Paraffin composition profiles

The third desorbent characteristic is that the desorbent material must be easily separated from the two Sorbex process products extract and raffinate. The adsorbent chamber s composition profile produces extract and raffinate streams comin-gled with desorbent. In order for the process to be economical, the separation of the feed components from the desorbent (achieved through fractionation) is set by the boiling point differences between the species. Depending on the selectivity possessed by the desorbent over that of the feed normals, the subsequent desorbent rates needed to flush feed normal paraffins from the adsorbent s selective volume and the resulting extract or raffinate streams from the Sorbex chambers could contain in some cases more than 50% desorbent. High concentration of desorbent demonstrates the importance of the desorbent characteristics when selecting a desorbent. 

McKay (1971) carried out experiments in a Loschmidt-type diffusion cell with a nine component system including nitrogen, carbon dioxide, and a number of paraffins. The experiments were carried out at the high temperatures and pressures typical of underground oil and gas reservoirs. McKay s paper includes a dimensioned drawing of the Loschmidt-type cell used for the experiment and the initial conditions for some of his experiments. Use the theory of Section 5.5 to predict the composition profiles in this system. State clearly any assumptions made in your calculations. You will need to estimate diffusion coefficients at high pressure. Consult Reid et al. (1987) for details of methods that can be used for this purpose. 

Crude oil compositions vary widely. Depending on the sources of carbon from which the oils are generated and the geologic environment in which they migrated and from which reservoir, they can have (1) dramatically varied compositions in the C5 to C42 carbon range such as relative amounts of paraffinic, aromatic and asphaltenic compounds (2) large differences in the w-aUcane and cyclic-aUcanes (such as aUcyl cyclo-hexanes) concentrations and distribution patterns and UCM profiles ... 

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