ECONOMIC COMPETITIVENESS OF RENEWABLE FUELS DERIVED FROM GRAINS AND RELATED BIOMASS
Location: Sustainable Biofuels and Co-Products
Title: Biothanol production from barley hull using SAA (Soaking in aqueous ammonia) pretreatment
Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 11, 2007
Publication Date: January 14, 2008
Citation: Kim, T., Taylor, F., Hicks, K.B. 2008. Biothanol production from barley hull using SAA (soaking in aqueous ammonia) pretreatment. Bioresource Technology. 99:5694-5702.
Interpretive Summary: Ethanol is a clean-burning supplement to gasoline that helps secure the nation’s supply of liquid transportation fuel. Ethanol can be produced from sugars using fermentation. Biomass such as wood and straw contains a kind of sugar that is hard to utilize because it is bound into a rigid and resistant structure. Conversion of biomass resources to ethanol can be achieved by fermentation only after an appropriate pretreatment to release the sugar. Ethanol production from barley hulls was studied in this report, using aqueous ammonia for pretreatment. Ammonia is a non-corrosive and non-polluting chemical, and it is easy to recover and reuse. When barley is used to make fuel ethanol, pretreatment of the hull releases more sugars, so more ethanol can be made from the same amount of barley. This will make the process more efficient and cost-effective, benefitting ethanol producers, farmers, transportation fuel consumers and taxpayers, especially on the East Coast.
Barley hull, a type of lignocellulosic biomass, was pretreated using aqueous ammonia to improve its enzymatic saccharification. Barley hull was soaked in 15-30 wt.% aqueous ammonia (SAA method) at 30-75'C for 1 day-11 weeks using a batch reactor. Under these conditions, SAA (soaking in aqueous ammonia) for 24-72 hours removed 50-66% of the original lignin from the solids while it retained 65-76% of the xylan without any glucan loss. The optimum pretreatment conditions were 75 degrees C, 48 h, 15 wt.% aqueous ammonia and 1:12 of solid:liquid ratio resulting in saccharification yields of 83% for glucan and 63% for xylan with 15 FPU /g-glucan enzyme loading. Utilization of these pretreated solids for simultaneous saccharification and fermentation of ethanol is feasible since SAA retains all the cellulose and lots of hemicellulose in the solid yet it removes the lignin, which is an inhibitor and toxic component for enzymes and fermentative microorganisms. In order to compare the SAA chemical pretreatment with mechanical milling pretreatment, we processed barley hulls with a SUPRATON mechanical mill for 15-60 minutes at 8000 rpm. However, its enzymatic saccharification results for glucan were only 22-27% and 19-24% with 30 and 15 FPU/g-glucan enzyme loading, respectively, which were significantly less promising than SAA pretreatment.