ASOG Method Research Articles

Modeling of liquid-liquid equilibrium for binary and ternary systems containing ionic liquids with the hexafluorophosphate anion using the ASOG method

Models capable of predicting thermodynamic equilibrium data are essential in developing projects for chemical processing plants. Liquid-liquid equilibrium data (LLE) for systems including ionic liquids are essential for the design and operation of separation processes, but are still scarce. In this sense, the objective of this work is to apply the group contribution ASOG method for calculating activity coefficient data to predict liquid-liquid equilibrium and evaluate their effectiveness in representing the calculated data. ELL experimental data are required for the prediction obtained from the literature for binary and ternary systems containing hexafluorophosphate anion. The modeling was performed with 19 binary and 27 ternary systems at 101.3 kPa and several temperatures. As a result, new ASOG pairs groups were obtained that serve to model new systems that include ionic liquids and other compounds. The average deviation (rms) is approximately 4%. It can be concluded that the ASOG method predicts with good accuracy.

Prediction by the ASOG method of liquid–liquid equilibrium for binary and ternary systems containing 1-alkyl-3-methylimidazolium hexafluorophosphate

Ionic liquids are neoteric, environmentally friendly solvents (since they do not produce emissions) composed of large organic cations and relatively small inorganic anions. They have favorable physical properties, such as negligible volatility and wide range of liquid existence. Moreover, many different cations and anions can be used to synthesize ionic liquid, so the properties can be designed by the use of selected combinations of anions and cations. Liquid–liquid equilibrium (LLE) data for systems including ionic liquids, although essential for the design and operation of separation processes, are still scarce. However, some recent studies have presented ternary LLE data involving several ionic liquids and organic compounds such as alkanes, alkenes, alkanols, water, ethers and aromatics. In this work, the ASOG model for the activity coefficient is used to predict the LLE for 11 binary and 17 ternary systems including the ionic liquid 1-alkyl-3-methylimidazolium hexafluorophosphate plus alkanes, alkenes, alkanols, ketones, carboxylic acids and aromatics. New group interaction parameters were determined by using a modified Simplex method, minimizing a composition-based objective function. The results are satisfactory, with rms deviations of about 4%.

Prediction of liquid-liquid equilibria for polyethylene glycol based aqueous two-phase system by ASOG and UNIFAC method

Liquid-Liquid equilibrium data were obtained for the polyethylene glycol2000(PEG2000)-sodium citrate-water system at 298.15, 308.15 and 318.15 K. The effect of temperature on binodal and tie line data was studied and published in a previous article (Murugesan and Perumalsamy, 2005). The interaction parameters of ASOG and UNIFAC models were estimated using the LLE data of PEG2000-sodium citrate-water system and are used to predict the LLE data for PEG6000-sodium citrate-water system at 298.15, 308.15 and 318.15 K (literature data). The predicted LLE data by both ASOG and UNIFAC models showed good agreement with the experimental and literature data.

Esterification of acetic acid with ethanol: Reaction kinetics and operation in a packed bed reactive distillation column

The reaction kinetics of the esterification of acetic acid with ethanol, catalyzed both homogeneously by the acetic acid, and heterogeneously by Amberlyst 15, have been investigated. The reactions were carried out at several temperatures between 303.15 and 353.15 K and at various starting reactant compositions. Homogeneous and heterogeneous reactions have been described using the models proposed by Pöpken et al. [T. Pöpken, L. Götze, J. Gmehling, Reaction kinetics and chemical equilibrium of homogenously and heterogeneously catalyzed acetic acid esterification with methanol and methyl acetate hydrolysis, Ind. Eng. Chem. Res. 39 (2000) 2601–2611]. These models use activities instead of mole fractions. Activity coefficients have been calculated using ASOG [K. Kojima, K. Tochigi, Prediction of Vapor–liquid Equilibria by the ASOG Method, Elsevier, Tokyo, 1979] and UNIFAC (Aa. Fredenslund, J. Gmehling, P. Rasmussen, Vapor–liquid Equilibria Using UNIFAC. A Group Contribution Method, Elsevier, Amsterdam, 1977] methods. A packed bed reactive distillation column filled with Amberlyst 15 has been employed to obtain ethyl acetate. The influence of feed composition and reflux ratio have been analyzed.

Vapour–liquid equilibria of dimethyl carbonate with linear alcohols and estimation of interaction parameters for the UNIFAC and ASOG method

Isobaric vapour–liquid equilibria have been experimentally determined for the binary systems methanol+dimethyl carbonate, ethanol+dimethyl carbonate, dimethyl carbonate+1-propanol, dimethyl carbonate+1-butanol and dimethyl carbonate+1-pentanol at 101.3 kPa. The activity coefficients were calculated to be thermodynamically consistent and were correlated with the Wilson and UNIQUAC equations. Interaction parameters related to the carbonate group (OCOO) and alcohols, in ASOG and UNIFAC methods, have been determined using our experimental VLE data. The experimental results, as well as those by other authors, agree with the calculated VLE using the new ASOG and UNIFAC parameters.

