ABSTRACT
Amine-functionalized anion-tethered ionic liquids (ILs) trihexyl(tetradecyl)phosphonium asparaginate [P(66614)][Asn], glutaminate [P(66614)][Gln], lysinate [P(66614)][Lys], methioninate [P(66614)][Met], prolinate [P(66614)][Pro], taurinate [P(66614)][Tau], and threoninate [P(66614)][Thr] were synthesized and investigated as potential absorbents for CO(2) capture from postcombustion flue gas. Their physical properties, including density, viscosity, glass transition temperature, and thermal decomposition temperature were determined. Furthermore, the CO(2) absorption isotherms of [P(66614)][Lys], [P(66614)][Tau], [P(66614)][Pro], and [P(66614)][Met] were measured using a volumetric method, and the results were modeled with two different Langmuir-type absorption models. The most important result of this study is that the viscosity of [P(66614)][Pro] only increased by a factor of 2 when fully complexed with 1 bar of CO(2) at room temperature. This is in stark contrast to the other chemically reacted ILs investigated here and all other amino acid-based ILs reported in the literature, which dramatically increase in viscosity, typically by 2 orders of magnitude, when complexed with CO(2). The unique behavior of [P(66614)][Pro] is likely due to its ring structure, which limits the number and availability of hydrogen atoms that can participate in a hydrogen bonding network. We found that water can be used to further reduce the viscosity of the CO(2)-complexed IL, while only slightly decreasing the CO(2) capacity. Finally, from temperature-dependent isotherms, we estimate a heat of absorption of -63 kJ/mol of CO(2) for the 1:1 reaction of CO(2) with [P(66614)][Pro], when we use the two-reaction model.
Subject(s)
Amines/chemistry , Carbon Dioxide/chemistry , Ionic Liquids/chemistry , Temperature , Water/chemistry , Absorption , Amino Acids/chemistry , Oxidation-Reduction , Phase Transition , ViscosityABSTRACT
Amino acid ionic liquid trihexyl(tetradecyl)phosphonium methioninate [P(66614)][Met] and prolinate [P(66614)][Pro] absorb CO(2) in nearly 1:1 stoichiometry, surpassing by up to a factor of 2 the CO(2) capture efficiency of previously reported ionic liquid and aqueous amine absorbants for CO(2). Room temperature isotherms are obtained by barometric measurements in an accurately calibrated stirred cell, and the product identity is confirmed using in situ IR. Density functional theory (DFT) calculations support the 1:1 reaction stoichiometry and predict reaction enthalpies in good agreement with calorimetric measurements and isotherms.
ABSTRACT
The decadic extinction coefficient of the hydrated electron is reported for the absorption maximum from room temperature to 380 degrees C. The extinction coefficient is established by relating the transient absorption of the hydrated electrons in the presence of a scavenger to the concentration of stable product produced in the same experiment. Scavengers used in this report are SF(6,) N(2)O, and methyl viologen. The room temperature value is established as 22,500 M(-1) cm(-1), higher by 10-20% than values used over the last several decades. We demonstrate how previous workers arrived at a low value by incorrect choice of a radiolysis yield value. With this revision, the integrated oscillator strength, corrected by refractive index, is definitely (ca. 10%) larger than unity. This result is fully consistent with EPR and resonance Raman results which indicate mixing of the hydrated electron wave function with solvent electronic orbitals. Oscillator strength appears to be conserved vs temperature.
ABSTRACT
The extinction coefficient of the hydrated electron (e(-))aq generated by pulse radiolysis is evaluated relative to the methyl viologen radical cation (*)MV(+), whose extinction coefficient at 605 nm has been carefully measured in the past. We find that the room temperature (e(-))aq extinction coefficients reported in the literature are underestimated by 10-20%. We obtain = 22,700 M(-1) cm(-1) for the 20 degrees C hydrated electron at 720 nm, assuming the (*)MV(+) extinction is 13,700 M(-1) cm(-1) at 605 nm. This has implications both for second-order reaction rate measurements of (e(-))aq and for the estimate of its integrated oscillator strength.
ABSTRACT
There has been long-standing uncertainty about the number of water molecules in the primary coordination environment of the OH- and F- ions in aqueous chemistry. We report the vibrational spectra of the OH-.(H2O)n and F-.(H2O)n clusters and interpret the pattern of OH stretching fundamentals with ab initio calculations. The spectra of the cold complexes are obtained by first attaching weakly bound argon atoms to the clusters and then monitoring the photoinduced evaporation of these atoms when an infrared laser is tuned to a vibrational resonance. The small clusters (n
