The reaction process is carried out in a hydrogen atmosphere, where plastic and catalyst are mixed and cracked to obtain the product oil; the pressure of the hydrogen atmosphere is between 0.5 MPa and 2 MPa; and the temperature of the cracking process is between 250 and 300°C.
2. The method for refining oil by hydrogenation catalytic cracking of waste plastics according to claim 1, characterized in that, The active centers of the catalyst, when loaded with two transition metals, have a combined content between 1% and 8% by mass fraction.
3. The method for hydrogenating and catalytic cracking waste plastics to refine oil according to claim 1, characterized in that, The transition metal element chromium is obtained by dissolving chromium nitrate nonahydrate in water and decomposing it; the transition metal element zirconium is obtained by dissolving zirconium nitrate pentahydrate in water and decomposing it.
4. The method for hydrogenating and catalytic cracking waste plastics to refine oil according to claim 1, characterized in that, The plastic component in the reaction process is polyethylene.
5. The method for hydrogenating and catalytic cracking waste plastics to refine oil according to claim 1, characterized in that, The reaction process is carried out in a high-pressure reactor lined with quartz.
6. The method for refining oil by hydrogenation catalytic cracking of waste plastics according to claim 1, characterized in that, The product oil is separated from the catalyst by dissolving it in an organic solvent.
7. The method according to claim 6, characterized in that: The mixture of the product oil and organic solvent is dried by evaporating the organic solvent in an oil bath at 10-50 degrees Celsius for 2-6 hours, finally obtaining the product oil.