Study On The Kinetics Of Self Hydrolysis Of Isopropyl Acetate And Its Effect On The Dehydration Process Of Acetic Acid

The dehydration of acetic acid is an important technological process in the production of polyvinyl alcohol.At present,the heterogeneous azeotropic distillation is mainly applied,and using isopropyl acetate as entrainer.Isopropyl acetate could hydrolyze slowly to produce isopropanol under acidic conditions,which would affect the stable operation of system.However,in the past,this factor was not fully considered in technological process design.The research on the formation and distribution of isopropanol in acetic acid dehydration process,could provide technical guidance for stabilizing product quality,increasing production,saving energy and reducing consumption.In this paper,the effects of temperature on the self-hydrolysis reaction of isopropyl acetate in the aqueous phase and in the ester phase were investigated by using a 500mL reaction kettle.It was known by the thermodynamics computational analysis,that the reaction enthalpy change?was 10.02 kJ/mol and the reaction entropy change?was 15.18 J/(mol·K),respectively.Through analysis and regression of kinetic experimental data,the reaction kinetic equations applicable for above different conditions were obtained respectively.In the aqueous phase,the kinetic equation was as following:(?)In the ester phase,the kinetic equation was as following:(?)The dehydration technological process of acetic acid with the hydrolysis reaction of isopropyl acetate was simulated by using the reactive distillation module in Aspen Plus simulation software.The simulation results were compared with those in the process without hydrolysis reaction.It was shown that,when there was not a stream for purging isopropanol in the process,isopropanol would be continuously accumulated in the system.The accumulation of isopropanol could result in the change of temperature profile in the azeotropic distillation column;increase the content of acetic acid in the vaporous phase at the top of column,and the heat duty in the reboiler.All these phenomena would have unfavorable effect on the separation process.The Aspen Dynamics software was used in modeling the dynamic process of dehydration of acetic acid,and to evaluate following three temperature control schemes:single-sensitive plate control scheme CS1,double-sensitive plate control scheme CS2and temperature difference control scheme CS3.The step disturbance tests showed that CS3 could eliminate the effect of pressure fluctuations on the sensitivity of bubble point,and still perform well when the larger feed disturbances occurred.Finally,the dynamic technological process of with constant accumulation of isopropanol was also simulated for the above three control schemes.It was found that,when CS2 and CS3 schemes were applied,the dynamic processes of the system were quite different with CS1,the temperature distribution in azeotropic distillation column was not changed,the stable operation of azeotropic distillation column coud be still carried out.