Volumetric and Transport Properties of Ternary Mixtures Containing 1-Butanol or 1-Pentanol,Triethylamine and Cyclohexane at 303.15 K: Experimental Data,Correlation and Prediction by the ERAS Model

The excess molar volumes, V _m^E, viscosity deviations, Δη, and excess Gibbs energies of activation, ΔG ^*E, of viscous flow have been investigated from density and viscosity measurements for two ternary mixtures, 1-butanol + triethylamine + cyclohexane and 1-pentanol + triethylamine + cyclohexane, and corresponding binaries at 303.15 K and atmospheric pressure over the entire range of composition. The empirical equations due to Redlich-Kister, Kohler, Rastogi et al., Jacob-Fitzner, Tsao-Smith, Lark et al., Heric-Brewer, and Singh et al. have been employed to correlate V _m^E, Δη and ΔG ^*E of the ternary mixtures with their corresponding binary parameters. The results are discussed in terms of the molecular interactions between the components of the mixture. Further, the Extended Real Associated Solution, ERAS, model has been applied to V _m^E for the present binary and ternary mixtures, and the results are compared with experimental data.     

Efficient methods for calculations of compressibility,density and viscosity of natural gases

This study presents two new methods for calculating properties of natural gases. The first is an efficient empirical model to calculate compressibility and density of natural gases containing high amount of heptane plus and none-hydrocarbon components. The model is derived from 2400 measurements of compressibility and density of various gases presented in this study. Accuracy of the model is compared to various equations of state (EOS), corresponding state, and empirical methods. The study shows that the new model is simpler and more efficient than EOS. It eliminates the numerous computations involved in EOS calculations. The new method also eliminates the characterization of the heptane plus fraction and estimation of binary interaction parameters needed for EOS calculations. Experimentally measured density of several gases has been used to study the validity of the proposed method. These measurements indicate that the new method successfully capture the physical trend of changing gas density as a function of pressure, temperature, and composition.The second method is a modification of Lee–Gonzalez–Eakin gas viscosity correlation. The new method accounts for the presence of heptane plus, hydrogen sulfide, and carbon dioxide in natural gases. The proposed method is compared to other EOS-based viscosity model, corresponding state methods, and correlations. The comparison indicates the superiority of the new method over the other methods used to calculate viscosity of natural gases.     

Theoretical scheme for the shear viscosity of Lennard-Jones fluids

We use the shear viscosity expression from the Enskog theory of dense gases in a perturbative scheme for the Lennard-Jones (LJ) fluid. This perturbative scheme is formulated by combining the analytic rational function approximation method of Bravo Yuste and Santos [Phys. Rev. A 43, 5418 (1991)] for the radial distribution function of hard-sphere fluids and the well known Mansoori-Canfield/Rasaiah-Stell perturbation theory to determine an effective diameter for the LJ fluid. The scheme is reliable on a wide range of temperatures and densities, and is very accurate around the critical point. Using this information, we build an accurate empirical formula for the shear viscosity in the liquid phase, which fits the recent data [K. Meier et al., J. Chem. Phys. 121, 3671 (2004)] in the whole simulation range.     

Dynamics from picoseconds to nanoseconds of trehalose in aqueous solutions as seen by quasielastic neutron scattering

We present a study of the dynamical behavior of trehalose, a cryoprotecting agent, in concentrated aqueous solutions. Dynamics in a wide time range from picoseconds to nanoseconds has been observed using both neutron time of flight and neutron spin-echo techniques. Fast dynamics has been described using a simple diffusion model, while dynamical processes at longer times show a more complex behavior, described by a stretched exponential decay. Obtained relaxation times show a good agreement with data from viscosity measurements on aqueous trehalose solutions by Magazu et al. [Branca, Magazu, Maisano et al., J. Phys.: Condens. Matter 11, 3823 (1999)]. Experimental data provide us with some insight into the cryoprotecting properties and processes of trehalose. We conclude that an increase of the solvent viscosity in embedded biological material due to the production or the presence of trehalose might prevent biomolecules from damage.     

Viscosity Prediction for Oxygen,Nitrogen and Their Mixtures at Zero and Moderately Dense Regimes via Semi‐Empirically Based Assessment

The viscosity coefficients for the gaseous states of N₂ and O₂ and their mixtures are determined at zero and moderately density regimes. The Lennard‐Jones 12–6 (LJ 12–6) potential energy function is used as the initial model potential required y the technique. The interaction potential energies from the inversion procedure reproduce the viscosity commensurate to the best measurements. The initial density dependence of gaseous viscosity coefficient according to the Rainwater‐Friend theory, which was given by Najafi et al., has been considered for pure N₂ and pure O₂.     

