Dependence of the relative retention of organic compounds on the nature and pressure of the carrier gas and on the thickness of the PEG-20M film in the capillary column

The effects of the carrier gas nature and pressure on the relative retention values of organic compounds were studied using a series of capillary columns differing in the film thickness of the polar stationary phase (PEG-20M). Relative retention depends linearly on the carrier gas pressure. This dependence becomes more pronounced in the following order of carrier gases: helium < nitrogen < carbon dioxide. The limiting relative retention at a carrier gas pressure approaching zero rather than relative retention values measured experimentally (relative retention time, Kovats retention index,etc.) is an invariant characteristic of a compound subjected to chromatography. For the carrier gases studied, the limiting retention values almost does not depend on the nature of the carrier gas used. The limiting indicating the complex absorption-adsorption nature of these parameters. Dissolution of a carrier gas in the stationary liquid phase has an effect on the relative retention. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2177–2186, December, 1997.     

Steam chromatography of aliphatic and aromatic amines on packed columns with aqueous potassium hydroxide as the stationary liquid phase

Aqueous alkali was proposed as the stationary liquid phase (SLP) for separation of amines by steam chromatography. Characteristic features of retention of amines of various structures were studied. The retention of primary and secondary amines on aqueous potassium hydroxide as the SLP differs fundamentally from that observed with common organic SLP. Primary amines are eluted in the following order,n-pentylamine <n-butyl-amine <n-propylamine <n-hexylamine <n-octylamine for secondary amines, the following sequence was established; diethylamine < dibutylamine < dimethylamine. Higher-boiling tertiary amines containing ethyl andn-butyl radicals are eluted ahead of diamines containing the same radicals. Translated fromIzvestiya Akademii Nau. Seriya Khimicheskaya, No. 8 pp. 1507–1509, August, 1999.     

Solubility and diffusion of CO2 and H2S in the ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate

The solubility and diffusion coefficient were determined for carbon dioxide and hydrogen sulfide gases in the ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate ([emim][EtSO₄]) at temperatures ranging from (303.15 to 353.15) K and pressures up to 1.6 MPa. The Krichevsky–Kasarnovsky equation was used to correlate solubility data and Henry’s law constants at different temperatures were obtained. The partial molar thermodynamic functions of solution such as Gibbs free energy, enthalpy, and entropy were calculated using the solubility data. A semi-infinite volume approach is used to obtain the diffusion coefficients for CO₂ and H₂S and a correlation equation with temperature is presented for each gas. Comparison showed that H₂S is more soluble than CO₂ and its diffusion coefficient is about two orders of magnitude as that of CO₂ in the ionic liquid studied in this work.     

Measuring the solubility of CO2 and H2S in sulfolane and the density and viscosity of saturated liquid binary mixtures of (sulfolane + CO2) and (sulfolane + H2S)

The density and viscosity of liquid sulfolane saturated (loaded) with single CO₂ and H₂S gases were measured simultaneously with the solubility of the single CO₂ and H₂S gases in sulfolane at temperatures ranging from (303.15 to 363.15) K and pressures of up to about 2.4 MPa using a new experimental set-up developed in our laboratory. The experimental density and viscosity values were correlated using a modified Setchenow-type equation. It was observed that the density and viscosity of mixtures decrease by increasing temperature and acid gas solubility (loading) in sulfolane. Acid gas loading has a much profounder effect on the viscosity of solutions than on their density, i.e. at a concentration of 1 mol CO₂/H₂S per kg of sulfolane the density decreases by less than 3%, but viscosity decreases by more than 30%. Results show that at fixed temperature and pressure H₂S is more than four times as soluble as CO₂ in sulfolane. The measured solubility and density values were respectively used to obtain Henry’s law constants and partial molar volumes at infinite dilution for dissolution of CO₂ and H₂S gases in the liquid sulfolane at the temperatures studied. The Henry’s law constants obtained at different temperatures were used to determine infinite dilution partial molar thermodynamic functions (Gibbs free energy, enthalpy and entropy) of solution. The measured solubility data were correlated by using a model comprised of the extended Henry’s law and the Pitzer’s virial expansion for the excess Gibbs free energy.     

Investigation of the role of the carrier gas in capillary gas-solid chromatography

Nonideal interactions of the sorbate and the carrier gas and adsorption of the sorbate on the adsorbent surface in capillary gas-solid chromatography were studied. Chromatographic retention was found to be largely determined by adsorption processes. With respect to the retention coefficients (capacity factors) of a sorbate (k) with different carrier gases (P₁ and P₂), the correlation relationshipk(P₂) =A·k(P₁) +B (A, B are parameters of the equation) is closely obeyed. The advantages of carbon dioxide as the carrier gas were analyzed; the use of carbon dioxide allows the efficiency of the column to be enhanced.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 627–633, March, 1996.     

