Effect of pelleting on the recalcitrance and bioconversion of dilute-acid pretreated corn stover under low- and high-solids conditions

271 ISSN 1759-7269 10.4155/BFS.13.14 © 2013 Battelle Energy Alliance, LLC, contract manager for Idaho National Laboratory Global demands for energy, diminishing petroleum reserves and growing concerns about climate change have prompted considerable interest in lignocellulosic biomass as a sustainable and renewable energy source. Under the US Energy Independence and Security Act of 2007, the RFS mandates the use of 36 billion gallons per year (BGY) of renewable fuels by 2022, of which 16 BGY are to be derived from cellulosic ethanol [1]. Recent estimates of a baseline scenario suggest that 600 million dry tons of biomass will be available by 2022 to supply sufficient feedstock for achieving this goal, with the potential to produce more than 20 BGY of cellulosic ethanol [2]. The costs associated with acquiring such quantities of biomass are significant, with an estimated cost of US$60 per dry matter ton. A consistent supply of high-quality, economical feedstock is critical to achieving national biofuels goals [3]; however, lowdensity biomass feedstocks pose challenges to supply chain operations and hinder the large-scale use of biomass for biofuel production. Consequently, increasing the bulk density of biomass through mechanical densification offers logistical benefits that translate into improvements in handling, storage stability and transportation costs [4]. The development of a uniform format, solid feedstock supply system is critical to achieve a consistent supply of feedstock with enhanced physical properties for bioenergy production [5]. The economics and physical properties of densified biomass formats produced from agricultural residues have been explored in several studies [6–9]. Pelleting of biomass can increase unit density of raw biomass resources by as much as tenfold [10], resulting in a flowable and durable product that is compatible with existing biomass supply system infrastructure. Biomass pellets are produced from raw, ground material that is conditioned with heat and/or moisture, compacted and extruded through a die [6,11]. It has been shown that activating or softening the natural binders in biomass, such as lignin, through a combination of moisture and temperature during the process of Effect of pelleting on the recalcitrance and bioconversion of dilute-acid pretreated corn stover under lowand high-solids conditions