Methods for Plastics Pyrolysis

Normal fixed-bed Melting fixed-bed Sand fixed-bed 

Melted Waste Plastics Flow through catalyst layer 

In the process of catalytic cracking, characteristic reactions such as chain scission, hydrogen transfer and condensation take place under certain temperature and pressure conditions and when an appropriate catalyst is utilized, products with certain range of molecular weights and structures are obtained. Catalysts with surface acid sites and with the ability of hydrogen ion donation such as silica-alumina and molecular sieve catalyst have been already widely utilized. These catalysts can also enhance the isomerization of products and increase the yield of isomeric hydrocarbons. However, large amounts of coke will deposit on the surface of catalysts and consequently lead to their deactivation. Therefore, the recycling of catalysts is difficult to achieve. 

Pyrolysis in supercritical water [67, 68] owing to the many special characteristics of supercritical water, waste plastics can be degraded efficiently in supercritical water, which has recently received great attention has been studied comprehensively. This technology can not only realize the recovery of valuable products from waste plastics, but also provide a solution to the ever-growing energy crisis and environmental pollution. No catalysts or reaction agents are needed here, so the cost is very low. 

Coliquefaction with coal [69-71] in the process of coal and waste plastics coliquefaction, the hydrogen atoms contained in plastics transfer from plastics to coal, leading to partial or even total liquefaction of coal. On the one hand, as hydrogen donors, plastics can reduce the hydrogen consumption for coal coliquefaction dramatically. On the other 

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There are mainly three methods for pyrolysis of plastics, namely thermal cracking, catalytic cracking, and cracking-catalytic reforming [62]. Each has its own suitable process, as shown in Figure 28.2. Other methods for plastics pyrolysis include hydrogenation... 

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