Predicting the dew point pressure for gas condensate reservoirs: empirical models and equations of state

This paper presents a new empirical model to estimate dew point pressure (DPP) for gas condensate reservoirs as a function of routinely measured gas analysis and reservoir temperature. The proposed model was developed using experimentally measured and collected data of 340 gas condensate samples covering a wide range of gas properties and reservoir temperatures. The new model has an average relative deviation (ARD) of 0.44% and average absolute deviation (AAD) of 7.68% or 346 psia (1 psia=6.894757E−3 mPa). The accuracy of the model has been compared to SRK-EOS, PR-EOS and other correlations. Gas condensate samples from this study as well as from literature have been used to check the validity of the proposed model against EOS simulation. These examples have shown that the model successfully captures the physical trend and that the model is reliable. This model is useful to provide an estimate of the DPP when experimentally measured ones are not available.The current study also shows that predicting the DPP for gas condensates depends on the EOS(s), the number of pseudo-components and the characterization of the plus fraction. For most of the gas condensates used in this study, a 10–12 pseudo-components of the heptane plus (C₇₊) fraction resulted in minimum error in calculation of DPP using PR-EOS with Pedersen et al. characterization of the plus fraction.     

Macroporous silicon and its application in sensing

Periodic silicon nanostructures can be used for different kinds of gas sensors depending on the analyte concentration. First, we present an optical gas sensor based on the classical non-dispersive infrared technique for ppm-concentration using ultra-compact photonic crystal gas cells (Pergande et al., 2011) [1]. It is conceptually based on low group velocities inside a photonic crystal gas cell and anti-reflection layers coupling light into the device. Secondly, we report on silicon nanotip arrays (Gesemann et al., 2011) [2], suitable for gas ionization in ion mobility microspectrometers (micro-IMS) having detection ranges in principle down to the ppt-range. Such instruments allow the detection of explosives, chemical warfare agents, and illicit drugs, e.g., at airports. Third of all, we describe the thermal emission properties of heated silicon photonic crystals (Gesemann et al., 2010) [3], revealing a photonic stop gap effect or strong silicon oxide emission, depending on the setup. All silicon microstructures have been fabricated by photo-electrochemical etching of silicon.     

The bulk viscosity of a fluid: the inverse power potential

The bulk viscosity coefficient of a moderately dense gas has been evaluated numerically for an inverse power potential. The calculation, to order density squared, is based on the microscopic theory of Snider et al. The results are compared to those from the corresponding expression of the modified Enskog theory. Agreement between the sets of values is within 1%.     

Calculation of the transport and relaxation properties of methane. I. Shear viscosity, viscomagnetic effects, and self-diffusion

Transport properties of pure methane gas have been calculated in the rigid-rotor approximation using the recently proposed intermolecular potential energy hypersurface [R. Hellmann et al., J. Chem. Phys. 128, 214303 (2008)] and the classical-trajectory method. Results are reported in the dilute-gas limit for shear viscosity, viscomagnetic coefficients, and self-diffusion in the temperature range of 80-1500 K. Compared with the best measurements, the calculated viscosity values are about 0.5% too high at room temperature, although the temperature dependence of the calculated values is in very good agreement with experiment between 210 and 390 K. For the shear viscosity, the calculations indicate that the corrections in the second-order approximation and those due to the angular-momentum polarization are small, less than 0.7%, in the temperature range considered. The very good agreement of the calculated values with the experimental viscosity data suggests that the rigid-rotor approximation should be very reasonable for the three properties considered. In general, the agreement for the other measured properties is within the experimental error.     

Resonance light scattering and derived techniques in analytical chemistry: past, present, and future

From 1993 to 1995, with a conventional fluorescence spectrophotometer (CFS) (convenient) and working in a synchronous scan model (easy-to-use), Pasternack et al. proposed the resonance light-scattering (RLS) technique, to efficiently characterize self-assemblies or self-aggregations of chromophores with good electronic coupling. Incident wavelengths were specially considered within their absorption envelopes (rather unorthodox), and their amplified signals were observed (good sensitivity and selectivity). Due to these absorbing benefits, RLS technique, as a novel readout method, commenced on its exciting analytical tours soon after Liu et al. and especially Li et al., separately, set out their corresponding pioneering investigations from 1995 to 1997. From then on, it has received an increasing attention by analysts, as a consequence exhibiting more and more fascinating analytical applications. Moreover, various attractive RLS-derived techniques have been developed successively to improve it or to enlarge its possibilities. Later on, Liu et al. and Li et al., Tabak et al., Yguerabide et al., Huang et al., Lakowicz et al. and Fernández Band et al. have made their outstanding contributions. In this review, we concentrate on major achievements of RLS in analytical chemistry for over a decade, involving the developments and analytical applications of RLS derived techniques treated as an impacting progress of RLS technique in analytical chemistry. Finally, an indication of future directions of RLS technique in analytical chemistry is provided.     

