(400e) Depth Filtration of Lignin and Protein Suspensions in Fibrous Media with Stimulus Responsive Surfaces

Complex suspensions such as lignocellulosic hydrolysate or yeast lysate are commonly clarified through depth filtration. Depth filters remove particles through capture mechanisms based on diffusion, interception, impaction and electrostatic interaction. Cellulose is often the primary component for fibrous depth filter media. For fibrous filters, fiber diameter, porosity, and bed depth correspond to overall removal efficiency. Filtration performance is evaluated by the trade-off between removal efficiency and pressure drop. Therefore, it is imperative to develop cost effective methods to adjust the properties of depth filter media to enhance the processability of complex suspensions.

Poly(N-isopropylacrylamide) (PNIPAM), a stimuli-responsive polymer, reversibly shrinks or swells in response to changes in temperature. PNIPAM can be immobilized onto cellulose fiber surfaces through grafting. Therefore: to develop stimuli responsive depth filters, PNIPAM is grafted onto cellulosic fibers, which are then formed into depth filter pads. The physical properties of the filters are tuned by the extent of PNIPAM grafting on the cellulose surface and through operating above and below the lower critical solubility temperature (LCST) of PNIPAM. The fibers swell or contract, altering the fiber diameter and porosity of the filter media. Optimization yields depth filters with high loading capacity and low pressure drop.

The LCST of the cellulose-g-PNIPAM fibers is evaluated. The surface structure of the developed filters above and below the LCST is examined. Lignocellulosic hydrolysate and yeast lysate are characterized through turbidity, particle size and zeta potential measurements. Filter characteristics such as permeability, porosity and specific surface area are derived from gravity drainage runs. The affinity of lignin and proteins to the filter media is analyzed through the development of adsorption isotherms at different temperatures, pH and ionic strengths. Pressure drop and removal efficiency are evaluated for constant flow operation of lignocellulosic hydrolysate and yeast lysate.

The experimental data on overall removal efficiency is compared to predictions made by analytical models. Parameters for single fiber efficiency are fitted to the experimental data to determine the influence of different capture mechanisms. Stimuli-responsive depth filters represent an advancement in filtration technology for the clarification of complex lignocellulosic and protein suspensions.