Optimization And Control Of Seperating Ethyl Acetate/acetonitrilr Azeotropic System Using Special Distillation

Ethyl acetate and acetonitrile are widely used in chemical industry and pharmaceutical industry.In this paper,the separation of ethyl acetate/acetonitrile system was carried out by special distillation.The optimization design and dynamic control of ethyl acetate/acetonitrile separation process are explored in Aspen Plus and Aspen Dynamics.Finally,the strict economic optimization and stable dynamic control of the separation process are realized.Conventional two column extractive distillation method is proposed for separating ethyl acetate\acetonitrile azeotrope,the process is designed and optimized by using the minimum total annual cost of TAC(Total Annual Cost)as the objective function.The study of dynamic control is investigated after getting the optimal process parameters.First,the basic control structure of fixed reflux ratio is proposed,the flow rate and compositions disturbance are introduced,the results show that the acetonitrile product purity fluctuation is too large,and the reboiler heat duty response slowly.Based on the problem,we put forward the reflux flow rate proportional to feed rate(R/Fn)and reboiler duty proportional to feed rate(QR/Fn)dynamic control scheme,this scheme has obvious advantages in the control of the purity of the product,and finally a stable control is achieved.The energy consumption of conventional two column extractive distillation of ethyl acetate acetonitrile azeotrope system is high,and the dividing wall column has the advantages of energy-saving.The dividing wall column is applied in the extractive distillation process,and the steady-state flowsheet and dynamic control of the extractive distillation dividing wall column is explored.First of all,the separation scheme of the the equivalent model of two column model extractive distillation dividing wall column is established,and the process optimization is carried out.Comparing with the conventional extractive distillation process,the TAC of the extractive distillation dividing wall column is reduced by about 19.7%.But due to the vapor spilt ratio in the separation scheme of the equivalent model of two column model can’t be adjusted,the separation scheme of the equivalent model of three column model extractive distillation dividing wall column is established based on the the equivalent model of two column model.Dynamic control is investigated based on the steady-state simulation.First,the control structure with vapor spilt ratio is proposed,after introducing the feed flow rate and composition disturbances,the results show that ethyl acetate and acetonitrile product purity having large deviation.Further improvements are made,the reflux rate proportional to side draw flow(R/Vn)feed-forward control structure is proposed to replace the fixed reflux ratio control structure,a composition controller of CC2 is added,and cascade with the vapor spilt ratio,disturbance results show that the deviation of two product purity is smaller,but the requirements of separation are still not reached.On the basis of the temperature controller,the QR/F proportional control is added to improve the structure.The final control structure can handle the feed flow and composition disturbance well.The study of the steady state optimization and dynamic control of ethyl acetate and acetonitrile azeotrope system in this paper will provide a theoretical basis for the practical industrial design and control for the special distillation to separating two component azeotropic system.