Superselective aqueous inorganic phases in vapor-phase gas chromatography

Chromatographic characteristcs of aqueous solutions of inorganic electrolytes, a new class of stationary liquid phases (SLP) for vapor-phase chromatography, are considered. The SLP are characterized by an unusually high selectivity to organic compounds of the R-X type (R is a hydrocarbon radical, X is a polar group,e.g., hydroxyl, carboxyl, and amine; for instance, light C₁-C₆ alcohols are eluted from the column with a water-containing phase in the following order: hexanol<pentanol<butanol<propanol<ethanol<methanol). The nature of the electrolyte used and its concentration in the water-containing SLP have a crucial influence on the column selectivity and the degree of separation of the compounds subjected to chromatography. This feature provides the possibility of controlling the column selectivity by changing the content of water vapor in the mobile phase. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1831–1840, October, 1999.     

Study of gas generation in real L/ILW containers

To obtain reliable estimates of the quantities and rates of the gas production in L/ILW a series of measurements was carried in the last 7 years in Hungary. The typical gas production rates were 0.05–0.2 STP litre gas/day for CO₂ and CH₄ generation, and less for H₂. No explosive gas mixture was indicated in the L/ILW drums during the investigated storage period. Compositions of headspace gases in closed L/ILW vaults were in agreement with gas generation processes observed in L/ILW drums. The stable carbon isotope measurements show that the main source of the CO₂ gas is the degradation of organic matter and indicates microbial degradation processes as the main sources of CH₄. Typical tritium activity concentrations were <10 Bq/l gas in the drums and <1,000 Bq/l gas in the vaults. Typical ¹⁴C activity values of the headspace gases were <2.0 Bq/l gas in the drums and <1,000 Bq/l gas in the vaults.     

Aqueous solution ofN-methylmorpholineN-oxide as a stationary liquid phase in steam chromatography

The retention of more than 70 voltatile organic compounds of different classes was studied by steam chromatography using aqueous solutions ofN-methylmorpholineN-oxide as the stationary liquid phase (SLP). The effects of temperature and composition of the mobile phase on the retention factors (k) for polar and nonpolar sorbates were elucidated. An unusual order of elution of aliphatic alcohols was noted, namely,tert-butyl alcohol <sec-butyl alcohol < isopentyl alcohol <isobutyl alcohol<isopropyl alcohol <n-pentyl alcohol <n-butyl alcohol <n-propyl alcohol <ethanol <methanol. The retention of cyclohexanol was longer than those of benzyl alcohol andn-hexyl alcohol. Nitrogen-containing compounds were selectively separated on the water-organic SLP studied. For example, the retention of aniline was much longer than those of its derivatives,N,N-dimethylaniline andN,N-diethylaniline, having higher boiling points. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1077–1084, June, 2000.     

The influence of carrier gas pressure on the retention of sorbates on monolithic capillary columns in gas chromatography

The influence of carrier gas pressure on the retention factor k′ of light hydrocarbons C₁–C₄ in a monolithic capillary column based on divinylbenzene was studied. It was shown that, for monolithic columns and nonideal carrier gases, the pressure dependence of lnk′ was nonlinear over a wide pressure range and could be described by the classic Everett equation. It was concluded that the competitive adsorption model failed to describe the experimental data correctly, especially for strongly retained sorbates and/or heavy carrier gases. Original Russian Text ? A.A. Korolev, V.E. Shiryaeva, T.P. Popova, A.V. Kozin, A.A. Kurganov, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 4, pp. 776–783.     

Direct Volumetric Measurement of Gas Oversolubility in Nanoliquids: Beyond Henry’s Law

The properties of condensed matter are strongly affected by confinement and size effects at the nanoscale. Herein, we measured by microvolumetry the increased solubility of H₂ in a series of solvents (CHCl₃, CCl₄, n‐hexane, ethanol, and water) when confined in the cavities of mesoporous solids (γ‐alumina, silica, and MCM‐41). Gas/liquid solubilities are enhanced by up to 15 times over the corresponding bulk values for nanoliquid sizes smaller than 15 nm as long as gas/liquid interfaces are mesoconfined in a porous network. Although Henry’s law constant apparently no longer applies under these confinement, the concentration of dissolved H₂ still increases linearly with increasing pressure in the range 1–5 bar. We discuss the role and main implications of surface excess concentrations at mesoconfined gas/liquid interfaces in enhancing gas solubility.     

