AN EMPIRICAL VIRIAL-LIKE CUBIC EQUATION OF STATE FOR PHASE EQUILIBRIUM CALCULATIONS

An empirical cubic equation of state(EOS) was obtained by truncating the virial expansion in reciprocal of molar volume after the third term. The constants of the EOS was generalized in terms of critical temperature, critical pressure and Pitzer's acentric factor. In pure component applications the EOS exhibited a performance comparable to Peng-Robinson (1976) EOS in the reduced temperature range of 0.5 to 1. The present EOS tends to predict better saturation liquid volumes at reduced temperatures below 0.8, and better estimations for second virial coefficient at high reduced temperatures. The EOS was successfully employed for vapor liquid equilibrium calculations for some mixtures of normal or slightly polar fluids with traditional one binary parameter mixing rule at moderately high pressures. At low reduced temperatures, where conventional one adjustable parameter applications of the cubic equations compare unfavorably with dual methods based on excess Gibbs energy functions for the liquid phase, a new two constant mixing rule introduced by Stryjek and Vera (1986) was employed for the present equation of state.Publisher's Versio

EVALUATION OF SECOND VIRIAL COEFFICIENTS FROM SATURATION DATA

A data reduction technique is introduced for the evaluation of second virial coefficients of gases at subcritical temperatures. The method makes use of the vapor-liquid equilibrium data, i.e., temperature, saturation pressure, liquid and vapor molar volumes and can be used to obtain second virial coefficients of a wide variety of fluids including polar, associating and quantum gases. The calculated second virial coefficients are in good agreement with their counterparts from literature, which are obtained from gas compressibility data by traditional data reduction methods

ON THE THERMODYNAMICS OF MICROBIAL-GROWTH PROCESSES

In this article, we provide a rigorous thermodynamic analysis of microbial growth processes, clarify the role of the generalized degree of reduction concept as it is used in both stoichiometric equations and as a characterizing factor for thermophysical properties, and introduce a classification method to account for errors when using the generalized degree of reduction to estimate the energy and free energy contents of molecules. We maintain the advantages of using the generalized degree of reduction while correcting for the large errors in the principle of energy regularity, especially for small molecules and for nitrogen-source compounds. As a result, we obtain more accurate energy balances (heat loads) and second law constraints, and are able to clarify contradictory statements in the literature as to whether nonphotosynthetic fermentation processes can produce oxygen or absorb rather than produce heat. Indeed, the answers to such questions become evident using the classification system introduced here

Effect of Feed Concentration in Equilibrium Parametric Pumps

The effect of high initial feed concentration in batch equilibrium parametric pumping was experimentally investigated at different bed temperatures and cycle times. The system studied was benzene-n-hexane over a silica gel bed. It was observed that the initial feed concentration which leads to the best separation is dictated by the shape of the equilibrium isotherms of the system. An increase in the temperature difference between hot and cold cycles was shown to improve the separation because it led to a more favorable equilibrium relationship. Experiments also indicated that a long enough cycle time must be selected for true equilibrium to be established within the system, otherwise maximum separation cannot be obtained. In mathematical modeling studies the effect of nonlineariry of equilibrium isotherms at high feed concentrations was shown to be very effective for predictions of the model.Publisher's Versio

The simplest cubic equation of state for low-pressure vapor—liquid equilibrium calculations

A simple, virial-like cubic equation of state has been developed from the general form of the perturbed hard core model. The equation simultaneously incorporates saturation liquid volume and saturation pressure information for pure compounds. With two adjustable parameters per binary, it can represent low-pressure vapor—liquid equilibria as well or better than dual methods. This model applies a single equation to both phases and necessitates only a fraction of the input information required by dual methods. The results indicate that the cubic equations do not necessarily need a van der Waals type hardcore term in order to successfully predict the phase equilibrium.Publisher's Versio