Thermodynamic model and data on the partitioning of nonprocess elements between kraft fibres and water in a pulp suspension

The partitioning of non-process elements in kraft fibre suspensions has been modeled using the Donnan equilibrium framework with activity coefficients introduced to account for the non-ideal nature of the electrolyte solutions. Activity coefficients have been obtained using Pitzer's model. Total anionic charge, dissociation constants, and mass of water within the fibres are used as input to the model and were determined by independent experiments. Partitioning data were also obtained for a post brown stock washer kraft pulp, from an interior BC mill, for the metal ions of Na⁺, Ca⁺² , and Mg⁺² over the pH range 2-13. Such data above a pH of 11 were not previously available in the literature. Two models were used to obtain the charge on the fibres at any pH; a two dissociation constant model (corresponding roughly to the carboxyl and phenolic hydroxyl) and an "exact" charge model. Results indicate that below a pH of 7 both models do a good job of representing the experimental data obtained in this work and data available in the literature. Above a pH of 7 the two dissociation constant model under-predicts the partitioning data while the exact charge model follows the experimental data over the entire pH range. This indicates Donnan equilibrium is an excellent framework for non-process element partitioning prediction as long as the fibre charge is known accurately. Experiments with elevated Mg and Ca contents were also performed, resulting in precipitation within the fibres at pHs above 10. The model does not account for precipitation phenomena that may occur when concentrations of Ca and Mg are increased above those naturally occurring in post brown stock pulps.Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat

Interaction parameter estimation in cubic equations of state using binary phase equilibrium and critical point data

Δημοσίευση σε επιστημονικό περιοδικόSummarization: Two methods for the estimation of the interaction parameters in cubic equations of state by using the entire binary phase equilibrium database and the critical point locus, respectively, are presented. The solution of the optimization problem is accomplished in both methods by a Gauss−Newton−Marquardt minimization algorithm. The methods are computationally efficient and robust because they are based on implicit objective functions and hence avoid phase equilibrium or critical point calculations during the parameter optimization. The use of the entire phase equilibrium database and the critical locus can be a stringent test of the correlational ability of the equation of state. In the illustrative examples, the results were obtained by using the Peng−Robinson and the Trebble−Bishnoi equations of state with quadratic mixing rules and temperature-independent interaction parameters.Presented on: Industrial and engineering chemistr