Prediction of the transport properties of paraffin hydrocarbons

The possibility of predicting physical properties for polyatomic gases entirely from molecular structure has been explored. Intramolecular force constants for the bonds can be drawn from spectroscopically established tables and applied successfully to molecules involving a large variety of structures. A vibrational analysis of the molecule using these constants yields the thermodynamic functions of the ideal gas. The intermolecular pair potential parameters for the spherical core model of Kihara can be obtained quantitatively from molecular constants, and this potential can be used in obtaining the dilute gas transport properties. A linear relationship was found between the Kihara spherical core size and Pitzer's acentric factor. Also from the Kihara model the critical constants are derived, which allows one to use Pitzer's compressibility tables for the dense gas corrections to the ideal gas law and the excess functions of the thermodynamic quantities. A complete package of computer programs which predict all important physical properties directly from input name alone has been written and tested. Suggestions are given for future work needed to improve many of the techniques presented. T. R, GALLOWAY University of California Sanitary Engineering Research LaboratoryRichmond, California 94804 SCOPEThe present scheme was developed to determine just how far our current knowledge could take us toward achieving this goal of a priori properties prediction from molecular structure. We sought to strike a balance between computer information retrieval from a large data base and properties prediction. Automated computer methods for properties are an important part of all process design engineering computer systems used in industry, and there is a great economic incentive to reduce the associated storage and computation costs for properties. For the past decade nearly all proprietary systems were based on the AIChE Physical Properties Estimation System (APPES) developed for IBM 7094 equipment which has proved to be a very expensive operation. Molecular structure information for a variety of molecules has become available in just enough detail to encourage development of new predictive methods for the physical properties. The kind of structural information needed is minimal, such as an accurate scale molecular model. This concept is directed toward future computer applications, when a user can enter the structural information at a remote console in a familiar language and select the type of properties desired and conditions of temperature, pressure, composition, etc. Even with no experimental data available to the user, predictions of physical properties may be possible. CONCLUSIONS AND SIGNIFICANCEThe thermophysical properties for many species important in chemical engineering now can be computed with engineering accuracy given a cipher with only molecular structure information. The properties of rigid, spherically symmetric molecules are quite adequate, whereas those for aspheric, flexible species involving complex energy ...

Section: Intermolecular Force Fieldmentioning

confidence: 96%

Section: Intermolecular Force Fieldmentioning

confidence: 98%

Section: Nonequlllbrlum Propertiesmentioning

confidence: 98%

Section: Intermolecular Force Fieldmentioning

confidence: 99%

“…From the available (Galloway and Sage, 1967) core sizes for the normal paraffins, the values of r and I were found to be constant within +0.5% for the paraffins through n-decane.…”

Section: Intermolecular Force Fieldmentioning

confidence: 99%

See 3 more Smart Citations

Equilibrium, thermodynamic, and transport properties of polyatomic gases from molecular structure

Galloway¹

1972

Soret‐modified hydrocarbon mass transport across compressed nonisothermal gases

Rosner

Arias‐Zugasti

2007

While engineering methods employed to predict mass transport rates across carrier fluids are often limited to either ideal gas mixtures or constant density liquids, we deal here with species mass transport across nonisothermal compressed gas “films”, with special reference to hydrocarbon fuel vapor transport across nonisothermal N2 or H2O boundary layers at pressures up to ca. 300 atm, and at temperatures often above 1000 K. We show that because of the pressure sensitivity of the Soret factor (which quantifies the relative importance of mass transfer due to temperature gradients compared to that due to concentration gradients) mass transfer coefficients become far more sensitive to pressure level than would have been anticipated from the pressure sensitivity of ρD 12∞. Motivated, in part, by combustion applications, we first examine the expected pressure dependence of the binary Soret factor, αT,12 for each of the n‐alkanes (CH4 to C20H42) dilute in compressed N2 or H2O, exploiting a rational formulation for “correcting” Chapman‐Enskog‐derived Soret factors (α T,120) to higher pressures based on the Thermodynamics of Irreversible Processes (TIP) combined with a Virial Equation of State (VES). Our TIP‐VES‐predicted Soret factors are used to demonstrate the pressure sensitivity of expected “Soret‐modified” mass transfer coefficients (Sherwood numbers) for the illustrative case of C12H26(g) transport across N2(g) at temperature ratios between 0.3 (“cold”‐wall) and 2.0 (“hot”‐wall) at pressures up to 300 atm. Because of the growing importance of compact, high‐pressure systems in fields beside combustion, including supercritical fluid extraction and even distillation, our present results suggest that reliable mass transfer rate predictions in nonisothermal dense vapor systems of engineering importance will generally require systematic inclusion of non‐Fickian molecular mass transport. © 2007 American Institute of Chemical Engineers AIChE J, 2007

Thermophoretic properties of nonspherical particles and large molecules

García‐Ybarra

Rosner

1989

The Kn, >> 1 gas-kinetic approach of Waldmann (1959, 1961) is extended to predict the thermophoretic properties of nonspherical aerosol particles, and massive nonspherical gas molecules. Calculations are presented for sphero-cylindrical particles (molecules) of arbitrary aspect ratio, L / R, predicting that in a local temperature gradient grad T they will thermophoretically drift: i) more rapidly when their major axis is aligned with -grad T; ii) at a velocity different from that of a sphere of radius R equal to the cylinder radius: iii) at an angle with respect to -grad T when their major axis is not parallel to, nor perpendicular to, -grad T; and iv) without a net torque tending to orient the particle with respect to -grad T. Important corollaries are that nonspherical particles in a temperature gradient should also experience new thermophoretically-induced coagulation mechanisms. We predict that the orientation-averaged thermal diffusion factor aT should increase approximately linearly with particle (molecule) length.