N-alkane Mixtures Research Articles

Competitive physisorption effects in hydroisomerisation of n-alkane mixtures on Pt/Y and Pt/USY zeolite catalysts

Physisorption isotherms and separation factors of n-C6–n-C12 alkanes on zeolite Y with Si/Al of 2.7 and on ultrastable Y (USY) zeolites with Si/Al ratios of 13 and 30 were determined using perturbation chromatography, at 506 K and for the hydrocarbon pressure range relevant to hydroisomerisation catalysis with platinum loaded versions of these zeolites. For the n-alkane pressure range from 0.3 to 0.9 bar, a refined Langmuir model with an interaction factor accounting for adsorbate–adsorbate interactions and surface heterogeneity gave the best agreement with the experimental single component adsorption data. Expressions for multicomponent adsorption equilibria among the n-alkanes, their isomers and cracked products, and expressions with interaction factors for the single components into multicomponent expressions were obtained. Separation factors among the n-alkanes and their variation with adsorbent loading derived from these multicomponent expressions are in agreement with experimental separation factors. The expressions for the adsorption equilibria were used to extract intrinsic kinetic constants of individual n-alkanes from experimental catalytic conversion data of pure compounds. It is demonstrated that the conversion of the individual components of a four component n-alkane mixture can be accurately predicted by a model combining intrinsic reaction constants for the individual components with the multicomponent adsorption isotherms. The approach was equally successful with the H-Y zeolite as with the strongly dealuminated USY zeolites exhibiting strongly different acidity, catalytic activity and adsorption behaviour.

Biodegradation of hydrocarbons by Prototheca zopfii in rotating biological contactors

The application of petroleum-degrading achlorophyllous micro-alga Prototheca zopfii cells to rotating biological contactors (RBCs) was investigated. The degradation activity of the biofilm, developed on the polycarbonate discs of the laboratory scale, single stage RBC was measured in batch operation at 25°C for 30 days. The volumetric biodegradation rate for n-alkanes (mixture of C 14, C 15 and C 16) as a model oil in the RBC system, was lower than that obtained for the bubble-column bioreactor, using immobilized biomass in polyurethane cubes. Abiotic attenuation of hydrocarbons by vaporization from the RBC rector during operation however, could be reduced significantly compared with the case of the bubble-column system. Mathematical modelling of the biodegradation characteristics of the RBC system was attempted, and validation of the model was confirmed. The model was extended to simulate the performance of the continuous biodegradation operation in the three RBCs in series.

Thermophysical properties of binary liquid mixtures of polyether and n-alkane at 298.15 and 323.15 K: heat of mixing, heat capacity, viscosity, density and thermal conductivity

An apparatus for a rapid and simultaneous determination of the thermophysical properties excess enthalpy, isobaric heat capacity, kinematic viscosity, density and thermal conductivity has been developed. The experimental setup is subject of this paper. At 298.15 and 323.15 K, the systems ethylene glycol dimethyl ether– n-dodecane, diethylene glycol dimethyl ether– n-dodecane, triethylene glycol dimethyl ether– n-dodecane, tetraethylene glycol dimethyl ether– n-dodecane and diethylene glycol dibutyl ether– n-dodecane have been investigated. The experimental results are correlated and the macroscopic properties are interpreted.

Degradation of polyolefines during various recovery processes

AbstractThe purpose of the presented research was the investigation of the stability and differences of degradation of polyolefines during various recycling processes. In modeling the recycling process during melting, extrusion with a one‐screw extruder was used. Recycling through selective dissolution was modulated by two different solvents (xylene and a definite mixture of n‐alkanes). Materials used for the investigations were polypropylene (PP), low‐density polyethylene (LDPE) and high‐density polyethylene (HDPE) (Ziegeler‐Natta technology with vanadium catalyst). Changes in the chemical structure of polymers were measured with infrared spectroscopy and differential scanning calorimetry (DSC). Flow properties were characterized by melt flow index, and mechanical characteristics by tension. Experimental results show that for PP and HDPE, utilizing all investigated recycling technologies, chain scission prevailed over branching. For the LDPE chain branching was obtained. By the same token, differences in crystallinity (and as follows, in molecular mass) between the same materials, recycled by extrusion and selective dissolution, was obtained. During selective dissolution changes of properties and morphology in dependence of the solvent used were observed with the trend being that the amount of the admixture of n‐alkane used in this investigation was more considerable with regard to the amount of material destruction as compared to xylene. Any reduction of the mechanical properties of any of the investigated polymers as a result of the various methods used was comparable.

