Recycling paraffin and olefins: Many plastics are pyrolyzed to form paraffinic or olefinic hydrocarbon gases, the amount of which varies greatly depending on the type of plastic. In the thermal decomposition of plastics such as polyethylene and polystyrene, such a gas is formed in a large amount, and as the reaction temperature increases, gaseous products increase and liquid products become less.
1 Decompose the oil. The low-density polyethylene is thermally decomposed at 4200 C for 2 h, and its product contains 60% of paraffin and 40% of olefin. For example, high-density polyethylene is continuously introduced into the reaction system by a melter, and is thermally decomposed at 400 to 4,500 C to obtain 94.5% of the decomposed oil and 5.5% of the decomposition gas. The amount of recovery is: propylene>ethylene, propane>methane>n-butane.
In order to increase the yield of the decomposed oil, an autoclave can be used to thermally decompose the polyethylene in an atmosphere of carbon dioxide, carbon monoxide, helium and hydrogen. The reaction temperature is about 340 ° C, and the oilization rate can reach 87% to 93%; Adding water to control local overheating during decomposition also increases the oiling rate. The use of lacquered nickel or Pt-C as a catalyst to hydrolyze the polyethylene, the oiling rate can reach 85% to 90%.
The decomposed oil of polypropylene which is thermally decomposed and recovered at about 4000C can reach 95%. If the polypropylene is hydrodecomposed in an autoclave using zinc chloride as a catalyst, a decomposition oil having an octane number of 83 can be obtained at 64%. This oil can be used as a gasoline in its entirety; if it is hydrolyzed by adding water, a decomposing oil having an octane number of 86 can be obtained, but the olefin content is 40%. The decomposition gas contains the most methane, followed by ethane and propane.
1 Decompose the gas. The thermal decomposition gasification reaction is mostly used for recovering olefin gas, and ethylene can be recovered from polyethylene, and propylene is mainly recovered from polypropylene.
2 The polyethylene is continuously introduced into the reaction system by a melting furnace, and is thermally decomposed at 590 to 8000 C, and the gasification rate is 75%. At about 7000 C, 32% of ethylene can be obtained, and propylene and butene-1 are added in total. Up to 58%. If a molten salt thermal decomposition furnace is used, the decomposition temperature is increased to 850 ° C, then ethylene can be obtained 30%, propylene is 17%, olefins can be obtained 60%; under the action of the catalyst, it is 2-7 faster than the thermal decomposition without the catalyst. Times. At 4800C, the order of catalyst activity versus gasification rate is (from large to small). SiO2·aL2O3, CaX, NaX, NaY, Caa, Naa.
The polypropylene is decomposed at 500-6000 C, and the gasification rate increases with the increase of the reaction temperature. At 6000 C, propylene is obtained 26%, followed by ethylene and methane. When a molten salt thermal decomposition furnace is used, the decomposition temperature is about 9000 C, from which 20% of ethylene, 20% of methane and only 10% of propylene are obtained. Similarly, the solid acid catalyst can be used to catalytically decompose polypropylene, that is, using silica and alumina as catalysts, using a fluidized bed type atmospheric pressure reactor, mainly generating methane at 4500 C, followed by propylene and ethane. The amount of liquid paraffin formed is greater than when no catalyst is present.
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