The promotive properties of alkali metal nitrate melts for the partial oxidation of methane to methanol

(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 degrees 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 O-2(-) and O-2(2-) 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 O-2(-) plays an important role for methanol formation.