In this paper

a pressure-swing distillation (PSD) process with two recycle streams for the separation of ternary mixture C2H5OH/C4H8O2-3/C4H8O-3 was proposed. According to the residual curve map (RCM) of the ternary mixture

each of the three pairs of components form a minimum-boiling azeotrope

and the composition of C2H5OH/C4H8O2-3 azeotrope changes significantly with pressure. Moreover

the coexistence of the three azeotropes results in a distillation boundary pinch

across which a practical distillation in normal pressure is impossible

and thus a traditional procedure to develop a PSD may be invalid. In this paper

such a difficulty was overcome by pressure optimization of the columns and a novel separation configuration was developed. Rigorous steady-state simulations of this process were carried out. Under six different pressures of the high-pressure column (column T1)

a sequential iterative approach was adopted to optimize the stage numbers

feed stages

reflux ratios and other design variables in order to reduce energy and equipment costs. By comparing the economics of these six processes

the optimal pressure of the T1 column was obtained

and heat integration was applied resulting in 14.9% extra reduction in the total annual cost (TAC) for the optimal process.