Alkane Systems Research Articles

Bulk structure and surface activity of semifluorinated alkanes

Semifluorinated alkanes of different even numbered hydrocarbon chain lengths and their solutions in alkanes were studied by scattering methods. The pure substances pass through several solid phases over a broad temperature range. In this study we analyzed the underlying molecular structures by means of powder X-ray diffraction. The molecular orientation of SFA molecules in their solid phases is found to correspond to smectic liquid crystalline phases. The second part of the present paper reports on recent results on surface-induced ordering effects, obtained by surface sensitive methods applied to binary systems of SFAs and alkanes. A kink in the temperature dependence of the surface tension of such solutions suggests the forming of a Gibbs film, i.e. a crystalline monolayer of SFA molecules at the solutions surface. Specular X-ray reflectivity measurements and Brewster angle microscopy conducted on the system strongly support this suggestion. It is also found that the concentration and chain length of the solute strongly influence the temperature at which crystallization of the surface film occurs.

Vapor–liquid equilibria predictions of hydrogen–hydrocarbon mixtures with the Huron–Vidal mixing rule

An excess Gibbs-equation of state ( G E-EoS) framework based on the Huron–Vidal mixing rule, has been applied to study vapor–liquid equilibria (VLE) of hydrogen–hydrocarbon mixtures. The mixing rule couples the Peng–Robinson–Stryjek–Vera (PRSV) EoS with a local composition solution model. The solution model is based on one-fluid theory treatment and assigns a single energy parameter to each binary pair. This energy parameter relates to the preference of the molecules for like to unlike interactions. The allocation of a system's number of interactions to the individual species in a binary mixture, incorporates the use of size parameters which gain significance only in the liquid phase. In a two parameter form, the framework has been used for the simultaneous data reduction of a large number of binary and several ternary hydrogen–hydrocarbon mixtures. These systems were taken over an extended range of pressures and temperatures. Results from the data reduction are reported in both tabular and graphical forms. Correlations for the model parameters have been identified with the acentric factor of the hydrocarbon in hydrogen–hydrocarbon binary mixtures. In a fully predictive mode, the model has shown to describe well VLE of binary hydrogen–linear alkane systems. Comparisons of these results with calculations from the Peng–Robinson (PR) EoS and the classical mixing rule (vdW) are included.

Thermodynamic Analysis of Solid−Solid and Solid−Liquid Equilibria in Binary Systems Composed of n-Alkanes: Application to the System Tricosane (C23H48) + Pentacosane (C25H52)

This paper presents the elements needed to carry out thermodynamic assessments of phase equilibria in binary systems of normal alkanes in the range from hexadecane (C16H34) to octacosane (C28H58) a...

Viscosities of Eight Binary Liquid n-Alkane Systems at 293.15 K and 298.15 K

The kinematic viscosities of the following eight n-alkane binary liquid systems were measured over the entire composition range at 293.15 K and 298.15 K and at atmospheric pressure: octane + undecane, octane + tridecane, octane + pentadecane, decane + pentadecane, undecane + pentadecane, tridecane + pentadecane, decane + tridecane, and undecane + tridecane. The data have been correlated by Heric's model (1967), as well as with the McAllister three-body interaction model (1960).

Solid-solution formation and phase segregation in binary systems of homologous extended-chain perfluorinated alkanes

Using differential scanning calorimetry (DSC) and X-ray analysis it is shown that binary systems of perfluorinated alkanes form solid solutions or exhibit eutectic phase behaviour, depending on their difference in chain length. A simple model, which successfully correlated experimental results for this aspect of phase behaviour of binary n-alkane systems, is demonstrated to quantitatively describe the behaviour of perfluorinated alkanes as well. From the model parameters and experimental observations, it appears that, at equal number of carbon atoms, binary perfluorinated alkane systems allow for a larger chain difference than their hydrogenated analogues, before eutectic phase behaviour sets in.

Phase-Boundary Calculations in Systems Involving More than Two Phases, with Application to Hydrocarbon Mixtures

An algorithm to track phase boundaries in systems with more than two phases is presented. The method follows the basic principles for phase diagram construction developed by Michelsen. The method is applied successfully to some normal alkane systems with solid−liquid−vapor (SLV) phase behavior. Some thermodynamic aspects of correlating the phase-boundary data for these systems are discussed, particularly the influence of equation of state parameters on the solid−liquid and SLV boundary calculation.

Assessment of Activity Coefficient Models for Predicting Solid−Liquid Equilibria of Asymmetric Binary Alkane Systems

Hydrocarbon fluids play an important role in today's society, being essential components of oil and fuels. Phase equilibria knowledge of such mixtures is important in designing equipment and processes. Among the least studied equilibriums is that between solid and liquid phases (SLE) which is required in, e.g., wax formation studies. Still, a number of models have been proposed for estimating the activity coefficient but are rarely investigated against SLE data. In this study, a number of “well-established” and “up-to-date sophisticated” activity coefficient models are tested for their capability in predicting solid−liquid equilibria of alkane systems. A large database covering 63 alkane/alkane systems for which SLE data are available is considered. The models include several of the popular approaches proposed during the past 30 years covering the gap of a comprehensive literature review. The capabilities and limitations of the models are discussed and those that provide successful predictions are recommended at various levels of accuracy and complexity.

