Measurement Of Vapor Liquid Equilibrium For Hydroxyethyl Ammonium Based Ionic Liquid-alcohol-water Systems And Process Simulation For Distillative Separation Thereof

As a kind of novel compounds, Ionic liquids (ILs) show manyunique properties in comparison with traditional molecular solventsbecause of their unique structure. Most of ILs are liquid at roomtemparature, which make them convenient for feeding and transport andthus for industry use. ILs also show good thermal stability and negligiblevapor pressure, which make them more environmental benign, safe foruse and easy for regeneration. This thesis mainly focuses on measurementof vapor-liquid equilibrium, thermodynamic modeling of theexperimental data, as well as process simulation for alcohol-water-ILdistillation systems at varying conditions.Three hydrophilic ILs, viz. mono-(2-hydroxyethyl) ammoniumformic [HMEA][HCOO], di-(2-hydroxyethyl) ammonium formic[HDEA][HCOO] and tri-(2-hydroxyethyl) ammonium formic[HTEA][HCOO], have been synthesized via acid base neutralizationreaction. Their structures are identified by¹³C NMR and¹H NMR and the purities are estimated above0.99(mole fraction). Their thermal stabilitiesare studied by TG-DTA, and their decomposition temperatures are allabove424K. In summary, the ILs can be used in the separation ofalcohol-water system for their good dissolubility in ethanol, methanol andwater. The ILs synthesized show other advantages like low cost and leasttoxicity to the environmemt.Using vapor-liquid equilibrium still (CL-II), vapor pressure atvarying IL contents and temperatures were measured for6binary and6ternary systems containing an IL and ethanol, methanol and water. Theresults indicate that ILs can depress the vapor pressure of the solvent butto differing degree with respect to different solvents. For an IL at fixedother conditions its effect is the strongest to water and weakest to ethanol.The binary systems of IL with methanol and water all show a negativedeviation from the Raoult's law, and the non-ideality increases with theincreasing IL-content. The ethanol-IL binary system shows a negativedeviation from the Raoult's law in the lower IL content region(w≤0.1),but also a positive deviation in the higher IL content region.The NRTL model was used to correlate the vapor pressure data ofbinary and ternary systems with the average absolute relative deviation(AARD) of0.62%and0.82%, respectively. Based on NRTL parameters,isobaric vapor-liquid equilibrium for ethanol-water has been estimated.The results indicate that (1) both ILs can enhance the relative volatiles of ethanol to water, and showed a salting-out effect to ethanol.(2) Theazeotropic point for the ethanol-water mixture shifts upwards as theincrease of the IL-content, and finally removed completely as ILconcentration above10wt%.(3) All5ILs based on (2-hydroxyethyl)ammonium showed a salting-out effect for ethanol aqueous solution inthe ethanol-rich region, but showed a salting-in effect in the water-richregion, and their salt effect follows the order of [HMEA][BF₄]<[HDEA][HCOO]<[HMEA][HCOO]<[HDEA][BF₄]<[HTEA][BF₄].Based on group contribution method and the ionic screening chargeconcept, the group segmentation method was improved, and accordinglythe accuracy of the density model with mass connectivity index parameteris increased greatly. The applicability of the present model was furthertested for54different ILs in a wide temperature range, its biggestinaccuracy is found to be1.83%, while the biggest inaccuracy is4.08%for the original model.Vapor pressure of ionic liquids is generally neglected in previousresearches due to their extremely low volatility. However, Vapor pressurehas been estimated here by the GC-PT equation of state, and integrated tothe present simulation process for the first time. As indicated by thesimulation results, the loss of ionic liquids in the separation process isnegligible being lower than0.001in terms of mass fraction.Concept design and process simulation were made for the extractive distillation separation of ethanol-water-IL system using Aspen Plussimulation software, the influences of process parameters, e.g. solventratios and reflux ratio, on separation effect were investigated, and theoptimal distillation conditions were determined. The separationperformance of ionic liquid and conventional glycol solvent is comparedand analyzed in terms of product purity and energy consumption. It isshowed that the heat duty of the reboiler using ionic liquid solventdecreases about28%, and the IL entraiment in distillate is lowered by4orders of magnitude in comparison with the conventional glycol solvent,showing a promising energy saving effect. Under the help of ionic liquids,the methanol component in the industrial ethanol solution is convertedfrom a lighter to a heavier component, and accumulated in the reboilertogether with the ionic liquid, which is helpful to obtain anhydrousethanol without methanol contamination.In conclusion, the (2-hydroxyethyl) ammonium based ionic liquidsare a novel class of extractive solvents with the advantages of facialpreparation, lower price, environmental benign, and safe for use, so it isexpected to be useful as solvents in ethanol-water separation process.