THERMODYNAMIC REPRESENTATION OF THE SOLUBILITY FOR POTASSIUM DIHYDROGEN PHOSPHATE (KDP) PLUS WATER PLUS ALCOHOLS SYSTEMS

The solubility of potassium dihydrogen phosphate (KDP) in water and in aqueous solutions of ethanol, 1-propanol and 2-propanol was experimen tally determined by means of a visual polythermal method. Solubility m easurements were performed in the temperature range of 293 to 333 K, f or an alcohol content varying between 0 and 0.30 kg/kg water for ethan ol and 2-propanol, and from 0 to 0.15 kg/kg water for 1-propanol. The phase equilibria condition and the mean ionic activity coefficients ca lculated by the Chen model allowed to describe the ternary solubilitie s. The mean ionic activity coefficients were calculated with nine bina ry parameters: six parameters for the binaries KDP/water and water/alc ohol (taken from literature), and three parameters for the binary KDP/ alcohol, regressed in this work. The binary interaction energy paramet ers were defined as tau(ij) = Delta g(ij)/RT, where Delta g(ij) = f(T) . The optimized parameters were two Delta g(ij) energy parameters and the nonrandomness factor alpha(ij) for the KDP/alcohol binaries. Terna ry solubility was described with a standard deviation of 0.0020 kg sal t/kg water and less than 0.9 degrees C, respectively in terms of conce ntration and temperature, for a 95% confidence interval. The sensitivi ty analysis of the model allows to conclude that the uncertainty on th e activity coefficients values obtained by the Chen model is mainly du e to the nonrandomness alpha(ij) and to the temperature. (C) 1997 Else vier Science B.V.