1Lawrence Berkeley National Laboratory, San Francisco, United States
One of the greatest challenges facing the energy transition of the world is the development of a viable, scalable, and profitable circular carbon economy to meet the world’s demands for fuels, chemicals, and materials from non-fossil sources. Lignocellulosic biomass (plant material made up of cellulose, hemicellulose, and lignin) from nonfood crops could provide a large fraction of those alternative fuels and products. There are approximately one billion dry tons of lignocellulosic biomass available annually in the U.S. with the potential to provide a significant and strategic renewable domestic source of nearly carbon-neutral, specialty (drop-in and/or fungible) biofuels and renewable chemicals. Mobilizing this strategic renewable carbon resource to enable the bioeconomy of the U.S. requires addressing significant roadblocks. These include the lack of scalable and sustainable energy crops; difficulty in separating and breaking down lignocellulose into targeted intermediates at high yields; lack of a robust feedstock agnostic pretreatment technology; and expense of enzymes used to produce fermentable sugars and other targeted intermediates. Multiple California woody biomass were studied for their potential to release fermentable sugars after IL pretreatment and enzymatic hydrolysis. Two IL pretreatment methods were studied: 1) the neat IL pretreatment method using 100 weight (wt) percent ethanolamine acetate combined with an early separation approach for IL recovery, and 2) the aqueous IL method using 10 wt percent cholinium lysinate in water in a one-pot bioprocess that combined all the steps of pretreatment, hydrolysis, and fermentation in one unit operation. To optimize this IL-based process on California woody biomass, the researchers tested different process conditions at the bench scale and then scaled them up to the 1500L scale of operations. Three types of California woody biomass from Paddock Inc. in Oakdale, California to assess potential in large-scale deconstruction and fermentation studies Almond and walnut wood waste was procured from local orchards, with pine wood obtained from forest thinning. As expected, sugar concentrations following pretreatment and saccharification were highest for the highest solid loading condition, resulting in a maximum of 57.2 g/L glucose and 31.9 g/L xylose in the final hydrolysate. Xylan conversion was near complete, exceeding 97 percent in each of the three conditions. Using a 1,500L ABEC fermenter for fermentation of a 680L batch of unfiltered hydrolysate. The pilot scale campaign achieved near complete glucose utilization after 24 hours, with >90 percent xylose utilization after 72 hours. The fermentation achieved a final titer of 27.6 g/L after 120 hours, with a fermentation efficiency of 93.3 percent as a function of the initial glucose and xylose present in the fermenter. When coupled to the deconstruction efficiency of 83.0 percent, this result yields an aggregate deconstruction and fermentation efficiency of 77.4 percent, the highest known efficiency reported on mixed woody biomass feedstocks.