Comparison Of The Intermediate Entrainer Separation Process And The Extractive Distillation Process

Extractive distillation is the widespread use to separate minimum azeotropic mixtures.But when the boiling point difference of the two separated components is large enough and an intermediate entrainer is possibly applied to the separation of the azeotrope system.In this work,through the analysis of the some realistic example,we have compared the extractive distillation process and the intermediate entrainer separation process(IE-I),including the state design and the dynamic performance.Methanol and toluene,as an important basic chemical raw material,is widely applied to chemical,pharmaceutical and other industries.Meanwhile,in the side-chain alkylation of toluene,methanol and toluene forms the minimum point azeotrope mixture,which need to be separated by the special distillation process.The separation of methanol-toluene by introducing aniline or triethylamine(Et3N)is investigated,with aniline and Et3 N as heavy and intermediate entrainers,respectively.First,the conventional extractive distillation process with aniline as the extractive entrainer(HE)and the direct/indirect separating sequences using Et3 N as intermediate entrainer(IE-D/IE-I)have been designed and optimized with rigorous simulations.Subsequently,the dynamic performances of these optimized processes are investigated with temperature control strategies.Finally,the steady-state process economics and dynamic performances for these processes are facilitated.In this work,the steady-state design has been optimized,based on the annual total cost(TAC)as the objective function.The IE-I process has a 7.26% total annual cost(TAC)saving compared with the HE process and the total energy cost of the IE-I process is 18.79 % lower than that of the HE process.As to dynamic performances,the maximum transient deviation of the methanol product purity in the IE-I process is much smaller than that in the HE process when ±20% feed flow rate disturbances are introduced.And when-20% step toluene composition disturbance is introduced,the new steady-state methanol product purity in the HE process is 99.5 mol% while that in the IE-I process is 99.8%.The numerical and graphic comparisons indicate that the IE-I process possesses advantages over the HE process to some extent.The small advantages possessed by the IE-I process are mainly those of the use of lower-grade heat source,lower energy consumption and smaller dynamic deviations under feed disturbances etc.