CONDUCTIVITY AND PHASE-DIAGRAM OF THE SO2 OXIDATION CATALYST MODEL SYSTEM - M(2)S(2)O(7)-V2O5 (M=80-PERCENT-K+20-PERCENT-NA)

The specific conductivities of the sulfuric acid catalyst model system M2S2O7-V2O5 (M = 80% K + 20% Na) were measured at 14 different compositions in the range χv2o2 = 0-0.3500 and in the temperature range 250-500°C. The phase diagram of the M2S2O7-V2O5 (M = 80% K + 20% Na) system was constructed by estimating the liquidus and the solidus temperatures for each composition from the marked change of the conductivity at the phase transition temperatures. The melting point of the pyrosulfate mixture K2S2O7-Na2S2O 7 (80%-20%) was found to be 378°C. Two eutectics were found at χv2o5 = 0.175 and χv2o5 = 0.30 with temperatures of fusion of 314 and 326°C, respectively. The local maximum exhibited in phase diagram at χv2o5 = 0.25 and t = 338°C probably corresponds to the formation of the mixed cation compound M3VO2SO4S2O7 (M = 80% K + 20% Na). The data indicate that the lowest temperature of operation for a widely used potassium and sodium promoted vanadium oxide based common sulfuric acid catalyst (VK 38, Haldor Topsøe A/S) in the oxidized form is 323°C. The results are considered to be of significance for the design of new low-temperature molten salt catalysts for SO2 oxidation and flue gas desulfurization. © 1994 Academic Press, Inc.