Applied Fundamental Research On The Separations Of Ethylene/Ethane And1-Hexene/n-hexane By Ionic Liquid

Lower olefin and paraffin are the important basic chemical materials. But the separation of olefin and paraffin mixtures is one of the most difficult and energy-intensive process in petrochemical industry due to the very small relative volatilities and similar molecular structure between the olefin and paraffin molecules. The thesis utilized the ionic liquid (IL) as the extractant or absorbent for the separation of ethylene/ethane and1-hexene/n-hexane based on the unique properties of IL such as negligible vapor pressure, the feasibility of structure and function tunability, as examples of new method for olefin/paraffin separation with ionic liquids.A few single and dual functional ILs were designed and synthesized, in which there were some unsaturated functional groups such as nitrile, amino, acetylamine groups. These groups have the π-π and hydrogen bond interaction with carbon-carbon double bond of olefin and would enhance the separation selectivity of olefin to paraffin, and the dual acetylamine functional IL ([(CON)2im][NTf2]) was synthesized for the first time. The nuclear magnetic resonance (H-NMR), infra-red spectrum (IR), elementary analysis and thermogravimetric analysis (TGA) were used to characterize the ILs.The extraction performance of16ILs for1-hexene/n-hexane separation was studied. The effects of the structure of anion, the length of alkyl side chain and the structure of substituted groups in cation were investigated. The results showed that ILs had significant effect for the separation of1-hexene/n-hexane. The selectivities of1-hexene to n-hexane were in the range of1.5-3.0. The distribution of1-hexene in ionic liquids with anion of [NTf2] was larger, and the distribution of1-hexene in biphasic system increased remarkably with the increase of the length of alkyl side chain. In [C6mim][NTf2], the distribution coefficient of1-hexene was0.27, which was twice higher than that in [C2mim][NTf2]. The ILs in which cation with a nitrile and acylamino functional group had high selectivities for1-hexene/n-hexane, but the distribution coefficients of1-hexene decreased. The selectivity coefficient for1-hexene to n-hexane was2.93with acetylamine functional IL ([CONmim][NTf2]).The solubilities of ethylene and ethane in single and dual functionals ILs with nitrile were measured at0.5-1.1bar to study the influence of functional group. The Henry’s coefficients of ethylene in conventional IL ([Bmim][NTf2]), and in single and dual functional ILs with nitrile group ([CPmim][NTf2],[(CP)2im][NTf2]) were75.4bar,124bar and131bar, respectively. The selectivities of ethylene to ethane were1.32,1.67, and2.17respectively. It showed that the functional group greatly enhanced the selectivity for ethylene/ethane separation.This work studied the effect of the silver-based ILs for olefin/paraffin separation, and discussed the equilibrium model of the absorption of ethylene and the extraction of1-hexene. The results showed that the silver-based ILs had a significant effect for the separation of olefin/paraffin, the solubility of olefin increased greatly with silver salt in ILs, but the solubility of paraffin was almost constant. The selectivity of1-hexene to n-hexane increased with the volume ratio of1-hexene/n-hexane decreased in organic phase, the selectivity coefficient was14.8when the volume ratio was0.05. The equilibrium model showed that when the ratio of silver ion to1-hexene in the range of1.59-0.09, the complex of silver ion and1-hexene was formed by the ratio of2:1, and when the ratio of the concentration of silver ion to ethylene in the range of0.31-0.20, the complex of silver ion and ethylene was formed by the ratio of1:1.The activity coefficients of58olefins, paraffins and other organic compounds at infinite dilution in dual acetylamine functional IL [(CON)2im][NTf2] were determined at different temperature (323.15K-353.15K) by gas chromatography. The Linear Solvation Energy Relationship (LSER) was used to study the characters of IL, the average absolute deviation was1.56%. The result showed that the IL was weakly for olefin/paraffin separation, but had the effect for the separation of homologues, isomers and azeotrope.