(Na, K)NO3 melts of various ratios were used as promoters for the partial oxidation of methane to methanol. Experiments were performed in a flow reactor system under atmo­spheric pressure and at various temperatures in the range of 525-600 °C. The influence of reaction temperature, melt composition, and reduced oxygen species on methane conversion and methanol selectivity were investigated systematically. The major reaction products were CH3OH, CO, CO2, and trace amounts of C2H6 and C2H4. A methane conversion of 1.8-12.4% and a methanol selectivity of 0.4-14.1% were obtained under these reaction condi­tions. Binary melts could achieve higher methanol selectivity than a single melt. The amounts of reduced oxygen species O2- and O22-were estimated from thermochemical data according to the ion equilibrium in molten nitrates. The promotive effect of nitrate melts was confirmed and the results indicate that superoxide O2- plays an important role for methanol formation.

The effect of reduced oxygen species on the partial oxidation of methane to methanol was examined with nitrite melts. The experimental results support the suggestion that the formation of methanol or C2 compounds depends on different reduced oxygen species, as observed in our previous work using nitrate melts. It has been suggested that the partial oxidation of methane proceeds to CH3OH or C2 compounds via parallel pathways. This suggestion was verified by increasing the oxygen concentration to carry out the partial oxidation of methane in 25 mol% NaNC>3 -75 mol% KNO3 melts. A methanol selectivity of 8.2% and a methanol yield of 0.43% were observed with CH4/O 2 = 15/1 at 575 °C, whereas with CH4/O 2 = 7/1 methanol selectivity and yield increased to 23.7% and 1.1%, respectively. The results further confirm the contribution of the superoxide ion O 2-on methanol formation.

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