Degradation of polyethylene and polypropylene into fuel oil by using solidacid and non-acid catalysts

The thermal and catalytic degradation of plastic polymers, polyethylene (PE ) at 430 degrees C and polypropylene (PP) at 380 degrees C into fuel oil we re carried out by batch operation. The catalysts employed were acid-catalys ts silica-alumina (SA-1, SA-2), zeolite ZSM-5 and non acidic mesoporous sil ica catalysts (silicalite, mesoporous silica gel and mesoporous folded sili ca (FSM). The yields of product gas, liquid and residues; recovery rate of liquid products, and boiling point distribution of liquid products by catal ytic degradation were compared with those of non-catalytic thermal degradat ion. The present work is divided into three sections: (1) a study of effect of catalytic contact mode and (2) a study of effect of types of catalysts on plastic degradation, and (3) the evaluation of catalysts during the degr adation of PE and PP by repeating batch operation. For PP degradation in li quid phase contact with SA-1, the yield of liquid hydrocarbons was obtained with 69 wt.%, and the boiling point (bp) of the oil ranged between 36 and 270 degrees C, equivalent to the bp of normal paraffins n-C-6 to n-C-15. Th e liquid products from catalytic degradation have a carbon number distribut ion very similar to commercial automobile gasoline. For vapor phase contact , the yield of liquid products was much lower (54%) and the rate of liquid recovery (or formation) was much slower. Catalysts possessing strong acid s ites such as zeolite ZSM-5 accelerated the degradation of PP and PE into ga ses which resulted in low liquid yields. For FSM, which possesses no acid s ites, the initial rates of PP and PE degradation into liquid were as fast a s that over an acid catalyst (SA-1) and the liquid yields were higher. The liquid products from catalytic degradation over FSM have a carbon number di stribution similar to a mixture of kerosene and diesel oil. Upon repeated u se SA-1 deactivated very rapidly due to coke deposition on the catalyst, wh ereas FSM deactivated much more slowly. These findings concerning the FSM c atalyst strongly suggest that the mesopores surrounded by the silica sheet may act as reservoir for radical species and the radical species accelerate the degradation of plastic melt. (C) 1999 Elsevier Science B.V. All rights reserved.