Dimitrios P. Tassios

Prediction of Vapor-Liquid-Equilibrium with the Lcvm Model - A Linear Combination of the Vidal and Michelsen Mixing Rules Coupled with the Original UNIFAC and the T-Mpr Equation of State

Abstract Boukouvalas, C., Spiliotis, N., Coutsikos, P., Tzouvaras, N. and Tassios, D., 1994. Prediction of vapor-liquid equilibrium with the LCVM model: a linear combination of the Vidal and Michelsen mixing rules coupled with the original UNIFAC and the t-mPR equation of state. Fluid Phase Equilibria, 92: 75-106. A new mixing rule, a linear combination of the Vidal and Michelsen rules, for the attractive term parameter in cubic equations of state (EoS) has been developed. This mixing rule, coupled with a translated and modified Peng-Robinson EoS and the original UNIFAC, leads to the LCVM model which provides successful prediction of vapor-liquid equilibria (VLE) of nonpolar and polar systems at low and high pressures. This also applies to systems of dissimilar component size, such as those containing gases (C2H6, CO2 and CH4) with large n-alkanes, where other EoS/GE predictive models, such as MHV2 and PSRK, perform poorly.

Thermophysical properties of n-Alkanes from C1 to C20 and their prediction for higher ones

Reliable values for the thermophysical properties: critical properties, acentric factors, vapor pressures (PS), saturated liquid volumes (VS1) and enthalpies of vaporization (ΔHv) for the C1 to C20 n-Alkanes are presented. The PS, VS1 and ΔHv values are successfully predicted with a translated form of the van der Waals (t-vdW) and of the Peng-Robinson (t-PR) equation of state (EoS) presented here. The two t-EoS give also reasonable predictions of vapor pressures, saturated liquid volumes and enthalpies of vaporization for n-Alkanes higher than C20 using extrapolated Tc, Pc, and ω values presented here. The t-vdW and t-PR predict, for example, the recent accurate PS data for C28 with average absolute error of 2.7% and 3.6% respectively.

Bioconcentration of heavy metals in aquatic environments: the importance of bioavailability

The importance of heavy metal bioavailability on the bioconcentration in aquatic biota is examined. To this purpose, mono- and multivariate statistical techniques are applied to develop correlations between heavy metal bioconcentration factor and sediment characteristics, that are expected to affect bioavailability, using a database of heavy metal concentrations in biota and sediment along with the available physicochemical characteristics. The statistical analysis shows that satisfactory correlations are obtained only when factors that affect bioavailability, such as metal oxides concentration and organic carbon content in the sediment, are taken into account.

Vapor-liquid equilibria for alcoholhydrocarbon systems using the CPA Equation of state

Abstract The recently developed Cubic-Plus-Association Equation of State (CPA EoS) is extended in this study to binary systems containing one associating compound (alcohol) and an inert one (hydrocarbon). CPA combines the Soave-Redlich-Kwong (SRK) equation of state for the physical part with an association term based on perturbation theory. The classical van der Waals one-fluid mixing rules are used for the attractive and co-volume parameters, α and b, while the extension of the association term to mixtures is rigorous and does not require any mixing rules. Excellent correlation of Vapor-Liquid Equilibria (VLE) is obtained using a small value for the interaction parameter (kij) in the attractive term of the physical part of the equation of state even when it is temperature-independent. CPA yileds much better results than SRK and its performance is similar to that of other association models, like the Anderko EoS, and the more complex SAFT and Simplified SAFT EoS.

How good is conformal solutions theory for phase equilibrium predictions ? Gibbs ensemble simulations of binary Lennard-Jones mixtures

Abstract It is generally believed that conformal solutions theory is valid only for mixtures with components having small differences in energy and size intermolecular potential parameters. To test this assumption, we have used the Gibbs ensemble Monte Carlo simulation technique to calculate phase diagrams of binary Lennard-Jones mixtures obeying the Lorentz—Berthelot combining rules for size parameter ratios equal to 0.5, 1.0 and 1.5 and for energy parameter ratios equal to 0.50, 0.66, 0.75 and 1.00. We generally find good agreement between simulation and theoretical predictions based on an equation of state for the pure Lennard-Jones fluid and the van der Waals one-fluid approximation. Our results establish the validity of conformal solutions theory for simple mixtures of much greater degree of asymmetry than previous investigations.

