Conversion of waste high-density polyethylene into liquid fuels

Abstract

The present work involves the experimental studies for the production of liquid fuel by thermal and catalytic pyrolysis of waste high-density polyethylene in a laboratory batch reactor. Thermal pyrolysis of virgin HDPE was performed at a temperature range from 400 °C to
550 °C and heating rate of 20 °C/min. The liquid yield is highest 50 wt. % at temperature 450 ºC. Reaction time decreases with increase in temperature. Maximum oil yield in
thermal pyrolysis of waste HDPE was 50.8 wt. % at optimum condition of temperature,which is improved to 58.8 wt. %, in kaolin catalyzed degradation under optimum condition of temperature and feed ratio. The rate of reaction, oil yield and quality of oil obtained in the catalytic pyrolysis are significantly improved as compared to thermal
pyrolysis.The catalytic activity of kaolin is further enhanced by treating it with four different acids and one base (acetic acid, phosphoric acid, nitric acid, hydrochloric acid and sodium hydroxide). Acid treatment increased the surface area, acidity and also alters the pore
volume distribution of kaolin, which support the cracking reaction. The maximum yield of oil in the acid treated kaolin catalyzed pyrolysis of waste HDPE was 79% under
optimum conditions. The composition of the oil was analyzed by FTIR and GC-MS. The oil obtained from the catalytic pyrolysis of waste HDPE mostly contains aliphatic
hydrocarbons. The fuel properties of the oil obtained from the catalytic pyrolysis of waste HDPE is similar with that of petro-fuels. So they can directly be used as an engine fuel after fractionation or as a feedstock to petroleum refineries.Response surface methodology (RSM) was used to optimize the catalytic pyrolysis process of waste high-density polyethylene to liquid fuel over modified catalyst. The reaction temperature, acidity of the modified catalysts and mass ratio between modified catalysts to waste high-density polyethylene (HDPE) were chosen as independent variables. Optimum operating conditions of reaction temperature (450 °C), acidity of catalyst (0.341) and catalyst to waste HDPE ratio (1:4) were produced with respect to