The catalytic pyrolysis of waste polyolefins by zeolite-based catalysts: A critical review on the structure-acidity synergies of catalysts

Polyolefin plastics have become an integral part of human life, but the uncontrolled disposal of waste plastics has led to severe environmental pollution. Therefore, it is crucial to address this issue urgently. Zeolite-based catalysts, known for their exceptional catalytic activity and stability, have gained significant attention in research endeavors. Nevertheless, comparing the performance of different catalysts poses challenges due to variations in reactor types and reaction conditions. This review aims to provide an objective evaluation basis for addressing the catalytic properties of new catalytic materials. Firstly, it summarizes the characteristics of polyolefins and the Brønsted acid induced catalytic pyrolysis process mechanism. Then, the features of different reactors were analyzed, and the influence of key reaction parameters (such as temperature, reaction time, catalyst load and carrier gas flow) on catalytic performance in the most widely studied batch and semi-batch reactors and fixed bed reactors was discussed in detail. By summarizing previous findings, it is found that these parameters exhibit limited impact on the overall conversion of plastic catalytic pyrolysis under common reaction conditions. The review also examines how the structure-acidity synergies influence the catalytic pyrolysis performance of zeolite-based catalysts. Basis of evaluation is established to study the impact of structure-acidity synergies on gas yield, liquid yield, and total conversion using batch or semi-batch reactors. Similarly, evaluation basis is established for fixed bed reactors to examine the effects of structure-acidity synergies on liquid yield, aromatics yield, and BTEX yield.