Barium, thermodynamic data

Sulfur oxides in the FCC regenerator flue gas can react with these alkaline earth metals to form sulfates. On the basis of thermodynamic data, the formation of calcium and barium sulfates is favored over the formation of vanadates at typical regenerator conditions[l 1,12]. The other trap materials may or may not be affected by sulfur competition, depending on the SOx concentration and regenerator conditions. In any case, the effect of sulfur competition can not be overlooked when designing effective vanadium traps. 

The concentration of barium in water solutions saturated with BaSe04(cr) was determined by a polarographic method (E1/2 = - 1.8 V with 0.1 M LiCI as supporting electrolyte). The measured solubilities are reported in Table A-9. There is no description of the method used to test for equilibrium and no thermodynamic data were calculated in the paper. 

Generally, a critical evaluation of chemical thermodynamic data involves a network approach. A small sample of such a network approach is illustrated in Figure 1, for a few barium compounds. Each line represents a reaction (process), each node, represents a compound. The network approach has been discussed in reference (1). Various techniques are used by the analyst in evaluation of the thermodynamic consistency and reliability of individual reaction measurements. One of these is to analyze a given thermochemical network of measurements into various combinations of reactions that result in identical initial and final states. For each such loop the algebraic sum of changes in a thermodynamic variable (AH, AG) should equal zero except for the combination of experimental uncertainties. Analysis of these residuals from the various loops may reveal certain measurements to be inconsistent with the remainder of the reactions. Similarly, solutions of the entire network using both least sums and least squares techniques are valuable (2). The least sums technique minimizes the sums of the residuals whereas the least squares technique minimizes the sum of the deviations squared. Large residuals found in the solution are indicative of thermodynamic inconsistency with respect to the total set of measurements. 

Table 7.25 Literature thermodynamic data for barium species at 25 °C.

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