Conversion of polymers to fuels in a refinery stream

The purpose of this study was to investigate the processability of LDPE, PP, PVC/LDPE and PVC/PP in the hydrocracking unit of a refinery. For this, LDPE or PP has been added to vacuum gas oil (VGO). The blends were hydrocracked over different catalysts using a batch autoclave at 425-450 degreesC under hydrogen atmosphere. The catalysts used were HZSM-5, Cobalt loaded active carbon (Co-Ac) and DHC-8 (commercial silica-alumina catalyst). Addition of polymer to VGO affected the cracking of VGO, leading to a decrease in the gas yield and an increase in the liquid yield. In hydrocracking over HZSM-5, the product distribution was similar for two blends. HZSM-5 gave higher gas yields than the other catalysts. When using Co-Ac and DHC-8 catalysts, the gas and liquid yields depend on the polymer type as well as temperature. In the case of the PVC-containing blends (PVC/PP/VGO or PVC/PE/VGO), the blends were firstly dechlorinated at 350 degreesC. Then the dechlorinated mixture was hydrocracked in the 400-450 degreesC range in the presence of DHC-8. HCl evolved by degradation of PVC during the dechlorination step partially degraded PE and PP and these predegraded polymers were more easily cracked in the hydrocracking step. In addition, we observed the effect of polyene formed from the PVC degradation residue on the thermal hydrocracking. The chlorine compounds in the hydrocracked feed affected the catalytic activity of the catalysts. (C) 2001 Elsevier Science Ltd. All rights reserved.