Processing and economic impacts of biomass delignification for ethanol production

Abstract

The need for chemical pretreatment of biomass for the enzyme-catalyzed production of ethanol from lignocellulosic feedstocks has been established. Past research in the Alternative Fuels Division of the National Renewable Energy Laboratory has focused on dilute-acid prehydrolysis processes as a means of hydrolyzing the hemicellulose component of biomass. Such processes provide a solid residue that is more easily hydrolyzable by cellulase enzymes, as well as a hemicellulose-sugar component that can be converted by pentose-fermenting microorganisms.

This work investigates the technical and economic feasibility of including a separate biomass delignification/fractionation step, either in conjunction with dilute acid prehydrolysis or as an independent pretreatment process. These alternatives would not only solubilize the hemicellulose component of a biomass feedstock, but the lignin fraction as well. The resulting residual solids would be primarily composed of cellulose. The benefits found in converting such material to ethanol may include lower cellulase requirements, shorter bioconversion times, higher effective cellulose concentrations resulting in higher ethanol concentrations, smaller reactor volumes, and more efficient enzyme recycle options. A technoeconomic assessment indicates that improvements in these process parameters can lead to significant savings that can cover the costs of such process additions.