Excess properties of mixtures of n-alkanes from perturbation theory

Excess properties of binary mixtures of n-alkanes have been evaluated from perturbation theory. A good equation of state for the reference system mixture is combined with a simple approximation to the perturbation term and with a reasonable set of potential parameters to yield a qualitatively correct description of the trends of excess volumes and excess Gibbs energies of n-alkane mixtures without the need for any adjustable parameter. Moreover, the theory can be made quantitative by introducing two adjustable parameters for each temperature. These two parameters have a clear molecular origin and they could be removed if some of the approximations of the theory proposed here were replaced by a more rigorous evaluation. In this sense this paper is just a first step toward a fully molecular theory of excess properties of alkanes. Excess properties estimated from perturbation theory by using these two adjustable parameters are in excellent agreement with experiment and are clearly superior to those obtained from the classic FOV theory proposed by Flory, Orwoll and Vrij [J. Am. Chem. Soc. 86, 3507, 3515 (1964)]. It is our view that the theory of this work is also conceptually superior to the FOV theory, since it rests on a more rigorous molecular basis.

Phase Equilibria and Volumetric Properties in Binary Mixtures Containing Branched Chain Ethers (Methyl 1,1-Dimethylethyl Ether or Ethyl 1,1-Dimethylethyl Ether or Methyl 1,1-Dimethylpropyl Ether or Ethyl 1,1-Dimethylpropyl Ether)

The solid−liquid equilibrium (SLE) has been measured above 280 K for eight mixtures of n-alkanes (octadecane, eicosane, docosane, tetracosane, pentacosane, hexacosane, heptacosane, octacosane) with methyl 1,1-dimethylethyl ether (MTBE). Experimental results of solubility are compared with values calculated by means of the Wilson, UNIQUAC, and NRTL equations utilizing parameters taken from the SLE. The existence of a solid−solid first-order phase transition in hydrocarbons has been taken into consideration in the solubility calculations. The solubility of hydrocarbons in branched chain ethers is lower than that in n-alkanes but higher than that in cycloalkanes, branched alkanes, 1-alcohols, and tert-alcohols. The best correlation of the solubility data has been obtained by the NRTL equation, where the average root-mean-square deviation of the solubility temperatures is 0.46 K. The liquid−liquid equilibrium (LLE) has been measured between 300 and 360 K for binary mixtures of water with ethyl 1,1-dimethyleth...

Effect of a mixed culture on co-oxidation during the degradation of saturated hydrocarbon mixture.

Two bacterial strains, Pseudomonas aeruginosa K1 and Rhodococcus equi P1, were used to degrade cyclo-alkanes (such as decalin) by a co-oxidation mechanism. Both strains possessed the capacity to degrade a broad range of n-alkane mixtures (C7 to C28) within 24 h of incubation. Strain P1 rapidly degraded 10 gl-1 pristane within 24 h of incubation (mu = 0.36 h-1 and Yx/s = 0.6). The addition of hexadecane as a growth substrate (above 0.5%, v/v) resulted in complete degradation of 1% (v/v) decalin by strain P1 via a co-oxidation mechanism. Co-oxidation to degrade decalin or pristane by strain K1 proved unsuccessful. Strain P1 was able to degrade decalin totally in a saturated hydrocarbon mixture. Strain K1 was only able to degrade hexadecane from the hydrocarbon mixture, but its degradation rate was higher than that of strain P1. Therefore, there was competition for the hexadecane needed to co-oxidize decalin. As a result, degradation of the hydrocarbon mixture, especially decalin, was incomplete in a mixed culture of strain P1 and K1. Serial addition of hexadecane (twice) allowed complete degradation of the remaining decalin by strain P1. Also, the biodegradation rate of the hydrocarbon mixture by a microbial population from gasoline-contaminated soil was delayed by addition of strain K1 to the population, while the addition of strain P1 resulted in an increase in the biodegradation rate.

