Study of the early deactivation in the catalytic pyrolysis of polymers

Abstract

The fast growth of the range of applications of plastics: packaging, agriculture, construction, household, etc. has turned to these materials in the a environmental problem since plastics comprise 10 wt% (>30 vol%) of municipal solid waste. Pyrolysis is one of the promising alternatives to dumping or incineration for the treatment of plastic wastes, where the polymer sample is heated in an inert atmosphere causing the cracking of the polymer backbone. The study of the catalytic pyrolysis of polymers using thermogravimetric analysis (TGA) shows a premature beginning of the process for some polymer-catalyst systems, that provokes a widening of the corresponding peaks in the derivative of TGA curves (DTG curves), and in some cases, the appearance of a shoulder [1]. This premature beginning of the decomposition’s reactions would be related to the acid sites located on the surface of the material [2,3]. The main objective of this work is to carry out a study detailed of such a phenomenon. In this way, TGA studies were carried out, and four cycles of heating-cooling were performed in order to analyse the influence of the first stages of decomposition over the activity of the involved active sites. Three polymers (Polyethylene, PE, polypropylene, PP and an ethylene-vinyl acetate copolymer, EVA) were selected, and MCM-41 was used as a catalyst. The behaviour of polymer-catalyst mixtures (20% w/w of catalyst) was studied and compared with the observed in the corresponding thermal degradation as well as in the conventional catalytic pyrolysis.