Ethane Absorption Research Articles

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The density, viscosity and absorption of ethane and ethylene were determined experimentally, as a function of temperature and at atmospheric pressure, in different imidazolium-based ionic liquids: 1-methyl-3-octylimidazolium bis(trifluoromethanesulfonyl)imide, [C1C8Im][NTf2], 1-methyl-3-(propyn-3-yl)imidazolium bis(trifluoromethanesulfonyl)imide [C1(C2H2CH)Im][NTf2], 1-(3-cyanopropyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C1C3CNIm][NTf2], 1-(3-cyanopropyl)-3-methylimidazolium dicyanamide [C1C3CNIm][DCA], 1-butyl-3-methylimidazolium dicyanamide, [C1C4Im][DCA] and 1-butyl-3-methylimidazolium methylphosphite [C1C4Im][C1HPO3]. The densities and viscosities of the ionic liquids studied are strongly dependent on the anion and, at 313 K, follow the order: [C1(C2H2CH)Im][NTf2] > [C1C3CNIm][NTf2] > [C1C3CNIm][DCA] > [C1C4Im][C1HO3] > [C1C4Im][DCA] and [C1C3CNIm][NTf2] > [C1C3CNIm][DCA] > [C1C4Im][C1HPO3] > [C1(C2H2CH)Im][NTf2] > [C1C4Im][DCA], respectively. The differences in the molecular structures of the ionic liquids allowed the identification of the influence of increasing the alkyl side chain of the cation, of the presence of unsaturated CC and CN bonds on the alkyl side chain of the cation and finally of a phosphite based anion on the selective absorption of ethane and ethylene. The solubility of ethylene is higher than that of ethane in the ionic liquids studied and varies from 18.41 × 10−3 in [C1C8Im][NTf2] at 303.17 K to 1.603 × 10−3 in [C1C4Im][DCA] at 343.61 K. The introduction of the different functional groups leads to a decrease on the gas absorption compared with that of [C1C8Im][NTf2] but to an increase of the ideal separation selectivity of ethane and ethylene.

Intensification of ethylene and ethane absorption in N-methyl-2-pyrrolidone (NMP) by adding silver nanoparticles

The absorption and solubility of pure ethane and ethylene gases were investigated in an experimental pressure decay setup, where a small amount of silver nanoparticles was added to pure N-methyl-2-pyrrolidone (NMP) solvent. All the experiments were performed at temperatures of 278.15, 298.15 and 328.15 K and different pressures (up to the gases dew points) as well as different concentrations of silver nanoparticles (0.05 and 0.1 g/l). The kinetic data of absorption, Henry’s law constants, heat of absorption, entropy, Gibbs free energy, and ideal selectivity were reported. Also, the effects of temperature, pressure, and nanoparticle concentration on the equilibrium results were evaluated. The absorption results revealed that the presence of small amounts of nanoparticles in the solvent intensified the absorption performance between 1.5–18 % for ethylene and 1–41 % for ethane. The results also showed that the solubility of ethylene in pure solvent and nanofluids was better than that of ethane. Increasing the nanosilver concentration up to 0.1 g/l resulted in reducing the absorption equilibrium time specially for ethylene/nanofluid experiments. Also, the ideal ethylene/ethane selectivity improved by increasing the nanoparticle concentration at the same temperature.

Time-resolved laser absorption imaging of ethane at 2 kHz in unsteady partially premixed flames.

In this work, laser absorption imaging is expanded in temporal resolution capability to kilohertz measurement rates by coupling sparsely sampled wavelength scanning and digital image postprocessing for diffraction correction. The setup employs an interband cascade laser near 3.34μm to backlight an unsteady flame for species-specific 2D imaging of ethane (C2H6) with a high-speed infrared camera. Injection-current laser tuning is achieved with a high-duty-cycle square wave that involves a sparse number of data samples per scan to recover an integrated absorbance area for the target ethane feature, thereby minimizing the number of camera frames needed. In conjunction, an image-by-image computational diffraction pattern removal scheme is employed based on inverse Fourier transformations with the aim to reject high spatial frequencies associated with diffraction while preserving spatial resolution of the flow field, without averaging in time. These methods are applied to achieve species-specific 2D cinematography of ethane absorption in an unsteady partially premixed flame with a spatial resolution of ∼415 μm and a temporal resolution of 2kHz.

