Pyrolysis of Polyvinyl Chloride (PVC)-Containing Mixed Plastic Wastes for Recovery of Hydrocarbons

摘要

The pyrolysis of mixed plastic waste (high-density polyethylene, polypropylene, polystyrene, and polyvinyl chloride) using a long residence time (25 min) in a horizontal tube reactor at 530 ℃ has been investigated. The reactor was fitted with atmospheric and vacuum distillation columns, so that the pyrolysis products could be separated into heavy oil, light oil, gasoline, and gases. The effect of the polyvinyl chloride (PVC) concentration on the properties of products was investigated. Products were characterized using gas chromatography, infrared spectroscopy, and energy-dispersive X-ray spectroscopy, whereas some other standardized methods were used to determine the main properties of hydrocarbons. Results show that the mixed plastic waste samples could be converted into gases, gasoline, and light oil with yields of 36.9-59.6% depending upon the composition of feed polymers, and the conversion of decomposition is significantly increased with an increasing concentration of PVC. It was found that products mostly consisted of paraffin, olefin, and aromatic compounds, with carbon numbers of C_1 - C_4, C_5-C_7, and C_(11) - C_(28) in the case of gases, gasoline, and light oil, respectively. Light aromatics (benzene, toluene, styrene, ethyl benzene, and xylenes) could be detected only in gasoline, while oligomers of styrene obtained by principal degradation of polystyrene were in heavy oil. Aromatics consist of mainly ethyl benzene and styrene. Gases and heavy oil had high caloric values of 46-47 and about 41 MJ/kg, respectively; therefore, they could also be used for energy generation. The favorable properties of all fractions were depreciated in consequence of increasing PVC content, because the concentration of chlorine increased with that. The highest chlorine content had been measured in gases, wherein the HC1 was the dominant compound, which had succeeded to neutralize in a scrubber filled with a solution of calcium hydroxide.