Gaseous Hydrocarbon Separations Using Functionalized Ionic Liquids

Abstract

-The functionalization of the side chains on the cation or the anion of an ionic liquid is a common approach to tailor its properties for different processes including the separation of gases. In this paper, we present the current state of the art concerning the usage of ionic liquids for hydrocarbon separations. We also show how the functionalization of ionic liquids or the appropriate anion/cation combinations can contribute to the increase of the performance of the ionic liquids for the separation of gaseous hydrocarbons -either by improving the capacity of the ionic liquid to absorb a given gas or by increasing the selectivity towards a particular hydrocarbon. Original results concerning the usage of olefin-complexing metal salts of lithium (I), nickel (II) and copper (II) dissolved in ionic liquids for selectively absorbing light olefins are presented. It is observed that the absorption capacity of an imidazolium-based ionic liquid is doubled by the addition of a copper (II) salt. This result is compared with the effect of the functionalization of the ionic liquid and the advantages and difficulties of the two approaches are analyzed.Résumé -Liquides ioniques fonctionnalisés pour la séparation d'hydrocarbures gazeux -La fonctionnalisation des chaînes latérales sur le cation ou l'anion d'un liquide ionique est une approche commune pour adapter ses propriétés pour les différents processus, y compris la séparation de gaz. Dans cet article, nous présentons l'état actuel des recherches concernant l'utilisation de liquides ioniques pour les séparations d'hydrocarbures gazeux. Nous montrons comment la fonctionnalisation de liquides ioniques ou des combinaisons d'anions/cations appropriées peuvent contribuer à l'augmentation de leur performance pour la séparation des hydrocarbures gazeux -soit par l'amélioration de la capacité du liquide ionique pour absorber un gaz donné ou en augmentant la sélectivité pour un hydrocarbure particulier. Des résultats originaux concernant l'utilisation de sels métalliques de lithium (I), le nickel (II) et le cuivre (II) dissous dans des liquides ioniques pour absorber sélectivement des oléfines légères sont présentés. On constate que la capacité d'absorption d'un liquide ionique à base d'imidazolium est doublée par addition d'un sel de cuivre (II). Ce résultat est comparé avec l'effet de la fonctionnalisation du liquide ionique. Les avantages et les difficultés de ces deux approches sont analysés.

Solution structure of propane and propene dissolved in the ionic liquid 1-butyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}imide from neutron diffraction with H/D substitution and empirical potential structure refinement modelling

“…The results show subtly different distributions of the two hydrocarbons in the IL, with propene exhibiting greater association with the [C 4 mim] + cation imidazolium ring through both the C(4/5)-and C(2)-sites whereas propane only exhibited association with the C(4/5)-position on the imidazolium ring and had a significantly greater correlation with the terminal-CH 3 group of the butyl chain. These results are remarkably consistent with, and support conclusions from, previous MD simulation [11] of ethane and ethene dissolved in [C 4 mim][NTf 2 ] where greater ethene/[C 4 mim] + -ring association was observed compared to preferred ethane-alkyl chain association driven by differences in the polarisation and charge distribution between ethane and ethene.…”

“…Different preferential solvations sites for the two gasses in the IL were identified using MD simulation, with ethene reported to solvate closer to the imidazolium ring than ethane which associates most strongly with the terminal −CH 3 groups of the cation's butyl chain. However, while the thermochemistry of hydrocarbon gas/IL mixtures has been studied [11] and modelled using regular solution theory [12], the molecular mechanisms for solvation are still not fully understood.…”

Synthesis and Granulation of a 5A Zeolite-Based Molecular Sieve and Adsorption Equilibrium of the Oxidative Coupling of Methane Gases

“…This process is extremely energy-intensive and requires large capital and operating costs. , A recent report indicates that the separation processes involved in ethylene and propylene production represent 0.3% of the world energy use . Among different in situ or downstream splitting alternatives for olefin/paraffin mixtures, swing adsorption systems, simulated moving beds, membrane separations, chemical complexation, and absorption have shown promising results. − In particular, current industrial OCM technology developers (e.g., Siluria Technologies, ExxonMobil) have mostly implemented swing adsorption separations. − …”

Unravelling free volume in branched-cation ionic liquids based on silicon

“…This simplification is useful to rationalize the solubility of argon in the different ionic liquids studied and has been proved valid for the absorption of other interacting gases in ILs. 43 In Figures 7 and 8, the enthalpy and entropy of argon solvation in the different ionic liquids at 313 K are represented. As depicted, the solvation of argon in all ionic liquids is dominated by entropic contributions.…”

“…Weaker interactions, such as dispersion, can also favour gas absorption enthalpically, as demonstrated, for example, by the increased solubility of ethane in ILs with longer alkyl chains. 9 …”