(229d) Modeling of Aqueous Electrolyte Solutions – From Simple Ions to Polyelectrolytes –

Electrolyte solutions play an important role in biotechnology and chemical engineering. To describe systems containing water and ions, an Equation of State (the PC-SAFT EoS) has been combined with a Coulomb approach (Debye-Hückel) [1] and applied to numerous aqueous inorganic salt solutions [2]. ePC-SAFT was found to be an excellent model for salt solutions containing of nearly spherical ions. In order to model systems with extensive ion-pair formation (e.g. solutions containing cadmium halides), a chemical-reaction approach accounting for dissociation/association equilibrium within ePC-SAFT [1] led to a successful description of experimental data [3].

Based on the results of those inorganic-electrolyte systems, phase equilibria of more complex, polyelectrolyte solutions are investigated. As the Debye-Hückel contribution alone is not able to describe the electrostatic interactions of polyelectrolyte chains, the ePC-SAFT model had to be extended to model polyelectrolyte systems. For that purpose, the reference term ?hard-chain? was replaced by a ?charged-hard-chain? contribution (as proposed in [4]). Moreover, the counter-ion condensation present in polyelectrolyte solutions was explicitly accounted for.

This approach is successfully applied to model the phase behavior of aqueous poly(acrylic acid) solutions as function of the degree of neutralization (different amount of charged monomer units in the polymer backbone). Moreover, the influence of added salt on the phase behavior of polyelectrolyte solutions can be described in good agreement with experimental data.

References

[1] L.F. Cameretti, G. Sadowski, J.M. Mollerup, Ind. Eng. Chem. Res. 44 (2005) 3355-3362; ibid., 8944.

[2] C. Held, L.F. Cameretti, G. Sadowski, Fluid Phase Equlilib. 270 (2008) 87-96.

[3] C. Held, G. Sadowski, Fluid Phase Equlilib. (2009), 279 (2009) 141?148.

[4] J. Jiang, J. Feng, H. Liu, Y. Hu, J. Chem. Phys. 124 (2006) 144908(1-6).