Diffusion and reaction in porous

The reactions are still most often carried out in batch and semi-batch reactors, which implies that time-dependent, dynamic models are required to obtain a realistic description of the process. Diffusion and reaction in porous catalyst layers play a central role. The ultimate goal of the modehng based on the principles of chemical reaction engineering is the intensification of the process by maximizing the yields and selectivities of the desired products and optimizing the conditions for mass transfer. 

Ryan, DJ Carbonell, RG Whitaker, S, A Theory of Diffusion and Reaction in Porous Media, AIChE Symposium Series 71, 46, 1981. 

Whitaker, S, The Method of Volume Averaging An Application to Diffusion and Reaction in Porous Catalysts. In Proceedings of the National Science Council, Part A Physical Science and Engineering National Science Council Taipei, Taiwan, Repubhc of China, 1991 Vol. 15, p 465. 

As mentioned earlier, if the rate of a catalytic reaction is proportional to the surface area, then a catalyst with the highest possible area is most desirable and that is generally achieved by its porous structure. However, the reactants have to diffuse into the pores within the catalyst particle, and as a result a concentration gradient appears between the pore mouth and the interior of the catalyst. Consequently, the concentration at the exterior surface of the catalyst particle does not apply to die whole surface area and the pore diffusion limits the overall rate of reaction. The effectiveness factor tjs is used to account for diffusion and reaction in porous catalysts and is defined as... 

I took the writing of a monograph on the mathematical theory of diffusion and reaction in porous catalysts [I ] as my sabbatical project when we went to Cambridge for the second time in 1971-1972. It is questionable whether... 

While catalytic HDM results in a desirable, nearly metal-free product, the catalyst in the reactor is laden with metal sulfide deposits that eventually result in deactivation. Loss of catalyst activity is attributed to both the physical obstruction of the catalyst pellets pores by deposits and to the chemical contamination of the active catalytic sites by deposits. The radial metal deposit distribution in catalyst pellets is easily observed and understood in terms of the classic theory of diffusion and reaction in porous media. Application of the theory for the design and development of HDM and HDS catalysts has proved useful. Novel concepts and approaches to upgrading metal-laden heavy residua will require more information. However, detailed examination of the chemical and physical structure of the metal deposits is not possible because of current analytical limitations for microscopically complex and heterogeneous materials. Similarly, experimental methods that reveal the complexities of the fine structure of porous materials and theoretical methods to describe them are not yet... 

Here we develop a heterogeneous model that is based on the more rigorous dusty gas model for diffusion and reaction in porous catalyst pellets. 

J.P. Sorensen, W.E. Stewart, Collocation analysis of multicomponent diffusion and reactions in porous catalysts, Chem. Eng. Sci. 37 (1982) 1103. 

Diffusion and reaction in porous catalysts have been the subjects of intensive investigations for almost half a century, and general treatments are available... 

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