Catalytic degradation of polyethylene and polypropylene to fuel oil

Thermal and catalytic degradation of plastic polymers, polyethylene and polypropylene to fuel oil were carried out in batch operations. The catalysts employed were acid silica-alumina (SA-I, SA-2) and zeolite ZSM-5, and nonacidic mesoporous silica FSM (folded sheet material). The yields of product gas, liquid and residues, recovery rate of liquid products, and boiling point ranges of liquid products due to degradation were compared with those of non-catalytic thermal degradation. Both the effect of catalytic contact mode and of catalyst type on the degradation were studied. In liquid-phase degradation of PP over SA-1, liquid hydrocarbon products were obtained in a yield of 69 wt.-% with a boiling point range 36-270 degrees C, equivalent to the boiling point of normal paraffins C6 - C15. The liquid products from catalytic degradation have a carbon-number distribution very similar to commercial motor gasoline. In vapor-phase contact, the yield of liquid products was much lower (54 %) and the rate of liquid recovery was much slower. With FSM, the initial rate of degradation of PP and PE to liquid products was as fast as that over acid catalyst SA-1, but the yield of liquid products was higher. The liquid products from catalytic degradation over FSM have a carbon-number distribution similar to kerosene and diesel oil. In repeated use, SA-I deactivated very rapidly due to coke deposition on the catalyst, whereas FSM deactivated much more slowly. These findings suggest that mesopores surrounded by the silica sheet may act as reservoir for radical species, which accelerate the degradation of plastic melt.