UNIFAC Interaction Parameters Research Articles

Liquid–liquid equilibrium calculations of systems containing vegetable oil + fatty acids + ethanol + water using new parameters for the unifac subgroups of ethanol and water

Deacidification removes free fatty acids (FFA) from crude vegetable oils during the refining process. The removal of FFA carried out by liquid–liquid extraction has some advantages over chemical and physical refining processes: it saves energy and decreases neutral oil losses caused by undesirable chemical reactions. The knowledge of phase equilibrium behavior of systems involving vegetable oils, solvents, and FFA is necessary to design and optimize the liquid–liquid extraction processes for deacidification. In this context, the present work aims to predict the liquid–liquid equilibrium (LLE) for systems consisting of vegetable oil + fatty acids + ethanol + water, readjusting new UNIFAC interaction parameters just for the ethanol and water subgroups. Several experimental LLE data for multicomponent fatty systems available in the literature are used to adjust the new UNIFAC interaction parameters for the ethanol (EtOH) and water subgroups. The temperature range studied was 288.15 K to 323.15 K, at atmospheric pressure. The new 18 interaction parameters provide a considerably lower mean square error (0.87%) than the other works available in the literature. The results show that the developed procedures improve the capacity of the UNIFAC method to predict LLE for systems involved in the deacidification process of crude vegetable oil. The methodology employed in this work results in reduced computational calculations and a relatively small split with the complex dataset established by the UNIFAC-LL model.

Thermodynamics of mixtures containing a fluorinated benzene and a hydrocarbon

Fluorobenzene, or 1,4-difluorobenzene or hexafluorobenzene + alkane mixtures and hexafluorobenzene + benzene, or + toluene, or + 1,4-dimethylbenzene systems have been investigated using thermodynamic properties from the literature and through the application of the DISQUAC and UNIFAC (Dortmund) models and the concentration-concentration structure factor (SCC(0)) formalism. DISQUAC interaction parameters for the contacts F/alkane and F/aromatic have been determined. UNIFAC interaction parameters available in the literature for these contacts have been used along calculations. Both models predict double azeotropy for the C6F6 + C6H6 system, although in different temperature ranges. TheHmE values of the fluorobenzene, or 1,4-difluorobenzene + n-alkane systems are positive and are accurately described by the models using interaction parameters independent of the n-alkane. This means that no Patterson’s effect exists in such mixtures. DISQUAC calculations allow state that such conclusion is still valid for C6F6 + n-alkane mixtures. DISQUAC provides better results than UNIFAC on CpmE of solutions involving n-alkanes, or on HmE of C6F6 + aromatic hydrocarbon systems. Mixtures with alkanes are characterized by interactions between like molecules, which are mainly of dispersive type, which is supported, e.g, by the negative CpmE values of these systems. It is shown that structural effects can contribute largely to HmE. This is investigated in terms of the excess molar internal energy at constant volume, UVmE, whose values are determined for the investigated solutions. For mixtures with a given n-alkane, the relative variation of HmE and UVmEwith the fluorohydrocarbons is different.HmEvalues change in the sequence C6F6 > 1,4-C6H4F2 > C6H6 > C6H5F, while UVmE changes in the order: 1,4-C6H4F2 > C6H6≈ C6H5F > C6F6 . C6F6 + aromatic hydrocarbon mixtures are characterized by interactions between unlike molecules as it is demonstrated by their negative HmE values. The application of the SCC(0) formalism reveals that homocoordination is more important in C6F6 + n-alkane mixtures than in the corresponding systems with C6H5F, and that heterocoordination is dominant in the solutions of C6F6 with an aromatic hydrocarbon.

Ethanol and methanol Unifac subgroup parameter estimation in the prediction of the liquid-liquid equilibrium of biodiesel systems

The biodiesel conventional production method is based on the homogeneous transesterification reaction, in which the quality and quantity of the raw materials used have considerable effect on the separation of phases of the generated products. The presence of glycerol in biodiesel, for example, has a maximum permissible value of only 0.02% (EM 14214). On the other hand, high purity glycerol needs to be marketed separately. In this way, a better understanding of the phase equilibrium becomes fundamental for the proper design, operation and optimization of the process. In the literature, the thermodynamic modeling focuses on the UNIQUAC and NRTL models. Such models can predict phase equilibrium for each system separately, and the interaction parameters are distinct and unique. However, the use of several types of vegetable or residual oils has been reported for biodiesel production. On the other hand, group-contribution thermodynamic models, such as UNIFAC, could be used to predict the phase equilibrium behavior of reactional biodiesel systems formed from these different types of oils. This work contributes to this subject, providing generalized UNIFAC interaction parameters for the already specified subgroup methanol (CH3OH) and a new specific subgroup, ethanol (CH3CH2OH). The UNIFAC-LL database parameters were used, except for methanol and ethanol subgroups proposed here, for calculations with ten vegetable oils, for which experimental data are available. The mean square error (0.92%, methanol; 1.20%, ethanol) was considerably lower when compared to the available UNIFAC-LL data (10.58%, methanol; 8.89%, ethanol) and work of the literature (2.21%, methanol; 3.92%, ethanol) that uses a greater number of adjustable parameters. The results show that the methodology employed is consistent and can be useful in predicting liquid-liquid phase equilibrium for both reactive methyl and ethyl biodiesel systems considered.

