Tuesday, May 3, 2011: 2:00 PM
Willow A-B, 2nd fl (Sheraton Seattle)
A number of biofuels produced by biomass sugar have been proposed and investigated. Here we developed a methodology to assess potential biofuels production by considering limits of thermodynamics and bioenergetics and product separation. Four biofuels -- ethanol, butanol, fatty acid ethyl ester (palmitate ethyl ester, PEE), and hydrogen were chosen as example Ethanol and butanol are produced in anaerobic fermentations; PEE is produced in semi-aerobic fermentation; hydrogen is produced by cell-free synthetic enzymatic pathway biotransformation (SyPaB), where enzymes are produced from carbohydrate by microbial fermentations. Hydrogen production by SyPaB would be most appealing because its energy-retaining efficiency is ~49% higher than ethanol, ~55% higher than butanol, and ~87% higher than PEE, even without considering the high conversion efficiency of hydrogen fuel cells. Our analysis suggests that it may be difficult to economically produce some advanced biofuels through aerobic fermentations due to low energy efficiency and some advanced biofuels would not compete with ethanol (now), butanol (short-term), and hydrogen (long term). It is strongly recommended applying this methodology to some developing advanced biofuels before intensive R&D, techno economics analysis and life cycle analysis.