The merits of semicontinuous, pressure-swing, azeotropic distillation are examined. In continuous
operation, two columns at different pressures are fed streams having compositions on opposite
sides of the azeotropic compositions. The distillates, which approach the azeotropic compositions
at high and low pressure, are cycled between the columns. In contrast, semicontinuous operation
involves only a single distillation column, which has lower investment costs and, when the
mixture to be separated is changed, shorter downtimes. An optimal-control algorithm is employed
to determine desirable campaigns, and to schedule pressure switch-over policies. Simulation
results for the dehydration of tetrahydrofuran, involving a pressure-sensitive azeotrope, indicate
that switch-over between steady states occurs quickly with on-spec product removed during
93% of the campaign. The column achieves production rates near 89% of the maximum
throughput of a single column in the continuous process and shows superior performance when
compared to reverse-batch operation.