Collisional dissipation of the laser-induced alignment of ethane gas: Energy corrected sudden quantum model.

We present the first quantum mechanical model of the collisional dissipation of the alignment of a gas of symmetric-top molecules (ethane) impulsively induced by a linearly polarized non-resonant laser field. The approach is based on use of the Bloch model and of the Markov and secular approximations in which the effects of collisions are taken into account through the state-to-state rates associated with exchanges among the various rotational states. These rates are constructed using the Energy Corrected Sudden (ECS) approximation with (a few) input parameters obtained independently from fits of the pressure-broadening coefficients of ethane absorption lines. Based on knowledge of the laser pulse characteristics and on these rates, the time-dependent equation driving the evolution of the density matrix during and after the laser pulse is solved and the time dependence of the so-called "alignment factor" is computed. Comparisons with measurements, free of any adjusted parameter, show that the proposed approach leads to good agreement with measurements. The analysis of the ECS state-to-state collisional rates demonstrates that, as in the case of linear molecules, collision-induced changes of the rotational angular momentum orientation are slower than those of its magnitude. This explains why the collisional decay of the permanent component of the alignment is significantly slower than that of the amplitudes of the transient revivals in both experimental and computed results. It is also shown that, since intermolecular forces within C2H6 colliding pairs weakly depend on rotations of the molecules around their C-C bond, the dissipation mechanism of the alignment in pure ethane is close to that involved in linear molecules.

Effect of cation on the solubility of ethane in three bis(fluorosulfonyl)imide ([FSI]) based low viscosity ionic liquids

The solubility of ethane (C2H6) in three ionic liquids (ILs) with the same anion, [C3C1pip][FSI], [C3C1pyrr][FSI] and [N1223][FSI], was measured at (303.15, 323.15, and 343.15) K and at pressures up to 1.1 MPa. Experimental data were correlated with Peng-Robinson (PR) equation of state using three different mixing rules: (i) van der Waals one (vdW1, based on a single binary interaction parameter), (ii) van der Waals two (vdW2, based on two binary interaction parameters), and (iii) Wong-Sandler mixing rules combined with NRTL model. Henry's law constants, enthalpy and entropy for the absorption of ethane in these ILs were also estimated. No significant change was found in the values of Henry's law constants of C2H6 in these three ILs which indicates a negligible effect of cations of these ILs on C2H6 solubility. The selectivity towards carbon dioxide (CO2) over C2H6 for these ILs was also reported. [FSI]-based ILs seem to have higher selectivity than all the other ILs, except for [C4C1Im][BF4] and possibly [C4C1Im][PF6], which may qualify them as promising solvents for CO2 removal from natural gas streams.

