Susana B. Bottini

A group contribution equation of state for associating mixtures

Abstract In the present work a group contribution-associating-equation of state (GCA-EOS) is developed for the modeling of phase equilibria found in the near critical fluid extraction and dehydration of oxygenated compounds from aqueous solutions. The new equation of state is obtained by the inclusion of a ‘group’ contribution associating term to the GC-EOS model. The definition of a unique hydroxyl group to represent the association effect of hydrogen bonding in water and alcohols, greatly simplifies the extension of the model to multicomponent mixtures. This approach has been applied to determine the parameters for a common hydroxyl group for water, primary and secondary alcohols. On this basis, revised group and binary interaction dispersive parameters for water, primary and secondary alcohols, alkane groups, light hydrocarbons and CO2 have been determined. Model predictions for binary and ternary data are presented.

Phase equilibria in mixtures of fatty oils and derivatives with near critical fluids using the GC-EOS model

Abstract The Group Contribution Equation of State (GC-EOS) is applied to model high-pressure phase equilibria in mixtures of fatty oils and acid alkyl esters with supercritical fluids. The fatty oil is represented by a pseudo-triacylglyceride with the same molecular weight and degree of unsaturation of the natural oil. The critical hard sphere diameter of the oil, i.e. the size-related parameter, is determined from the correlation of infinite dilution activity coefficients of n -alkanes in high molecular weight triacylglicerides and hydrocarbons. Good predictions of vapor–liquid, liquid–liquid and vapor–liquid–liquid equilibria in mixtures of supercritical solvents (propane, ethane and CO 2 ) with pure triacylglycerides, natural vegetable oils and fatty acid alkyl esters are obtained. These results show the capability of the GC-EOS model to describe the phase equilibria of size-asymmetric mixtures and its potential for modeling supercritical processes involving oils and derivatives.

A strategy for the design and selection of solvents for separation processes.

Abstract A knowledge based strategy for molecular design and selection of solvents for separation processes is presented. The solvent design problem as formulated by Gani and Brignole (1983) has been extended and revised to include improved procedures for solvent synthesis, solvent evaluation and solvent screening. Examples of industrial application are provided through the use of a computer program based on the proposed strategy.

High pressure phase equilibrium modeling of mixtures containing associating compounds and gases

In the present work, the group contribution-associating-equation of state (GCA-EOS) is applied for modeling high pressure phase equilibrium of mixtures containing gases and associating fluids. The GCA performance is compared with other group contribution local composition EOS. Based on extensive testing, it is concluded that the GCA-EOS is a reliable method for modeling the extraction and dehydration of alcohols from aqueous solutions using gases at near critical conditions as solvents (dehyextract process). The parameter tables for the GCA-EOS model have been revised and extended.

Phase equilibrium modelling of triglycerides with near critical solvents

Abstract The Group Contribution Equation of State (GC-EOS) is applied to calculate vapor–liquid and liquid–liquid equilibria of supercritical alkane–vegetable oil mixtures. A new functional group is defined, in order to represent the triglyceride nucleus of vegetable oil molecules. Pure group and binary interaction parameters for this group are given. The size of the high molecular weight triglyceride component is characterized by fitting its critical hard sphere diameter to infinite dilution activity coefficient data of hydrocarbons in the triglyceride.

Activity coefficients of associating mixtures by group contribution

Abstract A group contribution model is presented for the prediction of activity coefficients in associating mixtures. An association term has been added to the traditional UNIFAC residual and combinatorial contributions to the activity coefficients. The association term is based on Wertheims theory for fluids with highly directed attractive forces, as applied in the SAFT equation, and it follows the group contribution approach proposed by Gros et al. in the GCA-EOS model. Good predictions of both vapor–liquid and liquid–liquid equilibria are achieved, with a set of group interaction parameters determined from infinite dilution activity coefficients.

Phase equilibria in binary mixtures of ethane and propane with sunflower oil

Abstract The solubility of ethane and propane in sunflower oil has been measured at temperatures between 298 K and 373 K, and pressures up to 8.88 MPa. Partial liquid miscibility was observed, for mixtures of high hydrocarbon concentrations, in the near-critial region of the solvent; the compositions of the coexisting liquid phases were calculated from a mass balance in the equilibrimn cell.

Application of UNIFAC to vegetable oil-alkane mixtures

The prediction of the vapor-liquid equilibria of vegetable oil-hexane mixtures is studied. Activity coefficients are calculated by the UNIFAC model. Different entropic contributions to activity coefficients from the literature are analyzed. These modifications improve the performance of the original UNIFAC model in vapor-liquid equilibrium calculations.

Vapor liquid equilibria in ternary mixtures of water-aloohol-non polar gases

Abstract The feasibility of alcohol dehydration by the use of light hydrocarbon solvents has been recently confirmed by pilot plant and bench scale experiments. In this regard the study of vapor liquid equilibria (VLE) for alcohol - water - non polar gas mixtures is of interest for the dehydration of alcohols by high pressure entrainers. The potential for water entrainment of a given gas can be obtained from binary information alone; however, ternary data are required in order to know to wich extent the entrainment effect is affected by the presence of the alcohol. Experimental studies carried out with propane, propylene and carbon dioxide, indicate that the water-gas relative volatility in mixtures with alcohol is poorly predicted by the group contribution equation of state (GC-EOS). In the present work new experimental data are presented for the binary isopropanol-isobutane, and for the ternary isopropanol-isobutane-water. An extension of the GC-EOS model is proposed for dealing with the problem of associating mixtures.

Phase equilibria in mixtures of triglycerides with low-molecular weight alkanes

Abstract Phase equilibria of ternary ethane propane-sunflower oil mixtures were measured at 313, 333 and 353 K, and at pressures of up to 120 bar. The region of partial liquid miscibility, at high hydrocarbon concentration, was particularly explored. The Soave-Redlich-Kwong equation of state was used to fit experimental vapor-liquid and liquid-liquid equilibria of alkane-vegetable oil mixtures. The application of a quadratic mixing rule for the co-volume b with a binary interaction coefficient kbij greatly improves the performance of the model.