Enumeration of staggered conformers of alkanes and monocyclic cycloalkanes

Staggered conformers of alkanes are represented by systems which can be embedded in the diamond lattice. Previous enumerations of alkane systems (acyclic) are supplemented. Original contributions are supplied to the numbers and symmetries of monocyclic staggered cycloalkanes, of which cyclohexane is the key structure. These systems are represented by single cycles on the diamond lattice. In particular, the generation of monocyclic staggered cycloalkanes by successive addition of cyclohexane rings is treated in details.

Film Tension and Film Rupture of Alkanes at the Air−Water Interface Using Axisymmetric Drop Shape Analysis

In connection with interfacial tension measurements for n-hexadecane−water under conditions of mutual saturation, we accidentally found an extremely high tension value for the aqueous phase of approximately 80 mJ/m2, using axisymmetric drop shape analysis−profile (ADSA-P) for an air bubble formed in the water phase. This high tension value is that of an alkane film at the air−water interface. From static measurements (the drop surface area kept constant) at 25 ± 0.2 °C, we observed this film tension value to be 80.67 ± 0.06 and 77.20 ± 0.02 mJ/m2 at the 95% confidence level for hexadecane and dodecane films at the air−water interface, respectively. These film tension values were also confirmed in dynamic measurements (the drop surface area continuously increased) for both alkane systems. In addition, film rupture has been demonstrated both in the sudden change in the bubble profile and in the abrupt decrease in the tension value. The alkane film tension measured is approximately equal to the sum of the interfacial tensions of air−alkane and alkane−water. The method presented provides a new way to measure film tension; it utilizes axisymmetric drops or bubbles. This is less restrictive than other approaches that require the drop or bubble to be spherical. The measurements for film tension can be carried out under both static and dynamic conditions, and information about the surface area, drop, or bubble volume as well as the radius of curvature can all be obtained simultaneously.

Statistical Associating Fluid Theory Equation of State with Lennard-Jones Reference Applied to Pure and Binary n-Alkane Systems

A prototype equation of state, developed on the basis of thermodynamic perturbation theory of the first order (TPT1), using the Lennard-Jones potential for the reference fluid, is found to represent pure-fluid and binary phase equilibria in the systems of small chain molecules, such as normal alkanes.

Experimental excess volumes of organic carbonate+alkane systems. Estimation of the parameters of the Nitta–Chao model for this kind of binary mixture

Excess volumes at 298.15 K and atmospheric pressure of some organic carbonate+alkane binary systems have been measured using an Anton Paar 602 HP densimeter. For the first time, published data on excess enthalpies, excess volumes, excess Gibbs energies of the above-mentioned binary systems together with the vaporisation enthalpies and the molar volumes of the pure organic carbonates, were used to estimate the interaction parameters between the carbonate group O–CO–O and the methyl and methylene groups, CH3, CH2, respectively. The mean deviations between experimental and theoretical values were smaller than 6% for all the properties. We have also compared our results with those obtained by Garcia etal. with the Original, Tassios etal., Larsen etal. and Gmehling etal. versions of the UNIFAC model and with those obtained by Kehiaian etal. using the DISQUAC model.

Solid‐liquid equilibria in n‐alkanol+n‐alkane systems. Prediction by several group‐contribution theories

AbstractSeveral, widely used, group contribution models have been used to predict solid‐liquid equilibria for n‐alcohol+n‐alkane binary mixtures. They are: modified UNIFAC [1], DISQUAC [2, 3], Nitta‐Chao [4] and the Hole Model (HM) [5]. Also a recently reported group contribution model (AssoDis) including association [6] has been taken into account. The results have been compared with experimental data.

Activation of CH 4, C 2H 6, C 3H 8, and c-C 3H 6 by gas-phase Pd + and the thermochemistry of Pd-ligand complexes

The reactions of Pd + with CH 4, C 2H 6, C 3H 8, and c-C 3H 6 have been studied using guided ion beam mass spectrometry. It is found that elimination of CH 4 and H 2 are the dominant processes at low energies in the c-C 3H 8 reaction system, whereas only dehydrogenation is important in the c-C 3H 6 reaction system, and no exothermic channels are observed in the CH 4 and C 2H 6 systems. At high energies, CC bond cleavage processes dominate the product spectrum for the reactions of Pd + with the c-C 3H 6 reaction system, whereas both CC and CH cleavage processes are comparably important in the alkane systems. Modeling of the endothermic reaction cross-sections yields the 0 K bond dissociation energies (in eV) of D 0(Pd +CH 2) = 2.95 ± 0.05, D 0(Pd +CH 3) = 1.88 ± 0.10, D 0(Pd +C 2H 3) = 2.56 ± 0.09, and D 0(Pd +C 2H 5) = 2.41 ± 0.05. Observations of exothermic reactions set lower limits of D 0(Pd +C 2H 4) > 0.70 eV, D 0(Pd +C 3H 5) ≥ 3.40 ± 0.09 eV, and D 0(Pd +C 3H 6) > 1.12 eV. The reactions of Pd + with hydrocarbons can be largely explained by initial H − or R − abstraction at low kinetic energies, with H and R abstraction more important at elevated kinetic energies.

