Extractive Distillation Of Acetonitrile-Water Azeotrope With The Mixture Of Ionic Liquid And Molecular Liquid As Entrainer

To overcome the shortcomings of high melting point and high viscocity of some ionic liquid entrainers in extractive distillation, the mixture of ionic liquid and molecular liquid(MILML) is used as entrainer. In this paper, the extractive distillation process for the separation of acetonitrile-water azeotrope using MILML entrainer was investigated.The vapor-liquid equilibrium data of the quaternary system of acetonitrile + water + ethylene glycol + 1-Ethyl-3-methylimidazolium Chloride([EMIM][Cl]) were measured at 102.5 KPa. The equilibrium data were correlated with NRTL model, the binary interaction parameters of acetonitrile-[EMIM][Cl], water-[EMIM][Cl], ethylene glycol- [EMIM][Cl] were obtained. The calculating results agree well with the experimental data. The experimental results indicated that the mixed entrainer of ethylene glycol+[EMIM][Cl] can could eliminate the azeotropic point of acetonitrile-water. The viscosity of [EMIM][Cl], ethylene glycol, as well as the mixer of [EMIM][Cl] and ethylene glycol was determined, and the results showed that the viscosity of [EMIM][Cl] decreased sharply when it is mixed with ethylene glycol. The contributions of ethylene glycol and [EMIM][Cl] in the mixed enrtainer were compared. The selectivity of [EMIM][Cl] is higher than that of ethylene glycol; and there is no synergistic effect between [EMIM][Cl] and ethylene glycol. The selectivity of mixed entrainer is mainly determined by the ionic liquid [EMIM][Cl], while the main function of 1,2-ethanediol is to dissolve the ionic liquid [EMIM][Cl] and to decrease the viscosity of [EMIM][Cl].The extractive distillation with [EMIM][Cl] and ethylene glycol as mixed entrainer to separate acetonitrile and water was simulated by Aspen Plus, the operating parameters of steady state and structural parameters for the dnynmic control were obtained. The effect of feed location, entrainer location, entrainer temperature, reflux ratio, solvent to feed ratio, the content of ionic liquid in the mixed entrainer on the concentration of acetonitrile in the distillate and heat reboiler were investigated by simulation.The dynamics and control simulation of the extractive distillation was carried out via chemical software Aspen Dynamic. Three control structure were designed to hold acetonitrile purity specification in spite of the disturbance of ±10% feed flow rate and ±10% feed concentration load disturbance. The dynamic response showed that the second designed control structure which was the best can keep the columns under normal operation with both products purities at their specifications despite feed flow rate and feed concentration variations.