Catalytic conversion of low-density polyethylene using a continuous screw kiln reactor

Abstract

Both thermal and catalytic cracking of low-density polyethylene (LDPE) have been investigated using a screw kiln reactor. Thermal degradation gives rise to a broad product distribution whereas catalytic cracking over Al-MCM-41 leads mainly to hydrocarbons within the gasoline range (C5 ¿ C12) with selectivities up to 80%. The increase of the screw speed between 3 and 15 rpm in the catalytic experiments allows the plastic feed rate to be varied in the range 20 ¿ 41 g/h. The changes observed in the TOF values when varying the screw speed point out a decrease of the activity per site with increasing residence times, which may be due to the catalyst deactivation or to a contribution of the degradative extrusion at higher screw speeds. Likewise, a certain increase in the selectivity towards the gasoline fraction is observed at short residence times. On the other hand, PIONA analyses indicate that, regardless of the screw speed, the main components of the gasoline are olefins (50%) and isoparaffins (20%) whereas the aromatic content is always below 6%, with a proportion of benzene lower than 0.1%.