(714e) New Approach to Ammonia Pretreatment Integrates Better Feedstock Logistics with Improved Sugar Conversion

The implementation of a large scale bioeconomy, where lignocellulosic residues can be used for production of commodity products (fuels, chemicals, materials, food additives, animal feed, etc.) highly depends on the ability of moving large amounts of biomass across long distances. To be able to effectively transport low density materials, such as agricultural residues, it is necessary to apply densification methods (e.g., pelletization). Though densification is expensive, it opens a range of new possibilities for feedstock logistics (e.g., ability to use various transportation methods, safer feedstock storage, etc.) and the ability to implement very large scale lignocellulosic biorefineries, as these require economic transportation of lignocellulosic feedstocks within a wide feedstock production radius. By increasing the size of the biorefinery, it is possible to take advantage of economies of scale and thus, reduce the capital cost per unit of processed biomass. To extract further value from using densified biomass, it is important to explore biomass conversion methods that benefit from having high density feedstock, which can generate higher sugar yields with lower energy inputs.

In this work, we have developed a new ammonia pretreatment strategy called Compacted Biomass with Reduced Ammonia (COBRA) pretreatment. In COBRA pretreatment, liquid ammonia is added to biomass pellets in ratios lower than 1:1, allowing native cellulose I to be converted to cellulose III at relatively low temperatures (~70 °C) and residence times of 3 to 4 hours. As pellets occupy less volume per unit mass relative loose biomass, lower ammonia volumes are required to completely submerge the solid biomass. Thus, as pellets contain low moisture content, the presence of liquid ammonia around the cellulose fibers will allow the formation of a highly digestible cellulose III. As a result, COBRA pretreated biomass can be effectively digested with 60% less enzyme relative to the traditional AFEX pretreatment. Furthermore, as COBRA pretreatment uses densified biomass, it also allows the reduction of reactor size compared to AFEX, even though it uses longer residence times. By using low ammonia loadings, small sized reactors, relatively low temperatures and pressures, low enzyme loading and taking advantage of economies of scale, COBRA pretreatment has the potential to reduce overall processing costs in the biorefinery. Here, we will present a complete optimization of COBRA pretreatment for corn stover, an enzyme cocktail optimization to maximize sugar yields and determination of sugar fermentability using Saccharomyces cerevisiae 424A (LNH-ST). In addition, a complete mass balance and process economics will be presented.