The ν17 band of C2H5D from 770 to 880 cm−1

Atmospheric investigations rely heavily on the availability of accurate spectral information of hydrocarbons. To extend the ethane database we recorded a 0.0028cm−1 resolution spectrum of 12C2H5D from 650 to 1500cm−1 using a Bruker Fourier Transform spectrometer IFS-125HR at the Jet Propulsion Laboratory. The 98% deuterium-enriched sample was contained in a 0.2038m absorption cell; one spectrum was obtained with the sample cryogenically cooled to 130.5K and another at room temperature. From the cold data, we retrieved line positions and intensities of 8704 individual absorption features from 770 to 880cm−1 using a least squares curve fitting algorithm. From this set of measurements, we assigned 5035 transitions to the v17 fundamental at 805.342729(27)cm−1; this band is a c-type vibration, with often-resolved A and E components arising from internal rotation. The positions were modeled to a 22 term torsional Hamiltonian using SPFIT to fit the spectrum to a standard deviation of 7×10−4cm−1 (21MHz). The prediction of the 5035 line intensities at 130.5K agreed with observed intensities, but a small centrifugal distortion type correction to the transition dipole was needed to model the intensity of high Ka R and P transitions. The integrated band intensities of 3.6628×10−19cm−1/(moleculecm−2) at 296K in the 770–880cm−1 region was obtained. To predict line intensities at different temperatures, the partition function values were determined at nine temperatures between 9.8 and 300K by summing individual energy levels up to J=99 and Ka=99 for the six states up through ν17 at 805cm−1. We found the energy of A and E are inverted as compared to ground state (with the E state lower than the A state) and the splitting, −241.8(10)MHz, lies between the ground state value of +74.167(18)MHz and the first torsional state (ν18=271.1cm−1) value of −3382.23(34)MHz. The proximity of the energy splitting to the ground state suggests that the ν17 state has a similar torsional character. The resulting prediction of singly-deuterated ethane absorption at 12.5μm enables its detection in planetary atmospheres, including those of Titan and exoplanets.

Imidazolium-based ionic liquids with cyano groups for the selective absorption of ethane and ethylene

The density, viscosity and absorption of ethane and ethylene were determined experimentally, as a function of temperature and at atmospheric pressure, in different imidazolium-based ionic liquids: 1-methyl-3-octylimidazolium bis(trifluoromethanesulfonyl)imide, [C1C8Im][NTf2], 1-methyl-3-(propyn-3-yl)imidazolium bis(trifluoromethanesulfonyl)imide [C1(C2H2CH)Im][NTf2], 1-(3-cyanopropyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C1C3CNIm][NTf2], 1-(3-cyanopropyl)-3-methylimidazolium dicyanamide [C1C3CNIm][DCA], 1-butyl-3-methylimidazolium dicyanamide, [C1C4Im][DCA] and 1-butyl-3-methylimidazolium methylphosphite [C1C4Im][C1HPO3]. The densities and viscosities of the ionic liquids studied are strongly dependent on the anion and, at 313K, follow the order: [C1(C2H2CH)Im][NTf2]>[C1C3CNIm][NTf2]>[C1C3CNIm][DCA]>[C1C4Im][C1HO3]>[C1C4Im][DCA] and [C1C3CNIm][NTf2]>[C1C3CNIm][DCA]>[C1C4Im][C1HPO3]>[C1(C2H2CH)Im][NTf2]>[C1C4Im][DCA], respectively. The differences in the molecular structures of the ionic liquids allowed the identification of the influence of increasing the alkyl side chain of the cation, of the presence of unsaturated CC and CN bonds on the alkyl side chain of the cation and finally of a phosphite based anion on the selective absorption of ethane and ethylene. The solubility of ethylene is higher than that of ethane in the ionic liquids studied and varies from 18.41×10−3 in [C1C8Im][NTf2] at 303.17K to 1.603×10−3 in [C1C4Im][DCA] at 343.61K. The introduction of the different functional groups leads to a decrease on the gas absorption compared with that of [C1C8Im][NTf2] but to an increase of the ideal separation selectivity of ethane and ethylene.

Evidence for longitudinal variability of ethane ice on the surface of Pluto

We present the results of an investigation using near-infrared spectra of Pluto taken on 72 separate nights using SpeX/IRTF. These data were obtained between 2001 and 2013 at various sub-observer longitudes. The aim of this work was to confirm the presence of ethane ice and to determine any longitudinal trends on the surface of Pluto. We computed models of the continuum near the 2.405μm band using Hapke theory and calculated an equivalent width of the ethane absorption feature for six evenly-spaced longitude bins and a grand average spectrum. The 2.405μm band on Pluto was detected at the 7.5-σ level from the grand average spectrum. Additionally, the band was found to vary longitudinally with the highest absorption occurring in the N2-rich region and the lowest absorption occurring in the visibly dark region. The longitudinal variability of 12CO does not match that of the 2.405μm band, suggesting a minimal contribution to the band by 13CO. We argue for ethane production in the atmosphere and present a theory of volatile transport to explain the observed longitudinal trend.

