Reactive Dividing-wall Distillation Columns Employing An External Recycles To Streng-Then The Process Of The Transesterification Of Butyl Acetate And Ethanol

In the field of Mass-transfer and Separation Engineering of the modern chemical technology, reactive distillation column is a very important process coupling that can largely improve the efficiency of the reaction process and separation process and has great development potential. In the current study, not all of the reaction system has improve the reaction efficiency and reduce the total annual cost, but it will show much limitation in separating some reaction systems. For example, in order to separate the quaternary reacting mixtures whose rank of relative volatilities is disadvantage (reactants are the light and the heaviest compositions, products are the lightest and the heavy compositions),traditional reactive distillation column (CRDC) leads to adverse effect on the separation process that the reactants is difficult to fully contact because of the reactants which not conversion will be accumulated on the top and bottom of the column.To solve these problems, considering the structure of reaction distillation column (RDC) has huge influence on the separation process, a reactive dividing-wall distillation column with an external recycle from the middle part of the column’s right side to a certain stage of the reactive section (RDWC-ERMR) and a reactive dividing-wall distillation column with two reactive sections and an external recycle from the bottom to a certain stage of the reactive section which in the right side of the dividing wall (RDWC-TRSERBR) are proposed. The dividing wall can make the reactants separated in the public rectifying and stripping sections in the RDWC-ERMR and the RDWC-TRSERBR, external recycles can make reactants on the right side of the divided wall back to the reaction section on the left side of the divided wall in the RDWC-ERMR and make the heaviest reactants on the bottom back to the reaction section on the right side of the divided wall in the RDWC-TRSERBR,It can reduce the accumulation of reactants and improve the reaction conversion rate, strengthen the material and energy coupling, and has better effect of the steady state. Based on transesterification of butyl acetate and ethyl alcohol, an optimal RDWC-ERMR and the RDWC-TRSERBR were designed with Aspen Plus, employing the total cost (TAC) and reboiler thermal load (Qreb) as objective functions, analyzes the liquid distribution of the mole concentration,temperature distribution and the reaction rate distribution, also comparing with the CRDC to evaluate the economic performance.The results indicate that the reaction rate of the RDWC-ERMR and RDWC-TRSERBR were significantly higher than those of the CRDC, require less plate number of reaction section, and have better separation effect;RDWC-TRSERBR were significantly higher than those of the CRDC, require less plate number of reaction section, and have better separation effect;meanwhile, the TAC of the RDWC-ERMR and the RDWC-TRSERBR is significantly reduced compared to the CRDC, and the economic performance is better. As a consequence, in order to separate the quaternary reacting mixtures whose rank of relative volatilities is disadvantage, the reactive dividing-wall distillation column with an external recycle (RDWC-ER) should be considered.