Beyond basic UNIFAC

A new approach is proposed to extend UNIFAC to more complex substances. While first-order solution-of-groups methods such as UNIFAC can successfully represent measured phase equilibria for structurally simple systems such as mixtures of n-alkanes and linear alkanols with good accuracy, they are not as good for branched chain and polyfunctional substances such as secondary or tertiary alcohols and diols with branched or cyclic alkanes. Our method models departure from first-order behavior by adding second-order contributions to first-order correlations. The second-order contributions are derived from perturbations with respect to structural and energetic parameters. The basis of the extension and its ability to correlate and predict effects due to structural differences in VLE, SLE, and activity coefficients at infinite dilution ( γ ∞) for binary and multicomponent systems is described. Addition of a few second-order group parameters to the UNIFAC tables has improved the results for essentially all cases where the molecular structure justifies including such effects.

Binary and Ternary Adsorption of n-Alkane Mixtures on Activated Carbon

The adsorption isotherms of the binary n-alkane mixtures n-hexane/n-octane, n-octane/n-tetradecane, and n-hexane/n-tetradecane on the activated carbon TA 95 are measured at 298 K and described with mathematical functions. About 40 experimental values of the adsorption excess of the ternary mixture n-hexane/n-octane/n-tetradecane on activated carbon TA 95 at 298 K are gas chromatographically measured inside the ternary triangle. The ternary data are represented in the three-dimensional space with the help of transformation of coordinates and by utilization of the conception of the quasi-two-component representation of the mole fractions. A consistency test for the specific wetting Gibbs energies calculated from the binary data is carried out. The possibilities for a mathematical prediction of ternary data from adsorption data for the constituent binary mixtures are proved.

GEQUAC, an excess Gibbs energy model describing associating and nonassociating liquid mixtures by a new model concept for functional groups

The physically founded excess Gibbs energy model, GEQUAC, allows the description of excess properties for associating as well as nonassociating liquid mixtures. This is achieved by explicitly accounting for different poles of molecular surface between which strong interactions take place in a mixture. In previous work, the model concept and the subsequent model equation were tested against results of Monte-Carlo computer simulations and proved the ability to describe g E, h E and Ts E of ketone+ n-alkane and n-alcohol+ n-alkane mixtures. This work provides model parameters fitted to binary isothermal VLE and h E data for the mixtures butanone+ n-heptane, 1-butanol+ n-heptane and butanone+1-butanol as a first step in application. The model parameters show physical relevance and are used for prediction of isothermal VLE and h E data (own measurements) at 323 K of the ternary mixture butanone+ n-heptane+1-butanol.

Independent of local properties mathematical models for the calculation of retention indices in programmed temperature gas chromatography

Retention indices of some phthalates separated in temperature programming on SE-30 packed column were calculated by smoothing calibration data with Bezier curves, and from 2 to 6 order B-splines. The values thus obtained were compared to the corresponding ones calculated in a classical way. Whatever the standard n-alkane mixtures used (homologous series, alternate members with even or odd carbon atoms, any mixture with consecutive members not exceeding 4 carbon atoms between each two) the B-splines interpolations lead to retention indices values in better agreement with these ones, although Bezier curve smoothing still leads to values more consistent with the scheme of retention indices. Referring the phthalates to n-alkane stan - dard mixtures, with consecutive members not exceeding 3 or 4 carbon atoms between each 2, connecting the calibration data by B-splines, with orders from 2 to 5, and selecting the set of retention indices corresponding to the smallest value of the sum of squared second divided differences one may recover, with a good accuracy, classical programmed retention indices.