Effect of Unsaturation on the Absorption of Ethane and Ethylene in Imidazolium-Based Ionic Liquids

The influence of the presence of imidazolium side chain unsaturation on the solubility of ethane and ethylene was studied in three ionic liquids: 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide-saturated alkyl side-chain in the cation; 1-methyl-3-(buten-3-yl)imidazolium bis(trifluorosulfonyl)imide-double bond in the side-chain of the cation; and 1-methyl-3-benzylimidazolium bis(trifluorosulfonyl)imide-benzyl group in the side-chain of the cation. The solubility of both gases decreases when the side-chain of the cations is functionalized with an unsaturated group. This can be explained by a less favorable enthalpy of solvation. The difference of solubility between ethane and ethylene can be explained from a balance of enthalpic and entropic factors: for the ionic liquid with the saturated alkyl side-chain and the benzyl-substituted side-chain, it is the favorable entropy of solvation that explains the larger ethylene solubility, whereas in the case of the saturated side-chain, it is the more favorable enthalpy of solvation. Molecular simulation allowed the identification of the mechanisms of solvation and the preferential solvation sites for each gas in the different ionic liquids. Simulations have shown that the entropy of solvation is more favorable when the presence of the gas weakens the cation-anion interactions or when the gas can be solvated near different sites of the ionic liquid.

Computer study of the absorption of ethane by aqueous ultradispersed medium: IR spectra

Absorption of ethane molecules by water clusters containing 10–20 molecules is studied by the molecular dynamics method. The (H2O)n (I), C2H6(H2O)n (II), and (C2H6)2(H2O)n (III) cluster systems are composed on the basis of specific statistical weights. Spectral characteristics of system and single clusters are determined in the frequency range of 0 ≤ ω ≤ 1000 cm−1. In this frequency range, both real and imaginary parts of dielectric permittivity decrease monotonically after the absorption of C2H6 molecules by an aqueous ultradispersed system. Integral coefficient of IR absorption increases, while average (over frequency) reflection coefficient decreases after the absorption of ethane molecules. The intensity of IR scattering by the systems of clusters containing C2H6 molecules lowers. Maximal values of radiation power for water clusters with various sizes are balanced with the capture of ethane molecules by the clusters, whereas oscillations in the size dependence of the density of electrons that are active with respect to IR radiation decrease.

Continuous wave optical parametric oscillator for quartz-enhanced photoacoustic trace gas sensing

A continuous wave optical parametric oscillator, generating up to 300 mW idler output in the 3–4 μm wavelength region, and pumped by a fiber-amplified DBR diode laser is used for trace gas detection by means of quartz-enhanced photoacoustic spectroscopy (QEPAS). Mode-hop-free tuning of the OPO output over 5.2 cm-1 and continuous spectral coverage exceeding 16.5 cm-1 were achieved via electronic pump source tuning alone. Online monitoring of the idler wavelength, with feedback to the DBR diode laser, provided an automated closed-loop control allowing arbitrary idler wavelength selection within the pump tuning range and locking of the idler wavelength with a stability of 1.7×10-3 cm-1 over at least 30 min.Using this approach, we locked the idler wavelength at an ethane absorption peak and obtained QEPAS data to verify the linear response of the QEPAS signal at different ethane concentrations (100 ppbv-20 ppmv) and different power levels. The detection limit for ethane was determined to be 13 ppbv (20 s averaging), corresponding to a normalized noise equivalent absorption coefficient of 4.4×10-7 cm-1 W/Hz1/2.

