Study On Separation Of Ethyl Acetate-n-heptane Azeotrope By Extractive Distillation With Mixed Ionic Liquid Solvent

Energy saving and consumption reduction of extractive distillation has been a hot topic for a long time.Organic solvent-ionic liquid mixed solvent as extractant can give full play to the advantages of both,overcome the limitations of large amount of organic solvent and high volatility,and improve the economic performance of the process.It is a new idea for energy saving and consumption reduction of extractive distillation.In this work,aiming at the ethyl acetate n-heptane azeotrope produced in pharmaceutical and chemical processes,the micro-interaction mechanism between mixed solvent and azeotrope was discussed,the effect of extractant ratio on separation performance was studied,and the economic and environmental effects of the dividing wall extractive distillation and vapor recompression assisted extractive distillation under the optimal solvent ratio were explored.Firstly,the selectivity and solubility of 100 ionic liquids were calculated using the COSMO-RS model,and the thermal stability of the ionic liquids was taken into account to identify 1-ethyl-3-methylimidazolium bis（trifluoromethylsulfonyl）imide（[EMIM][NTF₂]）as the optimal ionic liquid.The thermal stability of[EMIM][NTF₂]was investigated.The results showed that it had good thermal stability within 244°C.The effect of four organic solvents,ethylene glycol,N-methylpyrrolidone,dimethylsulfoxide and N,N-dimethylformamide,on the relative volatility of the azeotropes was investigated and N-methylpyrrolidone was identified as the optimum organic solvent.Secondly,the non-bonded interaction energy and spatial distribution function between[EMIM][NTF₂]+N-methylpyrrolidone mixed extractant and ethyl acetate-n-heptane were investigated by molecular dynamics simulations.The non-bonded interaction energy results indicate an optimum solvent ratio of 9:1 for the mixed extractant N-methylpyrrolidone:[EMIM][NTF₂].The results of the spatial distribution function show that the area of[EMIM]⁺is mainly distributed around the oxygen atom on the double bond in N-methylpyrrolidone and the oxygen atom on the double bond in ethyl acetate,and thus[EMIM]⁺is able to form a strong hydrogen bond with ethyl acetate.Finally,an extractive distillation process for the separation of ethyl acetate-n-heptane in mixed solvents was designed and the process was optimised with the objective of minimising the total annual cost,and the optimum operating parameters were determined.Compared with the traditional extractive distillation of single extractant N-methylpyrrolidone and[EMIM][NTF₂],the total annual cost of mixed solvent（90 mol%n-methylpyrrolidone-10 mol%[EMIM][NTF₂]）is reduced by 2.23%and 21.35%respectively,and the emission of acid gas is reduced by 5.45%and 37.12%respectively.On the basis of the optimum solvent ratio,the dividing wall extractive distillation and vapor recompression assisted extractive distillation process were designed.The results show that the vapor recompression assisted extractive distillation process has excellent energy-saving effect,which can reduce the total annual cost by8.76%and the acid gas emission by 16.48%.Therefore,the vapor recompression assisted extractive distillation process using mixed extractants can realize the separation of ethyl acetate n-heptane azeotropes with high efficiency and low consumption,which has a guiding role for the industrial separation of alkyl-ester azeotropes.