Design And Control Of Separation Of Binary Azeotrope By Extractive Distillation Based On Isovolatility Curve

The separation of pressure-sensitive azeotropes by extractive distillation is a new separation method.Taking the separation of pressure-sensitive azeotropes ethanol-benzene and ethanol-ethyl acetate as examples,the influence of extractive distillation column pressure on process economy and dynamic controllability was investigated based on the change trend of isovolatility curve with pressure.For ethanol-benzene,four solvents,1,2-propanediol,dimethyl sulfoxide,p-xylene and chlorobenzene,were selected as candidate solvents according to the isovolatility curve at atmospheric pressure.The effects of different solvents on relative volatility of ethanol-benzene were further studied to determine different types of solvents1,2-propanediol and p-xylene.The isovolatility curves with different solvents had different trends with the change of pressure.Because the isovolatility curve is related to the amount of solvent,it can be concluded that the amount of solvent is related to the pressure.To obtain the relationship between the trend of isovolatility curve with pressure and the process economy,the parameters including extractive distillation column pressure were optimized,which took the minimum annual total cost(TAC)as the objective function.The results showed that when 1,2-propanediol was used as solvent,TAC decreased with the decrease of pressure,while when p-xylene was used as solvent,TAC decreased with the increase of pressure,which was consistent with the change trend of isovolatility curve with pressure.The economy of the process using1,2-propanediol as solvent at atmospheric pressure was better than that using p-xylene as solvent,and TAC decreased by 7.42%.After optimizing the pressure,the TAC of the process using p-xylene as solvent was smaller,and the TAC decreased by 9.17%.The same situation existed in the study of ethanol-ethyl acetate system.The change in pressure resulted in a change in the selection of the solvent,which provided more insight for the choice of a solvent in extractive distillation.The effects of pressure on dynamic controllability were discussed based on the minimal TAC.For ethanol-benzene,the control structures with two solvents,1,2-propanediol and p-xylene,under the optimal pressure were both more complex than that under atmospheric pressure.For ethanol-ethyl acetate,pressure had littleeffect on the controllability.The control structures under atmospheric pressure and optimal pressure were the same,and each had its own advantages and disadvantages in anti-disturbance ability.Extractive distillation column pressure played an important role in reducing the amount of solvent,reducing TAC,and selecting solvent.In dynamics,when the system was different,the influence of pressure on the dynamic controllability was different.