Ionic liquid silver salt complexes for propene/propane separation

Characterizing Olefin Selectivity and Stability of Silver Salts in Ionic Liquids Using Inverse Gas Chromatography

Separation systems utilizing silver(I) ion-olefin complexation have limitations since silver(I) ions can be poisoned or reduced to metallic silver. Ionic liquids (ILs) are used as solvents for silver(I) ions to facilitate separations since their physico-chemical properties can be easily tuned. To develop separation systems with sustainable olefin selectivity, factors that affect silver(I) ion stability need to be understood. In this study, a total of 13 silver salt/IL mixtures were examined by inverse gas chromatography to identify the effects of silver salt anion and IL cation/anion combination on silver(I) ion stability. The effects of temperature and three different exposure gases on silver(I) ion stability were systematically studied. Exposing silver salt/IL mixtures to hydrogen at high temperatures had a greater effect on decreasing silver(I) ion-olefin complexation. Silver(I) ions from the silver bis[(trifluoromethyl)sulfonyl]imide ([NTf₂ ^-]) salt were more stable in [NTf₂ ^-]-containing ILs than in [BF₄ ^-]-containing ILs. Optimum mixtures exhibited high olefin selectivity and were stable beyond 90 h when exposed to hydrogen gas.

A Bibliometric Survey of Paraffin/Olefin Separation Using Membranes

Bibliometric studies allow to collect, organize and process information that can be used to guide the development of research and innovation and to provide basis for decision-making. Paraffin/olefin separations constitute an important industrial issue because cryogenic separation methods are frequently needed in industrial sites and are very expensive. As a consequence, the use of membrane separation processes has been extensively encouraged and has become an attractive alternative for commercial separation processes, as this may lead to reduction of production costs, equipment size, energy consumption and waste generation. For these reasons, a bibliometric survey of paraffin/olefin membrane separation processes is carried out in the present study in order to evaluate the maturity of the technology for this specific application. Although different studies have proposed the use of distinct alternatives for olefin/paraffin separations, the present work makes clear that consensus has yet to be reached among researchers and technicians regarding the specific membranes and operation conditions that will make these processes scalable for large-scale commercial applications.

Surface Modified Polysulfone Hollow Fiber Membranes for Ethane/Ethylene Separation Using Gas-Liquid Membrane Contactors with Ionic Liquid-Based Absorbent

Olefin/paraffin separation is an important technological process. A promising alternative to conventional energy-consuming methods is employment of gas-liquid membrane contactors. In the present work, the membranes used were polysulfone (PSf) asymmetrical porous hollow fibers fabricated via the NIPS (non-solvent induced phase separation) technique in the free spinning mode. The surface of the fine-pored selective layer from the lumen side of the fibers was modified by layer-by-layer deposition of perfluorinated acrylic copolymer Protect Guard® in order to hydrophobized the surface and to avoid penetration of the liquid absorbent in the porous structure of the membranes. The absorbents studied were silver salts (AgNO3 and AgBF4) solutions in five ionic liquids (ILs) based on imidazolium and phosphonium cations. The membranes were analyzed through gas permeance measurement, SEM and dispersive X-ray (EDXS). Contact angle values of both unmodified and modified membranes were determined for water, ethylene glycol, ILs and silver salts solutions in ILs. It was shown that the preferable properties for employment in membrane contactor refer to the PSf hollow fiber membranes modified by two layers of Protect Guard®, and to the absorbent based on 1 M AgNO3 solution in 1-ethyl-3-methylimidazolium dicyanamide. Using the membrane contactor designed, ethylene/ethane mixture (80/20) separation was carried out. The fluxes of both components as well as their overall mass transport coefficients (MTC) were calculated. It was shown that the membrane absorption system developed provides absorption of approx. 37% of the initial ethylene volume in the mixture. The overall MTC value for ethylene was 4.7 GPU (gas permeance unit).

