(684b) Chemical Looping – A Novel Process for Partial Oxidation of Methane

Chemical looping combustion (CLC) is an emerging clean combustion technology which offers an efficient and elegant route for fossil fuel combustion with inherent CO₂ capture. In CLC, an oxygen carrier (typically a metal) undergoes cyclic reduction and oxidation with fuel and air, respectively. After condensation of the steam from effluent of the reducer reactor, a high pressure, high purity sequestration ready CO₂ stream is obtained. Thus CLC provides efficient, NO_x-lean, flameless combustion route with inherent CO₂capture.

While the efficiency of chemical looping as a combustion technology has been demonstrated for a broad range of fuels to-date, the chemical looping principle can also be extended onto other reactions, including reforming and partial oxidation reactions.  We have previously demonstrated that chemical looping reforming offers an attractive process alternative to conventional reforming by replacing air with steam and/or CO₂ as oxidant.  This allows for novel and efficient ways to produce hydrogen and activate CO₂via reduction to CO, respectively.

In the present contribution, we demonstrate that chemical looping is also an attractive process variant for partial oxidation reactions. By controlling the oxidation state of the oxygen carrier, total oxidation of the fuel can be avoided, and chemical looping hence opens a novel mode of reactor operation for highly efficient partial oxidation. This principle is demonstrated here with methane as fuel, resulting in catalytic partial oxidation of methane to synthesis gas (CPOM). The attractiveness of this novel CPOM process lies in the fact that it is possible to operate the process with air (rather than pure oxygen) without diluting the resulting syngas streams.

In our experiments, Fe and Ni supported on CeO₂ were chosen as oxygen carriers for chemical looping CPOM in a fixed bed reactor.  Ni-CeO₂ and Fe-CeO₂ were synthesized by simple incipient wetness, deposition precipitation technique and characterized by TEM, SEM, XRD, BET, and TPR/TPO, and then evaluated in fixed bed reactor studies as a function of oxidation state. Our results show that by limiting the duration of air oxidation of the carrier, CH₄can be selectively converted to syngas with high conversion. Interestingly, the use of a reducible support is critical for the process: Comparative studies with alumina-supported carriers show reduced performance, both in terms of syngas selectivity and methane conversion.

Overall, our results demonstrate that chemical looping offers a novel, highly attractive process variant for catalytic partial oxidation of methane, and thus suggest that the chemical looping principle could find application for a broader range of partial and selective oxidation reactions.