Sulfates decomposition

In a theoretical study, Lowell et al. W selected oxides from thermodynamic considerations for a process in which SO2 was adsorbed at temperatures greater than 100 C and desorbed by decomposition of the sulfate or sulfite formed, at temperatures below 750 C. Under these constraints, all of 47 oxides considered had potential for adsorption but only 16 had low enough decomposition temperatures to make a process economical. Intuitively, sulfate decomposition temperature should correlate loosely with reducibility of sulfates, so it is interesting that many of the 16 oxides chosen by Lowell, which included cerium and aluminum, have been shown to be useful in the UltraCat process. 

Although the values for sulfate decomposition agree fairly well, those for the oxysulfates are quite different, possibly because the Russian researchers ran this decomposition at a lower temperature, 1033 to 1073 K. 

Table I shows the results at 0°C and higher for several decomposition runs for acid mixtures containing butyl sulfate. These results Indicate the relative comparisons Including the effect of various operating conditions. The quality or research octane number (RON) of the hydrocarbon phase obtained In these butyl sulfate decomposition runs Increased either with reduced temperature, with higher ratios of acid to butyl sulfate, or when more dilute acids were used to produce the butyl sulfate.

Two points can be made based on the hypothesis that C, olefins are regenerated as a result of butyl sulfate decomposition In the alkylation reactors. 

Due to high T and 2 law efficiencies of sulfuric acid based cycles, to date, more than 20 sulfuric acid and/or metal sulfate decomposition based TCWSCs have been reported. Despite difficulties that challenge efficient electrolytic oxidation of sulfur dioxide (SO2), the Westinghouse hybrid cycle still remains as one of the most studied TCWSCs. The Westinghouse cycle is as follows [14] ... 

Dugger, G. L., Adams, J. B. and Bart, R., Ammonium sulfate decomposition . United States Atomic Energy Commission, RMO-2036 (1955). 

A question arises as to whether the formation of ammonium sulfate on the catalyst surface is possible at 400. a temperature jusi above that for ammonium sulfate decomposition. This is in principle possible according to the principle of capillary condensation in micropores ref. 2). It should be noted that pores of mordeniie zeolite range from 0,7 to 1.0 nm in radius. 

A feature of the literature on sulfate decompositions is the diversity of reported values of E. Mihalik and Horvath [95] found that the decompositions of Zn, Cu, Mg, Fe, Ni, Co and Mn sulfates could be described by the zero-order kinetic equation and that , was about 250 kJ mol. Kolta and Askar [96], however, described the decompositions of Zn, Fe, Co, Ni and Cu sulfates as being slightly deceleratory with , in the range 96 to 125 kJ mol. ... 

It was reported in the literature and also demonstrated in this laboratory that both Co304 and copper chromite are poisoned by sulfur. This results from the accumulation of sulfate groups on the catalyst surface. The base metal sulfates and aluminum sulfate are very stable, and they decomposed to the oxide only at temperatures above 650°C (see Table IV and Figure 2). Above 650°C, activity was restored because of sulfate decomposition. When a base metal catalyst was subjected to high temperatures before being cooled down for a CVS test, it had good activity for a short period of time which was dependent on the sulfur content of the gasoline and the surface areas of the washcoat and base metal catalyst. 

KAR/MAL] Karwan, T., Malinowski, C., Ptak, W., Sukiennik, M., Equilibrium parameters of nickel sulfate decomposition and its rate, Thermochim. Acta, 23, (1978), 269-282. Cited on page 194. 

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