Modeling solubility of acid gases in alkanolamines using the nonelectrolyte Wilson-nonrandom factor model

The nonelectrolyte Wilson-nonrandom factor local composition model (N-Wilson-NRF) by Haghtalab and Mazloumi is applied for modeling the vapor–liquid equilibrium of the acid gases (CO₂ and H₂S)–alkanolamine–water systems. The model is used to calculate the nonideality of species in liquid phase through the activity coefficient equations. In this work, we use the N-Wilson-NRF model for short-range forces in the aqueous electrolyte system of alkanolamines by using the concept of ion-pair. For the long-range interaction the Pitzer–Debye–Hückel theory is applied. The model is used to correlation of the solubility data of CO₂ and H₂S in aqueous monoethanolamine (MEA), diethanolamine (DEA), methyldiethanolamine (MDEA) and 2-amino-2methyl-1-propanol (AMP) systems over wide range of temperature (0–140 °C), partial pressure (0.001–1000 kPa) and acid gases loading (0.001–1.0 mol gas/mol amine). To show the predictability of the model, the interaction parameters without any additional adjustable parameters are used to predict the solubility of CO₂ in aqueous AMP solution at different conditions. The results of the model show a very good agreement with the experimental data.     

High pressure measurement and CPA equation of state for solubility of carbon dioxide and hydrogen sulfide in 1-butyl-3-methylimidazolium acetate

Removal of acid gases such as CO₂ and H₂S from natural gas is essential for commercial, safety and environmental protection that demonstrate the importance of gas sweetening process. Ionic liquids (IL) have been highly demanded as a green solvent to remove acid gases from sour natural gas and capturing of CO₂ from flue gases. In this work, the solubility of CO₂ in 1-butyl-3-methylimidazolium acetate ([bmim][Ac]) is measured at temperatures (303.15, 328.15, 343.15) K and pressure range of (0.1 to 3.9) MPa. Moreover, the experiments are carried out for simultaneous measurements of (CO₂ + H₂S) (70% + 30% on a mole basis) solubility in the same ionic liquid at T = (303.15, 323.15, 343.15) K and a pressure range of (0.1 to 2.2) MPa. To model the solubility of acid gases in IL, both physical and chemical equilibria are applied so that the (vapour + liquid) equilibrium calculation is carried out through Cubic-Plus-Association (CPA) EoS. The reaction equilibrium thermodynamic model is used in liquid phase so that the chemical reaction is taking place between IL and acid gasses. The Henry’s and reaction equilibrium constants are obtained though optimization of the solubility data. Using CPA EOS, the pure parameters of [bmim][acetate] are optimised and consequently using these parameters, gas partial pressure calculation is performed for the (CO₂ + IL) and (CO₂ + H₂S + IL) systems. For the (CO₂ + IL) system, the percent average absolute deviation (AAD%) of 4.83 is resulted and for the (H₂S + CO₂ + IL) system the values of 18.8 and 13.7 are obtained for H₂S and CO₂, respectively.     

Molecular model for solubility of gases in flexible polymers

We propose a model for a priori prediction of the solubility of gases in flexible polymers. The model is based on the concept of ideal solubility of gases in liquids. According to this concept, the mole fraction of gases in liquids is given by Raoult's law with the total pressure and the vapor pressure of the gas, where the latter may have to be extrapolated. However, instead of considering each polymer molecule as a rigid structure, we estimate the effective number of degrees of freedom from an equivalent freely jointed bead‐rod model for the flexible polymer. In this model, we associate the length of the rods with the molecular weight corresponding to a Kuhn step. The model provides a tool for crude estimation of the gas solubility on the basis of only the monomer unit of the polymer and properties of the gas. A comparison with the solubility data for several gases in poly(dimethylsiloxane) reveals agreement between the data and the model predictions within a factor of 7 and that better model results are achieved for temperatures below the critical temperature of the gas. The model predicts a decreasing solubility with increasing temperature (because of the increasing vapor pressure) and that smaller gas molecules exhibit a lower solubility than larger ones (e.g., CH₄ has a smaller solubility than CO₂), which agrees with the experimental data. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 701–706, 2003     

Gas transport in poly(vinyl methylbenzoates)

Permeation of eight gases (He, Ne, Ar, Kr, O₂, N₂, CO₂, and CH₄) in three isomeric poly(vinyl methylbenzoates) was measured by the time-lag method, and the effects of the shape of side groups on gas transport in the polymers were investigated. The p-methylphenyl side group of poly(vinyl p-methylbenzoate), which increases both interchain and intrachain distances, caused an increase in gas diffusivity. The diffusivity and density data were consistent with free volume theory. Two other isomeric polymers, poly(vinyl o-methylbenzoate) and poly(vinyl m-methylbenzoate), had lower gas diffusivities than poly(vinyl p-methylbenzoate) and poly(vinyl benzoate). The o-methyl and m-methyl groups on the phenyl ring were found to hinder gas diffusion, i.e., decrease the free volume. In contrast, the solubility of the gases in all these polymers was similar because of their similar chemical structures. The effects of hydroxyl groups also were investigated by the use of poly(vinyl m-methylbenzoate) containing a small number of vinyl alcohol units. The decrease in gas diffusivity was attributed to the decrease of free volume due to hydrogen bonding, but the change of gas solubility was still negligible.     

