Pyrosulfate melt

Flow of -700 K SO2/SO3 bearing gas around the loaded catalyst causes it to form a vanadium oxide-alkali metal pyrosulfate melt on the surfaces of the catalyst s porous silica substrate. 

For further elucidation of the mechanism of the overall reaction (V.57), one must determine the abundance of ionic species of tetravalent and pentavalent vanadium in a potassium pyrosulfate melt. Present data for the equilibrium of reaction (V.63) due to Mars and Maessen 53) are consistent with the assumption that tetravalent vanadium is present in form of VOi ions, whereas pentavalent vanadium is present in form of VOa and V0 + ions in comparable amounts 54). The concentrations of these ions are interrelated by the equilibrium of the reactions... 

V2O5 Oxides. - Supported V2O5 oxides are extremely important industrial catalysts for environmental pollution control, and are used in catalytic scrubbers for SO2 oxidation and NO reduction. During the operation of the catalyst (usually at 400-600 °C) in the SO2 oxidation reactions, pyrosulfate melts are formed in the pores of the catalysts, and V2O5 can dissolve in these melts forming vanadium oxo-sulfate complexes ... 

It speeds up SO2 oxidation at >400 °C, at which temperatures the vanadium oxide and K, Na, Cs pyrosulfates melt and form a molten layer on the pores of the substrate. 

The calculations of Villadsen do however show that measurements with thick layers of unsupported melts could give erroneous predictions when transposed to the much thinner SLP s, but the inevitable uncertainties in liquid film thickness and distribution in an actual SLP are likely in any experiments to give errors which are comparable in size. Further consequences of concentration changes in dissolved species arising from the partial precipitation of V species are discussed in the paper of Villadsen et dl (26). The detailed imderstanding of such processes requires more data on gas solubilities and gas diffusion coefficients. Comtat and Mahenc (57) show how the latter can be obtained in pyrosulfate melts using electrochemical methods. 

The analytical chemistry of titanium has been reviewed (179—181). Titanium ores can be dissolved by fusion with potassium pyrosulfate, followed by dissolution of the cooled melt in dilute sulfuric acid. For some ores, even if all of the titanium is dissolved, a small amount of residue may still remain. If a hiU analysis is required, the residue may be treated by moistening with sulfuric and hydrofluoric acids and evaporating, to remove siUca, and then fused in a sodium carbonate—borate mixture. Alternatively, fusion in sodium carbonate—borate mixture can be used for ores and a boiling mixture of concentrated sulfuric acid and ammonium sulfate for titanium dioxide pigments. For trace-element deterrninations, the preferred method is dissolution in a mixture of hydrofluoric and hydrochloric acids. 

C° total concentration of pyrosulfate and sulfate anions Cv concentration of biatomic vanadium complexes C3l concentration of S03 in the melt phase Cp specific heat (kcal/kg °C)... 

For this reason a lower melting electrolyte was sought, one which would melt below 350 °C. Potassium pyrosulfate, K2S207, was a natural choice though thermally unstable above 300 °C in the absence of S03,... 

While the peaks associated with sulfate and pyrosulfate are essentially the same with and without vanadia, the equilibrium potentials in the melts are not. In the vanadia-free melts (Table 3) the equilibrium potentials are well-correlated with Eq. (53) [50] ... 

Depending on the material of the crucible, various cleaning agents may be used. Whenever possible, water and mild abrasives like sand are preferred. Cleaning with acids is usually applicable to platinum crucibles, but should be avoided in the case of alumina crucibles. Platinum crucibles can be cleaned especially thoroughly in a melt of potassium pyrosulfate. In all such operations it is important for the crucibles... 

Low melting point and high V205 solubility are obtained by choosing a low melting point eutectic mixture of V205 and K, Na, Cs pyrosulfates. 

The bisulfate melts [92] at 420 K and subsequently yields the pyrosulfate or (>1114)311(804)2. The low temperature reactions are probably diffiision-controlled. 

In contrast to the preceding discussion, the so-called kinetic methods of melt acidity determination are usable for estimations of the concentration of acids in the melts based on alkali metal nitrates. Duke and Yamamoto investigated the interactions taking place in solutions of pyrosulfate ions in the molten equimolar mixture KN03-NaN03 [79, 80], The chemical reaction... 

The literature data show that many mediods were used for oxoacidity studies and estimation of the acidic properties of melts. One simplest mefliod involves indicator. Acid-base indicators usually employed in aqueous solutions for protic aeidity measurements have been used for acidity studies in molten KNOj-LiNOj at 210 C and KSCN at 200"C. The color of indicator solution, relative to acidity, changes during titration of bases (sodium hydroxide or peroxide) by potassium pyrosulfate, KjSjOy ... 

A kinetic method was used for Lux acidity studies in molten nitrates. The interaction between the nitrate melts KNOs-NaNOs and potassium pyrosulfate was studied. ... 

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