Upgrading of non-condensable pyrolysis gas from mixed plastics through catalytic decomposition and dechlorination

Abstract

The non-condensable pyrolysis gas from plastic pyrolysis is a suitable fuel and precursor for chemical synthesis. Depending on downstream applications, the selective removal of unsaturated hydrocarbons and HCl released from polyvinyl chloride (PVC) is required. This study investigated the selective decomposition of unsaturated hydrocarbons with simultaneous dechlorination of non-condensable pyrolysis gas using a catalytic sorbent containing 5% NiO loaded on CaCO3 support (Ni-Ca) and pristine CaCO3 (Ca) at different temperatures, doses of catalytic sorbent and HCl contents. As a result, Ca removed 98.8% of HCl and decomposed 89% of alkynes and 23% of dienes at 700°C. When applying Ni-Ca, the HCl removal was above 99% at all studied temperatures, while 90% decomposition of alkenes, dienes and alkynes was achieved, depending on temperature, Ni-Ca dose and HCl content. The higher HCl content in gas (43mg against 13mg) negatively influenced the catalytic activity of Ni-Ca, while increasing the selectivity towards the decomposition of alkenes, dienes and alkynes compared to alkanes. At 700°C, 99.6% removal of unsaturated hydrocarbons by Ni-Ca was attained at only 10.1% conversion of alkanes. Thus, depending on the applied catalytic sorbent, either selective decomposition of alkynes and dienes (over Ca) or a mixture of unsaturated hydrocarbons (over Ni-Ca) was achieved with the simultaneous HCl removal from non-condensable pyrolysis gas.