Naphtha Steam Reforming Kinetic Relationships

intrinsic = rate calculated with bulk fluid conditions The catalyst activity is calculated as a parameter, updated from operating data. 2.2 Naphtha Steam Reforming Kinetic Relationships 

One of the mechanisms (Reference 4, page 54) is based on the following sequence of adsorption, reaction, and desorption  

The symbol represents an active site on the catalyst surface. Concentration of - 2 is generally assumed to be negligible, so the step 2 rate constant , kH does not appear in the final rate expression. The rate constants kA and kr (adsorption and reforming) do appear in the rate expression. KW and KH are the adsorption equilibrium constants for water and hydrogen, respectively. 

The mechanisms account for chemisorption of the hydrocarbon and steam, followed by a-scission of the carbon-carbon bonds. The resulting adsorbed Cj species react with adsorbed steam to form carbon monoxide and hydrogen. These mechanisms alone would result in no formation of methane, which is of course generated from naphtha feed stocks which are totally free of methane. Methane concentrations of 8 to 10 mole percent (dry basis) are typical at the outlet of industrial naphtha steam reformers. Methane is generated when the hydrogen partial pressure is sufficiently high so that the reverse of the methane reforming reaction  

The concentration profiles that result from solving the methane and the higher hydrocarbon reaction rates simultaneously agree well with the profiles reported by others, and the reactor effluent species concentrations agree well with those observed fi om industrial reformers (Appendix A). The effluent concentrations are fairly insensitive to reaction rates, since industrial reformers operate near equilibrium conditions. Effluent conditions will only be noticeably affected by reaction rates as the catalyst activity declines significantly. The temperature profile, especially in the first on third of the reactor which is furthest from equilibrium, is affected significantly by reaction rates, and therefore is the most affected by the catalyst activity. The case study results in Appendix B illustrate the concentration profiles, and the effects of catalyst activity on temperature profiles. 

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