Equilibrium SO2 Oxidized as a Function of Temperature

Equilibrium % SO2 oxidized (O ) is related to equilibrium temperature by combining Eqns. (10.11) and (10.12), which gives  

Equilibrium % SO2 oxidized increases slightly with increasing volume% O2 in feed gas. This is because a high volume% 02 volume% SO2 product pushes SO2 oxidation to the right, Eqn. 10.7. 

Equilibrium % SO2 oxidized (O ) is related to equilibrium temperature by combining 

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Fig. 7.4. Maximum attainable (equilibrium) SO2 oxidation as a function of reaction temperature. It decreases markedly with increasing temperature. Calculation and plotting of this curve are described in Chapter 10.

Fig. 7.3. Equilibrium constant for SO2 + /2O2 —> SO3 oxidation as a function of temperature. It decreases nearly 80 000 times between 600 and 1400 K.

The dashed line in Figure 8-2 shows the equilibrium fractional conversion of SO2 as a function of temperature, for conditions that are typical of the first SO2 oxidation reactor in a sulfuric acid plant. The solid line shows the energy balance for adiabatic operation. This is the same line shown in Figure 8-1. The two lines intersect at one point S02 = 0-74 T = 593 °C. At this condition, both the energy balance and the equihbrium relationship are satisfied simultaneously. The intersection of the two lines is the only place where this requirement is met. 

The Pd-O bond also varies with the extent of oxidation of Pd. During the methane combustion reaction, the catalyst surface is a non-equilibrium, kineti-cally controlled structure. The oxygen concentration profile in the particle results from a combination of particle reconstruction, oxygen adsorption, bulk diffusion, and oxygen removal. This concentration profile varies as a function of time, and as the oxygen content increases, the Pd-O bond strength decreases. This increase is accompanied by an increase in the specific activity. The most widely accepted reaction pathway is the Mars and van Krevelen redox mechanism, which involves lattice oxygen and uneoordinated Pd centers as active species. Inhibition by products (H2O and CO2) and impurities (SO2) is a major drawback for low temperature combustion. The effect of sulfur is particularly important for catalytic converters for NGV applications because it drastically reduces the methane combustion activity. 

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