Key Issues to Biochemical Conversion of Woody Biomass

About 368 million dry tons of woody biomass (or ~30% of the total biomass) can be sustainably produced annually in the US. To achieve the goal of 16 billion gallons of annual cellulosic ethanol production, sustainable healthy forest and ecosystem management through forest thinning, and to create high paying manufacturing jobs and meet regional and local energy needs in many areas of US, forest biomass will be a critical part of the biomass feedstock supply. Forest biomass has several advantages over agricultural biomass for producing biofuel and bio-products. Its high density significantly reduces transportation cost, the flexible harvesting time eliminated storage cost. However, due to its unique physical structure and high lignin content, forest biomass exhibits a higher degree of recalcitrance for biochemical conversion than agricultural biomass. Two main barriers unique to forest biomass must be effectively removed through efficient pretreatment before forest biomass can play a significant role in the future biobased economy: (1) the significant energy consumption in physical size-reduction of forest biomass from logs to fiber/fiber bundle level for effective biochemical conversion, (2) the low enzymatic cellulose conversion efficiency especially biomass derived from softwood species, available in large quantities in many regions of US. Unfortunately, most existing pretreatment processes have failed to efficiently convert forest biomass, especially biomass derived from softwood species. Economical ethanol production using organosolv, the only known process effective on softwoods, requires high value lignin co-products yet to be developed and marketed. This suggests the lack of viable biochemical technologies for near-term commercial deployment using forest biomass (A proposed ethanol demonstration plant supported by DOE in Colorado using the organosolv process was recently terminated by Lignol Energy). In this presentation we will discuss recent advances we made that addresses these two critical barriers to woody biomass conversion. Specifically, we will discuss the SPORL pretreatment process that capable of achieving near complete cellulose conversion to glucose for softwoods with excellent hemicellulsoe sugar recovery and very low fermentation inhibitors. We will also discuss the post-pretreatment size-reduction approach for significant reduction of energy consumption for woody biomass size-reduction to about 50 Wh/kg, equivalent to those used by agricultural residues.