Rapid and Effective Oxidative Pretreatment of Woody Biomass at Mild Reaction Conditions and Low Oxidant Loadings

Abstract

Background: One 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. Results: We 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 H 2 O 2 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 H 2 O 2 loadings can be used that may result in up to a 50-65% decrease in H 2 O 2 application (from 100 mg H 2 O 2 /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.

The costs of sugar production from different feedstocks and processing technologies

“…Another alternative is that chemistries can be combined. Alkaline hydrogen peroxide (AHP) combined oxidative and alkaline chemistries to solubilize ester‐linked xylan and lignin . 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 .…”

EFFECTIVE ALKALINE PEROXIDE OXIDATION PRETREATMENT OF SHEA TREE SAWDUST FOR THE PRODUCTION OF BIOFUELS: KINETICS OF DELIGNIFICATION AND ENZYMATIC CONVERSION TO SUGAR AND SUBSEQUENT PRODUCTION OF ETHANOL BY FERMENTATION USING Saccharomyces cerevisiae

“…For each of these isothermals, the composition of pretreated sawdust was determined at reaction times 20,25,30,35,40, and 45 min. Pretreatment reaction kinetics is an important tool for the economics of a process since reactor volume, and hence the capital equipment requirement, is said to be proportional to the residence time in the reactor (Li et al, 2013). The kinetics of delignification were studied by following the amount of lignin removed from the pretreated solids (Table 1) and analyzed on the basis of the proportion of the total lignin removed with time (Esteves et al, 2005).…”

“…Alkaline peroxide oxidation pretreatment is one method that has been discovered to improve the accessibility of lignocellulosic biomass to cellulolytic enzymes (Kumar et al, 2009). This pretreatment approach has been studied extensively (Ayeni et al, 2013b;Wei and Cheng, 1985;Gould, 1984;Gould et al, 1989;Qi et al, 2009;Li et al, 2013). Studies on cellulosic biomass delignification (lignin removal) usually involve two different approaches, assuming that the lignocellulosic material contains one type of lignin, and that the material is composed of several species (usually initial, bulk, and residual lignin) dissolving at different rates (Kleinert, 1975;Springer, 1963).…”