Catalytica methane oxidation

FIGURE 12.5 A possible catalytic cycle for the Catalytica methane oxidation. C— bond breaking may occur by deprotonation of a methane complex. 

Proposed mechanism for the Catalytica methane oxidation system ... 

DMO [Direct methane oxidation] A process for converting methane to methanol or synthetic liquid fuels. Under development by Catalytica in 1997. 

This cycle, often referred to as the Shilov-cycle converts methane into methanol and chloromethane in homogeneous aqueous solution at mild temperatures of 100-120 °C (11). However, while Pt(II) (added to the reaction as PtCl ) serves as the catalyst, the system also requires Pt(IV) (in the form of PtCle-) as a stoichiometric oxidant. Clearly, this system impressively demonstrates functionalization of methane under mild homogeneous conditions, but is impractical due to the high cost of the stoichiometric oxidant used. A recent development by Catalytica Advanced Technology Inc., often referred to as the Catalytica system used platinum(II) complexes as catalysts to convert methane into methyl-bisulfate (12). The stoichiometric oxidant in this case is S03, dissolved in concentrated H2S04 solvent. This cycle is depicted in Scheme 3. 

Direct Partial Oxidation to Methanol. - The direct partial oxidation (DPO) route offers the advantage of direct conversion of methane to methanol. The oxidants include air, oxygen, and nitrous oxide. Recently, Pitchai and Klier, Gesser et al., Foster, Scurrell, and Kuo gave comprehensive reviews on this process. Catalytica Associates also discussed this subject in a client-private report. 

Economic Evaluation Methane to Liquid Hydrocarbon FuelsK -Evaluation studies on the above three processes to produce liquid fuels were performed by Mobil, MITRE,and Bechtel. Cost impact projections of additional potential improvements were independently estimated by Catalytica Associates. The potential for the partial oxidation route, together with an economic evaluation, was also reported by Edwards and Foster. An economic evaluation of producing gasoline and distillate fuels from methane coupling was also carried out by Union Carbide. ... 

The direct oxidation of methane to methanol has shown only limited success. The process would be very economical if it could achieve 80% selectivity at 80% conversion, based on Catalytica s evaluation. The development of selective catalysts and effective reaction processes is challenging. Bioprocessing that has potential for high selectivity is also worth further research. 

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