Measurements and predictions of density and carbon dioxide solubility in binary mixtures of ethanol and n-decane

The solubility of carbon dioxide (CO₂) in binary mixtures of ethanol and n-decane has been measured using an in-house developed pressure-volume-temperature (PVT) apparatus at pressures up to 6 MPa and two different temperatures (303.2 and 323.2 K). Three different binary mixtures of ethanol and n-decane were prepared, and the densities of the prepared mixtures were measured over the studied pressure and temperature ranges. The experimental data of CO₂ solubility in the prepared mixtures and their saturated liquid densities were then reported at each temperature and pressure. The solubility data indicated that the gas solubility reduced as the ethanol mole fraction in the liquid mixture increased. The dissolution of CO₂ in the liquid mixtures resulted in the increase in the saturated liquid densities. The impact of gas dissolution on the saturated liquid densities was more pronounced at the lower temperature and lower ethanol compositions. The experimental solubility and density data were compared with the results of two cubic equations of state (EOSs), Soave–Redlich–Kwong (SRK) and Peng–Robinson (PR). The modeling results demonstrated that both EOSs could predict the solubility data well, while the saturated liquid densities calculated with the PR EOS were much better than those predicted with the SRK EOS.     

Retention of organic compounds in capillary gas chromatography using humid carrier gases

The influence of humid carrier gases (nitrogen and carbon dioxide) on the retention of polar compounds in a capillary column with polypropylcyanophenylsiloxane stationary liquid phase OV-225 was studied. It is noted that when humid carbon dioxide is used as the carrier gas, the retention of primary amines sharply increases. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1129–1131, June, 1999.     

Transport properties of polyimides containing phenylquinoxaline moieties

The gas permeabilities of a number of new structurally related polyimides containing phenylquinoxaline moieties were studied for the first time. The test polymers had different dianhydride units, whereas their diamine components differed in the presence of flexible ether bonds-O-in the main chain, a structure that is reflected in the effective packing of chains and, as a result, in transport parameters. The permeability, diffusion, and solubility coefficients for the gases H₂, He, O₂, N₂, CO, CO₂, and CH₄, as well as the ideal separation factors for gas pairs, were determined. The transport characteristics of polymers were compared within the given polymer series and with published data for other polymer series.     

The Influence of the Natures of the Carrier Gas and the Stationary Phase on the Separating Properties of Monolithic Capillary Columns in Gas Adsorption Chromatography

A model mixture of light hydrocarbons was used to study the separation capacity of monolithic capillary columns based on divinylbenzene with five different carrier gases, including helium, hydrogen, nitrogen, carbon dioxide, and nitrous oxide. The results were correlated with the previously obtained data on monolithic columns based on silica gel. It was shown that the influence of the nature of the carrier gas was weaker than for silica gel columns; the polymeric columns studied behaved similarly to hollow capillary columns with polymeric stationary phases and exhibited an efficiency gain of 20–30% along the series He < H₂ < N₂ ～ N₂O < CO₂. Based on the minimum HETP (～15 μm) obtained for the investigated monolithic columns under optimum conditions with N₂O or CO₂ as a carrier gas, the conclusion was drawn that the creation of divinylbenzene-based monolithic capillary columns with a high specific efficiency was possible.     

Copolyimides containing alicyclic and fluorinated groups: Solubility and gas separation properties

A series of polyimides with alicyclic and fluorinated moieties previously synthesized were studied for gas separation applications. The solubility behavior of polyimides in various solvents was analyzed through the solubility parameter approach. Permeability coefficients and ideal selectivities were determined for common gases, that is, He, H₂, O₂, and N₂. Polyimide permeabilities were correlated to an improvement of the soluble character and were increased by the introduction of both alicyclic and fluorinated structures. The effect of the casting solvent on gas separation properties was also pointed out. It was found that it is enhanced with increasing diameters for the gas molecules. Finally, some correlations between permeability coefficients and microstructural parameters were discussed. The probability of correlation appears to be also dependent on the diameter and on the polarizability of the gas molecule. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2413–2426, 2005.