(262at) A Comprehensive Molecular Thermodynamic Model for Major Electrolytes in High Salinity Produced Water

Managing produced water in the rapidly developing shale gas industry is a major challenge for protecting the environment [1]. Desalination for reuse of high salinity produced water depends on novel material and process innovations. We present recent advances in the development of a comprehensive thermodynamic model aimed to support heat and mass balance calculations and process simulation of desalination processes with produced water. The major ions of concern for produced water management include Na⁺, K⁺, Mg²⁺, Ca²⁺, Ba²⁺, Sr²⁺, Cl^â??, HCO₃^â?? and SO₄^2â?? ions. Based on the electrolyte Non-Random Two Liquid theory (eNRTL) for electrolyte solutions [2], the concentration dependency of the solution nonideality is accounted for with two binary interaction parameters for each of the waterâ??electrolyte interaction pairs and the electrolyteâ??electrolyte interaction pairs. The temperature dependency of the binary interaction parameters is accounted for with a Gibbs-Helmholtz type expression with three temperature coefficients representing excess Gibbs energy, excess enthalpy, and excess heat capacity contributions. With the binary parameters regressed from thermodynamic data of aqueous single electrolyte binary systems and aqueous two electrolyte ternary systems, the model provides accurate representations and reliable predictions for various thermodynamic properties of quaternary and quinary systems examined thus far for the aqueous Na⁺â??K⁺â??Mg²⁺â??Ca²⁺â??Cl^â??â??SO₄^2â?? hexary system with temperatures from 273.15 K to 473.15 K and concentrations up to salt saturation. The model is being extended to cover Ba²⁺, Sr²⁺ and HCO₃^â?? ions and it should become an indispensable scientific tool in the development of novel desalination processes for high salinity produced water in oil and gas productions.

References

[1] D.L. Shaffer, L.H. Arias Chavez, M. Ben-Sasson, S. R.-V. Castrillón, N.Y. Yip, M. Elimelech, Environ. Sci. Technol. 2013, 47:9569-9583.

[2] Y. Song, C.-C. Chen, â??Symmetric Electrolyte Nonrandom Two-Liquid Activity Coefficient Model,â? Ind. Eng. Chem. Res. 2009, 48:7788-7797.