Extension of the A-UNIFAC model to mixtures of cross- and self-associating compounds

http://apps.isiknowledge.com/full_record.do?product=UA&search_mode=GeneralSearch&qid=4&SID=V21Di6PajaHLPoM3@AJ&page=1&doc=1&colname=WOSIn the present work an extended UNIFAC group contribution model is used to calculate activity coefficients in solutions containing alcohols, water, carboxylic acids, esters, alkanes and aromatic hydrocarbons. The limiting expressions for the association contribution to the activity coefficients at infinite dilution are presented and discussed. A new set of interaction parameters between associating and non-associating functional groups is reported. This set of parameters is applied in the association model to predict vapor–liquid, liquid–liquid equilibrium and infinite dilution activity coefficients.The authors are grateful to the National Research Council of Argentina (CONICET) and to Universidad Nacional del Sur (UNS) for financial support. O. Ferreira acknowledges financial support from the PRAXIS program, FCT, Lisbon, Portugal (SFRH/BD/879/2000)

Group contribution modeling of activity coefficients in associating solutions containing water, alcohols and carboxylic acids

A modified UNIFAC group contribution model for the prediction of activity coefficients in associating solutions (A-UNIFAC) is applied to calculate phase equilibria in binary and ternary mixtures of associating and non-associating species, including alcohols, water, carboxylic acids, esters, alkanes, aromatic hydrocarbons and alkyl chlorides. Self- and cross-association in these mixtures is adequately described by the definition of a single hydrogen-bonding group. The new model is able to give good predictions of vapor-liquid equilibria, liquid-liquid equilibria and infinite dilution activity coefficients, using a single set of group-interaction parameters.The authors are grateful to the Argentinian National Research Council (CONICET) and to Universidad Nacional del Sur (UNS) for financial support. M.O. Ferreira acknowledges financial support from the PRAXIS program, FCT, Lisbon, Portugal

Modeling of association effects in mixtures of carboxylic acids with associating and non-associating components

http://apps.isiknowledge.com/full_record.do?product=UA&search_mode=GeneralSearch&qid=6&SID=V21Di6PajaHLPoM3@AJ&page=1&doc=1&colname=WOSThe group contribution with association equation of state GCA-EOS has been applied to calculate thermodynamic properties of pure compounds and mixtures of carboxylic acids with paraffins, alcohols, water and gases, at low and high pressures. Two associating groups, OH and COOH, were defined. Self- and cross-association in these mixtures were quantified through two parallel COOH/COOH and OH/OH associations. The validity of this approach is supported by an excellent representation of pure compound properties (vapor pressures and compressibility factors) and phase equilibria in mixtures of (associating + inert) and (associating + associating) components at low and high pressures

The extended gca-eos model for mixtures of fatty oils and derivatives

The Group Contribution Equation of State GC-EOS has been satisfactory applied to the modeling of high-pressure phase equilibria of supercritical gases (CO2, propane, ethane, dimethylether) with pure triglycerides and natural vegetable oils. The GC-EOS model size-related parameter, i.e. the critical hard sphere diameter, of the high molecular weight compounds were determined by fitting infinite dilution activity coefficients of n-alkanes in these heavy compounds. In this way the GC-EOS model was able to correlate and predict vapor-liquid (VLE) and liquid-liquid (LLE) equilibria of these mixtures, using a unique set of parameters, in good agreement with experimental data. In this work the application of the model is extended to mixtures containing fatty oil derivatives, such as fatty acids, fatty acids esters, mono - and diglycerides. The associating effects between molecules are described using an upgraded version of the model, the Group Contribution Associating - EOS. Satisfactory correlation and prediction of experimental VLE, LLE and ginfinite data in binary and ternary mixtures of these products with supercritical gases are obtained

Application of the GCA-EOS model to the supercritical processing of associating oil derivatives: fatty acids, alcohols and triglycerides

