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The coal direct chemical looping (CDCL) combustion process using an iron-based oxygen carrier has been developed and demonstrated in a 25-kW th subpilot unit. The CDCL subpilot unit is the first chemical looping demonstration unit with a circulating moving bed for the solid fuel conversions. To date, the CDCL subpilot unit at OSU has been operated for more than 550 h. The feasibility of the subpilot unit with various types of solid fuels including sub-bituminous coal and lignite coal has been tested. This article discusses the operational experience of a successful 200-h integrated, continuous demonstration with sub-bituminous coal and lignite coal. Throughout the 200-h continuous operation, the CDCL subpilot unit showed steady behavior in terms of solid circulation, coal handling, and oxygen carrier reactivity and recyclability. Tests with both coals confirmed more than 90% coal conversion with 99.5 vol % purity of CO 2 achieved in the reducer. The sound design of the reducer allowed for nearly full coal conversion with a high purity of CO 2 , eliminating the need for additional downstream fuel polishing and separation units. The combustor gas contained lean oxygen concentrations with minute amounts of carbonaceous gases (CO 2 , CO, and CH 4 ) detected. The combustor gas analysis implied the proper regeneration of iron-based oxygen carriers, good gas sealing between the reducer and combustor, and no indication of unconverted carbon carry-over. Moreover, the fates of coal pollutants such as NO x and SO x that are commonly observed in the conventional coal combustion process were also investigated during the subpilot unit operation. The NO x analysis showed that the CDCL process is capable of significantly reducing NO x emissions by avoiding thermal NO x formation. The sulfur analysis indicated SO 2 generation in both reducer and combustor, agreeing with the sulfur chemistry in the CDCL scheme.

Directly upgrading natural gas is limited by the stability of its primary component, methane, and process economics. Since the 1980s, oxidative coupling of methane (OCM) has shown potential to produce ethylene and ethane (C2s). The typical OCM approach catalytically converts methane to C2 products using molecular oxygen, reducing process efficiency. To overcome this, chemical looping OCM converts methane to hydrocarbons via intermediate oxygen carriers rather than gaseous cofed oxidants. The chemical looping approach for OCM has been studied mechanistically for the first time with a Mn–Mg-based catalytic oxygen carrier (COC). The COC delivered stable performance in a fixed bed for 100 cycles for more than 50 h with a 63.2% C2 selectivity and 23.2% yield. These experimental results and original process simulations of an OCM chemical looping system for C2 or liquid fuel production with electricity cogeneration present a direct method for methane utilization.

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