Process Synthesis And Heat Integration Of Triple Column Pressure-swing Distillation For Separating Methanol/Acetonitrile/Benzene

Methanol(M),acetonitrile(A),and benzene(B)mixture forms more than one different azeotropes at atmospheric,however,conventional separation process cannot separate ternary azeotropic mixture efficiently.This paper studied the azeotropic characteristic of methanol/acetonitrile/benzene mixture using ternary phase diagram and explored a triple-column pressure-swing distillation(TCPSD)process.The economies of the different distillation sequences and heat integration processes were anylazed and the dynsmic characteristic of the differently heat-integrated triple-column pressure-swing distillation were investigated.The feasibilities of the different distillation sequences processes were confirmed using ternary phase diagram containing residue curve lines by Wilson thermodynamic model.On basis of the sequential iterative optimization of conventional PSD process,the sequential iterative optimization procedure and a triple-column pressure-swing optimization software(TCPSDOS)were explored with the minimum total annual cost as an economic target function.Then the optimial operating parameters in four different separation configurations were determined quickly and accurately.TACs of the A-M-B,A-B-M,M-A-B,and M-B-A distillation configurations are 8.239×105 $/y,1.138×10~6 $/y,1.204×10~6 $/y,and 1.260×10~6 $/y,respectively.The results shows that the economy of A-M-B distillation configuration is optimized.On basis of the optimal steady state flowsheet of A-M-B distillation configuration,the economies of the partially and fully heat-integrated TCPSD processes of two columns and three columns were explored.The economy of the partially heat-integrated TCPSD process between C1 and C2 is optimized with minimum TAC 6.634×105 $/y.The economy of the fully heat-integrated TCPSD process between C1 and C2 has a minimum TAC(6.406×105 $/y).With the help of the dynamic simulation soft namely Aspen Plus Dynamics,this paper investigated the dynamic strategies of three differently heat-integrated TCPSD processes.For the non-heat-integrated TCPSD process,the control structure which used stage 19 as the temperature sensitive stage in the second column,exhibited shorter time to reach a new steady state than that which used stage 4 as the temperature sensitive stage.The temperature-composition cascade control structure in partially heat-integrated process between C1 and C2 handled ±10 % feed disturbances well,however,dynamic response curves generated large oscillations.The pressure-compensation temperature control structure in fully heat-integrated process between C1 and C2 decreased oscillations and obtained better resist disturbance capacity.