Single-walled carbon nanotubes as stationary phase in gas chromatographic separation and determination of argon, carbon dioxide and hydrogen

A chromatographic technique is introduced based on single-walled carbon nanotubes (SWCNTs) as stationary phase for separation of Ar, CO₂ and H₂ at parts per million (ppm) levels. The efficiency of SWCNTs was compared with solid materials such as molecular sieve, charcoal, multi-walled carbon nanotubes and carbon nanofibers. The morphology of SWCNTs was optimized for maximum adsorption of H₂, CO₂ and Ar and minimum adsorption of gases such as N₂, O₂, CO and H₂O vapour. To control temperature of the gas chromatography column, peltier cooler was used. Mixtures of Ar, CO₂ and H₂ were separated according to column temperature program. Relative standard deviation for nine replicate analyses of 0.2 mL H₂ containing 10 μL of each Ar or CO₂ was 2.5% for Ar, 2.8% for CO₂ and 3.6% for H₂. The interfering effects of CO, and O₂ were investigated. Working ranges were evaluated as 40-600 ppm for Ar, 30-850 ppm for CO₂ and 10-1200 ppm for H₂. Significant sensitivity, small relative standard deviation (RSD) and acceptable limit of detection (LOD) were obtained for each analyte, showing capability of SWCNTs for gas separation and determination processes. Finally, the method was used to evaluate the contents of CO₂ in air sample.     

Kinetics and equilibrium of adsorption on 4A zeolite

Adsorption isotherms for Ar, 0₂, N₂, CO, CO₂, CH₄, and C₂H₆ on 4A zeolite at three or more temperatures were determined. An adsorption equation based on a 2-dimensional virial equation in terms of integer powers of the reciprocal of (A - σ) was shown to fit the equilibrium data accurately with three constants for C₂H₆ and two constants for other gases. Here A is the area per molecule and σ is the area of the molecule in a close-packed situation.Rates of adsorption and desorption of Ar, N₂, CO, CH₄, and C₂H₆ on 4A zeolite were determined over ranges of temperature in which the rate was moderately fast. Electron microscopy showed that the particles were cubes, and their size-distribution was determined. The conventional Fick's law rate equation for cubes was used to produce a generalized rate curve for the particle size distribution of the adsorbent. This curve was applied to the last 20% of the rate curve to obtain a diffusivity that could be related to the final amount adsorbed. This procedure also avoids the initial rapid portion of the adsorption, in which large variations of adsorbent temperature from that of the bath often occur.The diffusivities increased with amount adsorbed by a small extent for Ar and CH₄ and by larger amounts for N₂, CO, and C₂H₆. The activation energy for diffusion, as well as the heat of adsorption, were nearly independent of amount adsorbed for Ar and CH₄, but these quantities decreased substantially with coverage for N₂, CO, and C₂H₆. The dependence upon amount adsorbed of diffusivity and activation energy seemed related to the shape of the adsorption isotherm; those for Ar and CH₄ were nearly linear, whereas isotherms for the other gases had large curvatures. The activation energy for diffusion varied with coverage in the same way as heat of adsorption.     

Vapour—liquid equilibrium at elevated pressures from the perturbation theory. II. Binary systems

Vapour—liquid equilibria in binary systems of non-polar non-spherical molecule compounds were studied theoretically by combining the perturbation theory of convex molecule fluids with a new variant of the conformal solution theory. The recently proposed equation of state of hard convex body mixtures and the corresponding expressions for the contact values of distribution functions were employed to determine the reference thermodynamic functions and the perturbation terms. Ten binary systems, i.e. ArCH₄, N₂CH₄, N₂C₂H₄, N₂C₂H₆, CH₄C₂H₄, CH₄C₂H₆, C₂H₄C₂H₆, CO₂C₂H₄, CO₂C₂H₆, and ArCO₂ were studied at constant temperatures. Comparison of theoretical predictions with experimental data is given.     

Electrode erosion in plasma torches

Cathode erosion rates are reported (or copper electrodes in a simulated plasma torch operating at atmospheric pressure. The are current was 100A (or most experiments; the magnetic field used to move the arc varied between 0.001 and 0.15 T. Different plasma gases were used (Ar, He, air, N₂, CO, and mixtures of the noble gases with O₂, N₂, CO, CH₄, Cl₂, and H₂S) at flow rates varying between 0.2 and 20 liters/min. Different criteria (arc velocity, arc attachment residence time, arc current density) were used to analyze the erosion results.     

