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

•Microwave co-pyrolysis of waste cooking oil and waste polyolefins is performed.•The influence of using vacuum environment is compared to N2 atmosphere.•Vacuum pyrolysis shows higher heating rate, final temperature, yield of liquid oil.•Liquid oil contains C13-C24 hydrocarbons in diesel range with high energy content.•Liquid oil is potentially cleaner (free of sulphur, low in nitrogen and oxygen). 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 (