Design and Mechanism of Ionic Liquid for Extraction and Separation of Lower Alcohol Azeotrope
Author:Ma Yi Xin
In the coal chemical industry,the problem of separation of lower alcohol,water and alkane azeotrope is widespread.The traditional separation method has high energy consumption,long process and low separation efficiency.Therefore,it is of great practical significance and theoretical value to study the green and clean separation technology of lower alcohol azeotrope.Ionic liquid(IL)is a new kind of green solvent,which has the properties of designability,wide liquid range and non-volatility.In this paper,ionic liquids were used as extractant to separate lower alcohol-water and lower alcohol-hexane azeotrope systems.The combination design of anion and anion in ionic liquid was studied.The mechanism of extraction and separation between ionic liquids and lower alcohol is clarified.The liquid-liquid equilibrium(LLE)data of IL-lower alcohol-water/hexane systems were measured and the process simulation was carried out.The groups of 83 ILs were divided using UNIFAC-Lei model.Defined the ILs in Aspen Plus with the key physical parameters of ILs and the phase behavior of ILs-lower alcohol-water/hexane system was predicted.According to the size of the non-miscibility area,the selectivity and distribution coefficient of the systems,the ILs which can be used in the extraction and separation process is designed.[Dmim][NTf2]、[Opy][NTf2]、[Bmim][MeSO4]、[Hmim][MeSO4]、[Omim][MeSO4]are suitable for the separation of lower alcohol-water system.[Dmim][MeS04][Hmim][OTf]、[Omim][OTf]、[Hmim][BF4]、[Omim][BF4]、[Dmim][BF4]are suitable for separation lower alcohol-hexane system.Based on COSMO-SAC model,the surface charge density distribution of 40 cations,37 anions and ethanol,1-propanol,water and hexane was obtained through quantum chemistry calculation.The infinite dilution activity coefficient of ionic liquid-lower alcohol-water/hexane system is calculated.Then the distribution coefficient Dy selectivity S,extractant loss SL and solvent solubility SP of ILs as extractant for lower alcohol-water/hexane systems were calculated.The results showed that[Dmim][NTf2]、[Amim][Cl]and[C4mim][NTf2]are suitable for extraction of lower alcohols from water;[Dmim][NTf2]、[C4mim][Cl]and[Amim][NTf2]can be used as an extractant for 1-propanol extraction from water;[Hmim][BF4]、[Bnmim][Cl]、[Hmim][OTf]and[Hmim][NTf2]can be used to extracted lower alcohols from hexane;[Hmim][BF4]、[C4mim][Cl]、[Hmim][OTf]and[Omim][NTf2]can be used as an extractant for 1-propanol extraction from hexane.Combining the results of UNIFAC-Lei and COSMO-SAC model,[Dmim][NTf2]was selected as the extractant for extracting lower alcohol-water systems.[Hmim][BF4]and[Hmim][OTf]were selected as extractant for the lower alcohol-hexane systems.By analyzing the separation mechanism of extraction process through the bond length、interaction energy and charge density distribution of intermolecular interaction,the hydrogen bond between the designed ILs and lower alcohol was determined,providing theoretical basis for the extraction of lower alcohol-water/hexane systems by ILs.The LLE experimental data for the systems of[Dmim][NTf2]-ethanol-water,[Dmim][NTf2]-1-propanol-water system were measured using the designed ILs for the systems of[Dmim][NTf2].With the designed ILs of[Hmim][BF4]and[Hmim][OTf],the LLE experimental data of[Hmim][BF4]-ethanol-hexane,[Hmim][BF4]-1-propanol-hexane and[Hmim][OTf]-1-propanol-hexane were measured.The distribution coefficient and selectivity of the system are calculated.The reliability of the data is tested and the fitting result shows that it has good reliability.Then,the activity coefficient models of NRTL and UNIQUAC were used for data regression to obtain the corresponding binary interaction parameters,laying a foundation for the design and optimization of the extraction process of the lower alcohol azeotrope.Based on the simulation and optimization for the process for extraction of lower alcohol-water/hexane by ILs,the effects of the number of plates and solvent ratio on the extraction process were investigated.The process parameters,annual total cost and CO2 emission of extraction of ILs-lower alcohol-water/hexane systems were obtained.Compared with the annual total cost of extraction distillation and CO2 emission of the process with ethylene glycol as extractant,it is found that the liquid-liquid extraction process of ionic liquid as extractant has obvious advantages,laying a foundation for the industrial application of ionic liquid extraction and separation of lower alcohol azeotrope.