Application of Adsorbate Solid Solution Theory To Design Novel Adsorbents for Arsenic Removal Using CAMD

Arsenic is a carcinogenic contaminant that pollutes the groundwater, a consequence of poor arsenic disposal. Various techniques are used to remove arsenic, such as oxidation, coagulation–flocculation, membrane filtration, ion exchange, and adsorption, among which adsorption is the most efficient method. Current arsenic separating agents on the market have a limited adsorption capacity. The overall objective of this work is to develop a computational tool for the design of novel adsorbents for arsenic remediation using clay materials including beidellite, zeolite, and sepiolite that are cheap and readily available. In the first part of this research, we use the group contribution method (GCM) to predict thermodynamic properties and calculate the UNIFAC interaction parameters between arsenic and other functional groups that are selected from clay materials. In the second part of this research, we utilize a computer-aided molecular design (CAMD) framework that develops new adsorbent candidates with enhanced adsorption capacities based on the group interaction parameters generated in the first part. The efficient ant colony optimization (EACO) algorithm maximizes the adsorption capacity with certain structural possibilities, thermodynamic property correlations, and process conditions. It was found that the newly designed adsorbents have an order of magnitude higher removal capacity than the adsorbents’ reported in the literature.

Estimation of unknown UNIFAC interaction parameters between thiophene and olefin, and thiol and olefin functional groups

In this study, unknown UNIFAC interaction parameters between thiophene and olefin, and thiol and olefin functional groups are estimated. Experimental results for the activity coefficients for different binary mixtures from reported literature are used in the parameter estimation. The estimated parameters provides excellent predictions of the activity coefficients which validates the values of estimated parameters and also ensures the creditability of the UNIFAC model for mixtures containing these functional groups.

A new UNIFAC parameterization for the prediction of liquid-liquid equilibrium of biodiesel systems

The environmental adversities and the global concern about the conservation of non-renewable natural resources have stimulated a search for environmentally friendly energy sources. In this context, biodiesel has emerged as an important alternative to replace fossil fuels, due to its renewability, non-toxicity and biodegradability. Modeling, simulation and design of unit operations involved in the production of edible oils and biodiesel require knowledge of phase equilibrium. Several versions of the UNIFAC model are frequently used for process design when experimental determination of phase equilibrium data is difficult or time-consuming. In this work, the original UNIFAC model parameters are first checked for their predictive capability and then modified in terms of new readjusted binary interaction parameters. It was noted that the UNIFAC model without any changes in its parameters results in inadequate predictions. Thus, in order to obtain a good predictive tool, a comprehensive liquid-liquid equilibrium data bank of systems present in biodiesel production was organized and new UNIFAC interaction parameters were adjusted. At first, the molecules were divided into UNIFAC traditional structural groups. However, this first approach resulted in poor prediction, probably as a consequence of the strongly polar hydroxyl groups bonded to the consecutive carbon atoms of glycerol and acylglycerol molecules. Thus, a new group (‘OHgly’) was introduced and two matrices of parameters were adjusted. In general, satisfactory predictions were obtained and a significant improvement in the performance of this group contribution model has been achieved.

Liquid–liquid equilibria for ternary mixtures of 2,2-dimethyl-1,3-dioxolane-4-methanol with n-heptane, toluene, ethanol and water

Liquid–liquid equilibria (LLE) data are presented for three ternary systems: 2,2-dimethyl-1,3-dioxolane-4-methanol (DMDM)+n-heptane+ethanol, and DMDM+n-heptane (or toluene)+water. The most of the measurements were performed at 293.15K and atmospheric pressure, some data obtained relate to 273.15K. The phase diagrams for the ternary system containing n-heptane and water show the extended heterogeneous area between the water–hydrocarbon side of the concentration triangle and the n-heptane-DMDM side. Much smaller regions of immiscibility with the critical points are observed for the ternary mixtures DMDM+toluene+water and DMDM+n-heptane+ethanol. The experimental LLE data were correlated applying the NRTL model. The UNIFAC interaction parameters for CH2O groups of DMDM were estimated on the base of LLE in the DMDM+n-heptane+ethanol system. The UNIFAC model was applied to predict the LLE diagrams for ternary DMDM+n-heptane (or toluene)+water solutions. Both NRTL and UNIFAC models with the estimated parameters have provided satisfactory results.