Prediction of phase equilibria in water/alcohol/alkane systems

Abstract The Cubic Plus Association Equation of State (CPA EoS) is applied to the prediction of Vapor–Liquid Equilibrium (VLE) and Liquid–Liquid Equilibrium (LLE) in ternary associating mixtures containing water, alcohols and alkanes. The appropriate set of combining rules for the cross-association energy and volume parameters of the EoS is identified by evaluating the performance of four such sets in the correlation of VLE and LLE for water/alcohol mixtures. Using only one interaction parameter per binary mixture, in the physical part of the EoS, CPA gives very satisfactory predictions of ternary VLE and LLE.

A generalized correlation for the interaction coefficients of CO2—hydrocarbon binary mixtures

Abstract Kordas, A., Tsoutsouras, K., Stamataki, S. and Tassios, D., 1994. A generalized correlation for the interaction coefficients of CO 2 -hydrocarbon binary mixtures. Fluid Phase Equilibria 93; 141-166. A generalized correlation for the interaction coefficient (k ij ) of CO 2 / n -alkane binary systems with a translated modified Peng-Robinson equation of state (t-mPR EoS) is presented. The correlation involves the CO 2 reduced temperature and alkane acentric factor as independent variables and was developed using an extended data base up to n -C 44 . Through the use of an “effective” acentric factor the correlation is extended to other CO 2 -hydrocarbon systems. The correlation is limited and does not apply to very asymmetric systems where the hydrocarbon contains more than one ring. Typical errors in bubble point pressure predictions are below 5–6%. The proposed correlation can also be used with the PR EoS.

Correlation of liquid-liquid equilibria for alcoholhydrocarbon mixtures using the CPA equation of state

Abstract A recently developed equation of state, which combines the physical term of the classical SRK EoS with the association term based on the perturbation theory of Wertheim, called the Cubic Plus Association Equation of State (CPA EoS) (Kontogeorgis et al. [1]), is applied to liquid-liquid equilibrium (LLE) calculations in alcohol hydrocarbon mixtures. The CPA EoS performs very well in all cases using the conventional van der Waals one-fluid mixing rules in the parameters of the physical term and a temperature-independent interaction parameter. The performance of the CPA EoS is compared to that of the conventional SRK EoS and UNIFAC models, and with another association model, the ESD EoS of Suresh and Elliott [2]. The CPA EoS gives much better results than the two conventional models and results comparable to those obtained with the ESD model.

Application of the van der Waals equation of state to polymers. I: Correlation

Kontogeorgis G.M., Harismiadis V.I., Fredenslund A., and Tassios D.P., 1994. Application of the van der Waals equation of state to polymers. I. Correlation. Fluid Phase Equilibria, 96: 65-92. A reliable methodology for evaluating the energy and co-volume parameters of cubic equations of state for polymers is proposed. Only two low-pressure volumetric data points are used. The procedure is applied to the van der Waals equation of state and bubble-point pressure calculations are performed for a number of polymer solutions. The usual combining and mixing rules are used. It is shown that the van der Waals equation can correlate the equilibrium pressures of polymer solutions using one binary interaction parameter. The accuracy of the correlation is very good; it is comparable to or better than that achieved using the Flory-Huggins model. It is also shown that the necessary binary interaction parameters for the van der Waals equation of state can be estimated using a simple scheme based on the Berthelot combining rule. It is, thus, demonstrated that the van der Waals equation of state can be a simple and successful tool for the description of the vapor-liquid equilibria in polymer solutions.

Prediction of the bioaccumulation of persistent organic pollutants in aquatic food webs.

Predictive correlations of the bioaccumulation factor of persistent organic pollutants in aquatic biota are presented as functions of their octanol/water partition coefficient. The correlations demonstrate the importance of differentiating among the different levels in the food web and of accounting for the pollutants bioavailability by considering the amount freely dissolved in water instead of the total concentration. They also reveal the significance of the pollutants octanol/water partition coefficient value on its biomagnification along the levels of the trophic chain. Prediction results, finally, demonstrate that the correlations provide reasonably accurate estimates of bioaccumulation, typically within an order-of-magnitude.