Gamma-radiolysis of hydrogen—Oxygen-mixtures— Part I. Influences of temperature,vessel wall,pressure and added gases (N2, Ar,H2) on the reactivity of H2/O2-mixtures

The influence of pressure, temperature, of “matrix gases” N₂, Ar, H₂ and of the pretreatment of the vessel wall on the rate of reaction from ⁶⁰Co γ-radiolysis of hydrogen—oxygen-mixtures, in the region of slow reaction, was investigated. The G(-H₂)-value2 of H₂/O₂-mixtures (H₂:O₂ = 1:9−2:1) ranges from 1 to 14 with only slight dependence on pressure, temperature, H₂/O₂-ratio, and surface/volume ratio (S/V). The temperature has little influence (35–210°C). Replacing most of the O₂ in the H₂:O₂ (1:9)-mixtures with N₂, Ar or excess H₂ at higher temperature, causes the G(-H₂)-values to increase. The influence of these matrix gases increases with increasing temperature (35–210°C) and decreasing S/V ratio (0.59 and 3.8 cm^-1) of the reaction vessel; it depends also on the pretreatment of the wall surface. Varying the total pressure, the G(-H₂)-values show a temperature and gas mixture dependent maximum between about 20 and 200 mb. At higher temperature (210°C) we observed an influence of dose for 50 mb H₂/air-mixtures, whereas at 1 b and 35–90°C no influence of the dose on the rate of reaction of such mixtures was found.The activation by N₂, Ar, H₂ is discussed on the base of the H₂/O₂-reaction being a radical-chain reaction, built up by at least 38 coupled elementary steps (Ref⁽¹⁾ or see part 2). O₂ reacts with H₂, at increased rates of conversions (> 25%), in the expected stoichiometric ratio of 2:1. Oxygen may however also be converted in non-stiochiometric amounts under certain conditions.     

Solubility of nonpolar gases in 2,2,2-trifluoroethanol at 25°C and 101.33 kPa partial pressure of gas

Solubility measurements of several nonpolar gases (He, Ne, Ar, Kr, Xe, H₂, N₂, CH₄, C₂H₄, C₂H₆, CF₄, SF₆, and CO₂) in 2,2,2-trifluoroethanol at 25°C and 101.33 kPa partial pressure of gas are reported. Gibbs energy for the solution process at 25°C is evaluated from the experimental values of the solubility of gases expressed as mole fraction. Lennard-Jones 6–12 pair potential parameters for 2,2,2-trifluoroethanol are estimated by using the scaled particle theory (SPT); and experimental solubilities are compared with those calculated from the values of these parameters through the SPT model.     

Halogenomercury Salts of Sterically Crowded Triazenides – Convenient Starting Materials for Redox‐Transmetallation Reactions

Diaryl‐substituted triazenides Ar(Ar′)N₃HgX [Ar/Ar′ = Dmp/Mph, X = Cl ( 2a ), Br ( 3a ), I ( 4a ); Ar/Ar′ = Dmp/Tph, X = Cl ( 2b ), I ( 4b ) with Mph = 2‐MesC₆H₄, Mes = 2,4,6‐Me₃C₆H₂, Tph = 2′,4′,6′‐triisopropylbiphenyl‐2‐yl and Dmp = 2,6‐Mes₂C₆H₃] were synthesized by salt‐metathesis reactions in ethyl ether from the readily available starting materials Ar(Ar′)N₃Li and HgX₂. These compounds may be used for redox‐transmetallation reactions with rare‐earth or alkaline earth metals. Thus, reaction of 4b or 2b with magnesium or ytterbium in tetrahydrofuran afforded the triazenides Dmp(Tph)N₃MX(thf) ( 5b : M = Mg, X = I; 6b : M = Yb, X = Cl) in good yield. All new compounds were characterized by melting point, ¹H and ¹³C NMR spectroscopy and for selected species by IR spectroscopy or mass spectrometry. In addition, the solid‐state structures of triazenides 2a , 2b , 3a , 4b , 5b and 6b were investigated by single‐crystal X‐ray diffraction.     

Triple quadrupole mass spectrometry as applied to flame diagnostics: study of the C2H4/N2O/Ar flame

A recently developed research apparatus for characterization of low-pressure premixed flames has been developed and was used to characterize the C₂H₄/N₂O/Ar flame at 20 torr. This instrument incorporates several diagnostic techniques in one apparatus so that individual techniques can be quantitatively compared and the usable detection range (both in terms of resolution and species detection) expanded. Results discussed in this report include mass analysis by triple quadrupole mass spectrometer and temperature measurement by thermocouple. Concentration profiles in the one-dimensional flame include CO, N₂, and C₂H₄, at nominal m/z 28 as well as CO₂ and N₂O at m/z 44.     

