Physical properties pure component constants

The chemical literature is rich with empirical equations of state and every year new ones are added to the already large list. Every equation of state contains a certain number of constants which depend on the nature of the gas and which must be evaluated by reduction of experimental data. Since volumetric data for pure components are much more plentiful than for mixtures, it is necessary to estimate mixture properties by relating the constants of a mixture to those for the pure components in that mixture. In most cases, these relations, commonly known as mixing rules, are arbitrary because the empirical constants lack precise physical significance. Unfortunately, the fugacity coefficients are often very sensitive to the mixing rules used. 

The property program developed by the Design Institute for Physical Properties of the American Institute of Chemical Engineers, known as DIPPR, is widely known and used. The PC version of DIPPR contains 26 constant and 13 temperature-dependent, pure-component properties for 766 common industrial... 

An adsorption kinetic model was developed to evaluate the adsorption rates of five pure gases (Nj, O2, Ar, CO, and CH4) on a Takeda-3A CMS over a wide range of pressures up to ISatm. The kinetic characteristics of adsorption on the CMS were studied by using the adsorption equilibrium of five pure gases measured at three different temperatures and their physical properties. Since the diffiisional time constants of all the components showed much stronger dependence of pressure than those expected by the traditional Darken relation, a structural diffusion model was applied to predict the strong pressure dependence. The proposed model successfully predicted the dif ional time constant up to high pressure on the CMS. 

This simple linear variation of the vapom pressure is found very rarely in practice. In general the components influence one another in such a manner that the physical properties of the solution are no longer additive functions of the properties of the pure components. The vapour pressure curve (at constant temperature) may then be either concave or convex to the axis of abscissae, and may even have maxima or minima. 

Commercially available compilations of pure component characteristic physical property constants and temperature-dependent properties" for convenient use in process simulators have been developed by AlChE (DIPPR), DDBST, DECHEMA, NIST (TRC), and PPDS. They should be checked first before estimating thermophysical properties. DDBST has developed a comprehensive pure component thermophysical property estimation software (Artist), where many of the methods discussed in this chapter are implemented. 

On the basis of the derivations, the two constants of the Van Laar equations and the modifications of it are related to the physical properties of the pure components. When the best values of the constants are chosen to fit the data, they usually do not agree with the predicted values, although the trends are approximately the same. Generally the constants are chosen to agree with the data, and the equations are used empirically. 

The databanks can be regarded as the fuel for the PPDS-2 calculation engine. The most important bank in any bank set is the PC-BANK. It provides a set of physical constants and regression coefficients for the temperature-dependent properties. The PPDS SYSTEM bank has information for some 1500 pure components, in a form which... 

A quantitative description of chemical forces through pure component properties, even to the limited degree that was the case with physical forces, is not possible yet. Results from experimental measurements are usually correlated using association constants (see, for example, Weimer and Prausnitz). 

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