Photoacoustic trace gas detection of ethane using a continuously tunable, continuous-wave optical parametric oscillator based on periodically poled lithium niobate

A 1.2 W, continuous-wave, continuously-tunable, singly-resonant optical parametric oscillator (OPO) (idler tuning range 3.0–3.8 μm), pumped by a 10 W continuous-wave Nd:YAG laser, is used in combination with a photoacoustic cell for the detection of ethane. An intracavity solid-state etalon (thickness 400 μm) was used to stabilize the OPO cavity and could be used to mode-hop tune the idler wavelength over 10 cm−1. The usefulness of the system was demonstrated by determining a detection limit for ethane down to 10 parts per trillion. The selectivity was achieved by making a 24 GHz wide pump laser scan over the ethane absorption line at 2996.9 cm−1, after which a Lorentzian fit determined the total area of the absorption signal. Both area value and peak value proved to be linearly depending on the ethane concentration.

Diagnostics of the Jovian Aurora Deduced from Ultraviolet Spectroscopy: Model and HST/GHRS Observations

A model coupling an electron energy degradation code with a detailed synthetic spectrum of the H 2 Lyman and Werner band system is used to calculate the emerging auroral ultraviolet spectra from Jupiter's atmosphere excited by electrons with different initial energy distributions. The atmospheric model is adapted from the vertical P-T profile measured by the Galileo probe and mid-latitude model hydrocarbon photochemistry. Each altitude layer, with its own gas temperature, contributes to the emergent ultraviolet spectrum and the absorbers are vertically distributed within the source region of the auroral emissions. Examples of the calculated spectra are shown to validate the synthetic spectrum and to illustrate the importance of the electron energy distribution and the vertical structure. The model is then applied to the analysis of seven HST/GHRS spectra of the 1200–1700 Å region obtained with 5-Å resolution at various locations in the north and south Jovian aurora. These spectra have different color ratios which characterize the energy of the precipitated electrons, although they do not have a high enough spectral resolution to permit a determination of the H 2 temperature. We find that the characteristic energy of the assumed initial Maxwellian distribution ranges between 17 and 40 keV. A clear signature of acetylene absorption is observed near 1520, 1480, and 1440 Å where the C 2H 2 cross section shows strong absorption peaks. The acetylene column abundance overlying the emission peak varies from 0.02 to 0.2 of the methane column. A better fit is obtained for some spectra when ethane absorption is added. The C 2H 6 column abundance varies from 0 to 0.5 of the methane column. These changes relative to methane are presumably the result of perturbations by heat released by the fast electron thermalization and/or perturbations to the hydrocarbon chemistry resulting from the production of H atoms by the aurora. A spectrum of the Io flux tube footprint and its trailing tail shows an ultraviolet color and hydrocarbon absorption quite similar to some of the main oval spectra. This observation suggests that the electrons of the Io flux tube are energized to a few tens of keV, similar to the electron precipitated in the main ovals and polar caps. Echelle spectra between 1216 and 1220 Å at 0.07 Å resolution are also compared with the model fitting best the mid-resolution spectra. It is found that the effective H 2 rovibrational temperature associated with the echelle spectra are significantly higher than predicted by the mid-latitude model. A large vertical temperature gradient just above the methane homopause due to large heating by auroral precipitation is a plausible explanation for this difference.

Nonlinear absorption spectroscopy of the ethane molecule

By means of nonlinear absorption spectroscopy data necessary for the interpretation of molecular spectra can be obtained in such spectral regions, where conventional spectroscopic methods yield only a quasi-continuous absorption curve. Using a Zeeman-tuned He−Ne laser at the wavelength of 3.39μm we have measured significant differences in the intensity and temperature behaviour for several ethane absorption lines, the analysis of which made possible a preliminary qualitative assignment of these lines.