摘要：Most life cycle studies of biofuels have not examined the impact of process chemicals and
enzymes, both necessary inputs to biochemical production and which vary depending upon
the technology platform (feedstock, pretreatment and hydrolysis system). We examine
whether this omission is warranted for sugar-platform technologies. We develop life cycle
('well-to-tank') case studies for a corn dry-mill and for one 'mature' and two near-term
lignocellulosic ethanol technologies. Process chemical and enzyme inputs contribute only
3% of fossil energy use and greenhouse gas (GHG) emissions for corn ethanol.
Assuming considerable improvement compared to current enzyme performance,
the inputs for the near-term lignocellulosic technologies studied are found to be
responsible for 30%–40% of fossil energy use and 30%–35% of GHG emissions, not an
insignificant fraction given that these models represent technology developers'
nth plant performance. Mature technologies which assume lower chemical and enzyme
loadings, high enzyme specific activity and on-site production utilizing renewable
energy would significantly improve performance. Although the lignocellulosic
technologies modeled offer benefits over today's corn ethanol through reducing life cycle
fossil energy demand and GHG emissions by factors of three and six, achieving
those performance levels requires continued research into and development of the
manufacture of low dose, high specific activity enzyme systems. Realizing the
benefits of low carbon fuels through biological conversion will otherwise not be
possible. Tracking the technological performance of process conversion materials
remains an important step in measuring the life cycle performance of biofuels.
