Ionic Liquid/Metal–Organic Framework Composites for H₂S Removal from Natural Gas: A Computational Exploration

Abstract

The separation of H 2 S/CH 4 mixture was computationally examined in the composites of ionic liquids (ILs) supported on metal-organic frameworks (MOFs) at room temperature. Cu-TDPAT was selected as supporter for four types of ILs combined from identical cation [BMIM] + with different anions ([Cl] -, [Tf 2 N] -, [PF 6 ]and [BF 4 ] -). The results show that introducing ILs into Cu-TDPAT can greatly enhance the adsorption affinity towards H 2 S compared to the pristine MOF, and the strongest enhancement occurs in the composite containing the anion [Cl]with the smallest size. The H 2 S/CH 4 adsorption selectivities of each composite are significantly higher than those of the pristine Cu-TDPAT within the pressure range examined, and the selectivity generally shows an increasing trend with increasing the loading of the IL. By further taking the H 2 S working capacity into account, this work also reveals that the [BMIM][Cl]/Cu-TDPAT composite exhibits the best separation performance in both VSA and PSA processes. These findings may provide useful information for the design of new promising IL/MOF composites applied for H 2 S capture from natural gas. smaller. As a result, taking the working capacity and selectivity into account, it can be concluded that the [BMIM][Cl]/Cu-TDPAT composite with a loading of 25 IL molecules has the best properties for H 2 S/CH 4 separation in both the VSA and PSA processes. CONCLUSIONSMolecular simulations have been performed to investigate the performance of IL/Cu-TDPAT composites for the separation of H 2 S/CH 4 mixture. The ILs considered in this work are composed of identical cation [BMIM] + and four types of anions ([Cl] -, [Tf 2 N] -, [PF 6 ]and [BF 4 ] -) with a large diversity in chemical property, shape and size. The results show that the anions of the ILs are preferentially located near the Cu atoms of the MOF framework, while the cations are located near the organic linkers. The adsorption affinity towards H 2 S is significantly enhanced by incorporating each IL into the pores of Cu-TDPAT, with the highest heat of adsorption in the composite containing the anion [Cl]with the smallest size. In addition, this work demonstrates that the [BMIM][Cl]/Cu-TDPAT composite exhibits the best separation performance in both VSA and PSA processes, by taking both the adsorption selectivity and working capacity into account. On the basis of the results obtained in current study, it can be expected that the use of MOFs as the supporter for ILs is an alternative efficient strategy to generate new promising adsorbents for practical H 2 S separation related to natural gas purification. ASSOCIATED CONTENT Supporting Information. Details of the force field parameters, structures of some IL/Cu-TDPAT composites, and some simulation results. This material is available free of charge via the Internet at

Dissolution of Trihexyltetradecylphosphonium Chloride in Supercritical CO2

“…This body of literature can be summarized by two main goals: (1) the measurement of the phase behavior of CO 2 dissolved in ILs; and (2) the quantitation of CO 2 solubility in a bulk phase IL. As an example, in one recent study the solubility of CO 2 gas in [C 9 -imidazolium][PF 6 ] was shown to increase by~22% over a [C 4 -imidazolium][PF 6 ], as estimated from the liquid phase volume increase on going from low to high pressure at 298 K [43]. The main conclusion from all of this work is that CO 2 is effectively captured in the bulk IL phase.…”

“…RTILs are also designer solvents in the sense that a wide variety of cations and anions can be combined to tailor ILs for task-specific processes or reactions [1,2]. RTILs have unique characteristics, such as low volatility, non-flammability and water miscibility, that make them candidates for use in many applications, and has given rise to their use as cosolvents [3][4][5][6] in numerous applications [1,[3][4][5][6][7][8][9][10][11][12][13] that include electrochemistry [14][15][16], organic synthesis [17,18], gas separation/SLM's [19,20] and catalysis [17,21]. The inherent polar and nonpolar nanodomains that form in ILs allow them to readily solvate polar and non-polar solutes, and this has given rise to a significant increase in their study over the last decade [8,14,15,17,[19][20][21][22].…”

Multi-scale crystal engineering of metal organic frameworks

“…The popularity of ILs has much to do with their interesting physicochemical properties, such as good solvents for a wide variety of organic and inorganic compounds, tunable solubility properties and negligible vapor pressure. Usually in MOFs synthesis, the ILs behave as solvents [154][155][156], reactants [157][158][159], structure directing agents [160][161][162][163][164], charge-compensating templates in anionic networks [165][166][167][168][169], functional inclusions [170][171][172][173][174][175][176], and as template. As mentioned in the previous section, a remarkable example of the MOF morphology controlled electrochemical synthesis in pure ionic liquid (IL) system was reported by Yang et al [143].…”

Efficient new process for the desulfurization of mixtures of air and hydrogen sulfide via a dielectric barrier discharge plasma

“…Hydrogen sulfide is present in high concentrations within most natural gases, 2 but also in biogas 3 and landfill gas. 4,5 Currently, the most commonly used solutions for the removal of hydrogen sulfide are activated carbon and the Claus process.…”

“…However, its production is very expensive and the used up activated carbon can hardly be regenerated, thus most activated carbon has to be treated as hazardous waste after being used for H 2 S filtering purposes. 3,6 The Claus process operates above 900 • C, partly oxidizing the gas to produce water and atomic sulfur via the two steps given in equations (1) and (2). 1,7,8 H 2 S + 3/2 O 2 → H 2 S + SO 2 (1)…”