146 Figure 9. Mechanism for photocatalytic oxidation destruction of methane. The results have demonstrated that the simulated VAM is able to be completely oxidized by photocatalytic oxidation under ambient temperature and pressure conditions [9]. As shown in Figure 10, almost complete elimination of CH4 from 0.1 vol% simulated VAM can be achieved with extended irradiation in the batch mode tests. The continuous flow mode tests also reveal that the low concentration methane in the air can be oxidized and eliminated at the ambient temperature whilst the conversion rate of CH4 into CO2 is decreased with an increase in the flow rate. While the complete oxidation of dilute VAM is feasible with photocatalytic oxidation, there will be a challenge for photocatalytic process to deal with such a large VA flow (normally over hundreds m3/s) in practical application based on the low photocatalytic reaction rate obtained so far. The photocatalyst material holds the key for boosting the reaction rate. Engineering new photocatalysts for VAM oxidation should aim to enhance the light absorption, improve charge separation and transfer and increase the surface activity. Figure 10. (a) Photocatalytic oxidation of simulated 0.1 vol% VAM over two developed photocatalysts tested in a batch mode, and (b) variations of methane oxidation efficiency tested with different VAM concentrations and flow rates in a continuous flow mode. With the specific advantage of treating very low concentration methane, the photocatalysis technology is promising for open cut fugitive methane abatement for which no abatement technology is available. It also holds great potential in destroying atmospheric methane with sunlight for carbon offset as a negative emission technology. Low-cost catalysts for VAM catalytic oxidation 0 2 4 6 8 10 12 0.00 0.02 0.04 0.06 0.08 0.10 CH4 conentration (vol%) Irradiation time (hour) VAMO-1 A5-A-2 0 20 40 60 80 100 CH4 oxidised (%) (a) (b) 1 3 5 10 15 20 0 20 40 60 80 100 CH4 oxidised (%) VAM flow rate (sccm) 0.05% CH4 0.1% CH4 0.3% CH4
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