Parameter estimation and performance study during ultrafiltration of Kraft black liquor

Ultrafiltration of black liquor was carried out using an asymmetric membrane in a stirred batch cell, which was modified to work on a continuous mode. Different solute–membrane parameters like solute permeability (Pm) and reflection coefficient (σ) were estimated, based on the theories derived from irreversible thermodynamics. Kedem–Katchalsky (KK) and Spiegler–Kedem (SK) models, from irreversible thermodynamics, were utilized for the parameter estimation. The Pm and σ, so calculated from the above two models, were compared and their variations with other process variable like bulk concentration, pressure difference and stirrer speed were established. Finally, a three-parameter simulation model was developed based on film theory, osmotic pressure model and KK/SK models, which were capable to predict permeate flux and rejection at any operating conditions based on Pm, σ and Rm. The results of simulation studies were compared with experimental results, using cellulose acetate membrane of 5000 MWCO. The simulation results (in terms of flux and rejection) were found to be in good agreement with experimental data; though, the predictions based on SK model were found to be better compared to KK model and the absolute average deviations were 6.3% and 8.4% for the prediction of flux and rejection using SK and KK models, respectively.