In this work, the pressure-swing distillation process is extended to separate the pressure-insensitive binary azeotropes by using suitable entrainers. Design and control of new Pressure-swing distillation for separating pressure-insensitive maximum boiling phenol/cyclohexanone azeotrope using acetophenone as a heavy entrainer are investigated using Aspen Plus and Aspen Dynamics. Rigorous steady-state simulations are run for both fully and partially heat-integrated processes and a comparison of these two configurations is made. It is revealed that the partially heat-integrated process is more competitive than the fully heat-integrated one from the economical viewpoint. Two temperature control structures and one composition/temperature cascade control scheme are proposed to handle the feed flow rate and feed composition disturbances. It is indicated that the column operating at higher pressure cannot be perfectly controlled by the two temperature control schemes because of the existence of an intermediate nonkey component. A composition/temperature cascade control structure is proposed to cope with this control problem and a robust control is achieved.

A method for methylal/methanol separation using extractive distillation with N,N-dixnethylformamide as an entrainer is presented. Rigorous steady state and dynamic simulations for this process are implemented on commercial simulators (Aspen Plus and Aspen Dynamics). On the basis of global economic optimization, a design with optimized operation conditions for this process is developed. For dynamic simulations, feed flow rate and feed composition disturbances are used to evaluate the dynamic performance of several control structures. The dynamic simulation results reveal that the control structure with fixed reflux ratio can handle all disturbances well, except one kind of composition disturbance. An improved control structure with R/F (the reflux flow rate/the feed flow rate) ratio scheme is used to maintain the two products' purity requirements. Dynamic simulation results reveal that this control structure can handle feed flow rate and composition disturbances quite effective.

The design and control of extractive dividing-wall columns (EDWCs) have not yet been investigated, whereas those of dividing-wall columns (DWCs) and conventional extractive distillation columns (CEDCs) have been studied by many researchers. The control of EDWCs is more difficult than that of CEDCs and somewhat different from that of DWCs because of differences in the inner structure and interactions among control loops in EDWCs. In this work, the design and control of an EDWC for methylal/methanol separation are investigated using commercial chemical simulators (Aspen Plus and Aspen Dynamics). The optimum EDWC design based on the total annual cost (TAC) is screened first; then, the interaction between design and control is observed; and finally, two control structures for the EDWC are presented. The first proposed basic control structure featuring four composition controllers and an adjustable vapor split ratio alpha(v) can handle all disturbances well with small offsets in product purities, except for a 20% decrease in feed flow rate with a large deviation in methanol product purity. Then, an improved control structure with the Q(R)/F ratio is established. The large deviation is effectively suppressed, and all of the disturbances are well rejected with small offsets in product purities. It is also revealed that the vapor split ratio alpha(v) at the bottom edge of dividing wall must be adjusted at least for composition disturbances of key feed components.

A new method for methylal/methanol separation is presented by using fully heat-integrated pressure swing distillation. Rigorous steady state and dynamic simulations for this neat operation are implemented on commercial simulators (Aspen Plus and Aspen Dynamics). On the basis of the proposed partial optimization and global economical optimization, an optimized configuration for this fully heat-integrated pressure swing distillation is developed. From the simulation results, it is found that this process is more competitive than the one via extractive distillation from the economical view. Several control structures for this system are presented. The dynamic simulation results reveal that the proposed basic control structure is unable to maintain the two bottom products at their quality specification. This problem can be resolved by using a pressure-compensated temperature control scheme. The dynamic responses of this pressure-compensated temperature control show that this control structure works pretty well for this fully heat-integrated pressure swing distillation, even for large feed flow rate and composition disturbances. Contrast between the dynamic controllabilities of extractive distillation process and pressure swing distillation process is also made. Results show that the dynamic performances of the two alternative processes are somewhat similar.