Catalytic and Thermal Cracking Processes Typical Products

1 CATALYTIC AND THERMAL CRACKING PROCESSES TYPICAL PRODUCTS 

The high influence of cracking catalyst on PE conversion was confirmed by Aguado et al. [11] in a continuous screw kiln reactor. The application of a sophisticated laboratory Al-MCM-41 cracking catalyst and process temperature of 400-450°C led to 85-87% yield of gas and gasoline fractions (C1-C12). Besides olefins and n- and iso-paraffins some quantity of aromatics, 5 wt% was determined in the process products. In the same reactor system with a noncatalytic process the gas yield was halved while similarly as in case of the fluid reactor system yields of gas oil and heavy waxes fraction (C13-C55) attained values of 62% (compared with 4 wt% in catalytic process) [12]. 

Increase in thermal process temperature up to 685-715°C in a fluidized-bed system (Hamburg University Pyrolysis Process-HUPP) and application of a mixture of municipal plastic wastes resulted mainly in gaseous products, over 41 wt%, of which olefins constituted 15%, and aromatic (BTX)-containing liquid products [14], Considerably better results from the point of view of C2 and C3 olefins yield were obtained in other experiments. The application of steam as fluidization agent instead of circulation pyrolysis gas enabled an increase of C2-C3 olefins yield from 48 to 60%, accompanied by decrease in BTX yield from 24 to 11 wt% [15], 

Analogous results were achieved in the fluidized-bed system by Williams et al. [16], They found out that raising the PE pyrolysis temperature from 500 to 700°C gives an increase in gas yield from 11 to 71% and that C2-C4 olefins content increases from 7 to above 53%. Hydrogen content in the gaseous fraction attained a level of 1%. At the same time oil and wax yields were diminished from 89 to 28.5 wt% in which 25% was identified as mono- and polyaromatic hydrocarbons. Noticeable quantities of aromatics ( 2.5 wt%) in the products of the process at 600°C were determined (Table 4.1). 

Process temperature, as well as waste polyolefin composition and type of catalyst used are then the most important process parameters. It is evident that a process temperature below 500°C is the most suitable range for refinery fractions while 600°C and higher are appropriate for olefins production. 

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