Selective catalytic removal of carbon monoxide from ethylene-containing model pyrolysis gas streams

Pyrolysis is a promising chemical recycling route for plastic waste that is unsuitable for mechanical recycling. High-temperature pyrolysis can be used to increase the olefin-rich pyrolysis gas yield. The aim is to feed the pyrolysis gas directly to the recovery section of a steam cracker, thereby bypassing the cracker furnaces. The resulting gas consists primarily of methane, ethylene, propylene, C4+ hydrocarbons, together with smaller amounts of hydrogen, carbon dioxide, and carbon monoxide (CO). Before this gas can be introduced to the steam cracker recovery section, key impurities such as CO must be removed. This study evaluates the CO removal performance of selected industrially relevant catalysts for water–gas shift and methanation reactions. The catalyst selection included Fe 2 O 3 /Cr 2 O 3 , CuO/ZnO/Al 2 O 3 , NiO, CoMo and ZrO 2 -based catalysts. The catalytic performance was assessed with the dual objective of maximizing CO removal while minimizing C 2 H 4 conversion. The CO and C 2 H 4 conversion performance of the selected catalysts was investigated experimentally in an atmospheric pressure plug-flow reactor using a model pyrolysis gas consisting of CO, CO 2 , H 2 , CH 4 , C 2 H 4 and N 2 . Thermodynamic simulations were conducted to compare experimental CO conversion with equilibrium predictions. The best overall performance was obtained with Fe 2 O 3 /Cr 2 O 3 catalysts, which achieved 70–80% CO conversion while maintaining ethylene conversion below 5%. In contrast, CuO/ZnO/Al 2 O 3 catalysts reached CO conversion above 97%, but also converted more than 99% of ethylene. These results indicate that Fe 2 O 3 /Cr 2 O 3 high-temperature shift catalysts offer the most favorable balance between CO removal and olefin preservation for purification of pyrolysis gas streams intended for steam cracker recovery section integration.