(315d) Flocculation Dynamics of Lignocellulosic Hydrolyzates and Floc Characteristics

Lignocellulosic materials such as wood present as renewable and sustainable resources for the production of fuels and plastics. In one pathway to the production of liquid fuels and plastics fermentable sugars are extracted by treatment with hot water after which the hydrolyzates are purified and detoxified. Purification of such liquors constitutes an important step in biorefinery processes. Raw lignocellulosic hydrolyzates produced by acid or water treatment contain significant quantities of colloidal material. The particulates are composed mostly of lignin and its derivatives and are anionic in nature. These colloidal particulates not only inhibit the fermentation activities of microorganisms but also foul any filtration membranes used for separation and purification of extracts. Flocculation of the colloidal particles can make separations easier and reduce the fouling tendencies of membranes.

In this paper we investigated the dynamics of flocculation of wood extracts with particular emphasis on the action of three different flocculating agents ? alum, PEI and pDADMAC. The variation in zeta potential measurements showed that the colloidal particles in wood extracts are charge neutralized initially and particles were found to be increased in size after charge neutralization. The rate of sedimentation of aggregated particles was measured by turbidity of supernatants of the dispersed solution as a function of time. The optimal concentrations of flocculating agents to flocculate the colloidal particles were measured by both charge neutralization and rate of sedimentation. The pH sensitivity of flocculating agents was tested by varying the pH of wood extract between 3.5 and 8.0. The optimal concentrations of flocculating agents for sedimentation were found for different pH conditions.