COLIQUEFACTION OF WASTE PLASTICS WITH COAL

Polyethylene (PE), poly(ethylene terephthalate) (PET), polypropylene (PPE), and actual plastic wastes from such items as milk jugs, soft drink bottles, plastic wraps, plastic flatware, etc., have been successfully converted to oil in direct liquefaction experiments with coal. Comparative experiments were performed with and without the presence of coal under typical direct liquefaction conditions (420-450 degrees C, 60 min reaction time, 800 psig of H-2 cold). Two types of catalysts were used: highly dispersed iron-based catalysts, and an HZSM-5 zeolite catalyst. Using PE, PPE, PET, and a mixed waste plastic with the zeolite catalyst, oil yields of 80-98% and total conversions of 90-100% were obtained at liquefaction temperatures of 420-430 degrees C. A nanoscale ferrihydrite catalyst in a sulfided state was less active but also gave similar results at somewhat higher temperatures. Coliquefaction experiments were performed on coal-plastic mixtures (usually 50:50 mixtures) using a bituminous coal, a subbituminous coal, and a lignite. The HZSM-5 zeolite catalyst and nanoscale iron catalysts were used separately and together. The oil yields for these coliquefaction experiments were as high as 60-80%, while the total conversions reached levels of over 90%. Oil yields for coal-plastic mixtures were higher, typically by similar to 10%, than the average of the oil yields for the coal and plastic alone, implying synergistic effects.