Design And Optimal Control Of Reactive Distillation Process For Synthesis Of Isobutyl Acetate By Transesterification

The paper aims at systematically studying the reactive distillation process for the synthesis of isobutyl acetate by transesterification by using Aspen Plus and Aspen Dynamics.The transesterification of methyl acetate with isobutanol can realize high-value utilization of the former,while the other product is methanol that can improve added value of products.However,the conversion rate of this route is limited by chemical equilibrium and unfavorable relative volatility ranking which leads to high energy consumption in the conventional reactive distillation(RD)process.In order to further obtain the economic advantages of reactive distillation technology,the strengthening processes of conventional RD process for synthesizing isobutyl acetate are proposed based on synergistic effect,such as the thermally integrated pressure-swing reactive distillation process,the reactive dividing-wall column and pressure-swing reactive dividing-wall column.The energy saving status of each process is studied based on the total annual cost(TAC),and the changes of the±20%feed flow and 5%feed composition are introduced to analyze the anti-interference ability of its dynamic control strategy.Firstly,the feasibility of the reactive distillation process for synthesizing isobutyl acetate by transesterification is analyzed by using the residual curve.On this basis,the conventional RD process is established and optimized,and the TAC under the optimal operation parameters is 1334.63×10~3$/year.Then,the composition and temperature control structure are designed for the conventional RD process,and the dynamic response results under the disturbance of±20%feed flow and 5%feed composition have shown that the conventional RD process is easy to achieve robust control.The steady-state design and dynamic control of the thermally integrated pressure-swing reactive distillation process(PST-RD)are carried out by using rigorous heat exchanger models.Operation pressure is regarded as one of the important decision variables affecting TAC changes in the optimization process,the optimization results have shown that the minimum TAC of PST-RD process is 878.18×10~3$/year.Compared with the conventional RD process,42.32%energy saving and 34.20%TAC reduction can be achieved.Then,the dual temperature control structure and pressure/composition cascade control structure for the PST-RD process are proposed,and the dynamic response under±20%feed flow and 5%feed composition revealed the improved pressure/composition cascade control structure is more effective to realize the external heat integration of PST-RD process.Finally,the reactive dividing-wall column(RDWC)and its improved process pressure-swing reactive dividing-wall column(DP-RDWC)are proposed based on three column model.Steady-state optimization results have shown that the minimum TAC of two processes are 1161.32×10~3$/year and 906.80×10~3$/year respectively.Compared with the conventional RD process,the RDWC process can achieve 22.66%energy saving and 12.99%TAC reduction,while DP-RDWC process can achieve36.02%energy saving and 32.06%TAC reduction.For the most economical DP-RDWC process,we have developed and evaluated three control structures strategies under throughput and composition disturbances.Dynamic simulation results have shown that the robust control can be obtained under each control strategy;But,under the composition/temperature cascade control structure CS3,the stability time of the two products is shorter and the purity deviation is smaller.By comparing the three strengthening processes for the synthesis of isobutyl acetate by transesterification,it is not difficult to find that the thermally integrated pressure-swing reactive distillation process show the best steady-state economy,and the pressure-swing reactive dividing-wall column process is slightly less.However,if we balance the economy and controllability,the latter should be the best choice.