Optimization of the process parameters of catalytic plastic pyrolysis for oil production using design of experiment approaches: A review

Catalytic pyrolysis of plastics to produce oil has attracted substantial scientific attention owing to its renewability, environmental sustainability, and cost-effectiveness. This research intended to compare the efficiency of statistical optimization techniques such as response surface methodology (RSM) and the Taguchi method for optimizing catalytic plastic pyrolysis reactions and the parameters’ impact on oil production. The catalyst-to-plastic ratio and various types of acidic catalysts, such as synthetic zeolites and spent fluid catalytic cracking (FCC) catalysts, are the key factors regulating the optimal values of pyrolysis parameters, including reaction temperature (nearly 500 °C) and residence time (15–20 min), as well as oil yield (80–90%). The Lewis and Brønsted acid sites of zeolite or spent FCC or Si/Al enhance the bond breakage of long-chain hydrocarbons. Unlike the acidic sites in zeolites, the acidic sites in Si/Al appear weaker, even though the Taguchi optimization technique indicates that Si/Al is more actively producing oil than zeolite/FCC catalysts. Under similar pyrolysis conditions, polystyrene (PS) thermally breakdowns more efficiently and yields more oil than polypropylene (PP) and polyethylene (PE), as PS contains branched side chains that can break at low temperatures due to their low activation energy for bond-breaking. The order of the contribution of different parameters determined by the Taguchi techniques is catalyst types > plastic types > pyrolysis temperature. Nevertheless, this sequence of parameters contribution could vary depending on the experimental conditions. Non-catalytic pyrolysis has a longer optimal residence time yet yields less oil. RSM has more trials, which makes them more trustworthy techniques.