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

Abstract

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 ...

Theory of plasma chromatography/gaseous electrophoresis. Review

“…It is obviously possible to go considerably further in relating molecular structure to mobility; that is, in quantitatively accounting for the scatter in Figure 9. There is a long history of such wo/k on the properties of neutral gases, much of it now forgotten; it should suffice here to mention recent work by Kihara (59, 60) and Galloway (61). Similar attempts are now being made on ion mobilities (62), and we should expect to see more such work in the future.…”

“…Large deviations, however, can appear if E/N is large, or for macro-Expressions for the high-field deviations from Blanc's law can be obtained by generalizing the elementary derivations of the previous section to mixtures (52,53); they can, of course, also be obtained from rigorous kinetic theory (18). We do not present any details here because of their limited interest for plasma chromatography, but simply present a useful final approximate formula (54): dlnK< (1 -A,) (61) --IT K -l -1 y__ 2 ¡ Kj d In (E/N) <-» + "^'( §;)( (" + V,)(621 For macro-ions, in the continuum limit Stokes' law holds for mixtures as well as for single gases, and Equation 48for the mobility is still correct. The viscosity that appears in the formula now refers to the mixture.…”

Gas density balance and the mass chromatograph

“…(Under standard conditions, p = (1/22.4)M, where p is expressed as grams/liter and M as grams/mole.) The density of the pure carrier (or reference) gas can therefore be expressed as P =j^Mc (61) where Me is the molecular weight of the carrier gas. When a solute of molecular weight is introduced to the carrier gas stream, the density and molecular weight become p' and M', respectively.…”