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What are the byproducts of degraded plastic wrap?
Release time:
2021-04-22
Recycling wax and olefins from preservation bags: Many preservation bags can produce paraffinic or olefinic hydrocarbon gases through high-temperature decomposition. The amount produced varies greatly depending on the type of plastic. Plastics such as polyethylene and polystyrene produce large amounts of this gas during thermal decomposition. Moreover, as the reaction temperature increases, the amount of gaseous products increases, while the amount of liquid products decreases.
Recycling paraffin wax and olefins from plastic bags: Many plastic bags can produce paraffin or olefin hydrocarbon gases after high-temperature decomposition. The amount produced varies greatly depending on the type of plastic. The thermal decomposition of plastics such as polyethylene and polystyrene produces a large amount of this gas, and the amount of gaseous products increases with increasing reaction temperature, while the amount of liquid products decreases.
Plastic bag decomposition oil. When low-density polyethylene is thermally decomposed at 420°C for 2 hours, paraffin accounts for 60% and olefins for 40% of the products. If high-density polyethylene is continuously fed into the reaction system using a melter and thermally decomposed at 400-450°C, 94.5% decomposition oil and 5.5% decomposition gas can be obtained. The recovery amounts are: propylene > ethylene, propane > methane > n-butane.
To improve the yield of decomposition oil, a high-pressure reactor can be used to thermally decompose polyethylene in an atmosphere of carbon dioxide, carbon monoxide, helium, and hydrogen. The reaction temperature is around 340°C, and the oil yield is as high as 87%–93%; adding water to control local overheating during decomposition can also improve the oil yield. Using lacquer nickel or Pt-C as a catalyst to hydrogenolyze polyethylene can achieve an oil yield as high as 85%–90%.
Polypropylene plastic bags, when thermally decomposed around 400°C, yield up to 95% decomposition oil. If zinc chloride is used as a catalyst for catalytic hydrogenolysis of polypropylene in a high-pressure reactor, decomposition oil with an octane rating of 83 can be obtained with a yield of 64%. This oil is completely suitable for use as gasoline; if water is added during catalytic hydrogenolysis, decomposition oil with an octane rating of 86 can be obtained, but the olefin content is 40%. Methane is the most abundant component in the decomposition gas, followed by ethane and propane.
Plastic bag decomposition gas. Thermal decomposition gasification reactions are mostly used to recover olefinic gases. Ethylene can be recovered from polyethylene, and propylene is mainly recovered from polypropylene.
Using a melting furnace to continuously feed polyethylene into the reaction system, thermal decomposition is carried out at 590–800°C, with a gasification rate of 75%. At around 700°C, 32% ethylene can be obtained, and the total amount of ethylene, propylene, and butene-1 reaches 58%. If a molten salt thermal decomposition furnace is used and the decomposition temperature is increased to 850°C, 30% ethylene and 17% propylene can be obtained, with a total of 60% olefins. With the aid of catalysts, the thermal decomposition is 2–7 times faster than without catalysts. At 480°C, the order of catalyst activity on gasification rate (from high to low) is: SiO2·Al2O3, CaX, NaX, NaY, CaA, NaA.
When polypropylene plastic bags are decomposed at 500–600°C, the gasification rate increases with the reaction temperature. At 600°C, 26% propylene can be obtained, followed by ethylene and methane. When using a molten salt thermal decomposition furnace, the decomposition temperature reaches about 900°C, and 20% ethylene, 20% methane, and only 10% propylene can be obtained. Similarly, solid acid catalysts can be used for catalytic decomposition of polypropylene. Using silica and alumina as catalysts in an atmospheric fluidized bed reactor, at 450°C, the main product is methane, followed by propylene and ethane. The amount of liquid paraffin produced is higher than that without a catalyst.
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