Microwave Pyrolysis of Automotive Polypropylene Based on a Microwave Atmosphere Tube Furnace

Plastics have light weight and excellent performance, which are widely used in all kinds of automobiles. Polypropylene (PP) and its reinforcing materials are used in automotive components, where the surfaces of bumpers and fenders are coated with paint. Traditional recycling can frequently generate various pollutants, such as paint sludge. Microwave pyrolysis is a more environmentally friendly pyrolysis method with a higher heating coefficient than traditional electric pyrolysis. This study first explores the elemental composition of two types of automotive PP plastics and uses thermo-gravimetric analysis and the Kissinger-Akahira-Sunose method to preliminarily calculate the activation energy of automotive PP. The calculation results show that the activation energy of PP containing paint ranges from 189.145 kJ/mol- 199.513 kJ/mol, with an average value of 193.903 kJ/mol. The activation energy of PP without paint is between 215.506 kJ/mol-265.794 kJ/mol, with an average value of 242.425kJ/mol. Then, pyrolysis experiments on PP for vehicles without paint are conducted using a microwave atmosphere tube furnace at different temperatures and microwave powers. The experimental results showed that, when the pyrolysis temperature increased from 500oC to 620 oC, the total proportion of gas products rose from 0.75 wt.% to 4.81 wt.%, and the content of alkanes in the liquid products improved from 26.21 wt.% to 34.37 wt.%; when the microwave power increased from 900 W to 1100 W, the gas product rose to 20.77 wt.%, and the content of aromatic compounds in the liquid product improved to 17.78 wt.%. In addition, the pyrolysis experiment of automotive PP containing paint showed that paint had a relatively minor effect on the pyrolysis products of automotive PP. This study shows that using microwave pyrolysis to treat automotive PP and PP with paint is feasible, which provides a reference for the clean treatment of automotive polymers.