Heat capacities of binary mixtures of n-heptane with hexane isomers

Volumetric heat capacities were measured for binary mixtures of n-heptane with n-hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, and 2,3-dimethylbutane at 298.15 K in a Picker flow microcalorimeter. The results were combined with previously published excess molar volumes to obtain excess molar isobaric heat capacities. Use of the Flory theory of mixtures to interpret the latter is discussed.     

Can alkane isomers be separated? Adsorption equilibrium and kinetic data for hexane isomers and their binary mixtures on MFI

In this study we present a global overview of the adsorption behavior of hexane isomers on MFI. With an experimental approach that couples a manometric technique with Near Infrared (NIR) spectroscopy, which has been recently developed, we did address adsorption kinetic properties of n-hexane, 2-methylpentane, 2,2-dimethylbutane and 2,3-dimethylbutane, and their binary mixtures. The adsorption equilibrium properties of the binary mixtures were also assessed using the same technique. Whereas the adsorption isotherms and heats of adsorption for single components have been studied by a manometric technique coupled with a micro calorimeter. The differential heats of adsorption of n-hexane increase slightly with loading, on the other hand the heat of adsorption of branched hexanes exhibits a decrease with loading. The diffusion rates on MFI of n-hexane, 2-methylpentane and 2,3-dimethylbutane are in the same order of magnitude. However, the diffusion rate of 2,2-dimethylbutane is two orders of magnitude lower than rates of the other isomers. In the binary mixtures the components interact and the difference between the diffusion rates of the components decreases. The MFI zeolite presents equilibrium selectivity towards the less branched isomers. In conclusion, a separation process for linear/mono-branched alkanes + double-branched alkanes, has to be based on its equilibrium properties and not based on adsorption kinetics.     

Influence of size and shape effects on the high-pressure solubility of n-alkanes: Experimental data, correlation and prediction

(Solid + liquid) phase equilibria (SLE) of (n-hexadecane, or n-octadecane + 3-methylpentane, or 2,2-dimethylbutane, or benzene) at very high pressures up to about 1.0 GPa have been investigated at the temperature range from T = (293 to 353) K. The thermostated apparatus for the measurements of transition pressures from the liquid to the solid state in two component isothermal solutions was used. The pressure-temperature-composition relation of the high pressure (solid + liquid) phase equilibria, polynomial based on the general solubility equation at atmospheric pressure was satisfactorily used. Additionally, the SLE of binary systems (n-hexadecane, or n-octadecane + 3-methylpentane, or 2,2-dimethylbutane, or benzene, or n-hexane or cyclohexane) at normal pressure was discussed. The results at high pressures were compared for every system to these at normal pressure. The influence of the size and shape effects on the solubility at 0.1 MPa and high pressure up to 600 MPa was discussed.The main aim of this work was to predict the mixture behaviour using only pure components data and cubic equation of state in the wide range of pressures, far above the pressure range which cubic equations of state are normally applied to. The fluid phase behaviour is described by the corrected SRK-EOS and the van der Waals one fluid mixing rules.     

Excess enthalpies of binary mixtures of 1-hexene with some branched alkanes at the temperature 298.15 K

Measurements of excess molar enthalpies at the temperature 298.15 K in a flow microcalorimeter are reported for the five binary mixtures formed by mixing 1-hexene with the branched alkanes: 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane, and 2,2,4-trimethylpentane. Smooth Redlich–Kister representations of the results are described. It was found that the Liebermann–Fried model also provided good representations of the results.     

Isomerization of n-Hexane Over Platinum Ion-Exchanged Zeolite Beta

Zeolite Beta was synthesized from appropriate gels and crystallized under the controlled temperature and pressurized conditions. For isomerization of n-hexane, platinum ion-exchanged zeolite Beta exhibited high activity and selectivity for 2,2-dimethylbutane (2,2-DMB), 2,3-dimethylbutane (2,3-DMB), 2-methylpentane (2-MP) and 3-methylpentane (3-MP). As high as 72% of n-hexane conversion and 98% of product selectivity were obtained at 250°C, 1600 h^–1 for 20 min on stream. The influences of reaction temperature and space velocity were also studied. Pt/H-Beta zeolite was recommended as one of the promising catalyst for n-hexane isomerization due to its high activity and stability. The combined effect of the stronger acidity possessed by H-Beta and the dehydrogenation role played by Pt was believed to be responsible for the good catalytic performance of Pt/H-Beta.     