Excess enthalpies of binary mixtures { xdioxane isomer+(1− x)non-polar liquid} at 298.15 K

Molar excess enthalpies H m E have been measured at 298.15 K for binary mixtures {1,3-dioxane or 1,4-dioxane+cyclohexane or n-pentane or 2,2,4-trimethylpentane or tetrachloroethene or benzene} by using a home-made flow calorimeter constructed newly for determining excess enthalpy in the dilute concentration range. The positive H m E for alkane and cycloalkane systems were found. Those of the benzene systems were exothermic except for the 1,4-dioxane rich region. The experimental result was discussed qualitatively in view of intermolecular interactions in mixtures and the isomer effect on thermodynamic properties of dioxane mixtures.

A conjugation-based version of the UNIFAC method

A modification of the UNIFAC method is proposed, reducing the set of groups to individual atoms. The effects of the environment of each atom are captured by the conjugation operators in which it participates, based on the ABC property estimation approach. The proposed modified method is applied to the infinite-dilution activity coefficients in binary systems of alkanes, alcohols, amines, and ethers.

Staggered conformers of alkanes: complete solution of the enumeration problem

Staggered conformers of alkanes are represented as chemical graphs by angle-restricted trees which can be embedded in a diamond lattice; they are referred to as alkane systems. The enumeration of unbranched alkane systems, which correspond to staggered n-alkanes, are revisited. When the branched systems are included the corresponding enumeration problem is substantially more difficult, but was solved completely in terms of generating functions. This solution pertains to both non-overlapping and overlapping systems, where the latter category is characterized by the presence of vertices which occupy the same sites in the diamond lattice. Hand in hand with the mathematical solution, the alkane systems were also generated and enumerated by computer programming. In particular, this approach gave new information about the non-overlapping systems. Finally, several classes of systems, especially among the overlapping alkane systems, were generated by hand according to combinatorial constructions. A special classification of the alkane systems according to the constitutional isomers is supposed to be of particular interest in structural chemistry. Symmetry considerations, which imply the distribution of the alkane systems into sixteen symmetry groups, play an important role in this work.

ChemInform Abstract: Sequential “Double‐Michael” Additions of Dienolates to Fulvene: Rapid Access to the Tricyclo(5.3.0.n2,5)alkane Systems.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Vapor-liquid equilibria calculation in gas/large alkane systems using group contribution equation of state.

The MR1 mixing rule proposed in a previous work is extended to other gases, C 2 H 4 , CO, and H 2 . Generalized correlations for the parameter in the MR1 mixing rule are proposed for them as done before for CO 2 , CH 4 and C 2 H 6 . The SRK EOS with the MR1 mixing rule and the generalized correlations gives satisfactory accuracy for the calculation of VLE of these gases and large alkane systems. By this method, the existing PSRK group parameters can be used directly with greatly improved accuracy for gas/large alkane systems.

Sequential “double-Michael” additions of dienolates to fulvene: Rapid access to the tricyclo[5.3.0.n 2,5]alkane systems

A highly efficient and stereoselective approach to the tricyclo[5.3.0.n 2,5]alkan-4-one system has been achieved via the intermolecular double Michael reaction of lithium dienolates to fulvene.

Improved models for the prediction of activity coefficients in nearly athermal mixtures Part II. A theoretically-based GE-model based on the van der Waals partition function

This work, which is a continuation of a recent publication on the same topic (G.M. Kontogeorgis, P. Coutsikos, P. Tassios and Aa. Fredenslund, Fluid Phase Equilibria, 92 (1994) 35), presents a new theoretically-based G E-model (Chain-FV) for alkane systems. The model is based on a modified form of the generalized van der Waals partition function and attempts to account for all non-energetic effects of solutions of both short- and long-chain alkanes, including alkane polymers. Both the free-volume effects and the density-dependent rotational degrees of freedom are considered. The resulting G E-model which, despite its derivation from a partition function resembles the Flory-Huggins formula, is suitable for vapor-liquid and solid-liquid equilibrium calculations for nearly athermal polymer solutions as well as for alkane systems. We show that using plausible assumptions for the free-volume and the external-degree-of-freedom parameter, very good predictions are obtained for activity coefficients of asymmetric alkane systems at both concentration ends, for solid-liquid equilibrium calculations, as well as in extreme cases (polymer solutions, activity coefficients of heavy model alkane polymers in short-chain compounds recently available from molecular simulation studies). The predictions of the Chain-FV model are better than the Flory-Huggins and Elbro terms and equivalent to the recently proposed empirical R-UNIFAC and p-FV models. However, unlike the latter two models, the one proposed in this work offers a successful combination of simplicity and accuracy, with a solid theoretical basis.