(211a) Process Development of Manganese-Based Oxygen Carriers for Oxidative Coupling of Methane in a Pressurized Chemical Looping System

With the recent growth in global shale gas production, interest has increased in upgrading shale gas and its primary component, methane, to higher value-added products. However, a direct method for upgrading methane has been limited by methane’s high molecular stability and process economics. Since the 1980s, oxidative coupling of methane (OCM) has demonstrated promise in producing higher hydrocarbons, specifically ethylene and ethane (C₂ products). Typical OCM schemes catalytically convert methane to C₂ products using gaseous oxidants, which can lower process efficiencies by requiring energy-intensive air separation operations. In order to overcome these process limitations, the chemical looping technology platform presents an attractive opportunity to convert hydrocarbons to flexible products utilizing an intermediate oxygen carrier rather than gaseous oxidants.

This study investigates the application of the chemical looping approach for OCM to selectively control the redox reactions. Various reducible manganese-based oxidative catalysts or oxygen carriers were synthesized and compared. Specifically, parametric redox experiments were conducted in a high-pressure, fixed bed reactor with pressures between atmospheric and 5 atm, temperatures between 700 and 900°C, and at varied steam-to-methane ratios. The effects on the oxidation and reduction reactions are also investigated in a high-pressure thermogravimetric analyzer (TGA). The effects of high pressures on the oxygen carriers were structurally characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), and nitrogen physisorption (BET). The experimental results are coupled with sensitivity process simulations of a theoretical commercial OCM chemical looping system. Experimental results demonstrate the benefits of pressure and steam on methane conversion and C₂+ selectivity with the OCM chemical looping process. With proper heat management, the comprehensive OCM chemical looping process simulations present promising reactor and process designs for an alternative direct scheme for methane utilization.