HINT: A new method of empirical hydrophobic field calculation for CoMFA

Summary An empirical hydrophobic field-like 3D function has been calculated with the program HINT (hydrophobic interactions) and imported into the SYBYL implementation of CoMFA (Comparative Molecular Field Analysis). The addition of hydrophobicity appears to offer increased chemical interpretability of CoMFA models. An example is given using the steroid model reported by Cramer et al. (J. Am. Chem. Soc., 110 (1988) 5959). While addition of the HINT field did not improve statistical parameters in this model, the CoMFA coefficient contours from the hydrophobic field unambiguously define the most active steroid molecules in the chemical terms of hydrophobic and polar substituents.     

Estimation of the Nitta-Chao Parameters for the ether-group. Ether + n-alkane mixtures

In this work we have estimated the structural and interactional parameters of the ether- group for the group-contribution model of Nitta-Chao using a extensive experimental database of thermodynamic properties of ethers (monoethers, polyethers and acetals) and ether + n-alkane and ether + ether mixtures. The results obtained by Nitta-Chao model with this parameters get closer to the experimental values than those obtained with parameters of Eckart et al. (1986). The thermodynamic properties obtained by the Nitta-Chao model with old and new parameters were compared to predictions by other models such as Flory (1965) theory, DISQUAC (Kehiaian, 1977) model and UNIFAC model (versions of Dang and Tassios, 1986, and Larsen et al., 1987).     

An accurate empirical correlation for predicting natural gas compressibility factors

The compressibility factor of natural gas is an important parameter in many gas and petroleum engineering calculations. This study presents a new empirical model for quick calculation of natural gas compressibility factors. The model was derived from 5844 experimental data of compressibility factors for a range of pseudo reduced pressures from 0.01 to 15 and pseudo reduced temperatures from 1 to 3. The accuracy of the new empirical correlation has been compared with commonly used existing methods. The comparison indicates the superiority of the new empirical model over the other methods used to calculate compressibility factor of natural gas with average absolute relative deviation percent (AARD%) of 0.6535.     

Accuracy of recent potential energy surfaces for the He-N2 interaction. II. Molecular beam scattering and bulk gas relaxation phenomena

A new semiempirical exchange-Coulomb model potential energy surface for the N(2)-He interaction was reported recently [A. K. Dham et al., J. Chem. Phys. 127, 054302 (2007)] and, using it, the temperature dependence of bulk gas properties of N(2)-He mixtures, such as the second virial coefficient and traditional transport phenomena, most of which depend primarily on the isotropic component of the interaction potential energy surface, was determined. Values of these properties, along with values calculated using two high-quality ab initio potential energy surfaces [C.-H. Hu and A. J. Thakkar, J. Chem. Phys. 104, 2541 (1996); K. Patel et al., ibid 119, 909 (2003)] were compared critically to available experimental data. The present paper reports on the ability of the same three potential energy surfaces to predict state-to-state and total differential cross sections, total integral cross sections, and the temperature dependence of bulk gas relaxation phenomena (including magnetic field effects on transport coefficients). While all three potential energy surfaces give total differential and higher speed integral scattering results that fall within the experimental uncertainties, integral scattering results and state-to-state differential cross section measurements consistently exceed the calculated values. All three surfaces give similar agreement with the relaxation properties of N(2)-He binary mixtures, with the semiempirical exchange-Coulomb model potential energy surface giving slightly better overall agreement with experiment than the two ab initio potential energy surfaces.     

Power‐Law Kinetic Models for Synthesis of Ammonia Borane

In the past few years, there have been increasing numbers of studies for the production and dehydrogenation of ammonia borane (NH₃BH₃, AB), which has become a significant hydrogen storage material. However, kinetic model studies based on the synthesis of AB in the literature have not been encountered, though there are many kinetic modeling studies on dehydrogenation of AB (Akbayrak et al., Appl Catal B 2016, 198, 162–170; Choi et al., Phys Chem Chem Phys 2014, 16(17), 7959–7968; Esteruelas et al., Inorg Chem 2016, 55(14), 7176–7181; Park et al., Int J Hydrogen Energy 2015, 40(46), 16316–16322; Rakap, Appl Catal B 2015, 163, 129–134; Tonbul et al., Int J Hydrogen Energy 2016, 41(26), 11154–11162; Zhang et al., Int J Hydrogen Energy 2016, 41(39), 17208–17215). The paper describes the development of a kinetic model for synthesis of ammonia borane by using borohydride (NaBH₄) and ammonium salt (NH₄)₂SO₄. The synthesis of AB experiments was carried out at different temperature ranges between 25 and 50°C, different inlet molar ratios (NaBH₄/(NH₄)₂SO₄ = 1–4), and different molarities with respect to NaBH₄ (0.11–0.67 M NaBH₄). After the parametric experiments were conducted, empirical power law was evaluated for the synthesis reaction. The power‐law model represented the trends of the kinetics of the synthesis reaction and was reproduced as .     

