ABSTRACT
Although humans rst learned to use biomass as their almost exclusive source of chemicals and energy, fossil fuels have become the dominant energy and chemical source since the Industrial Revolution. Petroleum, natural gas, and coal were regarded as waste materials from ancient times. More recently, they have become the cheapest sources of energy and chemicals and have retained this status for over half a century. Full utilization of these “waste” materials has been the focus of much research and development, and the achievements have been remarkable. Compared with biomass, fossil energy sources have a higher energy density with much lower carbon dioxide output per unit energy output than biomass (not considering the other known pollutant gases that are emitted due to the composition of biomass, as described by Walker et al. (2010)). This situation has confused many members of the public and even policy-makers, leading them to label biomass as the worst or dirtiest fuel (worse than the generally accepted coal). However, the quantity of fossilfuel deposits on the Earth is nite. The time when fossil fuels will be completely depleted is now predictable and lies in the foreseeable future despite discoveries of new deposits. Therefore, it is imperative to nd alternatives to fossil sources because the time scale for fossil fuels to be recycled or to replenish naturally is, at best, on the order of 280 million
CONTENTS
22.1 Introduction ...................................................................................................................... 651 22.2 Hemicelluloses and Wood-Based Biorenery ............................................................. 662 22.3 Hot-Water Extraction: Kinetics and Process Characterization..................................664