Influence of the sodium and calcium non-framework cations on the adsorption of hexane isomers in zeolite BEA

We have performed configurational-bias Monte Carlo simulations to compute pure component adsorption isotherms of n-hexane, 3-methylpentane and 2,2-dimethylbutane in BEA-Polymorphs A and B at 423?K. The effect of the density and nature of influence of non-framework cations was systematically analyzed. Our results show that differences in the type and concentration of the non-framework cations lead to differences in adsorption loading. We found that this behavior is directly related to the preferential adsorption sites of the isomers as well as to the amount and location of the non-framework cations.     

Radiation-induced synthesis of branched liquid alkanes

The irradiation of gaseous alkane mixtures under circulation conditions was used for the synthesis of liquid branched hydrocarbons. It was found that the synthesized liquid product was a mixture of alkanes with the average molecular weight higher than the molecular weight of the parent gas by a factor of 3–4. The resulting liquids were characterized by boiling range from 35 to 200°C in atmospheric distillation. The average degree of molecular branching in the synthesized liquids was evaluated on the basis of their knock resistance. The octane ratings of liquid mixtures were above 95 (motor octane number) or 103 (research octane number). The fractional composition and detonation properties of the synthesized liquids suggested the prevalence of C₅–C₁₁ isomers with highly branched structures in these liquids. Depending on irradiation conditions, 2,3-dimethylbutane, 2-methylpentane, or 3-methylpentane was predominant among hexanes. As a rule, 2,2,3-trimethylbutane and 2,3-dimethylpentane prevailed among heptanes.     

Excess Enthalpies of 2,2-Dimethylbutane + Cyclohexane + (Octane or Dodecane) at 25°C

Measurements of excess molar enthalpies at 25°C in a flow microcalorimeter,are reported for the two ternary mixtures 2,2-dimethylbutane + cyclohexane +n-octane and 2,2-dimethylbutane + cyclohexane + n-dodecane. Smoothrepresentations of the results are described and used to construct constant enthalpy contourson Roozeboom diagrams. It is shown that useful estimates of the ternary enthalpiescan be obtained from the Flory theory using only the physical properties of thecomponents and their binary mixtures.     

Excess Enthalpies of Ternary Mixtures: (2-Methyltetrahydrofuran or Di-n-Butyl ether) + 3-Methylpentane + n-Decane at 25°C

Measurements of excess molar enthalpies at 25°C in a flow microcalorimeter are reported for the two ternary mixtures 2-methyltetrahydrofuran + 3-methylpentane + n-decane and di-n-butyl ether + 3-methylpentane + n-decane. Smooth representations of the results are described and used to construct constant-enthalpy contours on Roozeboom diagrams. It is shown that useful estimates of the ternary enthalpies can be obtained from the Liebermann–Fried model using only the physical properties of the components and their binary mixtures.     

The Complexing Abilities of Diethyleneoxy-and Xylene-bridged Cryptophanes with Alkanes

Abstract

The Syn isomers (3b and 4b) of xylene-bridged cryptophane showed selective complexing abilities for 2,2-dimethylbutane, 3-methylpentane, 3,3-di-methylpentane and 3-ethylpentane among the investigated alkanes, although the Anti isomers (3a,4a,5a) did not complex with these alkanes. However, both the Anti-and Syn-isomers (2a and 2b) of the diethyleneoxy-bridged cryptophane showed selective complexing abilities for 2,2-dimethylbutane, 3,3-dimethylpentane, 2,2,3-trimethylbutane and 2,2,3,3-terramethybutane among the investigated alkanes.     

