4. Biological Conversion of Plants to Fuels and Chemicals and the Effects of Inhibitors

  1. Charles E. Wyman3,4
  1. Eduardo Ximenes1,
  2. Youngmi Kim1 and
  3. Michael R. Ladisch1,2

Published Online: 5 APR 2013

DOI: 10.1002/9780470975831.ch4

Aqueous Pretreatment of Plant Biomass for Biological and Chemical Conversion to Fuels and Chemicals

Aqueous Pretreatment of Plant Biomass for Biological and Chemical Conversion to Fuels and Chemicals

How to Cite

Ximenes, E., Kim, Y. and Ladisch, M. R. (2013) Biological Conversion of Plants to Fuels and Chemicals and the Effects of Inhibitors, in Aqueous Pretreatment of Plant Biomass for Biological and Chemical Conversion to Fuels and Chemicals (ed C. E. Wyman), John Wiley & Sons, Ltd, Chichester, UK. doi: 10.1002/9780470975831.ch4

Editor Information

  1. 3

    Department of Chemical and Environmental Engineering and Center for Environmental Research and Technology, University of California, Riverside, USA

  2. 4

    BioEnergy Science Center, Oak Ridge, USA

Author Information

  1. 1

    Laboratory of Renewable Resources Engineering, Purdue University, West Lafayette, USA

  2. 2

    Mascoma Corporation, USA

Publication History

  1. Published Online: 5 APR 2013
  2. Published Print: 10 MAY 2013

Book Series:

  1. Wiley Series in Renewable Resources

Book Series Editors:

  1. Christian V. Stevens

Series Editor Information

  1. Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium

ISBN Information

Print ISBN: 9780470972021

Online ISBN: 9780470975831

SEARCH

Keywords:

  • biological conversion;
  • chemicals;
  • enzyme hydrolysis;
  • ethanol fermentation inhibitors;
  • fuels;
  • plants;
  • pretreatment

Summary

Pretreatments have the potential to both enhance the rates and extents of cellulose conversion by biological catalysts including cell-free enzymes, enzymes produced during consolidated bioprocessing, and simultaneous saccharification and fermentation. The efficiency of the enzymes that hydrolyze either hemicellulose or cellulose to monosaccharides (principally glucose and xylose) is affected by inhibitors released during pretreatment and hydrolysis. The inhibitory effects of glucose and cellobiose on β-glucosidase and cellobiohydrolase are well known. The combination of saccharification (i.e., hydrolysis) with fermentation steadily removes these inhibitory sugars. Recently, a more potent class of inhibitors and deactivators has been rediscovered and their effects studied with respect to enzymatic cellulose hydrolysis. Phenolics (e.g., vanillin, p-coumaric, ferulic, gallic and tannic acids) can reduce enzyme activity by over 50% and de-activate β-glucosidase, principally through precipitation. Phenolic inhibitors may be more potent than the hydrolysis products derived from cellulose itself. In addition, xylo-oligosaccharides also inhibit cellulase. Consequently, removing xylo-oligosaccharides either through enzymatic hydrolysis or washing after pretreatment has been considered numerous times. However, once xylo-oligosaccharides are washed away from the solid material, they still must be hydrolyzed to monosaccharides that can be fermented to ethanol, and thereby increase yield. To achieve this, one method is to use a solid-acid catalytic bed (i.e., ion exchange resin) over which the oligosaccharide solution is passed. At temperatures 150°C, hydrolysis is rapid and the formation of degradation products is minimized. This chapter provides an overview of biological processing of cellulosic biomass followed by a discussion of the important inhibitory impacts of lignin-derived phenolics and xylo-oligosaccharides on cellulolytic enzymes. In addition, the effect of major inhibitors on ethanol fermentation (furans and acetic acid) will also be discussed. Possible strategies are discussed for removing phenolics and xylo-oligosaccharides.