Large-scale fuel ethanol from lignocellulose
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Ethanol produced from lignocellulose is considered as a largescale transportation fuel in the United States. Five key issues are identified and considered in relation to the status of current and foreseeable technology. These are: conversion and production energy balances, suitability of ethanol as a transportation fuel, air quality impacts, raw material supply, and cost. Energy balances and fuel characteristics appear to be consistent with large-scale transportation fuel use of ethanol produced from lignocellulose. Local and global air-quality benefits are expected to accompany use of lignocellulose ethanol. Raw material availability is examined for wastes and for trees and grasses grown as energy crops. Ethanol production levels appear unlikely to be limited by raw material availability as long as economic and other factors are sufficiently favorable to justify allocation of land for this use. Projected ethanol production costs based on current directions of research would allow neat ethanol to become competitive with gasoline by the year 2000 according to current oil price predictions. Biological process steps have the largest contribution to overall costs, are among the least developed aspects of the technology, and appear to have the greatest potential for improvement. Research priorities are discussed.