FLUX DECLINE ANALYSIS IN ULTRAFILTRATION OF KRAFT BLACK LIQUOR

Ultrafiltration of black liquor was carried out using a cellulose acetate membrane of 5000 MWCO, in a stirred batch cell modified to work on a continuous mode. Poly(ethylene glycol)-6000, a standard macromolecule, was used to compare the results. The effect of operating variables on limiting flux phenomena was studied. Steady-state calculations, the basis for the concentration-polarization model, were used to study the flux decline during ultrafiltration. The membrane parameters, viz. reflection coefficient and solute permeability, were determined to characterize the membrane. A correlation was developed to relate polarized layer resistance (R(p)) with concentration-polarization modulus, osmotic to applied pressure ratio and Reynolds number. The mass transfer coefficient, k, was determined at the average concentration prevailing over the boundary layer and an iterative technique was adopted to obtain the membrane surface concentration.