Batch extractive distillation of maximal azeotrope with middle boiling entrainer

Separation of maximum boiling azeotropes using batch extractive distillation (BED) is feasible in a rectifying column with intermediate boiling entrainer. The main difference between BED and solvent-enhanced batch distillation (SBD) is the application of continuous entrainer feeding to the column or still. Finding a well-working intermediate boiling entrainer is more difficult than finding a heavy or light entrainer. The test mixture, selected according to didactic viewpoints, is chloroform and ethyl acetate with 2-chlorobutane. Operation steps (sequencing), limiting flows, and limiting stage numbers are determined by a feasibility study, based on profile maps; the design is validated by rigorous simulation. Results of parametric studies and comparison of SBD and BED, according to effectiveness, are presented. Separation of maximum boiling azeotropes in SBD and BED is feasible with an intermediate boiling entrainer, but the application of continuous feeding (characteristic to BED) makes the process more efficient. Pure-component A cannot be produced in SBD or BED, but producing component A mixed with entrainer and free of component B is feasible in both processes. The operation steps are similar in the two processes except for continuous feeding of the entrainer in step 2 of BED. With identical specification and comparable operation parameters, BED produces the same products in a shorter time and with a significantly smaller amount of maximum holdup in the still.