Diffusion of hydrocarbons

Smit B, Loyens L D J C and Verbist G L M M 1997 Simulation of adsorption and diffusion of hydrocarbons in zeoWtes Faraday Disc. Ohem. See. 106 93-104... 

Active matrix contributes significantly to the overall performance of the FCC catalyst. The zeolite pores are not suitable for cracking of large hydrocarbon molecules generally having an end point > d00 [-(482°C) they are too small to allow diffusion of the large molecules to the cracking sites. An effective matrix must have a porous structure to allow diffusion of hydrocarbons into and out of the catalyst. 

Basic research consists of exploratory studies into things for which an end use cannot be specified. It might include a study to determine the effect of chlorine molecules on the diffusivity of hydrocarbons or a study of the dissolution of single spheres in a flowing stream. The prospective dollar value of this research cannot be estimated. 

Chimie, C.R. (2005) Infrared spectroscopic investigation of diffusion, co-diffusion and counter-diffusion of hydrocarbon molecules in zeolites. Elsevier, Comptes Rendus Chimie, 8, 303-319. 

Diffusion of hydrocarbons and other simple molecules in A, X and Y zeolites has been studied by a range of experimental methods including direct sorption rate measurements, chromatography and NMR. The advantages and limitations of these techniques are considered and results of recent experimental studies are reviewed with emphasis on the detailed microdynamic information obtainable by NMR. 

High sensitivity, fast response, and well-defined flow patterns make the TEOM an excellent tool for determining diffusivities of hydrocarbons in zeolites. Moreover, the TEOM has provided a unique capability for gaining knowledge about the effects of coke deposition on adsorption and diffusion under catalytic reaction conditions. An application of the TEOM in zeolite catalysis by combining several approaches mentioned above can lead to a much more detailed understanding of the catalytic processes, including the mechanisms of reaction, coke formation, and deactivation. 

A theoretical understanding of the diffusion of hydrocarbons through the porous catalyst layer (see Fig. 2.45) may be obtained by simulations using semi-classical molecular dynamics (as in Fig. 2.3). Such calculations have been performed for the penetration of various hydrocarbons through AljOj catalysts with and without Pt insertions (Szczygiel and Szyja, 2004). As indicated in Fig. 2.46, it is found that fuel transport depends on both cavity structure and the adsorption on internal catalyst walls. 

Szczygiel, J., Sz)rja, B. (2004). Diffusion of hydrocarbons in the reforming catalyst molecular modelling. /. Molecular Graphics Modelling 22,231-239. 

Effect of Cohesion Energy Density of the Polymer on Diffusion of Hydrocarbons... 

The diffusion of hydrocarbons in source rocks is influenced by (Krooss and Leythaeuser, 1988) ... 

At higher temperature (>560K), over poisoned or unpoisoned catalyst, increased rates of diffusion of hydrocarbon products allow the shape-selectivity of the catalyst to become apparent. The isomerization reactions within the channels which lead to linear and singly branched hydrocarbons may also occur in reverse on the active sites of the external surface (most active sites at the zeolite surface occur at the mouth of the channels), which may thus mask some of the shape-selectivity of the zeolite. 

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