Study On The Separation Process For Allyl Alcohol-water Azeotrope System

Allyl alcohol and water can form an azeotrope at atmospheric pressure in the process of production,and it is difficult to separate such an azeotrope by conventional distillation process.In this paper,the total annual cost(TAC)was adopted as an objective function to develop and optimize the separation process by used Aspen Plus and Aspen Dynamics,a chemical simulation software.Meanwhile,the control structures of the separation process were analyzed with the disturbances of feed flow rate and feed composition.To separate the azeotrope of(allyl alcohol+water)by extractive distillation,N-methyl-2-pyrrolidone,N-methyl formamide and ethylene glycol were selected as extractive agents,and the isobaric VLE data for the binary systems of(allyl alcohol+N-methyl-2-pyrrolidone),(allyl alcohol+N-methyl formamide)and(allyl alcohol+ethylene glycol)were determined at 101.3 kPa by a modified Rose type recirculating still.And the values of saturated vapor pressure(P*),activity coefficient(y;)and excess Gibbs energy(GmE),were calculated by fitting the VLE data.The thermodynamic consistency of the experimental data was checked by the Herington,van Ness,infinite dilution,and pure component consistency method.Meanwhile,the experimental data were correlated by the NRTL,UNIQUAC and Wilson activity coefficient models,and the binary interaction parameters of the three models were regressed.According to the correlation results,the UNIQUAC activity coefficient model was used.The residue curve maps(RCM)of the ternary system(allyl alcohol+N-methyl-2-pyrrolidone+water),(allyl alcohol+N-methyl formamide+water)and(allyl alcohol+ethylene glycol+water)drawn and the x-y diagram of allyl alcohol and water by Aspen Plus using the UNIQUAC model were obtained.Compared to the residue curve maps and the x-y diagram,N-methyl-2-pyrrohdone was selected as the entrainer to design the extractive distillation process for the separation of the azeotrope(allyl alcohol+ water).An economic model of total annual cost(TAC)was adopted to optimize the extractive distillation process following the sequential iterative optimization procedure,which gives the minimal TAC values of 6.35×105$/y and the optimal entrainer flow rate of 130 kmol/h.Based on the optimal steady states of extractive distillation process,the control structure with fixed reflux ratios,the QR/F ratio control system,R/F control systems and structure of with composition controller were investigated,respectively.The dynamic performances of control structure were examined by introducing the flow rate and composition disturbances in feed stream.It was found that the control structure of with composition controller can improve the ability for handling the disturbances in a large extent in the extractive distillation process.The control structure was good at handling the disturbances of feed flow rate and feed composition through increasing the entrainer flow rate to 140kmol/h.However,the TAC was 10.1%higher than the former due to the increase of entrainer flow rate.Further analysis of each control structure is made by changing the disturbance to ± 10%.The results show that the control structure with composition controller and entrainer flow rate of 140 kmol/h performed well in dealing with feed disturbances for the extractive distillation process.