Activation of Acetonitrile with (C2 F5 )3 PF2 and Amines

Acetonitrile is deprotonated by a combination of the strong Lewis acid (C₂ F₅ )₃ PF₂ and triethylamine. The resulting cyanomethyl function is bound to the phosphorus moiety, affording the highly stable salt [HNEt₃ ][P(C₂ F₅ )₃ F₂ (CH₂ CN)]. Salt metathesis reactions furnished the corresponding [Cu(MeCN)₂ ]⁺ and [Ag(MeCN)]⁺ derivatives in which the CH₂ CN substituent of the anion [P(C₂ F₅ )₃ F₂ (CH₂ CN)]^- coordinates to the metal. An investigation of the gas separation capability of the silver salt [Ag(MeCN)][P(C₂ F₅ )₃ F₂ (CH₂ CN)] shows an uptake of 1.7 equivalents of isobutene from a propane/isobutene mixture. The reaction of (C₂ F₅ )₃ PF₂ with acetonitrile and diethylamine furnishes [P(C₂ F₅ )₃ F₂ {NHC(CH₃ )NEt₂ }]-a phosphate featuring an amidine ligand which formally results from hydroamination of acetonitrile by HNEt₂ . Exchange of HNEt₂ with the primary amines H₂ NPh and H₂ NBu leads to comparable amidine salts that exhibit a solvent-dependent conformational isomerism.

Novel Protic Ionic Liquid Composite Membranes with Fast and Selective Gas Transport Nanochannels for Ethylene/Ethane Separation

Protic ionic liquids (PILs) were utilized for the fabrication of composite membranes containing silver salt as the C₂H₄ transport carrier to perform C₂H₄/C₂H₆ separation for the first time. The intrinsic nanostructures of PILs were adopted to construct fast and selective C₂H₄ transport nanochannels. The investigation of structure-performance relationships of composite membranes suggested that transport nanochannels (polar domains of PILs) could be tuned by the sizes of cations, which greatly manipulated activity of the carrier and determined the separation performances of membranes. The role of different carriers in the facilitated transport was studied, which revealed that the PILs were good solvents for dissolution and activation of the carrier due to their hydrogen bond networks and waterlike properties. The operating conditions of separation process were investigated systemically and optimized, confirming C₂H₄/C₂H₆ selectivity was enhanced with the increase of silver salt concentration, the flow rate of sweep gas, and the feed ratio of C₂H₄ to C₂H₆, as well as the decrease of the transmembrane pressure and operating temperature. Furthermore, the composite membranes exhibited long-term stability and obtained very competitive separation performances compared with other results. In summary, PIL composite membranes, which possess good long-term stability, high C₂H₄/C₂H₆ selectivity, and excellent C₂H₄ permeability, may have a good perspective in industrial C₂H₄/C₂H₆ separation.

Liquid silver tris(perfluoroethyl)trifluorophosphate salts as new media for propene/propane separation

A series of silver tris(perfluoroethyl)trifluorophosphate (Ag[FAP]) complexes with various ligands (acetonitrile ACN, chloroacetonitrile Cl-ACN, acrylonitrile acryl-CN, pyridine py, ethylenediamine en and propene C₃H₆) have been synthesized starting from Ag[NO₃] and K[FAP] using three different routes. Physicochemical properties as well as crystal structures ([Ag(ACN)_2/4][FAP], [Ag(py)₂][FAP]) were determined and the suitability of such Ag salts for propene/propane separation processes was investigated. The investigated silver complexes exhibit either low melting points or form liquid complexes when contacted with gaseous propene at 30 °C. This makes them promising separation materials for both liquid membranes and absorber fluids due to their high silver content and significant propene capacity. Single (iGSC) and mixed (NMR) gas solubilities as well as diffusion coefficients (PFG-NMR) of propene and propane were determined to predict the theoretical selectivity of solubility, membrane selectivity, capacity and transport properties of the silver salts according to the solution diffusion model. A strong influence of the number and type of ligands on chemical complexation, physicochemical properties and separation performance has been observed.

An adaptive self-healing ionic liquid nanocomposite membrane for olefin-paraffin separations

An adaptive self-healing ionic liquid nanocomposite membrane comprising a multi-layer support structure hosting the ionic salt [Ag](+) [Tf(2) N](-) is used for the separation of the olefin propylene and the paraffin propane. The ionic salt renders liquid like upon complexation with propylene, resulting in facilitated transport of propylene over propane at benchmark-setting selectivity and permeance levels. The contacting with acetylene causes the ionic salt to liquefy without showing evidence of forming explosive silver acetylide.