Extraction of hemicellulose from hardwood chips prior to pulping is a proposed method for producing ethanol and acetic acid. The hemicellulose is currently dissolved during pulping and burned to generate energy. Because hemicellulose has a low heating value, more revenue would be generated by producing commodity chemicals. In an integrated bio-refinery, hemicellulose could provide the sugars for fermentation into ethanol, and also generate acetic acid.

Hemicellulose was extracted from hardwood chips using green liquor, a solution of NaOH, Na₂CO3, and Na₂S produced as an intermediate in the pulping process. This treatment was done in a 10L rocking digester at 160°C for 110 minutes. Extracts mainly contain xylo-oligosaccharides and acetic acid. Following hydrolysis and neutralization, approximately 5g/L of total monosugars were present. Fermenting such low sugar concentrations into ethanol is economically unfavorable due to the high energy cost of distillation; therefore the hemicellulose extracts were concentrated. Extracts were removed from the evaporator at 3, 6 and 10% solids. Higher sugar content was thus achieved, but also higher concentrations of inhibitors such as acetic acid and sodium salts.

Fermentation experiments were conducted with E. coli K011. The initial 3% solids extract generated 1.2g/L of ethanol in the presence of 10g/L acetic acid. The 6% solids extract was also fermentable, producing 2.1g/L ethanol in the presence of 15g/L acetic acid. The 10% solids extract wasn’t initially fermentable due to the high concentration of inhibitors, including 25g/L acetic acid. Strain adaptation is underway to select for organisms capable of withstanding this level of toxins.