(192m) Separation and Purification of Lignocellulosic Wood Hydrolyzates by Polymer Flocculation and Scale up Studies

Lignocellulosic hydrolyzates produced by hydrothermal treatment of wood chips contain hemicellulose sugars, acetic acid and significant quantities of colloidal material. The purification of the hydrolyzate stream and the separation of fermentable sugars from it thus constitute an important step in biorefinery processes. Raw lignocellulosic hydrolyzates produced by acid or water treatment contain hemicelluloses (primarily xylooligomers, xylose and xylan), acetic acid and significant quantities of colloidal material. The particulates are composed mostly of lignin and its derivatives which were ranging in between the nanometers to micrometers particle sizes and are anionic in nature.

Here, we report the separation of hot water based hydrolyzates of sugar maple by polymer induced flocculation. In the polymer induced flocculation, we investigated the dynamics of flocculation of wood extracts with particular emphasis on the action of four different flocculating agents – Alum, PEI, pDADMAC and PEO. 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 2 and 8.0. The optimal concentrations of flocculating agents for sedimentation were found for different pH conditions. Flocculation and clarification with PEO were demonstrated on large pilot scale batches of 1000 kg of extracts. Further the flocculated extract was filtered and the filtrate showed a 99.5% reduction in turbidity, from 12000 NTUs in the raw extract to 50 NTUs in the filtrate.