Catalytic pyrolysis of plastic wastes in a continuous microwave assisted pyrolysis system for fuel production

The soaring use of plastics has resulted in alarming issues such as environmental pollution and unsustainable production of plastics. Pyrolysis of plastic wastes has emerged as a promising chemical recycling method, to recover energy and materials from this resource. In this study, the pyrolysis of plastic wastes was conducted in a novel, continuous, microwave-assisted pyrolysis (CMAP) system for fuel production; the effects of temperature, plastic composition, and catalysis on the product yields and composition were investigated. Higher pyrolysis temperatures promoted the cracking of wax and production of lighter and more stable hydrocarbons. Talc as a plastic filler in polypropylene showed a high cracking activity. Incorporating ZSM-5 catalysts at a weight hourly space velocity of 10 h⁻¹ and a pyrolysis temperature of 620 °C resulted in a liquid yield of 48.9%, and this product consisted of 73.5% gasoline-range hydrocarbons rich in aromatic (45.0%) and isomerized aliphatic (24.6%) contents. The catalyst rapidly lost its activity at a feedstock/catalyst ratio of 5. Energy balance analysis showed that 5 MJ of electrical energy was required to process 1 kg of HDPE with the CMAP system, giving an energy efficiency as high as 89.6% 6.1 MJ electrical energy could be generated from the gas products alone, making the process energy self-sufficient. Overall, the CMAP system, featuring a combination of microwave heating with a SiC mixing-ball-bed, is a promising design for industrial application of energy recovery from plastic wastes due to its advantages, including: 1) higher energy efficiency, and 2) lower processing temperature than conventional fluidized-bed reactors.