Polyelectrolyte adsorption on packed beds of pulp fiber

Industrial applications such as pulp washing and displacement bleaching of pulp are using the flow of reactants and products through a packed bed of fibers, because this is the most efficient contact process in terms of energy requirements.;The adsorption phenomenon can be quantified using a packed bed of pulp fibers, and measuring the exit concentration of polymer (breakthrough curve) for various polymer inlet concentrations. The concentration of the polymer at the exit can be monitored on-line by UV-Vis spectroscopy, and by polyelectrolyte titration. The kinetics of polymer adsorption can be evaluated under different solution conditions (pH, concentration). The amounts of adsorbed polyelectrolyte can be calculated from differences between the breakthrough curves of an inert tracer and those of the polymers.;The transport and adsorption behaviour of two cationic polyelectrolytes were studied in columns of packed beds of pulp fibers: polyethylenimine (PEI), and poly-trimethyl aminoethyl chloride acrylate (p-TMAEAC).;The results show that polyelectrolyte adsorption on fibers in packed beds is similar to that on suspended fibers subjected to flow. The kinetics of adsorption of PEI on pulp fibers is faster at pH 10 than at pH 6, while the adsorbed amount is about 4 times as large. This is ascribed to the porosity of the fibers, the polydispersity of PEI and the pH-dependence of the size of PEI molecules.