Mixtures of numerous different n-alkanes: 1. Structural studies by X-ray diffraction at room temperature—Correlation between the crystallographic long c parameter and the average composition of multi-alkane phases

Two quaternary equimolar alloys (C 22/C 26/C 30/C 34 and C 24/C 28/C 32/C 36) and three commercial products, which respectively consist of 23 and 33 consecutive n-alkanes with chain lengths between 20 and 52 carbon atoms, are studied by X-ray diffraction analyses. A single orthorhombic solid solution, identical to one of the two intermediate phases seen in binary n-alkane systems, is observed in two commercial products and in their 50–50 wt% mixture. The n-alkane molar concentrations and the long crystallographic c parameters have been determined and allow us to demonstrate that the molecule layer stacking periodicity is quasi-equal to the average length of n-alkane chains of these complicated mixtures: this periodicity corresponds to that of a hypothetical orthorhombic pure n-alkane whose equivalent carbon atom number is quasi-equal to the average carbon atom number of commercial multi- n-alkane mixtures. Discontinuous distributions of chain lengths lead to the observation of two or three orthorhombic phases in the quaternary alloys and the presence of an orthorhombic solid solution and of an amorphous solid in the third commercial multi- n-alkane product.

Mixtures of numerous different n-alkanes: 2. Studies by X-ray diffraction and differential thermal analyses with increasing temperature

The structural behaviour of the orthorhombic multi- n-alkane crystalline β′ phase, observed in mixtures consisting of 23 (19< n<43) and 33 (19< n<53) n-alkanes, respectively, is studied by X-ray diffraction with increasing temperature. A Rotator single-phase domain of rhombohedral (or hexagonal) α-RII type is observed below the solidus point. The product, consisting of 23 n-alkanes, undergoes this structural transition ( β′→ α-RII) through two two-phase domains: first, a region with the β′ and β(Fmmm) phases; then, a domain with the two β(Fmmm)-RI and α(R 3 ̄ m)-RII Rotator phases. For two β′ solid solutions consisting of 33 n-alkanes, a single two-phase domain ( β′+ α-RII) is observed in the course of this structural crystal–Rotator transition.

Excess molar volumes of liquid 1-bromoalkane + alkane mixtures. Nitta–Chao characterization of the bromine–bromine and bromine–methylene interactions in binary 1-bromoalkane + alkane mixtures

Excess molar volumes at 298.15 K for the binary mixtures of a 1-bromoalkane with a n-alkane are reported. The VE values were obtained from measurements of the density with an Anton Paar densimeter. Literature data of excess Gibbs energies, excess enthalpies, excess volumes, and activity coefficients at infinite dilution for this kind of mixtures together with molar volumes and vaporization enthalpies of pure bromoalkanes were used to calculate the characteristic parameters of the Nitta-Chao group contribution model. With the obtained parameters, this model consistently describes the experimental data of the 1-bromoalkane + n-alkane mixtures. Furthermore, we have determined the energetic parameters for the Larsen version of the UNIFAC model.Key words: liquids, mixtures, thermodynamics, group contributions.

Excess molar volumes of liquid 1-bromoalkane + alkane mixtures. Nitta-Chao characterization of the bromine-bromine and bromine-methylene interactions in binary 1-bromoalkane + alkane mixtures

Excess molar volumes at 298.15 K for the binary mixtures of a 1-bromoalkane with a n-alkane are reported. The V E values were obtained from measurements of the density with an Anton Paar densimeter. Literature data of excess Gibbs energies, excess enthalpies, excess volumes, and activity coefficients at infinite dilution for this kind of mixtures together with molar volumes and vaporization enthalpies of pure bromoalkanes were used to calculate the characteristic parameters of the Nitta-Chao group contribution model. With the obtained parameters, this model consistently describes the experimental data of the 1-bromoalkane + n-alkane mixtures. Furthermore, we have determined the energetic parameters for the Larsen version of the UNIFAC model.

Predicting excess enthalpies of ether and/or hydrocarbon binary mixtures

Previous applications of the Flory–Patterson theory in the analysis of the excess molar enthalpies at 25°C for some binary mixtures composed of ethers, n-alkanes, br-alknes, and cycloalkanes are reviewed. The possibility of correlating the Flory interaction parameters X ij in terms of the acentric factors of the components is examined. For selected ether (1) + n-alkane(2) mixtures, a set of linear relations between X 12 and the acentric factors of the n-alkanes are reported.

