Ethanol bio-refineries in Brazil use bagasse from sugarcane as source of heat and electricity, which makes this process very energy efficient. However, this process can be considered very inefficient from a carbon perspective. Only about a third of the carbon content in sugarcane is converted into ethanol through fermentation, the rest of it is lost as CO2 during fermentation itself and when bagasse is burnt for heat and electricity for the process. Here, we propose a novel integration of the hybrid hydrogen-carbon (H2CAR) process with sugarcane-ethanol production in Brazil. This H2CAR process uses bagasse and CO2 produced during fermentation as sources of carbon for the production of liquid hydrocarbon fuels. The excess heat of this process can be used to supply the entire thermal energy requirement of an ethanol bio-refinery.

The integration of these two processes increases the overall carbon efficiency (~100%), and the energy efficiency of the process is increased from 29.2% to 55%. The most important result of this integration is the reduction in the amount of biomass required to support the entire Brazilian transportation sector by a factor of 3. Sugarcane ethanol alone would require 2.1% of the total land area of Brazil in order to completely support the transportation sector, while the H2CAR process integrated with ethanol bio-refineries would require 0.78% of the total land area to grow sugarcane. This is less than what is harvested today in Brazil, a significant result that could one day make Brazil the world's largest exporter of sustainable fuels.

Reference:

“Sustainable fuel for the transportation sector,” Rakesh Agrawal, Navneet R Singh, Fabio H. Ribeiro & W. Nicholas Delgass. PNAS, 104 (12), 4828-4833 (2007). http://www.pnas.org/cgi/content/full/104/12/4828