High‐efficiency ethanol production from lignocellulosic residues pretreated with alkaline H2O2

The close physical and chemical association between lignin and plant cell-wall polysaccharides is a major limitation to efficient utilization of lignocellulosic materials for ethanol prod~ction.'-~A variety of pretreatments have been applied to agricultural residues and wood in an effort to increase the susceptibility of cellulose in these materials to enzymatic hydrolysis.Most of these pretreatments are based upon processes originally developed by the pulp and paper industry, although recently a number of novel processes have also been reported (for a recent review, see ref.2).Most of these pretreatments do increase the yield of glucose obtainable from lignocellulosic materials, but the yields are still well below the theoretical maximum.2A few pretreatments have been reported that allow essentially quantitative conversion of cellulose into glucose, but these pretreatments require substantial energy input4 or utilize expensive and/or toxic reagent^.^Another important problem with many pretreatments is the generation of side products that inhibit microbial growth and ethanol production during subsequent fermentation In nature, lignin is degraded by various organisms, primarily to increase the amount of cellulose available for enzymatic digestion.*Although the mechanism of natural lignin degradation is largely unknown, it is thought that oxidants such as H20, may play an important r ~l e .~J ~ Hydrogen peroxide is known to react with lignin under certain conditions, l 1 and has been widely used for many years to bleach high-lignin wood p u l ~s .l ~* ~~ Recently we reported that, under appropriate conditions, H202 will delignify wheat straw and other crop residues to a point where the cellulose can be enzymatically converted to glucose with near quantitative yield.I3 In this communication, we demonstrate that H202-treated lignocellulosic materials can, in the presence of cellulase, be rapidly fermented to ethanol with greater than 90% overall efficiency.*The mention of firm names or trade products does not imply that they are endorsed or recommended by the United States Department of Agriculture over other firms or similar products not mentioned.tTo whom all correspondence should be addressed.