Predicting the High-Pressure Phase Equilibria of Binary Mixtures of n-Alkanes Using the SAFT-VR Approach

The phase behavior of selected alkane binary mixtures is studied using SAFT-VR, a version of the statistical associating fluid theory for potentials of variable attractive range (SAFT). We treat the n-alkane molecules as chains formed from united-atom hard-sphere segments with square-well potentials of variable range to describe the attractive interactions. We use a simple relationship between the number of carbon atoms in the n-alkane molecule and the number of segments in the united atom chains in order to predict the phase behavior of n-butane with other n-alkanes. The calculated vapor pressures and saturated liquid densities of the pure components are fitted to experimental data from the triple point to the critical point. These optimized parameters are rescaled by the respective experimental critical points and used to determine the critical lines and phase behavior of the mixtures. We use the Lorentz-Berthelot combining rule for the unlike interactions. We predict the phase behavior of n-butane + n-alkane binary mixtures, concentrating mainly on the critical region. The gas-liquid critical lines predicted by SAFT-VR for the n-alkane mixtures are in excellent agreement with the experimental data, and improve significantly on the results obtained with the simpler SAFT-HS approach where the attractive interactions are treated at the mean-field level.

Predicting the High-Pressure Phase Equilibria of Binary Mixtures of Perfluoro-n-alkanes + n-Alkanes Using the SAFT-VR Approach

The phase behavior of perfluoro-(n)-alkane + (n)-alkane binary mixtures is of particular interest given their unexpected large positive deviations from Raoult's law. Binary mixtures of perfluoromethane + (n)-alkanes from methane to heptane are studied here, illustrating the continuous change in phase behavior from type II to type III that these systems exhibit. Some symmetrical systems that display heteroazeotropy are also examined. Using the statistical associating fluid theory for potentials of variable attractive range (SAFT-VR),we predict the high-pressure phase diagram for each binary mixture studied. The perfluoro-n-alkane and n-alkane molecules are treated as attractive spherical segments tangentially bonded together to form chains. We use simple empirical relationships between the number of carbon atoms and the number of segments in each chain. The attractive interactions are included as a square-well potential of depth ε and range λ. The pure component parameters are obtained by fitting to experimental vapor pressure and saturated liquid density data from the triple to the critical point. These optimized parameters are rescaled by the respective experimental critical points and used to determine the critical lines and phase behavior of the mixtures. The critical lines predicted by SAFT-VR for the perfluoro-n-alkane + n-alkane mixtures are in excellent agreement with the experimental data and improve significantly the results obtained with the simpler SAFT-HS approach, where the attractive interactions are treated at the mean-field level. This is particularly gratifying as the unlike dispersion interaction between the perfluoroalkane and alkane segments is obtained from a single mixture (perfluorobutane + n-butane) and then transferred to the other systems.

Intermolecular Forces in Introductory Chemistry Studied by Gas Chromatography, Computer Models, and Viscometry

An experiment on intermolecular forces for first-term introductory college chemistry is presented. The experiment integrates traditional viscometry-based measurements with modern chromatographic analysis and use of computer-based molecular models. Students performing gas chromatographic (GC) analyses of mixtures of n-alkanes and samples that simulate crime scene evidence discover that liquid mixtures can be separated rapidly into their components based upon intermolecular forces. Each group of students is given a liquid sample that simulates one collected at an arson scene, and the group is required to determine the identity of the accelerant. Students also examine computer models to better visualize how molecular structure affects intermolecular forces: London forces, dipole-dipole interactions, and hydrogen bonding. The relative viscosities of organic liquids are also measured to relate physical properties to intermolecular forces.

Changes in aliphatic hydrocarbon tracer composition during the digestive process of the marine worm Nereis virens. Preliminary results

In the laboratory, marine worms were fed with a mixture of algae and several aliphatic hydrocarbons for 15 days. By comparing hydrocarbons in food and in faeces, it appeared that the worm's digestive process led to changes in the distribution of the n-alkanes mixture. These changes were different from those only due to physical processes in the experimental conditions, indicating that marine worm feeding could substantially affect the fate of hydrocarbons in the sedimentary marine ecosystem.