Separation Study Of Isopropyl Acetate And Isopropanol Azetropic Mixture With Ionic Liquid As Entrainers

Isopropyl acetate and isopropanol are important chemical raw materials.In the industry process of producing isopropyl acetate with isopropanol,the separation of isopropanol and isopropyl acetate is necessary in order to obtain the target product isopropyl acetate,which has become a research hotspots in separation field.The extractive distillation is a common process for separating the azeotrope due to the simple operation and high separation efficiency.In recent years,owing to the state's promotion of green chemical,the separation process using dimethyl sulfoxide as extractant has been phased out.The ionic liquids(ILs)have become a alternative to conventional organic solvent due to their low vapor pressure,high chemical,thermal stability and designability.Among them,the superior advantage of ILs is that they can be designed with anionic and cations,and artificially synthesize target ionic liquids to meet the production standards of the process.However,due to the wide variety of anions and cations,an efficient and accurate screening method is necessary to obtain high separation efficiency ILs,which can be applied to the extractive distillation.For this purpose,the main research contents of this paper are as follows:(1)In this work,the 18 cations and 22 anions were designed by Guassian 03,and composed 396 IL to select the superior ILs.Then,the selectivity and viscosity of ionic liquid were employed as two index to evaluate the outstanding IL with COSMOtherm X software based on COSMO-RS theory.[Ac]-based ILs perform the obviously selectivity compared with other anions,imidazolium-based ILs characterize the higher selectivity and lower viscosity compared with other cations.Simultaneously,considering the mutual solubility between IL and azeotrope,1-hexyl-3-methylimidazolium acetate [HMIM][Ac] was found as the superior ionic liquid,1-octyl-3-methylimidazolium acetate [OMIM][Ac] and 1-decyl-3-methylimidazolium acetate [DMIM][Ac] were selected as comparison items to verify the superior separation performance of [HMIM][Ac].(2)The vapor-liquid equilibrium of binary system(isopropyl acetate + isopropanol)and ternary system containing ionic liquid(isopropyl acetate + isopropanol + [HMIM][Ac] / [OMIM][Ac] / [DMIM][Ac])was measured at 101.3 k Pa.The experimental result indicated the dramatic salting-out effect on isopropyl acetate due to the addition of ILs,which leads to an increase in the content of isopropyl acetate in the vapor phase.And the phenomenon is particularly obvious with increasing the content of ILs.Simultaneously,the addition of IL makes the azeotropic point move towards right and the azeotropic phenomenon could be completely eliminated.The experimental data were correlated using the NRTL activity coefficient model,and the model values were regressed from the experimental data using the Levenberg-Marquardt method to minimize the objective function.The deviation between the model correlation value and the experimental value was less than 1%,indicating that the NRTL model is suitable for IL-containing system.Based on NRTL model,the minimum molar fraction of the three ionic liquids required to separate isopropyl acetate and isopropanol azzetrope are: [HMIM][Ac]=0.036,[OMIM][Ac]=0.045,[DMIM][Ac]=0.060,respectively.The result indicates that the separation performance of [HMIM][Ac] is stronger than [OMIM][Ac] and [DMIM][Ac].(3)In order to explore the extraction separation mechanism,the excess enthalpy change of [HMIM][Ac]/[OMIM][Ac]/[DMIM][Ac]+isopropyl acetate/isopropanol at 298.15 K were predicted with COSMOtherm X software.The results show that hydrogen bond dominated the weak interactions between the ionic liquid and the isopropanol.The hydrogen bond between [HMIM][Ac] and isopropanol is stronger than other ILs between isopropanol,which is the key to excellent separation selectivity of [HMIM][Ac].The conformational optimization and electronic structure density analysis of [HMIM][Ac] + isopropanol structure with reduce density gradient function based on density functional theory to investigate the position and strength of the interaction between ionic liquid and isopropanol.The results show that there are C1-H13...O42,C6-H18...O42 weak hydrogen bonds between [HMIM]+ and isopropanol,O42-H50...O54 hydrogen bonds between [Ac]-and isopropanol,these interactions result in a "bundling" between [HMIM][Ac] and isopropanol,which lead to the separation of isopropyl acetate and isopropanol azeotrope.(4)Based on the Aspen Plus simulation software.The separation of isopropyl acetate and isopropanol using 1-hexyl-3-methylimidazolium acetate([HMIM][Ac])as entrainer was simulated.Simultaneously,the mass fraction of the top product,the thermal load of the tower top condenser and the tower kettle reboiler are used as indicators,which were employed to analyze the effects of the solvent ratio,the theoretical number of the whole tower,the reflux ratio on separation performance with the sensitivity analysis tool.Among them,the optimal process parameters of the extractive distillation column: the theoretical number of the whole column is 20,the ionic liquid and the raw material feeding position are the third and the ninth block,respectively,the reflux ratio is 0.5,and the solvent ratio is 0.7.Under the optimal process conditions,the mass fraction of isopropyl acetate in the top of the column is 99.9%,meeting the separation requirements.The solvent recovery tower adopts an atmospheric distillation column;the theoretical number of plates is 5.The recovery liquid feed position is the third block,the reflux ratio is 1.2,and the top of the column can obtain isopropanol with a mass fraction of 99.8%,[HMIM][Ac] with a mass fraction of 99.7%.It is indicated that [HMIM][Ac] has an industrial prospect as an entrainer for separating isopropyl acetate and isopropanol mixture.