(325e) The Effect of Ferrous Ion On High Solids Dilute-Acid Low Severity Steam Explosion Pretreatment of Corn Stover

Chen, X., National Renewable Energy Laboratory
Kuhn, E., National Renewable Energy Lab
Tucker, M., National Renewable Energy Lab
Ji, Y., University of North Dakota

Acid-catalyzed steam explosion pretreatment is capable of solubilizing significant amounts of hemicellulose from lignocellulosic biomass, producing more digestible solids for enzymatic hydrolysis. Dilute sulfuric acid is commonly used because it is less expensive than other acid catalysts. However, dilute-sulfuric acid pretreatment requires expensive acid resistant reactors, rapid degradation of desired monomeric sugars into fermentation inhibitors occurs during pretreatment, and addition of post pretreatment neutralization reagents are needed. Lowering the severity of pretreatment by lowering the sulfuric acid concentration can lower these costs, as well as the production of furfural and other degradation products. However lower yields in pretreatment and enzymatic hydrolysis result. A process must be developed that overcomes the limitations of low severity dilute-acid pretreatment. In this study, high solids (~45% w/w) dilute acid pretreatment with co-catalyst supplementation of ferrous ions was investigated using corn stover. Results show that dilute acid with ferrous co-catalyst pretreatment increased xylose yields in pretreatment by 1~7% (on xylose basis) compared to dilute-acid only pretreatment at the same conditions. However, the effect is highly dependent on the ferrous ion concentration and reaction temperature. Furthermore, the enzymatic hydrolysis of washed acid-ferrous co-catalyst pretreated solids indicate enhanced enzymatic yields over controls. The pretreatment results for xylan hydrolysis kinetics were fitted into a four-step linear sequence of first order irreversible reactions. Activation Energy (Ea) was derived from the rate constants and fitted into Arrhenius plots where a 30~50% reduction in Ea was found with the supplementation of small catalytic amounts ferrous ions into the low severity dilute-acid pretreatments.