Prediction of vapor–liquid equilibria in non-polymer and polymer solutions using an ASOG-based equation of state (PRASOG)

An ASOG-based equation of state called PRASOG (Peng–Robinson ASOG) has been developed to predict vapor–liquid equilibria in non-polymer and polymer solutions. It makes use of the zero-pressure G E mixing rule consistent with the second virial coefficient condition for calculating the mixture parameters in Peng–Robinson EOS and predicts the G E using ASOG method. The first object of this paper is to predict low-pressure vapor–liquid equilibria (VLE) using PRASOG for 37 binary systems containing alcohols, hydrocarbons, ketones, esters, ethers, aromatic compounds and water. The PRASOG model has been then used to predict high-pressure VLE for ammonia-containing systems. In order to apply PRASOG to polymer solutions, PRASOG-FV has been proposed by calculating G E from ASOG-FV and VLE in polyisobutylene solutions have been then predicted.

Measurement and prediction of water activity in electrolyte solutions by a modified ASOG group contribution method

A set of new ionic type functional groups for the prediction of water activities ( a w) in aqueous solutions of electrolyte solutes using the ASOG group contribution method is proposed. Previously published experimental data on water activities, osmotic coefficients and freezing temperatures for binary solutions of electrolyte salts and water at different temperatures were used to calculate interaction parameters. With such parameters, values of a w for binary (14), ternary (28) and quaternary (3) systems, at different temperatures, were predicted and compared with experimental data. This data included both published and new data, measured with an electric hygrometer, for sodium nitrate (at 20°C) and potassium nitrate (at 20°C and 30°C). Calculated average relative deviations of a w predictions using the ASOG method were 0.21%, 0.28% and 0.20% respectively.

Vapor−Liquid Equilibria for the Binary Systems of 1-Butanol with Some Halohydrocarbons at 40.0 and 101.3 kPa

Isobaric vapor−liquid equilibrium measurements at 40.0 and 101.3 kPa are reported for 1-butanol + chlorocyclohexane, + chlorobenzene, + bromocyclohexane, + bromobenzene. Some of the studied systems show minimum temperature azeotropes. The experimental data were tested for thermodynamic consistency and satisfactorily correlated with the Margules, Van Laar, Wilson, NRTL, and UNIQUAC equations. Predictions with the UNIFAC method and ASOG method were also obtained.

Prediction of Excess Enthalpy and Excess Entropy Using Modified UNIFAC Group Contribution Methods.

We have examined the accuracy of recent versions of the UNIFAC group contribution method (Larsen et al., 1987; Weidlich and Gmehling, 1987 and Gmehling et al., 1993) for predicting excess enthalpy and excess entropy. For comparison, we also include the results predicted according to the ASOG method

Analysis of a modification of the ASOG method for vapor—liquid equilibrium prediction

A group contribution method has been developed for the prediction of vapor—liquid equilibria. It consists of a modification of the ASOG method using an equation similar to NRTL, adapted for group contribution, for the calculation of the residual activity coefficient. The interaction parameters have been determined for 16 pairs of groups. The prediction has been applied to a series of binary mixtures and the results obtained were compared with those from calculations employing ASOG and UNIFAC methods.

Prediction of High Pressure Vapor-Liquid Equilibria Using a Group Contribution Equation of State with Low Pressure ASOG Parameters.

The ASOG group contribution method for calculating the excess Gibbs energy at low pressures has been combined with the recently developed zero pressure MHV mixing rules of Michelsen for cubic equation of state. By using these models, high pressure vapor-liquid equilibria were predicted for 7 systems containing mostly polar substances. A comparison was made with the performance of the models which use the UNIFAC group contribution method, and in all tested cases the predictions were found comparable. The results indicate that the built-in temperature dependence of the ASOG method allows a reliable extrapolation well into high temperature region

Group contribution methods for the estimation of activity coefficients

Group contribution methods for estimating activity coefficients play an important role in solving varied types of problems in both the chemical and petrochemical industries. Although the results produced by these methods are generally satisfactory, attempts to improve the models and parameters used are continually being made. At the same time, the database available for taking into account concentration and temperature effects when fitting the parameters is steadily becoming larger. The improvements in the results obtained make these methods suitable for other areas of application (e.g. estimating retention data, taking into account supercritical components). The target must be to prepare a parameter matrix for the improved models which is comparable in size to that for the UNIFAC or ASOG method.

Prediction of non-polar gas solubilities in water, alcohols and aqueous alcohol solutions by the modified asog method

Tochigi, K. and Kojima, K., 1982. Prediction of non-polar gas solubilities in water, alcohols and aqueous alcohol solutions by the modified ASOG method. Fluid Phase Equilibria, 8: 221–232. The non-polar gas solubilities in water, alcohols and aqueous alcohol solutions are correlated and predicted by the modified ASOG method for a gas partial pressure of 1 atm and a temperature range of 10°C to 40°C. Solubilities in normal alcohols from methanol to octanol are considered. The non-polar gaseous solutes are oxygen, nitrogen, hydrogen, carbon dioxide, argon, methane, ethane, ethylene, propane and butane. The gas solubilities are first correlated and then predicted in pure solvents. Next, the gas solubilities are predicted for mixed solvents by using group pair parameters determined only from the data for gas solubilities in pure solvents. The deviation between the observed and the predicted gas solubilities is 6.0% in pure and 10.2% in mixed solvents.

Prediction of liquid-liquid equilibria for ternary systems by the asog method.

Prediction of liquid-liquid equilibria for ternary systems by the asog method.