Liquid–liquid equilibria for multicomponent mixtures of 2,2-dimethyl-1,3-dioxolane with n-heptane, toluene, ethanol and water

Liquid–liquid equilibria (LLE) data are presented for two quaternary systems: 2,2-dimethyl-1,3-dioxolane (DMD)+n-heptane (or toluene)+ethanol+water, – and for three ternary subsystems: DMD+ethanol+water and DMD+n-heptane (or toluene)+water. The measurements were performed at 293.15K and atmospheric pressure. The phase diagrams show extended heterogeneous areas for ternary systems containing n-heptane (or toluene) and water, the region going from water–hydrocarbon side of the concentration triangle to water–DMD side. A much smaller region of immiscibility with the critical point is observed for ternary mixtures of DMD with water and ethanol. The experimental LLE data were correlated and partly predicted applying the NRTL model. The UNIFAC interaction parameters for CH2O groups of dioxolane alkyl-derivatives were estimated. The model was applied to predict the LLE diagrams for ternary DMD+n-heptane (+toluene)+water solutions and for the quaternary systems containing ethanol. Both NRTL and UNIFAC models with re-estimated parameters have provided satisfactory results.

ChemInform Abstract: Prediction of Different Thermodynamic Properties for Systems of Alcohols and Sulfate‐Based Anion Ionic Liquids Using Modified UNIFAC

AbstractReview: 13 refs.

Prediction of different thermodynamic properties for systems of alcohols and sulfate-based anion Ionic Liquids using modified UNIFAC

Activity coefficients at infinite dilution in the temperature range between 303.15K and 353.15K, vapor–liquid equilibria at 353.15K and excess enthalpies at 353.15K of binary systems containing the Ionic Liquids 1-ethyl-3-methyl-imidazolium ethylsulfate [EMIM]+[EtSO4]−, 1-ethyl-3-methyl-imidazolium methylsulfate [EMIM]+[MeSO4]− and 1-ethyl-3-methyl-imidazolium hydrogensulfate [EMIM]+[HSO4]− have been measured. The obtained experimental data are used together with literature data to fit modified UNIFAC interaction parameters between the sulfate anion and the main groups OH and CH3OH. The predictions are compared with the experimental values. Additionally an overview about the current status of the modified UNIFAC parameter matrix for Ionic Liquids is given.

Vapour–liquid equilibria of the system 1,1,1,2-tetrafluoroethane + monoethylene-glycol dimethylether from 283.15 to 353.15 K: New modified UNIFAC parameters

The vapour–liquid equilibria ( p, T, x) of a 1,1,1,2-tetrafluoroethane + ethylene-glycol dimethylether mixture was measured using the static method in the temperature range (283.15–353.15) K in steps of 10 K. The vapour–liquid equilibrium data were correlated by the temperature-dependent five-parameter non-random two-liquid (NRTL) equation. The data obtained in this experiment together with our previous experimental data for the binary system 1,1,1,2-tetrafluoroethane + triethylene-glycol dimethylether were used to calculate the UNIFAC interaction parameters for the CF 3 and CH 2F groups with the CH 3, CH 2, CH 3O and CH 2O groups. The resulting interaction parameters were used to predict the vapour pressures of the various mixtures studied in the literature.

Thermodynamic property calculations with the universal mixing rule for EoS/ GE models: Results with the Peng–Robinson EoS and a UNIFAC model

The universal mixing rule (UMR), which incorporates an activity coefficient model in a cubic equation of state (EoS), and is applicable to all type of system asymmetries up to solvent/polymer ones, has been recently developed in our laboratory [Voutsas et al., Ind. Eng. Chem. Res. 43 (2004) 6238]. The original UNIFAC model with temperature-independent interaction parameters was used in the original publication, which leads, however, to unsatisfactory VLE predictions at high temperatures and poor heats of mixing predictions. In this study the UMR is applied by coupling the translated and modified Peng–Robinson (t-mPR) EoS with an original UNIFAC-type model that utilizes linearly temperature-dependent interaction parameters, eliminating, thus, the aforementioned weaknesses. The performance of the resulting EoS/ G E model, referred to as UMR-PRU, utilizing the available UNIFAC interaction parameters, as well as some parameters developed here for gas involving pairs, is evaluated in the prediction and, when necessary, correlation/prediction, of various thermodynamic properties, i.e. VLE, LLE, VLLE, SGE and heats of mixing. The results indicate that the new model represents a unique, simple and reliable tool for thermodynamic property calculations for systems of various degrees of non-ideality and asymmetry, including polymer solutions.