Sorption and partial molar volume of gases in polybutadiene

Sorption of He, H₂, N₂, O₂, Ar, CH₄, C₂H₆, and C₂H₆ in polybutadiene and the dilation of the polymer due to sorption of the gases are investigated over the pressure range 0-50 atm at 25°C. For CO₂ the measurements are made at temperatures ranging from 15 to 80°C. Partial molar volumes of the gases in the polymer are determined. The temperature dependence of partial molar volume is discussed on the basis of the data for CO₂. The Flory-Huggins interaction parameters of CO₂, C₂H₄, and C₂H₆ are also estimated.     

Solubility of nonpolar gases in tetrahydrofuran at 0 to 30°C and 101.33 kPa partial pressure of gas

Solubility measurements of several nonpolar gases (He, Ne, Ar, Kr, Xe, H₂, D₂, N₂, CH₄, C₂H₄, C₂H₆, CF₄ and SF₆) in tetrahydrofuran from 0 to 30°C and 101.33 kPa partial pressure of gas are reported. Thermodynamic functions for the solution process (Gibbs energy, enthalpy, and entropies) at 25°C are evaluated from experimental values of gas solubility as mole fractions and their variation with temperature. Lennard-Jones 6–12 pair potential parameters for tetrahydrofuran are estimated using the scale particle theory; experimental solubilities as mole fraction are compared with values calculated using this theory.     

PMMA Surface Functionalization Using Atmospheric Pressure Plasma for Development of Plasmonically Active Polymer Optical Fiber Probes

In this paper, we demonstrate the development of plasmonically active PMMA optical fiber probes by the attachment of gold nanoparticles to the probe surface functionalized by means of flowing post-discharges from dielectric barrier discharge (DBD) plasmas for the first time. Polymer optical fiber (POF) probes (U shape to improve absorbance sensitivity) were subjected to reactive gas atmospheres in the post-discharge region of a coaxial DBD plasma reactor run at atmospheric pressure in different gases (Ar, Ar + 10 % O₂, O₂, N₂, N₂ + 0.5 % H₂). Plasma treatments in Ar or N₂ gave rise to water-stable electrophilic functional groups on PMMA surface, whereas the amine groups generated by N₂-containing plasmas were not stable. Subsequently, PMMA surfaces were treated with hexamethylene diamine (HMDA) to obtain stable amine groups through the reaction of electrophilic groups. Gold nanoflowers (AuNF, 37 nm, peak 570 nm) binding to the amine functionalized fiber probes was monitored in real-time by recording the optical absorbance changes at 570 nm with the help of a UV–vis spectrometer. Absorbance response from Ar or N₂ plasma treated probes are 100 and 60 times, respectively, that of untreated control probes. A 25 fold improvement in absorbance response was obtained for Ar plasma treated POF in comparison with only HMDA treated POF. The shelf life of the hence fabricated plasmonically active probes was found to be at least 3 months. In addition, plasmonic activity of U-bent fiber probes treated in Ar plasma is better than the conventional wet-chemical activation by environmentally hazardous acid pre-treatment approaches.     

Synthesis and Structure of N,N-Dimethyldithiocarbamates of Tetraphenylantimony and Tetra-p-tolylantimony

Tetraphenylantimony N,N-dimethyldithiocarbamate (I) and tetra-p-tolylantimony N,N-dimethyldithiocarbamate (II) were synthesized via the reaction of tetraarylantimony chloride Ar₄SbCl (Ar = C₆H₅ or C₆H₄Me-4) with sodium N,N-dimethyldithiocarbamate in water. According to the X-ray diffraction data, the tetraarylantimony N,N-dimethyldithiocarbamate molecules have a distorted octahedral configuration. The Sb–S bond lengths are equal to 2.7158(5) Å, 2.7440(5) Å and 2.761(2) Å, 2.8002(2) Å for I and II, respectively.     

Quenching rate constants for Ne3P2) metastable atoms at room temperature

Rate constants for quenching of Ne³P₂) metastable atoms have been measured at room temperature by the flowing afterglow technique for 12 reagents; Ar, Kr, Xe, H₂, N₂, CO, HCl, F₂, Cl₂, NF₃, N₂F₄ and N₂O. The values range from ≈5 × 10^?11 cm³ molecule^?1 s^?1 for H₂ and CO up to ≈42 × 10^⊥-11 cm³ molecule^?1s^?1 for Cl₂ and F₂. Comparison with similar data for He(2³S) and Ar(³P₂) suggests that the thermal quenching cross sections follow the trends δ(Ar, ³P₂) > δ(Ne, ³P₂) ? δ(He, 2 ³S). The major exceptions seem to be N₂, CO and Kr which have usually small quenching cross sections for Ar(³P₂).     

