Microwave co-pyrolysis of waste polyolefins and waste cooking oil: Influence of N2 atmosphere versus vacuum environment

Abstract

Microwave co-pyrolysis (MCP) of waste cooking oil (WCO) and waste polyolefins (WP) was examined for its potential to convert these wastes into liquid fuel. The influence of performing the pyrolysis process under N2 atmosphere and vacuum environment was investigated with emphasis on the temperature profile, heating rate, and the yield and properties of the liquid oil obtained. Different ratios of WP to WCO (1:2, 1:1.5, 1:1, 1.5:1, and 2:1) were also investigated. MCP performed under vacuum environment recorded higher heating rates (20–24 °C/min) and higher yield of liquid oil (up to 62 wt.%) compared to that performed under N2 atmosphere (18–22 °C/min of heating rate and 24–50 wt.% of liquid oil). The high heating rate resulted in shorter reaction time and lower power consumption, leading to lower energy consumption by the pyrolysis process. The liquid oil comprised C13–C24 hydrocarbons (aliphatics, aromatics) within the hydrocarbon range of diesel fuel. It also showed promising green properties comprising low nitrogen and oxygen content, and free of sulphur. Combined with the detection of high energy content (42–49 MJ/kg) and low moisture content (<1 wt.%), the liquid oil shows great potential to be used as a fuel. Our results show that MCP performed under vacuum environment shows potential as a promising pyrolysis approach with improved heating performance and production of hydrocarbon fuel with desirable fuel properties.