(482a) Effects of Sodium Sulfide Supplementation On Alkaline Pretreatment of Herbaceous Biomass

In alkaline pretreatments of biomass, it is feasible to retain most of carbohydrates while removing a large fraction of lignin. The enhancement of digestibility is caused primarily by lignin removal. Retention of hemicellulose after pretreatment gives a significant economic benefit since it eliminates the need of detoxifying hemicellulose sugars. Sulfur containing reagents are highly reactive with lignin, thus can serve as delignification enhancer. We have investigated the effects of adding small amount of sodium sulfide in alkaline pretreatment of herbaceous biomass. The alkaline reagents tested were either recoverable ones (ammonia, sodium carbonate) or inexpensive one (lime). Pretreatments were applied to switchgrass, corn stover, and palm residue with and without supplementation of sodium sulfide to see the isolated effects of sodium sulfide. Pretreatments were done in batch mode under low severity conditions:  90 - 120 °C, 12 - 24 hr reaction time, 5 - 15 % alkali, 1 - 3% sodium sulfide, and  5~10:1 of L:S ratio. The treated substrates were put through enzymatic digestibility tests using commercial cellulase (Novozyme CTec 2). Addition of sodium sulfide did not change carbohydrates retention, but increased delignification by 20 - 25 %.  Addition of sodium sulfide has significantly increased digestibility for all alkali treatments: 15 – 45 % in glucan digestibility and 10 – 40 % in xylan digestibility depending on type of substrate and pretreatment severity. The results were further assessed to determine the optimum set of pretreatment conditions considering carbohydrate retention and digestibility as criteria. Details of the performance data are also presented.