Optimum Topological Configuration for the Vapor-Recompressed Dividing-Wall Distillation Columns Processing an Intermediate-Component-Dominated and Wide-Boiling-Point Ternary Mixture

Abstract

The configuration of double columns and multiple separating sections for a dividing-wall distillation column (DWDC) makes the applications of vapor recompression heat pumps (VRHPs) a challenging task with great complexity and tediousness. Although many researchers revealed the great advantages of the VRHP-assisted dividing-wall distillation columns (VRHP-DWDCs), they have actually neglected such inherent issues in process development. In the current work, the optimum topological configuration of the VRHP-DWDC, i.e., a DWDC with a middle partition facilitated by two VRHPs, is derived for the separations of intermediate-component-dominated and wide-boiling-point ternary mixtures in terms of steady-state operating characteristics. Because of the maximized mass and thermal coupling between the prefractionator and main distillation column involved, excessive heat always exists around the location of the intermediate product. Via the two VRHPs, the excessive heat can effectively be used to aid the separation operation in the stripping section of the prefractionator or in the common stripping section. The first VRHP helps to reduce the operation irreversibility by taking the advantage of the small temperature elevation available between the location of the intermediate product and the common stripping section and releasing the excessive heat at an elevated temperature to the latter. The second VRHP serves to reduce further the operation irreversibility by compressing the overhead vapor stream preheated by the condensed liquid from the first VRHP and releasing its latent heat at an elevated temperature to the stripping section of the prefractionator or the common stripping section. Two case studies on the separations of intermediate-component dominated and wide-boiling-point ternary mixtures of benzene, toluene, and o-xylene and n-pentane, n-hexane, and n-heptane demonstrate the economic optimality of the proposed VRHP-DWDC. For the DWDC with a top or bottom partition, the optimum topological configuration of the VRHP-DWDC can also be derived in the same manner. The capability of predetermining the optimum topological configuration of the VRHP-DWDC can lower considerably the complicated and time-consuming work of process modeling, structural and operating parameter searching, and process screening in process development and is of great significance to the applications of this process intensification technology.