Design And Control Of Methyl Lactate Dividing-walls Reactive Distillation Column With Double Dividing-walls

The reactive distillation column combined reaction operation and separation operation into one unit,which can simultaneously accelerate the reaction operation and the separation operation,and has great advantages in reducing equipment investment and energy consumption.The research results show that the conventional reactive distillation column is easy to be used for reaction and separation process of the mixtures belonged to the most favorable and somewhat favorable relative volatility category.However,for the reaction system which has the last favourable relative volatility category(the boiling point of products are ranked between two reactants),some unconverted reactants will accumulate at the top and bottom of the distillation column,so conventional reactive distillation columns are difficult to separate such reaction mixtures.This unfavorable aggregation is usually dealt with in the form of an external circulation or in the form of a reaction section at the bottom of the tower.Although these methods improve the material coupling in the distillation column and promote the progress of the reaction.The subsequent separation process often requires 1-2 conventional distillation column to separate product mixtures which have an adverse impact on reduces equipment investment and energy consumption.In view of the above problems,based on the existing reaction separation structure,a kind of complex reactive dividing-wall distillation column(R-DWDC)structure which have double separators is designed.According to select different excess reactants,two forms of external recycle are designed:bottom-top of reaction section and top-bottom of column.The arrangement of the dividing-wall allows the reaction process and product mixtures separation process to occur in one column,effectively enhancing the coupling of material and energy,and having better steady-state performance than the conventional two-column system.Based on the esterification reaction of lactic acid and methanol,the total annual cost(TAC)is used as the objective function.Conventional reaction structure and the R-DWDC with double dividing-wall are designed and optimized in the chemical process software Aspen Plus.Then describe and analysis the graph of reaction rate and the liquid phase distribution.Based on the optimal structure of the economic performance indicators of the three,a three-point temperature control strategy was used to compare the dynamic performance of the dual separator R-DWDC and the conventional reaction separation structure under the application of feed flow and feed composition disturbance.The results show that the TAC of the double dividing-wall structure with methanol excess is reduced about 28.4%,of which the equipment investment(CI)is saved about 36.86%,and the operating cost(OC)is saved about 22.132%.In the case of step disturbance of feed flow and feed composition,the double dividing-wall distillation structure has shorter adjustment time and overshoot,indicating that it has better anti-interference ability.