Deactivation and regeneration of ZSM-5 zeolite in catalytic pyrolysis of plastic wastes

In this work, a study of the regeneration and reuse of ZSM-5 zeolite in the pyrolysis of a plastic mixture has been carried out in a semi-batch reactor at 440 °C. The results have been compared with those obtained with fresh-catalyst and in non-catalytic experiments with the same conditions. The use of fresh catalyst produces a significant change in both the pyrolysis yields and the properties of the liquids and gases obtained. Gases more rich in C3–C4 and H2 are produced, as well as lower quantities of aromatic liquids if compared with those obtained in thermal decomposition. The authors have proved that after one pyrolysis experiment the zeolite loses quite a lot of its activity, which is reflected in both the yields and the products quality; however, this deactivation was found to be reversible since after regeneration heating at 550 °C in oxygen atmosphere, this catalyst recovered its initial activity, generating similar products and in equivalent proportions as those obtained with fresh catalyst.

► Pyrolysis transforms plastic wastes in valuable liquids and gases useful as fuels or source of chemicals.
► The use of ZSM-5 zeolite in pyrolysis favours the production of gases and of lighter and more aromatic liquids.
► ZSM-5 zeolite is almost completely deactivated after one plastics pyrolysis experiment.
► ZSM-5 zeolite used in plastic wastes pyrolysis can be regenerated by burning the deposited coke in an air stream.
► Regenerated ZSM-5 recovers its activity and produces liquids and gases equivalent to those obtained with fresh catalyst.