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Shiflett M.B.,DuPont Company | Corbin D.R.,DuPont Company | Elliott B.A.,DuPont Company | Subramoney S.,DuPont Company | And 2 more authors.
Adsorption | Year: 2014

Sorption isotherms for trifluoromethane (R-23) in activated carbon have been measured at ca. 298 and 323 K using a gravimetric microbalance. High-resolution TEM images of the activated carbon show a very uniform microstructure with no evidence of any contaminants. The adsorption in the activated carbon reaches about 22.8 mol kg-1 at 2.0 MPa and 298 K or 17.6 mol kg-1 at 2.0 MPa and 323 K. Three different adsorption models (Langmuir, multi-site Langmuir, and BET equations) have been used to analyze the activated carbon sorption data, with a particular interest in the heat of adsorption (-ΔH). The heat of adsorption for R-23 in the activated carbon was about 29.78 ± 0.04 kJ mol-1 based on the multi-site Langmuir model and is within the range of typical physical adsorption. According to the IUPAC classification, the activated carbon exhibits Type I adsorption behavior and was completely reversible. Compared with our previous work for the sorption of R-23 in zeolites (5A (Ca,Na-A), 13X (Na-X), Na,K-LSX, Na-Y, K,H-Y, Rb,Na-Y) and ionic liquids ([omim][TFES] and [emim][Tf2N]) the activated carbon had the highest adsorption capacity. The adsorption process in the activated carbon also took less time than in the zeolites or the ionic liquids to reach thermodynamic equilibrium. © 2014 Springer Science+Business Media New York.


Shiflett M.B.,DuPont Company | Corbin D.R.,DuPont Company | Elliott B.A.,DuPont Company | Yokozeki A.,32 Kingsford Lane
Journal of Chemical Thermodynamics | Year: 2013

Sorption isotherms for trifluoromethane (R-23) on three zeolites, Na-Y, K,H-Y, and Rb,Na-Y and ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [emim][Tf2N] have been measured at ca. 298 and 323 K, using a gravimetric microbalance. The adsorption on the zeolites reaches about 3 mol·kg-1 at 0.025 MPa and 298 K while in the ionic liquid the absorption reaches 3 mol · kg-1 at about 2.5 MPa (100 times higher pressure). Three different adsorption models (Langmuir, multi-site Langmuir, and BET equations) have been used to analyze the zeolite sorption data, with a particular interest in the heat of adsorption (-ΔH). The heat of adsorption for zeolites Na-Y, K,H-Y, and Rb,Na-Y were about 35 ± 3 kJ · mol-1, 29 ± 3 kJ · mol-1, and 34 ± 5 kJ · mol-1, respectively. These values are within the range of typical physical adsorption. According to the IUPAC classification, the zeolites exhibit Type II adsorption and according to the Scott and van Konynenburg classification the ionic liquid is predicted to be Type V phase behavior. The adsorption process on the zeolites took more time than the absorption process in the ionic liquid to reach the thermodynamic equilibrium and both processes were reversible. © 2013 Elsevier Ltd. All rights reserved.


Shiflett M.B.,DuPont Company | Elliott B.A.,DuPont Company | Yokozeki A.,32 Kingsford Lane
Fluid Phase Equilibria | Year: 2012

We have measured for the first-time the gas solubility of vinyl fluoride (VF, H 2CCHF) in room-temperature ionic liquids (RTILs), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [emim][Tf 2N], 1-butyl-3-methylimidazolium dicyanamide [bmim][N(CN) 2], 1-butyl-4-methylpyridinium tetrafluoroborate [bmpy][BF 4], 1-butyl-3-methylimidazolium 1,1,2,3,3,3-hexafluoropropanesulfonate [bmim][HFPS] and 1-octyl-3-methylimidazolium 1,1,2,2-tetrafluoroethanesulfonate [omim][TFES] at isothermal conditions from about 278 to 373K using a volumetric view cell. The observed pressure-temperature-composition (PTx) data have been analyzed by use of a generic RK (Redlich-Kwong) equation-of-state (EOS) model, which has been successfully applied in our previous works. The interaction parameters have been determined using our measured VLE (vapor-liquid-equilibrium) data. EOS model predictions suggest that these systems show VLLE (vapor-liquid-liquid equilibrium) and demonstrate Type III and Type V phase behavior, according to the classification of van Konynenburg and Scott. The global phase behavior of VF has also been compared with our measured data for ethylene (C 2H 4, H 2CCH 2) in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. The addition of a fluorine atom in VF significantly increases the gas solubility due to hydrogen bonding with the ionic liquid. Henry's law constants were calculated and compared at about room temperature (298K). Enthalpies and entropies of absorption were determined by considering the temperature effects on gas solubilities. © 2011 Elsevier B.V.


