## 3 AHB Research and Development, 2012-2017  
The AHB research and development program was organized within three domains: (1) Feedstock production through growth, harvest, and delivery of biomass; (2) biomass conversion to liquid fuels; and (3) environmental and economic sustainability of the production and conversion system. Feedstock Production--Under AHB, GreenWood Resources managed large-scale hybrid poplar farms in Idaho, Oregon, California, and Washington to demonstrate biomass yields, production costs, and harvesting technology in growing renewable feedstock. The yield of the top-performing hybrid varieties during the three-year coppice production cycle at the Idaho farm was 15.7 dry metric tons per hectare per year (Mg ha\({}^{-1}\) yr\({}^{-1}\)), 18.1 Mg ha\({}^{-1}\) yr\({}^{-1}\) at the Oregon farm, 12.9 Mg ha\({}^{-1}\) yr\({}^{-1}\) in California, and 22.2 Mg ha\({}^{-1}\) yr\({}^{-1}\) in Washington. The cost of land, labor, fuel, and equipment involved in growing, harvesting, and transporting poplar feedstock to refineries within a 65-km radius were compiled and described in a biomass production cost calculator for each of the four regions assuming leased land and yields of the top-performing varieties [25]. The breakeven price for delivered biomass ranged from $66.64 Mg\({}^{-1}\) (Washington) to $152.49 Mg\({}^{-1}\) (California). GreenWood also studied the sensitivity of internal rates of investment return to key variables using a discounted cash flow analysis [26]. Returns were found to be most sensitive to assumptions related to biomass prices, yields, and land costs. Farm investment returns averaged 4% in real, inflation-adjusted terms across all sites with an assumed market biomass price of $100 Mg\({}^{-1}\); this result is unlikely to attract private-sector capital into biomass farm investments. Yet, while dedicated energy farms may be among the costlier components of a refinery's feedstock supply portfolio, they are indispensable in that they alone reduce supply and pricing uncertainties associated with other cellulosic feedstock sources such as forestry and agricultural residuals. Fuels Conversion--Much of the AHB conversion work is based on [PERSON]'s biochemical process that begins with biomass fractionation and the recovery of the hemicellulose and cellulose components. Carbohydrates are enzymatically hydrolyzed with the resulting five- and six-carbon sugars fermented to acetic acid by acetogenic microbes (e.g., _Moorella thermoacetica._) The acetic acid undergoes esterification to produce acetate ester. The acetate ester is then hydrogenated to ethanol. An alternative fermentation path to propionic acid and propanol has also been developed. The process is well suited for hybrid poplar, because of the feedstock's relative ease of fractionation and its high acetyl and xylose contents. An advantage of the acetogenic pathway is its excellent carbon yields which result in a large absolute reduction in global warming potential on a unit land basis. The University of Washington has shown that the process leads to a global warming potential that is 66% lower than that of petroleum-based jet fuel depending on the specific process design and operating conditions. Both ethanol and propanol can be treated to make hydrocarbon fuels; the University of Washington has demonstrated the efficiency of dehydration in converting ethanol to ethylene with high yields. A nickel oligomerization catalyst has been developed to produce olefins, paraffins, and napthenes from ethylene [27]. The hydrogen required for the hydrocarbon fuels can be produced from residual lignin or natural gas with the natural gas reforming approach being technically efficient. Environmental and Economic Sustainability--The University of California, Davis evaluated the economic sustainability of producing fuels and chemicals from poplar using a series of integrated models covering the entire production system [28].