| Dichloromethane(DCM)and methanol are common organic solvent in the chemical engineer industry,however,they would form an azeotrope whose azeotropy formation is 0.849 at atmospheric pressure,which are often separated by high performance-price ratio method extractive distillation.The core of extractive distillation to separate azeotrope is chosing excellent extractant.Ionic liquid,as a special late-model green heteropolar compound,has some good characteristic such as being liquid phase in normal atmospheric temperature,nearly having no vapour pressure,good solubility,stable in high temperature and environment-friendly and so on,so it's a high potential extractive solvent.However,the research about using ionic liquid in the area of extractive distillation are less at present,also the thermodynamics data about ionic liquid are not comprehensive,so this article aims at studying the actual effect of using ionic liquid to separate DCM-methanol system,also we'11 study the correlation effect of common thermodynamics models to this system to extend the research about ionic liquid.This article choose three kinds of ionic liquid to experiment:1-butyl-3-methylimidazolium tetrafluoroborate([Bmim][BF4]),1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide([Hmim][NTf2])and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide([Bmim][NTf2]).1.Before the experiment,we choose 24 kinds of common ionic liquids,and through UNIFAC model to use group contribution method to analyse the infinite dilution activity coefficient of DCM and methanol in these 24 kinds of ionic liquids,and then we can get the ionic liquid which is potential to have good ability to separate DCM-methanol systems.Through this step we have chosed[Bmim][BF4],[Hmim][NTf2]and[Bmim][NTf2]to continue our subsequent experiment.2.The main device we have used in our experiment is modified Othmer still.We have measured the vapor-liquid equilibrium data of DCM-methanol systems containing different kinds of ionic liquids and different concentration of ionic liquids respectively.By research the experiment results we find that the adding of ionic liquids would make the curve of vapor-liquid equilibrium deviate from its original trajectory,which expressed as the enlargement of relative volatility of the original binary system,which makes the azeotropic points have the trends of disappearing,and the higher the concentration of ionic liquids added,the more obvious the trend is.In addition comparing the separation ability of the ionic liquids we find that[Bmim][BF4]>[Hmim][NTf2]>[Bmim][NTf2].3.In this article,we also used 4 common thermodynamics models to correlate the vapor-liquid equilibrium data:Wilson model,NRTL model,UNIQUAC model and e-NRTL model,the results of the study shows that Wilson model,NRTL model and UNIQUAC model could analyse the system containing ionic liquids well,the average relative deviation of the results are no higher than 3%.In other hand the correlation result of e-NRTL is not well,so it's no recommended to be used to correlate the system containing ionic liquids.4.At the end of the experiment we used the software Aspen Plus to simulate extractive distillation of DCM-methanol systems containing ionic liquids,the property method we have used is NRTL.The results of simulation shows that the using of ionic liquids as extractant could get high purity product.Also we have optimized the operating parameters of the process such as number of stage,reflux ratio and the feed stage,to reduce the energy consumption on the premise of not reducing the purity of product. |
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