Modelling of the equilibrium properties of the system H3PO4-H2O: representation of VLE and liquid phase composition

In the present work we have applied Fitter's model for the representation o f equilibrium properties of the system H3PO4-H2O at 25 degreesC. The databa se used consist mainly of experimental values of osmotic coefficients and o f speciation data over the apparent molality range 0-9 mol kg(-1) of H3PO4 The model considers four solutes: H3PO4, H+, H2PO4- and H5P2O8-. Seven adju stable parameters are used and several assumptions which allows to lower th e number of adjustable interaction parameters. The results from the model c ompare well with experimental data. The results are also compared with prev ious results from models used to describe the equilibrium properties of the system H3PO4-H2O. It is shown that, contrary to our approach, these older models do not represent the speciation of the system accurately. (C) 2000 E lsevier Science B.V. All rights reserved.