The Promotive Properties of Alkali Metal Nitrate Melts for the Partial Oxidation of Methane to Methanol

Abstract

(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 Partial Oxidation of Methane to Methanol with Nitrite and Nitrate Melts

“…O22" is apparently too active and promotes methane oxida tion to CO2 and H2O in nitrate melts. In our present and previous work [10] trace amounts of C2H2 and C2H4 were observed above 575 °C. This suggests that the formation of methanol or C2 compounds may follow parallel reaction routes requiring different reduced oxygen species for their formation.…”

“…Based on this suggestion, a simplified reaction route for the partial oxidation of methane with nitrate melts has been proposed as follows:°2 'J-r C H 3Ox ------► C H 3OH CO, C 0 2, H20 C,H 2 4 In order to verify this assumption, we tried to increase the amount of O2-in the (Na, IQNO3 system by increasing the oxygen concentration as suggested by eqs (1) - (5). We performed the ex periments with CH4/O 2 = 11/1 and 7/1 in the melts of 25 mol% NaNÜ3 -75 mol% KNO3, and com pared the results to our previous results obtained with CH4/Ü 2 = 15/1 [10]. The results are given in Table II.…”

“…It was also shown that the variation of the amount of 0 2 _ followed the trend of the methanol selectivity. Furthermore, a comparison of the results with those of other studies [4,5] which suggested that 0 22-plays an important role in the C2 compound formation indicated that 0 2 _ should lead to methanol formation [10] while 0 2 2~ should lead to C2 compound formation [4,5], and nitrate ions were considered to promote the ox idation of O2-and 0 22-to C>2~ according to eqs (4) and (5). In order to further confirm the role of 0 2~ in methanol formation, in the present work we used molten (Na, K)N02 as medium to perform the par tial oxidation of methane to methanol.…”

“…The data of our previous work are also shown for comparison. The amounts of reduced oxygen species in molten nitrites were calculated according to eqs (1) -(7) using thermo chemical data as in previous work [10]. Methane conversion is larger than that obtained with ni trate melts, but the methanol selectivity is very low.…”

“…In our previous work [10], we used (Na, K)NC>3 melts as reaction media for the partial oxidation of methane to methanol, and tried to estimate the amounts of reduced oxygen species by thermo chemical calculation according to eqs (1) - (7). …”