Kinetics of the reaction of oh radicals with a series of branched alkanes at 297 ± 2 K

Relative rate constants for the reaction of OH radicals with a series of branched alkanes have been determined at 297 ± 2 K, using methyl nitrite photolysis in air as a source of OH radicals. Using a rate constant for the reaction of OH radicals with n-butane of 2.58 × 10^?12 cm³/molecule · s, the rate constants obtained are (× 10¹² cm³/molecule · s): isobutane, 2.29 ± 0.06; 2-methylbutane, 3.97 ± 0.11; 2,2-dimethylbutane, 2.66 ± 0.08; 2-methylpentane, 5.68 ± 0.24; 3-methylpentane, 5.78 ± 0.11; 2,2,3-trimethylbutane, 4.21 ± 0.08; 2,4-dimethylpentane, 5.26 ± 0.11; methylcyclohexane, 10.6 ± 0.3; 2,2,3,3-tetramethylbutane, 1.06 ± 0.08; and 2,2,4-trimethylpentane, 3.66 ± 0.16. Rate constants for 2,2-dimethylbutane, 2,4-dimethylpentane, and methylclohexane have been determined for the first time, while those for the other branched alkanes are in generally good agreement with the literature data. Primary, secondary, and tertiary group rate constants at room temperature have been derived from these and previous data for alkanes and unstrained cycloalkanes, with the secondary and tertiary group rate constants depending in a systematic manner on the identity of the neighboring groups. The use of these group rate constants, together with a previous determination of the effect of ring strain energy on the OH radical rate constants for a series of cycloalkanes, allows the a priori estimation of OH radical rate constants for alkanes and cycloalkanes at room temperature.     

Formation of alkyl nitrates from the reaction of branched and cyclic alkyl peroxy radicals with NO

The yields of C₅ and C₆ alkyl nitrates from neopentane, 2-methylbutane, 2-methylpentane, 3-methylpentane, and cyclohexane have been measured in irradiated CH₃ONONO-alkane-air mixtures at 298 ± 2 K and 735-torr total pressure. Additionally, OH radical rate constants for neopentyl nitrate, 3-nitro-2-methylbutane, 2-nitro-2-methylpentane, 2-nitro-3-methylpentane, and cyclohexyl nitrate, relative to that for n-butane, have been determined at 298 ± 2 K. Using a rate constant for the reaction of OH radicals with n-butane of 2.58 × 10^?12 cm³ molecule^?1 s^?1, these OH radical rate constants are (in units of 10^?12 cm³ molecule^?1 s^?1): neopentyl nitrate, 0.87 ± 0.21; cyclohexyl nitrate, 3.35 ± 0.36; 3-nitro-2-methylbutane, 1.75 ± 0.06; 2-nitro-2-methylpentane, 1.75 ± 0.22; and 2-nitro-3-methylpentane, 3.07 ± 0.08. After accounting for consumption of the alkyl nitrates by OH radical reaction and for the yields of the individual alkyl peroxy radicals formed in the reaction of OH radicals with the alkanes studied, the alkyl nitrate yields (which reflect the fraction of the individual RO₂ radicals reacting with NO to form RONO₂) determined were: neopentyl nitrate, 0.0513 ± 0.0053; cyclohexyl nitrate, 0.160 ± 0.015; 3-nitro-2-methylbutane, 0.109 ± 0.003; 2-nitro-2methylbutane, 0.0533 ± 0.0022; 2-nitro-2-methylpentane, 0.0350 ± 0.0096; 3- + 4-nitro-2-methylpentane, 0.165 ± 0.016; and 2-nitro-3-methylpentane, 0.140 ± 0.014. These results are discussed and compared with previous literature values for the alkyl nitrates formed from primary and secondary alkyl peroxy radicals generated from a series of n-alkanes.     

