UTILIZATION OF SOLAR ENERGY IN BIOETHANOL PRODUCTION FOR TRANSPORTATION FUELS

Successful utilization of solar energy, which is renewable, abundant, and cheap, for bioethanol production from biomass has potential to solve the fuel shortage problem. Solar energy could be an important alternative energy source, even if only a portion of it is harnessed for heating applications. For efficient utilization of solar energy and for making the bioethanol production process cost-effective, our work focuses on using solar energy for conversion of starch to ethanol in a single-step process. A solar reactor was developed to perform the fermentation of starch. This is the first study on the utilization of solar energy for driving the fermentation reaction leading to ethanol formation as well as separating the produced ethanol from the broth.

An aqueous starch solution (5 wt.%) was fed into the reactor bed charged with Baker’s yeast (Saccharomyces cerevisiae) and amylase, resulting in approximately 0.5 M (2.5 wt.%) ethanol collected daily. A significant amount of ethanol was collected over 63 days, corresponding to 84% of the theoretical yield. The ethanol produced in the solar reactor was separated from the broth soon after its formation by evaporation-condensation process. The solar energy was used as a heating element of the catalyst and the reaction volume, replacing an oven or a heating plate. In the same way, the distillation was also helped by this heating element. The process was scaled up to 15 wt.% starch producing 1.3 M (6 wt.%) ethanol which was demonstrated as a potential and sustainable fuel for direct ethanol fuel cells (310 mAmg_Pt^-1, +0.75 V). Additionally, the secondary metabolite glycerol was fully reduced to a value-added product 1,3-propanediol, which is the first example of a fungal strain (Baker’s yeast) converting glycerol in situ to 1,3-propanediol.