High-Temperature Shift Conversion HTS

The classical HTS iron catalyst is resistant against sulfur compounds, but this is of greater importance in partial oxidation processes and less for the practically sulfur-free steam reforming gas. 

The reaction kinetics were studied by many researchers with sometimes different or contradictory results. Reviews are found in [592], [602], [603], [609]. A reason for this is that often diffusional effects were not eliminated, and therefore no real intrinsic reaction rates were obtained [610], [611]. In industrial practice equations are required for dimensioning reaction vessels and catalyst. The mathematical expressions used for this purpose are for the most part not based on theoretical assumptions and research 

To make allowance for mass transport restrictions, the equation can be modified by including a term containing the diffusion coefficient of CO. For operating pressures between 10 and 50 bar, when the reaction rate is controlled by bulk diffusion, Equation (83) can be applied  

The same equation was derived empirically from the experimental observations, indicating that the forward rate with respect to CO is first order and with respect to water zero order and that the forward reaction rate is proportional to the square root of the total pressure between 10 and 50 bar ( ° 60 for 1-10 bar some authors report a maximum reaction rate between 11 and 30 bar [613], [614]). Bohlbro [613] proposed a power law type rate expression (Eq. 84) which fitted well his experimental data covering a wide range of conditions, diffusion-free and diffusion-controlled, atmospheric and elevated pressure, with commercial catalysts of various particle sizes. 

Virtual activation energies of 114.6 to 59.8 kj/mol were found, depending on catalyst particle size. Chinchen [612] found for the intrinsic reaction measured on an ICI catalyst the real activation energy to be 129.4 kj/mol. 

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