Shiflett M.B.,DuPont Company | Elliott B.A.,DuPont Company | Lustig S.R.,DuPont Company | Sabesan S.,DuPont Company | And 2 more authors.
ChemPhysChem | Year: 2012

Carbon dioxide solubility (vapor-liquid equilibria: VLE) in an ionic liquid, 1-ethyl-3-ethylimidazolium acetate ([eeim][Ac]) was measured using a gravimetric microbalance at four isotherms (about 283, 298, 323, and 348 K) up to about 2 MPa. An equation-of-state (EOS) model was used to analyze the VLE data and has predicted vapor-liquid-liquid equilibria (VLLE: or liquid-liquid separations) in CO 2-rich solutions. The VLLE prediction was confirmed experimentally using a volumetric method and likely the liquid-liquid equilibria will intersect with the solid-liquid equilibria such that no lower critical solution temperature can exist and the binary system may be classified as Type III phase behavior. Carbon dioxide solubility in the ionic-liquid-rich solution show extremely unusual behavior. CO 2 dissolves in the ionic liquid at large concentrations (up to about 20 mole% of CO 2) with almost no vapor pressure above the mixtures. This result is similar to our previous findings with 1-butyl-3-methylimidazolium acetate ([bmim][Ac]) and 1-ethyl-3-methylimidazolium acetate ([emim][Ac]). In all three cases the CO 2 forms a molecular complex (or chemical reaction) with the ionic liquid. 13C NMR spectroscopy has identified the structure for CO 2 absorbed in [eeim][Ac] to be [eeim]-2-carboxylate. Addition of water to the carboxylate leads to the dissolution of CO 2. The thermodynamic excess properties (enthalpy, entropy, and Gibbs energy) for all three systems have been calculated using the EOS and support the complex formation of the type AB 2 (where A is CO 2 and B is ionic liquid). Isothermal differential scanning calorimetry has verified the heat of reaction calculations and found for CO 2 absorbing in [emim][Ac], [eeim][Ac] and [bmim][Ac] to be about -38 kJmol -1. Additional experiments have examined the effect of water on the density, viscosity and CO 2 solubility in [eeim][Ac] and the CO 2 solubility in mixtures of [eeim][Ac] with other acetate salts. © 2012 Wiley-VCH Verlag GmbH& Co. KGaA, Weinheim.


Shiflett M.B.,DuPont Company | Niehaus A.M.S.,DuPont Company | Elliott B.A.,DuPont Company | Yokozeki A.,32 Kingsford Lane
International Journal of Thermophysics | Year: 2012

The gas solubility of nitrous oxide (N 2O) in room-temperature ionic liquids, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-3- methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium dicyanamide, 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium thiocyanate, and ethylammonium nitrate has been measured at isothermal conditions from about (283 to 348)K using a gravimetric microbalance. The observed pressure-temperature composition (PTx) data have been analyzed by use of a generic Redlich-Kwong equationof- state (EOS) model, which has been successfully applied in our previous works. The interaction parameters have been determined using our measured vapor-liquid equilibrium data. Vapor-liquid-liquid equilibrium measurements have been made and validate EOS model predictions which suggest that these systems demonstrate Type III and Type V phase behavior, according to the classification of van Konynenburg and Scott. The global phase behavior of N 2O has also been compared with both the measured data from this study and literature data for carbon dioxide (CO 2) in each ionic liquid and Henry's law constants are compared at room temperature (298.15 K). © Springer Science+Business Media, LLC 2012.


Shiflett M.B.,DuPont Company | Corbin D.R.,DuPont Company | Yokozeki A.,32 Kingsford Lane
Adsorption Science and Technology | Year: 2013

In this study, trifluoromethane (R-23) has been adsorbed on three zeolites, namely 5A, LSX and 13X, and their adsorption isotherms have been measured at approximately 298 and 323 K using a gravimetric microbalance. All cases belong to the adsorption Type II (one of the six IUPAC classifications), and the adsorption (and desorption) processes are reversible. Three different adsorption models [original Langmuir, multi-site Langmuir and BET equations] have been adopted to analyze the data, with a particular interest in calculating the heat of adsorption (-ΔH), which was found to be about 10, 30 and 40 kJ·mol-1 for zeolite 5A, LSX and 13X, respectively. These values are within the range of typical physical adsorptions. Solubility of R-23 in ionic liquid 1-octyl-3-methylimidazolium 1,1,2,2-tetrafluoroethanesulfonate ([omim][TFES]) has been measured at approximately 298 and 323 K using the same gravimetric microbalance and the value was compared with the adsorption results. The solubility capacity of R-23 in ionic liquid reaches about 3 mol kg -1 around 2.5 MPa at 298 K, while the adsorption capacity on zeolites becomes around 3 mol kg-1 at around 0.25 MPa (ten times smaller). The adsorption on zeolites took more time than the absorption in the ionic liquid to reach thermodynamic equilibrium.

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