Comparison of various catalysts in pyrolysis process: A review

Abstract

The existence of polarity between production and recycling rates, as well as extravagant fossil fuel consumption has has led to the development of waste plastic to fuel conversion technology. Pyrolysis technology shows great potential in recovering liquid oil from plastic waste through thermal and catalytic degradation processes. Catalytic pyrolysis process has advantages over thermal degradation in terms of energy consumption, reaction time and oil grade. The choice of catalyst plays a dominant role in determinating reaction temperature, time, and product distribution. This paper reviews various types of catalysts, including fluid cracking catalyst (FCC), zeolites based catalysts, silica-alumina catalysts, and reforming catalysts, and the impact of various parameters include the mode of contact with plastic solid wastes - direct phase contact of catalyst (either liquid or solid), and vapor phase contact of catalyst, choice of catalyst, catalyst to polymer ratio, and acid-base nature of the catalyst on the product dispersion. The product distribution obtained from catalytic pyrolysis of different types of plastics such as polyethylene, polypropylene, polystyrene, polyethylene terephthalate, and polyvinylchloride using ZSM – 5 and red mud catalysts at different temperatures are as follows: 56.9 wt%(liquid), 40.4 wt%(gases), 3.2 wt%(char) at 450 0C in the presence of 10 wt% of Zeolite Socony Mobil − 5 (ZSM – 5) catalyst and 57 wt% (liquid), 41.3 wt% (gases), 1.7 wt% (char) at temperature 500 0C in the presence of 10 wt% of red mud as a catalyst. When catalytic pyrolysis is applied to municipal plastic waste (a heterogenous plastic waste) using 50% natural zeolite as a catalyst at 450 0C the distribution is 50 wt% (liquid), 34 wt% (gases), and 16 wt% of char Although there is a negligible difference in the product distribution of thermoplastics, the use of red mud as a catalyst results in increased energy consumption., highlighting the impact of the acidic and basic characteristics of catalysts. In case of heterogenous feedstock i.e., mixed plastic highly acidic catalysts are used to achieve the desired product distribution.