Benchmarking performance of equilibrium fluid catalytic cracking catalysts in the catalytic cracking of polypropylene

Abstract

With the transition of the chemical industry towards renewable and recycled feedstocks, cracking catalysts are explored for a new application in converting difficult to recycle polyolefin plastics to feeds for the chemical industry. The refining industry generates large volumes of equilibrium fluid catalytic cracking catalysts (ECAT) as waste materials, which might find a secondary end-of-life application as plastic cracking catalyst. Herein, we aim at establishing which ECAT materials are particularly attractive for plastic waste conversion. We screened a broad range of materials selected for both their activity and accessibility. We establish the range of activity which is achievable with this type of catalyst, placing important boundaries on process conditions. We find that an industry standard vacuum gas oil (VGO) cracking activity test, namely the fluid bed simulated test, not only predicts plastic cracking activity, but is also a very good indicator for propylene selectivity. Historical data gathered by industrial researchers might therefore prove highly useful in identifying more active and selective plastic cracking catalysts, offering concrete guidance on catalyst selection. This finding further suggests that the active sites critical for cracking of VGO are of similar importance for plastic cracking. However, we find that various characterization techniques including physisorption, contaminant analysis and determination of external acidity do not offer concrete guidance on catalyst selection. This work therefore demonstrates the limitations of routine catalyst characterization as an indicator of performance, but showcases how established activity metrics can aid in the transition of the chemical industry to recycled feedstocks.