Synthesis and gas permeation properties of silicalite-1 zeolite membrane

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A convenient synthetic route to new bis(arenediazo) complexes of molybdenum and tungsten

Complexes of the type [(C₅H₅)Mo(N₂Ar)(N₂Ar′)(PPh₃)] [PF₆] have been prepared and shown to be useful starting materials for the synthesis of a variety of neutral, cationic or anionic compounds containing [cis-Mo(N₂Ar)(N₂Ar′)]²⁺ units.     

Rate constant for the OH + CO reaction: Pressure dependence and the effect of oxygen

The effect of pressure on the rate constant of the OH + CO reaction has been measured for Ar, N₂, and SF₆ over the pressure range 200–730 torr. All experiments were at room temperature. The method involved laser-induced fluorescence to measure steady-state OH concentrations in the 184.9 nm photolysis of H₂O-CO mixtures in the three carrier gases, combined with supplementary measurements of the CO depletion in these same carrier gases in the presence and absence of competing reference reactants. The effect of O₂ on the pressure effect was determined. A pressure enhancement of the rate constant was observed for N₂ and SF₆, but not for Ar, within an experimental error of about 10%. The pressure effect for N₂ was somewhat lower than previous literature reports, being about 40% at 730 torr. For SF₆ a factor of two enhancement was seen at 730 torr. In each case it was found that O₂ had no effect on the pressure enhancement. The roles of the radical species HCO and HOCO were evaluated.     

Computational tests of the factorization of cross sections in the sudden approximation

The factorization expressions for cross sections reported by Goldflam, Green and Kouri and independently by Khare are tested using accurate close coupling input for e^? + H₂, H + H₂, He + (HF, DF, HCl, DCl) and Ar + N₂. The results at the degeneracy averaged cross section level are used to illustrate accuracy criteria given for the factorization. Effects studied include variation of the projectile reduced mass, influence of initial and final rotor state, collision energy and potential anisotropy.     

On the use of the variational method for interpreting the solubilities of gases in liquids

The Variational theory of mixtures due to Mansoori and Leland is modified to account for translational quantum effects in solution, and this modified form of the theory is applied to the problem of gas solubilities in liquids. The theory is used to derive expressions for the Henry's law constant, the molar heat of solution at infinite dilution, and the partial molar volume at infinite dilution for a solute in a liquid solution. These expressions are applied, over a range of temperatures, to the following systems; H₂ in each of Ar, N₂, and CH₄; He in each of Ar, N₂, and CH₄; and Ne in each of Ar and N₂. Lennard-Jones 6–12 pair potentials are used for these calculations. The Lennard-Jones parameters are taken from gas-phase second virial coefficient data. The results obtained are compared with experimental data and with previous calculations on these systems based on the Leonard-Henderson-Barker theory. The variational results appear to be in better agreement with experiment for the He-containing systems, while the Leonard-Henderson-Barker theory seems better for the other systems. An explanation for this is suggested.     

Solubility of nonpolar gases in tetrahydropyran at 0 to 30°C and 101.33 kPa partial pressure of gas

Solubility measurements of several nonpolar gases (He, Ne, Ar, Kr, Xe, H₂, D₂, N₂, CH₄, C₂H₄, C₂H₆, CF₄, and SF₆) in tetrahydropyran at the temperature range 0 to 30°C and 101.33 kPa partial pressure of gas are reported. Thermodynamic functions for the solution process (Gibbs energy, enthalpy, and entropies) at 25°C are evaluated from the experimental values of the solubility of gases as mole fraction and their variation with the temperature. Lennard-Jones 6–12 pair potential parameters for tetrahydropyran are estimated by using the scale particle theory (SPT); and experimental solubilities are compared with the calculated values using this model. Experimental solubilities of gases in tetrahydropyran and intermolecular potential parameters are compared with those obtained for the same gases in other cycloethers.     

A GC-system for the analysis of residual geothermal gases

Summary The gases evolved from geothermal fields, after condensation of H₂O, CO₂, H₂S and NH₃ in caustic solution, contain He, H₂, Ar, O₂, N₂, CH₄ and higher hydrocarbons. The analysis for the major components in these residual gas mixtures can be achieved by use of two simple gas chromatographs in parallel, and using 5Å molecular sieve. The separation of He and H₂ to baseline is achieved by using low temperatures (30°C) coupled with a relatively long column; and the difficult separation of Ar and O₂ is achieved by use of a cryogenically cooled column. The use of switching valves to backflush and bypass columns ensures that a minimum time for analysis can be achieved whilst retaining baseline separations of the He/H₂ and Ar/O₂ pairs.