Supercritical processes are of interest in the fatty oil industry for a variety of applications: extraction and refining, removal of pollutants, recovery of specialties, hydrogenation of oils and derivatives, etc. Typical process mixtures include heavy compounds and gases at near critical conditions. At high pressures these asymmetric systems present a complex multiphase behaviour, difficult to model. This complexity increases if some of the mixture components are able to self- and/or cross associate. In the present work, the group contribution with association equation of state (GCA-EoS) [3] is extended to represent high pressure phase equilibria in mixtures of supercritical gases (carbon dioxide, propane, ethane) with fatty oil derivatives, such as mono- and di-glycerides, fatty acids, alcohols, water and esters. Self- and cross association between associating groups present in these mixtures are considered. Satisfactory correlation and prediction of equilibrium data are obtained. The capacity of the model to follow the behaviour of solutions towards the limit of infinite dilution of the associating components is of particular importance

Extension of UNIFAC to associating systems

An extended UNIFAC group contribution model for the prediction of activity coefficients in associating mixtures was presented recently (Mengarelli et al.,1999). In the present work the model is applied to solutions containing alcohols, water, carboxylic acids and inert components. The residual UNIFAC local composition term is re-parameterized in order to take into account only dispersive forces between associating and inert functional groups. Good representation of vapor-liquid and liquid-liquid equilibrium, as well as infinite dilution activity coefficients is achieved by using a single set of group interaction parameters

A-UNIFAC modelling of binary and multicomponent phase equilibria of fatty esters+water+methanol+glycerol

The production of methyl and ethyl esters of fatty acids is of great industrial interest, considering the direct application of these esters as biodiesel. For biodiesel purification and by-products recovery processes design and optimization, the prediction of the phase behaviour of mixtures containing fatty esters, alcohols, glycerol and water is of utmost importance. In this work we show the capability of a A-UNIFAC to correlate and predict phase behaviour of these mixtures. This GE model is an extension of UNIFAC that explicitly includes association effects between groups based on the statistical Wertheim theory [1]. For the water-esters binary systems, the residual and association parameters have been previously estimated using low pressure VLE data [1]. The use of these parameters to predict liquid-liquid equilibrium results in good agreement with experimental information on binaries of water with acetic, octanoic or dodecanoic acids methyl esters. The association effect in methanol and glycerol are represented with the same hydrogen bonding hydroxyl groups (OH) with two associating sites, one group in methanol and three in glycerol. For the residual contribution, both molecules are considered as molecular groups (CH3OH and C3H8O3). The residual interaction parameters between CH3OH and C3H8O3 were obtained by fitting isothermal liquid-liquid equilibrium data on the ternary system dodecanoic acid methyl ester-methanol–glycerol [2]. The glycerol/paraffin (C3H8O3/CH2) and glycerol/ester (C3H8O3/CCOO) interaction parameters were estimated by fitting experimental data on liquid-liquid equilibrium and infinite dilution activity coefficients of the binary systems dodecanoic acid methyl ester-glycerol and hexanoic acid methyl ester-glycerol between 320-438 K [2]. A-UNIFAC with the final set of parameters is able to predict with good agreement experimental data on binary and ternary liquid-liquid equilibria of glycerol + methanol + fatty esters as well as infinite dilution activity coefficient for this system. References [1] O. Ferreira, E.A. Macedo, S.B. Bottini, Fluid Phase Equilib. 227 (2005) 165-176. [2] F.M. Korgitzsch, Study of Phase Equilibria as a Fundament for the Refinement of Vegetable and Animal Fats and Oils. Ph.D. Dissertation, TU Berlin, 1993

A group contribution model for activity coefficients in associating solutions

A group contribution model is presented for the prediction of activity coefficients in associating mixtures. The new model adds an association term to the traditional UNIFAC residual and combinatorial contributions to the activity coefficients. The association term is based on Wertheim’s 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, vaporliquid and liquid-liquid equilibria are achieved in the whole concentration range, with a single set of group interaction parameters

A general group contribution model for activity coefficients in associating solutions

A modifed UNIFAC group contribution model for the prediction of activity coefficients in associating mixtures was proposed recently (Mengarelli et al., 1999). In the present work, the model is extended to carboxylic acids by defining a general associating group which allows a straightforward extension to multicomponent mixtures. The residual UNIFAC local composition term is re-parameterized in order to take into account only dispersive forces between associating and inert functional groups. Good correlation and prediction of experimental VLE, LLE and g∞ data for mixtures containing water, acids, alcohols and inert compounds are obtained