Catalytic thermal degradation system

The effect of local activation accounts for such features of PCSs as catalytic and stabilizing properties, autocatalysis, specific properties of thermal degradation, structural modification, and a number of other phenomena typical of polymers with a system of conjugated bonds. 

The choice of the appropriate catalyst system will have an impact on the potential formation of the heavy polymers and coke. Cracking the high molecular weight precursors catalytically will significantly reduce the possibility of thermally degrading these components. The zeolite activity should be optimized in combination with an active matrix selective to upgrading the heavy feed components. 

A number of two-step processes (thermal and catalytic treatments) have been reported in the patent literature for the conversion of plastic wastes. Fukuda et a/.48 have proposed the thermal degradation of polyolefinic plastics in a stirred reactor at 420-470 °C, the volatile products being subsequently passed through a fixed bed reactor at 250-340 °C, containing a ZSM-5 zeolite catalyst. The process developed by Lechert et al49 also consists of a two-reactor system plastics are first pyrolysed above 600 °C in a sand fluidized bed reactor, and the gases produced are catalytically converted over ZSM-5 zeolite at 350-410 °C in a fixed bed reactor to increase the overall yield of liquid products. 

Conventional organie systems are based on the acid catalysed dehydration of carbonifics sueh as dipentaerythritol. Metal oxides also have a use as catalytic flame retardants. For example, both antimony and tin have been used to impart flame retardancy to cellulosics without any assistanee from halogen eompounds. They appear to alter the condensed phase thermal degradation pathways in such a way that more non-volatile ehar and less flammable gases are generated. It has been found that low levels of potassium biearbonate significantly modify the pyrolysis kinetics of a cellulose to yield more ehar. 

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