Prediction of Solubility of Solid Organic Compounds in Solvents by UNIFAC

Predictions of solubility of nine different solid organic fine chemical compounds in water and organic solvents of relevance to industrial processing are examined. UNIFAC interaction parameters are taken from standard reference literature, extracted from liquid−vapor equilibria. For most systems, predicted solubilities deviate more than 15% from experimental values. Deviations are due to uncertainties in the estimation of the activity of the pure solid as well as to deficiencies in the estimation of activity coefficients in the solution. By comparison with results from ab initio quantum chemical calculations of the elecrostatic potential on the molecular surface of the solutes, it can be shown that a key assumption of the UNIFAC approach is not necessarily fulfilled. The properties of a functional group may depend significantly on the properties of the rest of the molecule.

A UNIFAC model for phase equilibrium calculations in aqueous and nonaqueous sugar solutions

A UNIFAC type model is proposed to describe and predict phase equilibria in aqueous and nonaqueous sugar solutions. One new main UNIFAC group, CHOH sugar, has been introduced to describe all monosaccharides. This main group contains three different subgroups, CH 2OH, CHOH axial and CHOH equatorial, which are introduced based on considerations of the actual saccharide ring forms in solution. UNIFAC interaction parameters between the new group and the CH 2; OH; H 2O; CH 2–O groups have been estimated from the solubility data of monosaccharides in water, alcohol and their binary solvent mixtures. Another UNIFAC main group, CH–O–CH, has been introduced to describe the disaccharide osidic bond. Interaction parameters between the new group and the CH 2; OH; H 2O; CH 2–O; CHOH sugar groups have been estimated too. The model gives very satisfactory correlation and prediction of solute activity properties (i.e. solubility and i-butanol/water partition coefficients of sugars are determined by the activity of the solute) as well as satisfactory prediction of solvent activity properties (i.e. bubble and freezing points are determined by the activity of the solvent). A comparison with the UNIFAC model developed recently by Peres and Macedo [Fluid Phase Equil. 139 (1997) 47–74], which is the only other predictive model applicable to nonaqueous sugar solutions, suggests that both models provide similar results for aqueous sugar solutions, but the proposed model is more suitable for the prediction of phase equilibrium of sugar solutions involving also nonaqueous solvents as well as in such two-phase systems.

A modified UNIFAC model for the calculation of thermodynamic properties of aqueous and non-aqueous solutions containing sugars

A UNIFAC based model is proposed to describe experimental thermodynamic properties of aqueous and non-aqueous solutions containing common sugars, e.g., d -glucose, d -fructose and sucrose. A new group ‘OHring’ is introduced due to proximity effects. New temperature-independent UNIFAC interaction parameters are estimated based on the binary data available for both d -glucose and d -fructose and only on the solubility data for sucrose. The UNIFAC model used in this work is able to accurately predict the water activity, boiling temperature and freezing point of aqueous sucrose solutions. However, the predictions of the osmotic coefficients for the sucrose/water system present relative deviations up to 9%. Satisfactory predictions of vapor-liquid and solid-liquid equilibrium data for ternary and quaternary mixtures of d-fructose, sucrose and water components are also obtained. This approach uses the symmetric convention for all the components, i.e. the pure fused sugar at solution pressure and temperature is its reference state. Therefore, it allows to carry out in a straightforward way, calculations of solid-liquid equilibria of sugars in mixed solvents. It is shown that the new UNIFAC model is able to qualitatively predict the ternary solubility data of d -glucose d -xylose, d -mannose and sucrose in mixed solvent mixtures of ethanol/water, methanol/water and ethanol/methanol. A comparison with a modified UNIQUAC—essentially correlative model—and a UNIFAC—correlative and predictive model—approaches available in the literature is also given: the performance of the model proposed in this work is in general inferior to that of the UNIQUAC model, however it gives always a better agreement with the experimental data when compared with another UNIFAC based model available in the literature.

