Reactive vapor-recompression distillation for green hexamethylene-1,6-dicarbamate synthesis

Abstract

Green synthesis of hexamethylene-1,6-dicarbamate (HDC) by reacting 1,6-hexanediamine with dimethyl carbonate (DMC) has garnered considerable attention recently because of the usage of DMC, which substitutes toxic phosgene. In this study, some plant-wide processes are proposed for green HDC synthesis. In the first process, HDC is synthesized using two reactive distillation (RD) columns in series. Excess DMC is used and the mixture of unreacted DMC and byproduct methanol from the RD column tops is separated by using a series of conventional distillation columns. Next, each RD column is enhanced by vapor recompression (VR) to reduce energy consumption by fully utilizing a small temperature difference between the column bottom and top. By the latent heat released from the overhead vapors of the RD columns, VR eliminates all reboiler duties of RD columns and conserves a substantial energy demand from conventional distillation columns. Compared with the process designed by RD, the process designed by RD + VR can reduce total operation cost and total annual cost by 42.6 % and 34.6 %, respectively. Finally, HDC synthesis by using CSTR is designed to compare with the RD- and RD + VR-intensified processes. Simulation results demonstrate that the reactive VR distillation process provides the most economical design for green HDC synthesis.