(229e) Thermodynamic Modeling of Kraft Black Liquor Solutions with the Electrolyte NRTL Model

The kraft pulping process is the most widely used paper pulping process across the world due to its ability to recover the necessary chemicals for wood digestion. One of the most important parts of the chemical recovery process involves the evaporation and combustion of black liquor. Black liquor solutions are comprised of a complex mixture of both organic and inorganic compounds, and due to this complexity, modeling the boiling point elevation with a rigorous thermodynamic framework is often difficult to achieve. This work focuses on using the Electrolyte Nonrandom Two-Liquid (eNRTL) model to correlate vapor-liquid equilibrium (VLE) and solid-liquid equilibrium (SLE) data to predict the boiling point elevation of inorganic and organic sodium salts and black liquor solutions. The eNRTL model connects the nonideality of the solutions with the composition by using two binary interaction parameters for each electrolyte-electrolyte and molecule-electrolyte pair in the system. Each parameter contains up to three temperature-dependent coefficients which are regressed from experimental data such as vapor pressure, osmotic and activity coefficients, liquid enthalpy, heat capacity, and solubility.