Vapor-phase diethyl oxalate pretreatment of wood chips: Part 2. Release of hemicellulosic carbohydrates

Abstract Wood chips of pine, spruce, aspen, and maple were treated at 135–140°C with diethyl oxalate (DEO) and analyzed for extractable and residual carbohydrates. Under these conditions, DEO hydrolyzes to ethanol and oxalic acid (OA). The amount and identity of carbohydrates released from the chips were species-dependent. For all wood species, increasing the amount of chemical, time, or temperature resulted in an increment in carbohydrates released. Approximately 50% (by wt) of extracted carbohydrates were monosaccharides. In addition, acetic acid was detected in the water extracts. When extracts were subsequently alkaline-treated, more acetate was released, indicating the presence of acetyl esters. The composition of water extracts and of wood chips after treatment indicates that these treatments primarily affect hemicelluloses. In summary, treatment of wood chips with DEO or OA releases carbohydrates suitable for fermentation, with no evidence of cellulose degradation.