Densities Of N-alkanes Research Articles

Equation for compressibility factor and density of saturated n-alkanes (C1–C10) vapor, parahydrogen, and water at the boiling line

An equation is obtained for calculating the compressibility factor and saturated vapor density of n-alkanes (C1–C10), parahydrogen, and water at temperatures of the triple point up to critical point. The calculation error is close to that for experimental data.

Modeling the physical properties of a homologous series on the melting temperatures and densities of n-alkanes and their simple alkyl-derivatives

AbstractSeveral aspects of the melting temperatures (MT) of linear chain homologs are discussed. It is shown that with some reasonable modifications of Einstein's model of simple solids, the MT of n-alkanes and their derivatives can be successfully modeled. Results are compared with those obtained by previous authors who have used numerical methods and thermodynamics. Results of investigation of quadratic recurrence relations of the second order and forms including exponential functions are reported. Finally, the correlation of MT with density at T = 298.15 K gives the limiting value, 0.86 gcm-3 , at the temperature of nearly 420 K. It is expected that proper correlations should use densities of liquids just at the MT, because some available data suggest a linear dependence of MT on density. All results obtained are mutually consistent

Prediction of molecular weight and density of n-alkanes (C 6–C 44)

Heavy n-alkanes and their mixtures were characterized by high temperature-simulated distillation using gas chromatography with a capillary column. In this work, the atmospheric boiling point is determined by the HT-SimDis GC method. In this study, molecular weights and density of n-alkanes were evaluated with this method by using retention times and normal boiling points as input data. ASTM D2887 calibration mixture containing 17 n-alkanes in the C 6–C 44 range were used for qualitative analyses. Retention times ( t R) of n-alkanes were measured with this method. The other input data that normal boiling points ( T b) and molecular weight ( M) had been taken in the literature. Experimental densities (at 20 °C) of n-alkanes were obtained from API Research Projects. Empirical molecular weight and density correlations were developed by using the nonlinear and multiple regressions with correlation coefficients. The results of calculations were compared with experimental data. Normal boiling point predictions were obtained as an average absolute deviation of 1.07%. Molecular weight and density results were evaluated as average absolute deviations of 0.68% and 0.21%, respectively.

EXTENSION OF LINEAR ISOTHERM REGULARITY TO LONG CHAIN ALKANES

In this work, we consider each normal alkane as a hypothetical mixtureof methyland methylene groups, in which the interaction potential of each pair is assumed to be the average effective pair potential. Then, the LIR equation of state (EOS) is extended for such a hypothetical mixture. Also, three basic compounds, namely, propane, n-butane and cyclohexane, are used to obtain the contribution of each carbonic group in the EOS parameters. Using the calculated EOS parameters along with the modified EOS, the density of n-alkanes and their mixtures at different pressures and temperatures are calculated. The average percentage error in density is found to be less than 1.5% for both the pure normal alkanes and their binary mixtures.

Vapor−Liquid Phase Equilibria for Linear and Branched Alkane Monolayers Physisorbed on Au(111)

Histogram-reweighting Monte Carlo simulations in the grand canonical ensemble were used to obtain vapor−liquid coexistence curves for a series of alkanes physisorbed on a flat gold substrate. The critical temperatures and densities of n-alkanes from methane to decane as well as the branched molecules 2-methylpropane, 2,2-dimethylbutane, and 2,3-dimethylbutane were determined through a mixed-field analysis. The ratio of the 2D (two-dimensional) to the 3D (three-dimensional) critical temperature was found to depend weakly on the chain length for n-alkanes, decreasing from Tc2D/Tc3D = 0.38 for methane to Tc2D/Tc3D = 0.31 for n-decane. In contrast to typical bulk fluid behavior, the branched isomers were found to have higher critical temperatures than their linear counterparts.

Understanding the critical properties of chain molecules

The vapour-liquid equilibrium of n-alkanes is computed from a simple perturbation theory. A very accurate equation of state for the repulsive n-alkane chain is combined with a mean-field term which accounts for the contribution of attractive forces to the free energy. The theory correctly predicts the existence of a maximum in the critical density of n-alkanes. When differences in the energetic interactions between methane, methyl and methylene groups are included, a maximum in the critical pressure is found for ethane, in good agreement with experiment. The simplicity of the perturbation scheme allows for an analysis of the conditions that a chain model should possess in order to present maxima either in critical density or pressure. It is shown that the conditions needed for the existence of a maximum in the critical density are (1) overlaps between contiguous sites and (2) small differences in mass between monomer, exterior and interior sites. The conditions needed for the existence of a maximum in the...

High-pressure viscosity and density of n-alkanes

High-pressure viscosities and densities of n-butane, n-pentane, n-hexane, and n-octane have been measured with a specially designed falling cylinder viscometer. Data cover the pressure range from 10 to 70 MPa at temperatures from 310 to 450 K. When the viscosity is plotted as a function of density, the data at all temperatures and pressures are shown to reduce to a single curve for each alkane. An exponential relationship of the form η = B 1 x exp(B 2xρ) + B 3 is used to describe the density dependence of viscosity. The logarithmic viscosity of the alkanes changes linearly with the inverse temperature at all pressures. The density shows a linear dependence on temperature.

The critical temperatures and densities of the n-alkanes from pentane to octadecane

The critical temperatures and densities of n-alkanes from pentane to octadecane have been measured using a rapid heating sealed ampoule technique. The measurements were compared with critical properties reported in the literature and with the results of several estimation methods. In general, our measurements of the critical temperature compared well with values reported in the literature, but those for the critical density only agreed with literature values for the lower members of the alkane series. An interesting trend observed with the critical densities was that the experimental values decreased with carbon number after attaining a maximum. This is contrary to the trend predicted by all estimation methods, and suggests a need for new methods for this property.

Densities of n-alkanes and their mixtures at elevated pressures

Accurate density data for n-alkanes over a wide range of temperature and pressure have been used to test existing correlation and prediction methods. It is found that the most successful representation at temperatures up to 0.66 times the critical temperature and pressures up to 150 MPa is given by the Tait equation in the form (ρ−ρ0)/ρ=C log [(B + P)/(B + P0)], where subscript 0 refers to 0.101 MPa, with C equal to 0.2000, and [B+(Cn−6)], where Cn is the number of carbon atoms in the alkane chain, is a smooth function of reduced temperature. A simple extension of this method to mixtures gives an excellent prediction of densities at pressures up to 150 MPa over the same reduced temperature range.

The prediction of the densities of n-alkanes

The prediction of the densities of n-alkanes