Aromatics by distillation

The process to separate the four Cg aromatics by distillation is very difficult because of their closeness in boiling points (table 11.3), so that only o-xylene can be separated by distillation. / -Xylene has a unique high melting point, and can be separated by cryogenic crystallization, but this is an expensive process that requires refrigeration. What is desired is an economic separation process that singles out jo-xylene among these four compounds. 

Sulfolane process. A flow sheet for the Sulfolane process is shown in Fig. 20.15. The hydrocarbon feed is introduced near the middle of the extractor and the heavy solvent is fed at the top. In the top section, nearly all the aromatics are extracted from the raffinate, but the solvent at this point also contains a few percent paraffins and naphthenes. The boiling point ranges overlap, so preparation of pure aromatics by distillation of this material is not practical. Also, Sulfolane and the... 

Axens/Uhde Benzene, Toluene Reformate and/or hydrotreated Pyrolysis gasoline BT cuts In extractive distillation, the addition of a selective solvent modifies the vapor pressures of the hydrocarbons in the feed in such a way that paraffinic and naphthenic components can be separated from the aromatics by distillation. 65 2009... 

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