Depolymerization of waste plastics with coal over metal-loaded silica-alumina catalysts

Catalytic effects of various hydrogenation-hydrocracking catalysts on the coliquefaction of coal with high-density polyethylene (HDPE) and commingled plastic were systematically investigated under typical liquefaction conditions: 430 degrees C, 2000 psig H-2 for 1 h. Silica-alumina impregnated with Pt, Ni, Pd, or Fe showed higher catalytic activities for oil conversion than did metal-free catalysts. Apparently, the hydrogenation function was created on active metal sites while hydrocracking took place on active sites on silica-alumina High total conversions were obtained even without a solvent added. Product analyses and characterization have assisted in the determination of reaction pathways and possible mechanisms. Ni K-edge extended X-ray absorption near-edge spectroscopy (EXANES) and extended X-ray fine structure spectroscopy (EXAFS) show that Ni is present as NiO with nanoscale particles. In this study, two-stage processing of coal with HDPE was also investigated. Very high total conversions (up to 92%) were obtained while using this technique.