An association UNIFAC model for aqueous and alcohol solutions of sugars

In this work, a modified UNIFAC model [1] that explicitly takes into account association effects is applied to mixtures containing common sugars, alcohols and water. Following the same strategy adopted before [2], four residual groups were defined to represent the sugars family: the pyranose ring (PYR), the furanose ring (FUR), the osidic bond (-O-) and the hydroxyl ring group (OH ring) [2]. For the association term, a general two sites OH associating group is used to represent association effects in these solutions, allowing a straightforward extension to multicomponent mixtures. Correlation of both solvent activity properties (water activities, vapour pressures, boiling and freezing points of aqueous D-glucose and D-fructose solutions) and sugars (D-fructose, D-glucose and sucrose) solubility in water, ethanol and methanol give very good results. Satisfactory predictions are obtained for vapour-liquid equilibrium and solid-liquid equilibrium of ternary and quaternary mixtures of sugars in mixed solvents

Solubility of salts in mixed solvents: experimental data and modeling

Phase equilibria in electrolyte systems has been receiving much attention from different research groups. Much of the experimental and theoretical work has been carried out on aqueous systems or in the study of salt effect in vapor-liquid equilibria. However, the design and simulation of unit operations such as, The recently developed extractive crystallization, requires experimental solubility data as well as The ability to correlate and predict electrolyte activity coefficients in mixed-solvents. Moreover, this kind of data can give many relevant indications about ion-solvent interactions and allows the calculation of other thermodynamic properties. Thus, in this work, the solubilities of the salts NaBr and KBr were measured, by an analytical isothermal method, in water, methanol, ethanol and their binary mixed-solvent mixtures, water/methanol, water/ethanol and methanol/ethanol, at temperatures from ambient up to 80 O( The obtained data, were used, together with osmotic and mean ionic molal activity coefficients data available in the literature, to test the capabilities of UNIQUAC-based models for the representation of the thermodynamics properties of these systems. Results are shown and comparisons with other approaches are given

The effect of the alcohol content on the solubility of amino acids in aqueous solutions

The solubility of me most simple a-amino acid, glycine, was measured in the temperature range between 25 and 60°C for the aqueous system of ethanol and at 25 °C for the aqueous system 0V 1-propanol. Theoretical work was essentially focused on the application of the excess solubility approach with conventional thermodynamic models such as the Margules and Wilson equations. The simple three suffix Margules model, with only one parameter to be estimated, gave the best results, with an average absolute deviation of 3.8%

Solubility of amino acids in mixed solvent systems

The solubilities of L-serine, L-threonine and L-isoleucine in the aqueous systems of ethanol, 1-propanol and 2-propanol were measured in the temperature range between 298.15 K and 333.15 K by means of a gravimetric method and a spectrophotometric technique based on a ninhydrin reaction. The solubility data from this work and from literature were used to explore the potentialities of the application of the excess solubility approach with the NRTL [1], modified NRTL [2], modified UNIQUAC [3, 4] equations and the model presented by Gude et al. (1996) [5, 6]. These four models give a global average relative deviation of 12.2 %, 12.0 %, 15.1 %, and 16.2 % for correlation and 16.3 %, 14.6 %, 27.3 %, and 22.0 % for prediction, respectively

Electrolyte effect on the solubility of amino acids in aqueous solutions

The precipitation and crystallization of biomolecules have been widely used for their separation and concentration. The presence of electrolytes in solution may affect significantly the solubilities of biochemicals, which has been used for salt-induced separation of proteins. Although amino acids are among the simplest biochemicals, they have many similarities with more complex biochemicals and are the building block of proteins. So, the study of the electrolyte effect In the solubility of amino acids in water is a good starting point for further developments. Although some studies have been published concerning the measurement and thermodynamic properties modeling of aqueous solutions of amino acids with electrolytes, the information available is very scarce. Therefore, in this work, the solubility of Glycine and OL-Alanine were measured in the temperature range between 25 and 60 °C for aqueous systems of KCI, Na2SO4 and (NH4)2S04, salts most often used in industrial separation processes. A comparison is given with values recently published in the literatures. It was possible to find out big discrepancies, and for the solubility of OL-Alanine in aqueous solutions an inverse dependence with the concentration of the KCI salt was obtained, The new experimental data were used together with information already available concerning the activity coefficients and solubilities, to explore the capabilities of a modified Wilson model, recently developed in our group, for the thermodynamic description of these complex systems. Despite the difficulties that arose for the description of these highly non-ideal systems, the results shown are satisfactory for the correlation of the solubilities

Solubility of amino acids: a group-contribution model involving phase and chemical equilibria

A new model is proposed to represent the solubility behavior of 14 amino acids and 5 small peptides in water. The UNIFAC model is combined with a Debye-Huckel term to describe the activity coefficients of the species present in the biomolecule/water system. New groups have been defined according to the group-contribution concept, and chemical equilibrium is taken into account simultaneously with the physical equilibrium. To estimate the new interaction parameters, molal activity coefficient data from the literature were used. These parameters, in addition to solubility data, were the basis for the correlation of the solubility product of the amino acids. Using this approach, satisfactory results were obtained in the representation and prediction of the solubilities of amino acids in aqueous solutions at different conditions of temperature and pH

Pure solvent solubility of some pharmaceutical molecules

During the search for novel or improved therapies, new drugs are proposed. Solubility of drug-candidates is important both for drug production and its therapeutic use. Many separation processes in the pharmaceutical industry are based on the solubilities in different solvents. Solvation plays an important role in the organism in each stage of drug transport and delivery. Properties like lipophilicity, hydrophilicity, the ability to establish hydrogen bonds and other interactions of the molecules with the surrounding media play an important role in the solvation process. Although some predictive thermodynamic tools can be used to determine drug solubility, the availability of experimental data is still fundamental for an appropriate model development and evaluation. In this work, solubilities of some drugs, such as paracetamol, budesonide, furosemide and allopurinol, were measured in the temperature range between 25 °C and 42 °C, in pure solvents (water, ethanol, acetone, n-hexane, ethyl acetate and carbon tetrachloride). The Non-random Two-Liquid Segment Activity Coefficient (NRTL-SAC) equation (Chen and Song 2004), one of the most successful models for the representation of drug solubility, was used to model the data. The obtained agreement is very satisfactory (root mean square deviation of 0.051)

A new modified Wilson equation for the calculation of vapor–liquid equilibrium of aqueous polymer solutions

A local composition model based on the lattice theory and two-fluid theory, considering the excess heat capacity, which is a modified Wilson equation, is developed for the excess Gibbs energy of aqueous polymer solutions. The model represents a synergistic combination of the excess entropy for mixing molecules of different sizes and the temperature dependent residual contribution, which combines the attractive interactions between solvent molecules and the segments with the contribution of the excess heat capacity. The results of the extrapolation with respect to molecular weight of phase equilibrium in aqueous polymer solutions with this model are very satisfactory, with only two adjustable parameters.Fundação para a Ciência e a Tecnologia (FCT) – postdoctoral fellowship, Programa Operacional “Ciência, Tecnologia, Inovação” POCTI/1999/EQU/33185