Co-diffusion with a slow species in zeolites: cyclic experimentation and advanced modeling

In this study, a new experimental method based on cyclic breakthrough curves is presented, in order to estimate the co-diffusion coefficients for mixtures at high adsorption loadings. For this purpose, cyclic liquid phase breakthrough curves of mixtures of 2-methylpentane 3-methylpentane (fast-diffusing species) and 2,2-dimethylbutane (slow-diffusing species) have been measured experimentally for different feed compositions at 185°C. Estimation of Langmuir coefficients and self-diffusivities was attempted from simple binary breakthrough curves with the above components using a modified Maxwell-Stefan-type model. However, for the slow-diffusing species, the parameters cannot be estimated accurately from such experiments, because the quantity of 22DMB entering the zeolite network in the experiment duration is not sufficient. On the other hand, a clear influence of the slow diffusing species (22DMB) on the fast diffusing species (3MP) breakthrough curves during cycles has been demonstrated. This phenomenon confirms that 22DMB slowly accumulates in the adsorbent during the cycles, and that is becomes therefore possible to estimate the 22DMB parameters from the cyclic data.     

Adsorption of liquid mixtures on silicalite-1 zeolite: a density-bottle method

A technique that measures the effective density of a zeolite after adsorption from the liquid phase was developed to measure the absolute amounts of liquid mixtures adsorbed on zeolites without using a nonadsorbing solvent. Since the fugacities of the adsorbing components in solution can be dramatically different with or without the addition of a nonadsorbing solvent, this technique measures mixture isotherms that can be used for analyzing pervaporation through zeolite membranes. A nonideal solution, methanol/acetone, was used as an example to show that its adsorption isotherms on silicalite-1 zeolite at 294 K differ dramatically from those measured with the nonadsorbing solvent method. The methanol/acetone fugacity ratio is different for the two methods because of different concentrations in the liquid phase. Methanol preferentially adsorbs on silicalite-1 at low methanol concentrations and acetone preferentially adsorbs at high methanol concentrations. The density bottle method was used to show that n-hexane preferentially adsorbs from n-hexane/3-methylpentane liquid mixtures, and at high n-hexane concentrations, essentially no 3-methylpentane adsorbs, as has been predicted previously by simulations. A larger molecule, 2,2-dimethylbutane, adsorbed so slowly at 294 K that silicalite had only 16% of saturation coverage after 370 h, but it was saturated after 1650 h; at 423 K, saturation was obtained in less than 24 h.     

Transport properties of alkanes through ceramic thin zeolite MFI membranes

Polycrystalline randomly oriented defect free zeolite layers on porous α-Al₂O₃ supports are prepared with a thickness of less than 5 μm by in situ crystallisation of silicalite-1. The flux of alkanes is a function of the sorption and intracrystalline diffusion. In mixtures of strongly and weakly adsorbing gases and a high loadings of the strongly adsorbing molecule in the zeolite poze, the flux of the weakly adsorbing molecule is suppressed by the sorption and the mobility of the strongly adsorbing molecule resulting in pore-blocking effects. The separation of these mixtures is mainly based on the sorption and completely different from the permselectivity. At low loadings of the strongly adsorbing molecules the separation is based on the sorption and the diffusion and is the same as the permselectivity. Separation factors for the isomers of butane (n-butane/isobutane) and hexane (hexane/2,2-dimethylbutane) are respectively high (10) and very high (> 2000) at 200°C. These high separation factors are a strong evidence that the membrane shows selectivity by size-exclusion and that transport in pores larger than the zeolite MFI pores (possible defects, etc) can be neglected.     

Measurement and estimation of rate constants for the reactions of hydroxyl radical with several alkanes and cycloalkanes

Relative rate experiments were used to measure ratios of chemical kinetics rate constants as a function of temperature for the reactions of OH with isobutane, isopentane, 2-methylpentane, 3-methylpentane, 2,3-dimethylbutane, 2,3-dimethylpentane, 2,4-dimethylpentane, 2,3,4-trimethylpentane, n-heptane, n-octane, cyclopentane, cyclohexane, and cycloheptane. The results have been used to calibrate a structure-reactivity rate constant estimation method for k(298 K) which, when combined with previously determined relationships between k(298 K) and the Arrhenius parameters, is capable of determining the temperature dependence accurately. The estimation method reproduces most of the observed rate data within experimental accuracy but appears to fail for 2,3-dimethylbutane, which has an anomalously high rate constant. Curvature in the Arrhenius plots at low temperatures is not present for compounds with a single type of C-H bond and, for compounds with different C-H bonds, is shown to be consistent with effects due to different group sites on the molecule.     

