Divide to Conquer: On the Use of Distributed Feed Strategies in Oxidative Coupling of Methane

Abstract

The oxidative coupling of methane (OCM) represents a promising method for the direct conversion of methane into ethylene, the most highly sought-after olefin in the petrochemical market. Nevertheless, the adoption of the OCM in industrial applications has been hampered by inherent chemical and engineering challenges. As a result, research endeavors have been directed toward developing innovative strategies to enhance the performance of the OCM process. This review offers a comprehensive overview of the challenges faced by the OCM, which has led to research exploring the use of a distributed feed policy. In this approach, methane and oxygen (the reactants for the OCM) are introduced separately, either through multiple oxygen injection points in the case of packed-bed reactors or into two distinct compartments in the case of membrane reactors. Additionally, we present an overview of the various types of membranes utilized in this context. More particularly, we focus on the use of mixed-ionic-electronic-conducting (MIEC) membranes to address the challenges of OCM. Due to their unique ionic conductive properties, MIEC membranes help to increase the overall efficiency of the OCM process. For example, an MIEC membrane intensifies the process for both air separation and the OCM reaction being conducted in a single unit, consequently simplifying upstream processing. It also aids in conducting the OCM reaction in a much safer environment, where gas-phase reactions of methane and oxygen are eliminated. With oxygen being a limited reactant in the OCM, this configuration also helps achieve higher methane conversion by allowing the safe feeding of more oxygen. Additionally, higher selectivity can be achieved by suppressing gas-phase reactions. In this case, oxygen is directly available in the catalyst zone. Finally, this review investigates the chemical and mechanical stability of MIEC membranes for OCM applications, and we conclude with important remarks and outlooks.