Low chlorine oil production through fast pyrolysis of mixed plastics combined with hydrothermal dechlorination pretreatment

Abstract

Fast pyrolysis of the mixed plastics (PE: PP: PS: PVC = 0.5: 0.3: 0.15: 0.05) with and without hydrothermal dechlorination pretreatment were investigated in a fixed bed reactor to determine the effects of pyrolysis parameters (temperature, carrier gas flow rate and particle size) on the distribution and the quality of the products. The results showed that high pyrolysis temperature, high carrier gas flow rate and small particle size promoted the migration of organic chlorine in condensable products to inorganic chlorine in gas products. And the optimal conditions for fast pyrolysis of mixed plastics to produce oil were the pyrolysis temperature of 500 °C, carrier gas flow rate of 40 ml/min and particle size of 0.1–0.15 mm with the maximum oil yield of 67.88 wt%. Hydrothermal pretreatment of mixed plastics has shown an excellent dechlorination efficiency of 99.9 %. Furthermore, the total yield of oil and wax was increased by 7.06 wt%, meanwhile the content of C5-C9 components in the pyrolysis oil showed an upward trend when compared with fast pyrolysis without pretreatment. Besides, the concentration of methane achieved 50.68 % due to the possible weakening effect of hydrothermal pretreatment on CC bond energy of β-position.