Scrap Plastic Pyrolysis Machine Depolymerization reaction
Waste plastic pyrolysis Waste plastic pyrolysis is to have a clear impurities in the plastic placed in an oxygen-free or low-oxygen sealed containers heated to crack into low molecular weight compounds. The basic principle is to plastic products in the polymer to complete the macromolecule cracking, to return to low molecular weight state or single state. According to the different positions of macromolecule bonds, pyrolysis can be divided into depolymerization reaction type, random pyrolysis type and intermediate type. The polymer is dissociated when the depolymerization reaction is heated and pyrolyzed to produce a monomer, which cleaves the chemical bonds between the single molecules. These plastics are α-methylstyrene, polymethyl methacrylate, etc., they are almost 100% cracked into monomers. Random cleavage of plastic when the chemical bonds within the molecular bond is random, resulting in a certain number of carbon atoms and hydrogen atoms combined with molecular compounds, such plastic polyethylene, polypropylene and so on. Most of the plastic cracking of the two, both in the middle, but in the appropriate temperature, pressure, catalyst conditions, which can make some of the specific number of chain length of the product greatly increased, so as to obtain a certain economic value of the product , Such as gasoline, diesel and so on. The temperature required for cracking depends on the type of plastic and the product of the recovered product. If the temperature exceeds 600 ° C, the main product of pyrolysis is mixed fuel gas such as CH4 and C2H4. When the temperature is 400 ~ 600 ℃, the main cracking products are mixed light hydrocarbons, naphtha, heavy oil, kerosene and waxy solid. The cracking products of PE and PP are mainly fuel gas and fuel oil. The pyrolysis products of PS are mainly styrene monomer. Pyrolysis reaction is mainly C-C bond fracture, accompanied by C-H bond breakage, thermal effect for the endothermic process. That is, the outside world must provide greater than the C-C bond energy, the reaction can be carried out smoothly. Therefore, the early plastic pyrolysis methods are simple thermal cracking, that is simply through the heating, so that the waste plastic cracking. However, this method has obvious shortcomings, namely, high energy consumption, low efficiency, selectivity is not strong. Therefore, the rapid development of the catalytic cracking method, in the pyrolysis stage if the catalyst, not only can reduce the reaction required for activation energy, improve efficiency, and can improve the product selectivity, relative to high temperature pyrolysis has obvious advantages. As the use of the catalyst increases the cost, and the catalyst is prone to coke inactivation, and the catalyst itself is not easy to recover. After the people have developed a thermal cracking - catalytic reforming process, making the catalytic pyrolysis process has been further improved. In summary, the waste plastic pyrolysis mainly includes thermal cracking, catalytic pyrolysis, thermal cracking - catalytic modification, which has a different form of technology,
First, the classification of waste pyrolysis(3) by the elimination of substituents or functional groups to produce small molecules, accompanied by the production of unsaturated compounds and polymer crosslinking and even coking (1) by eliminating the substituents or functional groups to produce small molecules, accompanied by the production of unsaturated compounds and polymer cross-linking or coking The The method has the advantages of high pyrolysis reaction temperature, long reaction time, low octane number of gasoline and large amount of olefins, and short induction period. The diesel point is high, the cetane number is low and the wax content is high. The products of thermal decomposition of waste polyethylene are mostly paraffin or α-olefins. The reaction conditions for producing diesel fractions are about 475 ℃, and the reaction time is about 4h under low pressure or atmospheric pressure.