Infinite Dilution Activity Coefficients Predicted from UNIFAC Model. New Experimental Data for the Solvolytic Reactions of 2-Chloro-2-methylpropane in Methanol/Ethanol, Methanol/2-Methoxyethanol, and Ethanol/2-Methoxyethanol

The UNIFAC group contribution method was used to calculate the infinite dilution activity coefficients (γ∞) of 2-chloro-2-methylpropane (t-BuCl) in the binary mixtures methanol/ethanol, methanol/2-methoxyethanol, and ethanol/2-methoxyethanol at 298.15 K. For each system, nine different compositions of the solvent mixtures were considered. The modified Flory-Huggins equation in the combinatorial term was used, as well as the group contribution parameters from the vapor-liquid equilibrium parameter table in the residual term, due to the nonavail-ability of specific γ∞ UNIFAC interaction parameters for the relevant groups. The γ∞ values were combined with a set of new and experimentally determined kinetic parameters of the solvolytic reactions of the same substrate in the same solvents to describe quantitatively the contributions of the initial state and the transition state to the solvent effect. By using this approach, the Gibbs energies of transfer of the reactants and the activated complex were obtained, which allows us to better understand the reaction mechanism and to influence reaction rates through a coherent selection of solvents.

Phase equilibria in binary systems containing N-monosubstituted amides and hydrocarbons

The binary vapour-liquid equilibrium of seven systems of ε-caprolactam + octane, + decane, + dodecane, octane, + decane, + dodecane, of N-methylacetamide + octane, of N-ethylacetamide of N-methylpropionamide + octane and of N-methylpropionamid + ε-caprolactam was measured in the temperature range from 363 to 423 K and in the low pressure region. A static equilibrium apparatus for the measurements was constructed. In the system N-methylpropionamide + octane measurements of liquid-liquid equilibrium were carried out in the temperature range from 310 K up to the critical solution temperature. The experimental results were correlated applying activity coefficients models such as NRTL. The data obtained from our measurements were used to estimate UNIFAC interaction parameters for the groups CH 2 CONHCH 2 , CH 2 C 5H 10CONH and CONHCH 2 C 5H 10CONH .

The vapour‐liquid equilibria of several binary systems of fluorocarbons and hydrocarbons, part II

AbstractThe vapour‐liquid equilibria of the binary systems perfluoromethylcyclohexane‐pentafluorobenzene, benzene‐pentafluorobenzene, benzene‐methylperfluorobutanoate and perfluoromethylcyclohexane‐methylperfluorobutanoate have been measured at 333.07 K and 343.12 K using a dynamic circulation still of the Sieg‐Röck type. The thermodynamic consistency of the measurements was tested by two different methods. New UNIFAC interaction parameters [1] were calculated for the following groups: ACH‐ACF, ACF‐CF2, CF2‐COO, ACCH2‐ACF, ACH‐CF2. The abbreviations stand for the following increments: ACH = aromatic CH group, ACF = aromatic CF group, CF2 = aliphatic CF2 group, COO = ester group and ACCH2 = side chain CH group.

VLE data and UNIFAC-parameters of binary mixtures with methylisocyanate

Vapor pressures of binary mixtures of methylisocyanate with hexane and benzene in the temperature range of −5°C to 200°C have been measured. There was no indication of thermal instability or polymerisation within that range. Based on the experimental VLB data, UNIFAC interaction parameters have been correlated for the new main group of isocyanate. The parameters allow good prediction of VLE from different binary systems composed of molecules with the same functional groups. In addition, literature data of binary mixtures were taken to calculate interaction parameters of chlorine-substituted aliphatic hydrocarbon-groups with the isocyanate group.

Infinite-dilution activity coefficients by comparative ebulliometry. Binary systems containing chloroform and diethylamine

Coutinho, J.P., and Macedo, E.A., 1994. Infinite-dilution activity coefficients by comparative ebulliometry. Binary systems containing chloroform and diethylamine. Fluid Phase Equilibria, 95: 149-162. New data were determined by comparative ebulliometry for infinite-dilution activity coefficients of the following systems: chloroform/methanol, chloroform/acetonitrile, chloroform/ tetrahydrofuran, chloroform/methyl acetate, chloroform/diethylamine and diethylamine/ n-hexane, at both the upper and lower concentration limits and at two different temperatures. The measured infinite-dilution activity coefficients were compared with the predicted values obtained with the MOSCED (Modified Separation of Cohesive Energy Density) and UNIFAC models. For the UNIFAC model the predictions were made using group-interactions from the VLE parameter Tables. The differences between experimental and calculated infinite-dilution activity coefficients show that both methods predict fairly well the majority of the experimental data. The data obtained were used to estimate UNIFAC interaction parameters for the groups CCl3/CH3OH, CCl3/CCN, CCl3/CH2O, CCl3/CCOO, CCl3/CNH and CH2/CNH, which are not available in the infinite-dilution specific Parameter Table. These parameters were used to predict VLE data for systems containing the same groups, and a comparison between experimental and predicted values is presented.