Transformations in gas mixtures based on butane under irradiation in the circulation mode

Radiolysis of gaseous mixtures based on n-butane was studied in the circulation mode of irradiation, and the component composition of liquid products was measured. The apparent yield of n-butane decomposition is 13.7 molecules/100 eV. Radiolysis is accompanied by a monotonous decrease in the molecular mass of the irradiated mixture. It was shown that the liquid product contains alkanes from C₅H₁₂ to C₁₂H₂₆ with the prevalence of C₆H₁₄ and C₈H₁₈ isomers. The main products are 2-methylbutane, 3-methylpentane, 3,4-dimethylhexane, and 3-methylheptane. A low yield of heptane isomers (～5%) is due to a small rate of degradation of propane and a low yield of propyl radicals as a result of propane formation mainly via the ionic mechanism.     

Thermodynamic properties of (an ethyl ester + a branched alkane). XV. HmE and VmE values for (an ester + an alkane)

This paper presents H_m^E and V_m^E measurements taken at T=298.15 K and at the atmospheric pressure of 100.65 kPa for 22 binary mixtures composed of one of four ethyl esters (methanoate, ethanoate, propanoate, and pentanoate) and one of seven alkane isomers, C₆ to C₈. The H_m^E of four binary mixtures of ethyl propanoate and pentanoate with n-C₆ and n-C₈, measured at the conditions mentioned above are also presented. The results indicate that the mixing process is endothermic for all the mixtures, with H_m^E varying regularly with the components chain length, increasing with alkane chain length and decreasing with the acid chain length in the ester. The V_m^E values vary also regularly in a manner similar to that of the H_m^E slight contractions are observed for (ethyl pentanoate + 2-methylpentane).A new form of a polynomial equation used previously was employed to correlate the experimental values of the excess quantities and yielded good results in all cases. In addition, the behaviour of these mixtures is explained in terms of an interaction model proposed in previous work.     

Viscosity of heavy n-alkanes and diffusion of gases therein based on molecular dynamics simulations and empirical correlations

The viscosity of pure n-alkanes and n-alkane mixtures was studied by molecular dynamics (MD) simulations using the Green–Kubo method. n-Alkane molecules were modeled based on the Transferable Potential for Phase Equilibria (TraPPE) united atom force field. MD simulations at constant number of molecules or particles, volume and temperature (NVT) were performed for n-C₈ up to n-C₉₆ at different temperatures as well as for binary and six-component n-alkane mixtures which are considered as prototypes for the hydrocarbon wax produced during the Gas-To-Liquid (GTL) Fischer–Tropsch process. For the pure n-alkanes, good agreement between our simulated viscosities and existing experimental data was observed. In the case of the n-alkane mixtures, the composition dependence of viscosity was examined. The simulated viscosity results were compared with literature empirical correlations. Moreover, a new macroscopic empirical correlation for the calculation of self-diffusion coefficients of hydrogen, carbon monoxide, and water in n-alkanes and mixtures of n-alkanes was developed by combining viscosity and self-diffusion coefficient values in n-alkanes. The correlation was compared with the simulation data and an average absolute deviation (AAD) of 11.3% for pure n-alkanes and 14.3% for n-alkane mixtures was obtained.     

Capillary reaction gas chromatography

Summary Thermal decomposition of C₆ hydrocarbons (hexane, cyclohexane, 2-methylpentane, 2,2-dimethylbutane and trans-2-hexene) on a nickel catalyst and on alumina was studied by reaction gas chromatography. The products were analyzed on two capillary columns containing squalane and Citroflex and were identified on the basis of their retention indices. The degree of conversion of the initial substances and the relative contents of the products were determined. On the basis of the results obtained, the probable course of the catalytic decomposition is discussed.