LIMITING FLUX PHENOMENA IN ULTRAFILTRATION OF KRAFT BLACK LIQUOR

Limiting flux phenomena were studied in the ultrafiltration of black liquor. The experiments were carried out using an asymmetric membrane, in a stirred batch cell modified to work on a continuous mode. Polyethylene glycol 6000, a standard macromolecule, was used to compare the results. The effects of operating variables (viz., differential pressure, bulk concentration and stirrer speed) on permeate flux and observed rejection for both the solutes were studied and analysed. The osmotic pressure model was used to analyse the experimental results. Adsorptive resistance was taken into account quantitatively. The polarized layer resistance was found to be a function of membrane surface concentration, applied differential pressure and flow pattern. To relate these, the following correlation was considered and tested with the experimental results: [GRAPHICS] where a, b, c and d are constants.