Methane conversion to aromatics via chemical synergy with OCM: Effect of periodic operation, temperature profile, and catalyst loading

Abstract

The transition from indirect to direct methane conversion marks a significant advancement in chemical processing. One promising direct reaction is methane dehydroaromatization, which converts methane to aromatics in a single step with zero CO₂ emissions. However, the commercialization of MDA faces major challenges including thermodynamic limitations, rapid catalyst deactivation, and high temperature requirements. Integrating MDA with another reaction offers a potential solution to these challenges combined. This work explores the potential opportunities and limitations for chemical synergy when coupling the oxidative coupling of methane (OCM) to MDA through mass integration. Experimental studies were conducted by passing the oxidative coupling of methane (OCM) reactor effluent to a downstream MDA reactor. Periodic feeding of OCM to the MDA catalyst showed limited improvement, indicating that OCM composition alone does not maintain stable MDA performance. Varying the temperature over time in MDA reactor demonstrated that C₂ coming from OCM contribute to aromatic production even at low temperatures (450 °C). However, at such temperature, the conversion of CO₂ to CO and CH₄ to aromatics does not occur, highlighting the need for high operating temperatures in the OCM-MDA coupling process. The coupling of OCM and MDA was tested with different MDA space velocities as 3750, 1875, and 1250 mL/g/h, corresponding to 0.2 g, 0.4 g and 0.6 g catalyst loading, respectively. The case of 1250 mL/g/h maintained a stable 14 % conversion and 2.5 % yield of benzene over 10 h, converting all CO₂ to CO. Characterization using TGA, Raman spectroscopy, and XPS on spent catalysts indicated limited carbon removal by OCM effluent, and confirmed that CO₂ is causing the oxidation of Mo₂C to MoO_x. A reaction scheme for the OCM-MDA coupling using Mo/ZSM-5 is proposed to guide future exploration of this promising two-step process.