COMBINED REMOVAL OF SO2, H2S AND NOX FROM GAS STREAMS BY CHEMICAL ABSORPTION WITH AQUEOUS-SOLUTION OF 12-MOLYBDOPHOSPHORIC ACID AND ITS REDUCED SPECIES

Selective removal of SO2, H2S and NOx from gas streams (air or towngas ) was investigated using aqueous solutions of 12-molybdophosphoric aci d and its reduced molybdenum blue species. The experimental results sh owed that H2S and SO2 in the gas streams can be removed quantitatively by yellow solution of 12-molybdophosphoric acid. The H2S was oxidized into recoverable elemental sulfur and SO2 into H2SO4, while the yello w solution was reduced into blue species (reduced molybdenum blue). Th e obtained reduced molybdenum blue solution was then used for the quan titative removal of NOx, which was reduced into N-2 and the blue solut ion was then oxidized back into yellow species. It is possible that th e regeneration of scrubbing solution is not required and no chemical i s consumed during absorption, when NOx, SO2 and/or H2S coexisted in wa stegases and the molar ratios of NO2/(SO2 + H2S) is just equal to 1/2, although, in most cases, the ratio in real practical wastegases is no t always equal to the value. The absorption mechanism was studied in d etail. It was found that only one molybdenum atom in 12-molybdophospho ric acid was reduced from Mo(VI) to Mo(V) by H2S or H2SO3 and the Mo(V ) was oxidized back into Mo(VI) in the case of No-x absorption. 12-mol ybdophosphoric acid used in this work is inexpensive, commercially ava ilable, easily regeneratable, relatively nontoxic, and gives no second ary pollutant in the process.