(222c) Membrane Extraction for Removal of Acetic Acid and Other Compounds From Dilute Acid Pretreated Lignocellulosic Hydrolysates

Grzenia, D., Colorado State University
Schell, D., National Renewable Energy Laboratory

Separations account for 60-80% of the processing costs of most mature chemical processes. Membrane based separations offer several advantages over conventional technology such as lower energy costs and easy scale up. We have explored the use of membrane extraction for removal of acetic acid, sulfuric acid, furfural, HMF and other toxic compounds from dilute acid pretreated biomass hydrolysates. The primary objective however was to remove and recover acetic acid, a potent inhibitor of fermentative microorganisms.

Experiments were conducted using the liquor fraction of a dilute sulfuric acid pretreated corn stover slurry. Acetic acid, in its protonated form, is extracted into an organic phase consisting of octanol or oleyl alcohol and Alamine 336, a tertiary amine, containing aliphatic chains of 8-10 carbon atoms. Acetic acid removal was most efficient at pH values below 4.8, the pKa of acetic acid. Further, co-extraction of sulfuric acid leads to an increase in hydrolysate pH. The effect of aqueous and organic phase flow rates and temperature on the rate of extraction of acetic acid and sulfuric acid was investigated. Changes in extraction rates may be explained by considering the structure of the acid-Alamine complexes formed in the organic phase. Extraction of furfural, HMF and other toxic compounds was also quantified. Hydrolysates treated by membrane extraction and conventional conditioning technologies were fermented using a glucose-xylose fermenting bacteria to determine the viability of membrane technology to detoxify biomass hydrolysates. Membrane extraction could be a viable hydrolysate detoxification technology because the other conditioning technologies do not remove acetic acid.