Process Engineering Economics of Bioethanol Production

This work presents a review of studies on the process economics of ethanol
production from lignocellulosic materials published since 1996. Our objective was to
identify the most costly process steps and the impact of various parameters on the fi-
nal production cost, e.g. plant capacity, raw material cost, and overall product yield,
as well as process configuration. The variation in estimated ethanol production cost is
considerable, ranging from about 0.13 to 0.81 US$ per liter ethanol. This can be explained
to a large extent by actual process differences and variations in the assumptions
underlying the techno-economic evaluations. The most important parameters for the
economic outcome are the feedstock cost, which varied between 30 and 90US$ per
metric ton in the papers studied, and the plant capacity, which influences the capital
cost. To reduce the ethanol production cost it is necessary to reach high ethanol
yields, as well as a high ethanol concentration during fermentation, to be able to decrease
the energy required for distillation and other downstream process steps. Improved
pretreatment methods, enhanced enzymatic hydrolysis with cheaper and more effective
enzymes, as well as improved fermentation systems present major research challenges
if we are to make lignocellulose-based ethanol production competitive with sugar- and
starch-based ethanol. Process integration, either internally or externally with other types
of plants, e.g. heat and power plants, also offers a way of reducing the final ethanol
production cost.