Mathematical Modeling of the Filtration of Lignocellulosic Hydrolyzates

Hot water extracts (HWE) of wood are a complex mixture of various compounds. Depending upon the time of extraction, the size of the colloidal particles decreases from 500 nm to 250 nm.  Their surface potential also decreases with increased extraction levels (Duarte et al., 2010).  Separation of lignin from lignocellulosic hydrolyzates can be achieved by membrane separation. Dead end filtration of the hydrolyzates has shown the formation of a cake layer consisting of the colloidal particulates in the suspensions.  In this work, we present mathematical models of fouling behavior considering the combined actions of membrane pore constriction, pore blockage and cake formation under constant pressure conditions. Parameters representing each of these mechanisms were obtained by fitting to experimental filtrate flux data. 

Experimental flux data were obtained for dead end filtrations over ranges of pressure, temperature, concentration, extraction time and molecular weight cutoff of filters.  The models provide a clear picture of the transition from the pore blockage to cake filtration regimes. The results provide important insights into the underlying mechanisms of HWE fouling during microfiltration.