Propane-propylene separation heat required

Extractive distillation is evaluated as an alternative to ordinary distillation for the separation of propylene-propane mixtures. Particular attention is given to the necessary compromises between different design factors solvent concentration within the primary column, solvent selectivity, solvent loss, etc. A major expense is associated with the sensible heat requirements of the circulating solvent process modifications so as to minimize this expense are discussed. The process analysis explores combinations of solvent selectivity and other solvent properties which might make extractive distillation attractive. It appears that in almost all cases extractive distillation offers no advantage compared with ordinary distillation. Only in special cases may circumstances warrant extractive distillation. External factors favoring the use of extractive distillation are identified. 

Vapor produced in the condenser is compressed back to column bottom pressure before entering the column. Figure 17.13 shows the application of this scheme to the propylene-propane separation problem. The bottoms liquid is flashed to 72psia to remove the required heat in the condenser. Additional heat added during isentropic compression is insufficient to make up the difference between reboiler and condenser duties. Therefore, the auxiliary steam-heated reboiler is needed. 

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