Design And Comparison Of Reactive Dividing Wall Columns To Enhance Reactive Selectivity

Distillation is the most energy-consuming and pollution-heaviest link in the chemical production process,so it is an important task to optimize the energy saving.In the process of reaction and separation of the quaternary reversible reactant system with adverse kinetic characteristics such as low reaction selectivity,the low reaction selectivity will cause considerable difficulties in the reaction and separation of the reactant system,which will greatly increase the energy consumption of the reaction and separation process.At this point,in addition to solving the problems of low reaction rate and low conversion rate,improving the selectivity of the reaction has also become the key to the efficient reaction and separation of this system.Conventional reaction and separation sequences are often unable to efficiently accomplish the task of reaction separation of this system.However,the development and application of reactive distillation,dividing wall distillation and reactant excess technology make it more possible to carry out efficient reaction separation for such systems.Taking an ideal quaternary reversible reaction(the main reaction is A+B?2C,the side reaction is A+C?2D)as an example,this paper conducts a comprehensive and in-depth study on the reaction and separation of low selectivity systems in view of the most unfavorable relative volatility.First of all,in view of its low reactive selectivity,this paper chooses to use excess reactant technique,and according to the features of the system,B is selected as the excess reactant to improve the selectivity.Secondly,the appropriate location of the reaction section should be selected.Since the relative volatility of reaction mixture is ranked as the most unfavorable case,the reactive section can only be set at the top or/and bottom of the reactor in order to form favorable material coupling with the reactor section.Finally,three reactive separation schemes with the reactive section at the top or bottom of reactive column,and double reactive sections column are proposed.The reactive distillation sequence and the reactive dividing wall column of each scheme are designed and compared to evaluate the effect of the reactive dividing wall column on improving the reactive selectivity.In this paper,the total annual cost(TAC)is taken as the economic objective function,and the optimization strategies of the six structures of three schemes are presented,the steady-state modeling and design of the six structures are carried out respectively in Aspen Plus.The design results show that all the six structures can complete the reaction and separation task,and the steady-state performance of RDWC-BRS,RDWC-TRS and DRS-DDWC is better than their corresponding conventional reaction distillation sequence,which can enhance the selectivity of the reaction and complete the reaction and separation task with high efficiency.Through the deep comparison and analysis of the structure and steady state performance of RDWC-BRS,RDWC-TRS and DRS-DDWC,it can be concluded that DRS-DDWC has higher operating freedom and stronger coupling degree of mass and energy,which can maximize the selectivity of reaction,reduce energy consumption and have the best steady-state performance.