Biorefinery sustainability assessment

This article presents a comparative sustainability assessment of three biorefineries that produce liquid fuels used in current infrastructure. The three options considered are biochemical production of ethanol from grain and from cellulosic feedstocks and thermochemical production of Fischer-Tropsch diesel from biomass-derived syngas. These biorefineries were compared using numerous environmental, economic, and social metrics, with numerical values derived from a thorough review of recent literature. For each of the three biorefinery options, the metrics were not determined from a specific process design, but from a variety of different designs reported in literature. Where necessary, corn was selected as the feedstock for grain ethanol and switchgrass was selected for cellulosic ethanol and Fischer-Tropsch diesel. These sustainability metrics were used in an Analytic Hierarchy Process decision analysis to compare the sustainability of the different biorefineries. Thus, a new decision-making tool has been created in which the user can assign different weights to each category and its metrics. This tool was used to explore the influence of different weights, different market conditions, and uncertainties in the values of the metrics on the relative sustainability of the different options. Based on the results of this assessment, cellulosic ethanol biorefineries are modestly more sustainable than grain ethanol and Fischer-Tropsch diesel. Grain ethanol was favorable economically whereas Fischer-Tropsch diesel had the highest score on the societal metrics. (c) 2010 American Institute of Chemical Engineers Environ Prog, 2010