The photophysics of all-trans polyenes from ttbP5, a nonphotolabile pentaene

The all-trans pentaene, 3,12-di(tert-butyl)-2,2,13,13-tetramethyl-3,5,7,9,11-tetradecapentaene (ttbP5) fluoresces in two different regions of the visible spectrum. It produces an extremely weak emission in the gas phase that can also be detected in the condensed phase; such an emission exhibits a negligible Stokes shift with respect to the 1Ag-->1Bu absorption transition and can in principle be assigned to the 1Bu-->1Ag emission of the compound. ttbP5 also exhibits a second fluorescence emission at approximately 520 nm in both the gas phase and the condensed phase. The emission in the condensed phase increases in strength and structure, with no change in spectral position, as the solvent viscosity increases by effect of the solution temperature being lowered. The spectral behavior of this pentaene (ttbP5) is different enough from that reported [J. Catalan et al., J. Chem. Phys. 128, 104504 (2008)] for its tetraene counterpart (ttbP4) to warrant a separate analysis in order to facilitate a better understanding of the way the photophysics of these polyenes changes as their chain is lengthened.     

CF3CH3 --> HF + CF2CH2: a non-RRKM reaction?

The experimental shock tube data recently reported by Kiefer et al. [J. Phys. Chem. A 2004, 108, 2443-2450] for the title reaction at temperatures between 1600 and 2400 K have been compared to master equation simulations using three models: (a) standard RRKM theory, (b) RRKM theory modified by local random matrix theory, which introduces dynamical corrections arising from slow intramolecular vibrational energy randomization, and (c) an ad hoc empirical non-RRKM model. Only the third model provides a good fit of the Kiefer et al. unimolecular reaction rate data. In separate simulations, all three models accurately reproduce the experimental 300 K chemical activation data of Marcoux and Setser [J. Phys. Chem. 1978, 82, 97-108] when the energy transfer parameters are freely varied to fit the data. When experimental energy transfer parameters for a geometrical isomer (1,1,2-trifluoroethane) are used, the standard RRKM model fits the chemical activation data better than the other models, but if energy transfer in the 1,1,1-trifluoroethane is significantly reduced in comparison to the 1,1,2 isomer, then the empirical ad hoc non-RRKM model also gives a good fit. While the ad hoc empirical non-RRKM model can be made to fit the data, it is not based on theory, and we argue that it is physically unrealistic. We also show that the master equation simulations can mimic the Kiefer et al. vibrational relaxation data, which was the first shock tube observation of double-exponential relaxation. We conclude that, until more data on the trifluoroethanes become available, the current evidence is insufficient to decide with confidence whether non-RRKM effects are important in this reaction, or whether the Kiefer et al. data can be explained in some other way.     

Reaction mechanism of oxidation, hydroxylation, and epoxidation by hypofluorous acid: a theoretical study of unusual H-bond-assisted catalysis

The oxidation of organic molecules by hypofluorous acid (HOF) was studied extensively and systematically by Rozen et al. Therefore, it seems appropriate to refer to the process as Rozen oxidation. An entire set of model molecules was selected for quantum chemical investigation of the oxidation mechanism: a C=C double bond in ethylene, sulfur and selenium in dimethyl derivatives, nitrogen and phosphorus in trimethyl derivatives, as well as methyl azides. In the gas phase, van der Waals complexes between HOF and the previously mentioned species easily are formed, but these complexes are reluctant to undergo oxidation. The addition of another HOF molecule connected with the formation of a cyclic complex (i.e., substrate and two molecules of HOF) seems to be decisive for the oxidation process. The attempt to substitute the second HOF molecule with H2O demonstrated the superiority of HOF. Complexes of this kind decompose along the reaction path smoothly (i.e., with a low activation energy) to the respective oxidation product. A potential role of the hydroxyl cation (HO+) in the oxidation step is mentioned. Besides an oxidation product, one HOF molecule is released (an essential feature of catalysis), and furthermore, hydrogen fluoride is formed. It was suggested by Sertchook et al. (J. Phys. Chem. A 2006, 110, 8275) that the interaction between the substrate to be oxidized and HOF is catalytically influenced by the HF molecule. The mechanism suggested here is more feasible and, particularly at the early stages of the oxidation process, decisive. Also, the role of acetonitrile, used as a solvent by Rozen et al., is discussed in terms of a continuum model. Moreover, passing from potential energies to Gibbs energies is considered.