An improved model for the calculation of CO 2 solubility in aqueous solutions containing Na +, K +, Ca 2+, Mg 2+, Cl −, and SO 42−

Abstract

An improved model is presented for the calculation of the solubility of carbon dioxide in aqueous solutions containing Na +, K +, Ca 2+, Mg 2+, Cl −, and SO 4 2− in a wide temperature–pressure–ionic strength range (from 273 to 533 K, from 0 to 2000 bar, and from 0 to 4.5 molality of salts) with experimental accuracy. The improvements over the previous model [Duan, Z. and Sun, R., 2003. An improved model calculating CO 2 solubility in pure water and aqueous NaCl solutions from 273 to 533K and from 0 to 2000 bar. Chemical Geology, 193: 257–271] include: (1) By developing a non-iterative equation to replace the original equation of state in the calculation of CO 2 fugacity coefficients, the new model is at least twenty times computationally faster and can be easily adapted to numerical reaction-flow simulator for such applications as CO 2 sequestration and (2) By fitting to the new solubility data, the new model improved the accuracy below 288 K from 6% to about 3% of uncertainty but still retains the high accuracy of the original model above 288 K. We comprehensively evaluate all experimental CO 2 solubility data. Compared with these data, this model not only reproduces all the reliable data used for the parameterization but also predicts the data that were not used in the parameterization. In order to facilitate the application to CO 2 sequestration, we also predicted CO 2 solubility in seawater at two-phase coexistence (vapor–liquid or liquid–liquid) and at three-phase coexistence (CO 2 hydrate–liquid water–vapor CO 2 [or liquid CO 2]). The improved model is programmed and can be downloaded from the website http://www.geochem-model.org/programs.htm.