Design And Control Of A Process To Produce Ethylene Glycol Diacetate By Transesterification

In this paper,the process of transesterification of methyl acetate with ethylene glycol is simulated and optimized by using Aspen Plus.Then dynamic control structures are designed by using Aspen Dynamics.First,the traditional two columns process is improved,which consists of a reactive distillation column and an atmospheric column.But the improved process consists of a reactive distillation column,a pressurized column and an atmospheric column.In order to achieve the purpose of saving energy and reducing the total cost,a differential pressure thermally coupled technology,which makes the heat duty of the pressurized column's condenser as the heat source of the atmospheric column's reboiler,is adopted in the process.The reaction kinetics of transesterification of methyl acetate with ethylene glycol are described by the pseudohomogeneous model.The influences of design parameters on the conversion of methyl acetate are studied,such as feed mode,the number of theoretical stages and reflux ratio.These parameters are further optimized to minimize the total annual cost.The result shows that,comparing with the traditional two columns process,the energy consumption and the annual total cost of the process can be reduced 66.09% and 60.61%,respectively.To perform the dynamic simulation,the physical size of equipments is first calculated.And the right temperature control stage of each column is chosen by using singular value decomposition.Then the basic control structure is set up.The feed flow rate disturbance and the component disturbance are added to explore its dynamic control performance.Since the dynamic response of the basic control structure is unsatisfactory,three schemes are proposed to improve the performance of the basic control structure.The control structure CS1 enhances the connection of units by using a flow feed-forward compensation,but the result is undesired.The control structure CS2 introduces a cascade control of component with temperature.However,the purity of ethylene glycol diacetate and methyl still can't meet the requirement.It can be seen that the component control is not effective to all processes.The control structure CS3 introduces a cascade control of the temperature controller with the reboiler's heat duty which is in proportion to the corresponding feed flow rate.Though the system will fluctuate sometimes,the purity of ethylene glycol diacetate and methyl both can meet the requirement after the system recovers steady state fast.In conclusion,the control structure CS3 is suitable for this process.