Ethylene production by partial oxidation of biogas using lime as catalyst

Abstract

AbstractBACKGROUNDThe oxidative coupling of methane (OCM) is an interesting route for direct conversion of methane into ethylene and ethane. Nevertheless, COx is a secondary product of this route, which decreases the selectivity of hydrocarbons. In this work it is proposed to overcome this drawback by using biogas as source of methane. In addition to being a renewable source of methane, the presence of CO2 in biogas may shift the balance of the methane combustion. For this purpose, it was evaluated how process conditions such as O2 and CO2 flow rates and temperature affect biogas‐based OCM, in the temperature range of 650–800 °C, using lime as catalyst.RESULTSThe increase in CO2 flow from 0 to 15 mL.min−1 increased the ethylene selectivity from 25.9% to 44.5% at 800 °C. As consequence, CO2 formation dropped from 53.9% to 18.3%. Methane conversion was not affected significantly by CO2 flow rate, remaining in the range of 22–25%. O2 flow was essential to activate the OCM reaction and the presence of higher concentrations of O2 favored the selectivity of ethylene, but also increased the CO2 produced through methane combustion. In the OCM experiments with variable flow of CO2, the highest C2 yield of 18% was obtained for the highest flow of co‐fed CO2, whereas the experiments with biogas and variable O2 flow showed the highest yield of ethylene for the highest flow of air co‐fed.CONCLUSIONThus, biogas‐based OCM was shown to be a promising route to improve C2 selectivity, since the CO2 present in the biogas minimizes the formation of CO2 in the reaction. The use of lime as a low‐cost catalyst proved to be viable for the OCM reaction, presenting results compatible with those obtained for catalysts with more complex composition. © 2023 Society of Chemical Industry.