S144: Cell-Free Synthetic Pathway Biotransformations for Low-Cost Production of Biofuels and More

SyPaB is the in vitro assembly of a number of purified enzymes and coenzymes for implementing complicated biochemical reactions.  SyPaB has several advantages, including engineering flexibility, high product yield, fast reaction rate, and  high product titer.  Although SyPaB cannot duplicate itself, (stabilized) enzyme mixtures may have great advantages over microbial fermentations due to several orders of magnitude higher weight-based total turn-over number.  The first example of SyPaB is the production of ~12 H₂ per glucose unit of starch or cellulosic materials and water as C₆H₁₀O₅ (aq) + 7 H₂O (l) à 12 H₂ (g) + 6 CO₂ (g). These entropy-driven biochemical reactions achieve the chemical energy output (hydrogen)/input (sugars) > 1 by absorbing ambient-temperature thermal energy.  The second example is biohydrogenation of biomass sugars for producing polyols (e.g., xylitol), an important biofuel precursor before aqueous phase reforming.  The third example is high-energy density enzymatic fuel cells that can completely oxidize biomass sugars and produce 24 electrons per glucose (i.e, Columbic efficiency = ~100%).

The future sugar-hydrogen-electricity power train system called “sugar fuel cell vehicle (SFCV)” would not only have similar or higher BTK efficiencies than the battery electric vehicle but also have high energy storage densities plus benefits in operations, safety, infrastructure costs,  and environmental  impacts.  When SFCVs are widely implemented in 2030-2050, our analysis suggest that ~ 5% of the annual USA net biomass production or ~50% of the collected biomass would be sufficient to meet 100% of the national light-duty transportation fuel needs.