(330c) Purification of Lignocellulosic Hydrolyzates Using Flocculants to Separate Lignin and their impact on Fermentability of Sugars

Hydrolyzates produced by pretreatment of lignocellulosic materials contain phenolic compounds, organic acids and aldehydes such as furfural in colloidal and dissolved form. Since these compounds can be potent inhibitors for fermentation, they need to be separated and isolated ahead of such biological treatments. We found that the application of a strongly binding non-ionic polymer, polyethylene oxide causes flocculation and rapid separation of lignin from the hydrolyzates, while preserving the carbohydrates in solution to a large extent. The effect of flocculation is measured by the reduction in turbidity and enhancement of the suspension settling velocity. The maximum flocculation was found to depend on the dosage of the polymer and its MW, but was independent of the pH of the hydrolyzates (from 2 through 9).  PEO dosages were between 20 to 50 ppm at the maximum flocculation and reduction in suspension turbidity. The suspension temperature plays an important role, with temperatures below 21.5 C showing no flocculation.

The hemicellulose fraction in the supernatants was close to the raw extract showing that flocculation does not remove significant amount of fermentable sugars. Hence such pretreatment clarification is not likely to affect downstream bioproduct yields. Flocculation and clarification with PEO were also demonstrated on large pilot scale batches of 1000 kg of extracts. 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. The impact of flocculation on solid liquid separations was quantified and flocculation was optimized with respect to dosage, suspension concentration, temperature and pH.