Rapid and effective oxidative pretreatment of woody biomass at mild reaction conditions and low oxidant loadings

Abstract

BackgroundOne route for producing cellulosic biofuels is by the fermentation of lignocellulose-derived sugars generated from a pretreatment that can be effectively coupled with an enzymatic hydrolysis of the plant cell wall. While woody biomass exhibits a number of positive agronomic and logistical attributes, these feedstocks are significantly more recalcitrant to chemical pretreatments than herbaceous feedstocks, requiring higher chemical and energy inputs to achieve high sugar yields from enzymatic hydrolysis. We previously discovered that alkaline hydrogen peroxide (AHP) pretreatment catalyzed by copper(II) 2,2΄-bipyridine complexes significantly improves subsequent enzymatic glucose and xylose release from hybrid poplar heartwood and sapwood relative to uncatalyzed AHP pretreatment at modest reaction conditions (room temperature and atmospheric pressure). In the present work, the reaction conditions for this catalyzed AHP pretreatment were investigated in more detail with the aim of better characterizing the relationship between pretreatment conditions and subsequent enzymatic sugar release.ResultsWe found that for a wide range of pretreatment conditions, the catalyzed pretreatment resulted in significantly higher glucose and xylose enzymatic hydrolysis yields (as high as 80% for both glucose and xylose) relative to uncatalyzed pretreatment (up to 40% for glucose and 50% for xylose). We identified that the extent of improvement in glucan and xylan yield using this catalyzed pretreatment approach was a function of pretreatment conditions that included H2O2 loading on biomass, catalyst concentration, solids concentration, and pretreatment duration. Based on these results, several important improvements in pretreatment and hydrolysis conditions were identified that may have a positive economic impact for a process employing a catalyzed oxidative pretreatment. These improvements include identifying that: (1) substantially lower H2O2 loadings can be used that may result in up to a 50-65% decrease in H2O2 application (from 100 mg H2O2/g biomass to 35–50 mg/g) with only minor losses in glucose and xylose yield, (2) a 60% decrease in the catalyst concentration from 5.0 mM to 2.0 mM (corresponding to a catalyst loading of 25 μmol/g biomass to 10 μmol/g biomass) can be achieved without a subsequent loss in glucose yield, (3) an order of magnitude improvement in the time required for pretreatment (minutes versus hours or days) can be realized using the catalyzed pretreatment approach, and (4) enzyme dosage can be reduced to less than 30 mg protein/g glucan and potentially further with only minor losses in glucose and xylose yields. In addition, we established that the reaction rate is improved in both catalyzed and uncatalyzed AHP pretreatment by increased solids concentrations.ConclusionsThis work explored the relationship between reaction conditions impacting a catalyzed oxidative pretreatment of woody biomass and identified that significant decreases in the H2O2, catalyst, and enzyme loading on the biomass as well a...

Transgenic ferritin overproduction enhances thermochemical pretreatments in Arabidopsis

“…Recently published studies have reported that copper (II) 2,2 0 -bipyridine complexes (Cu(bpy)) can significantly enhance alkaline hydrogen peroxide (AHP) pretreatment of hybrid poplar heartwood and sapwood etc., and improve subsequent enzymatic glucose and xylose release at modest reaction conditions [37,38]. Although in our study the biomass subjected to ferritin overexpression was designed for dilute acid pretreatment, published work suggests that some pretreatment specificity should be investigated in the future, including alkaline and oxidative pretreatments.…”

The costs of sugar production from different feedstocks and processing technologies

“…Alkaline hydrogen peroxide (AHP) combined oxidative and alkaline chemistries to solubilize ester-linked xylan and lignin. 62,63 Organosolv and ionic liquid treatments are somewhat unique in that they convert crystalline to amorphous cellulose and solubilize lignin, which greatly lowers the required loadings of cellulases. 53,64,65 Fungi, including white, brown, and soft-rot fungi, which naturally degrade lignin, have also been proposed for biological pretreatment.…”

Reviews of Science for Science Librarians: Second-generation Biofuels Feedstock: Crop Wastes, Energy Grasses, and Forest Byproducts

“…The keys to cleaner burning appear to be first debarking the wood and then turning it into the most finely ground dust possible to be sprayed into boilers (Jacob et al 2013). There are, however, also a good many studies on saccharifying ground soft hardwood pulp lignin, hemicellulose, and cellulose via a series of alkali and acid baths prior to fermentation by yeast or enzymatic breakdown, leading to bioalcohols (Jacob et al 2013;Li, Chen, Hegg, et al 2013;Yuan et al 2013). Meanwhile, genomics has been increasing our understanding of how we might accomplish the seemingly contradictory goals of raising trees-which grow tall and thick owing to their high lignin contentwith less lignin, so their wood might become more readily fermentable.…”