The use of ethanol for electricity generation is an attractive opportunity for sugar-cane agricultural-based countries mainly considering its use with fuel cell systems. The advantages of sugar-cane ethanol are superior to those of the com ethanol due to the higher ratio output energy (ethanol heat capacity) to input energy (consumed during cultivation and fuel processing). For sugar-cane ethanol, this ratio is about 7, whereas for com, it is 1.3.
Another advantage for ethanol utilization is its higher energy density per volume when compared to hydrogen. This suggests an interesting option for hydrogen storage to be used in fuel cell electric vehicles. This solution is directly applicable for countries where the fuel distribution logistics and refueling infra-structure is consolidated, as it is in Brazil. Considering the volume of fuel storage, the energy gain with the hydrated ethanol (ethanol fuel for internal combustion engines – ICE) storage is about 11.5 times as much as that of hydrogen at 200 bar. The storage of ethanol on pure or hybrid fuel cell vehicles also increases the system safety since it is less likely to leak compared to hydrogen, the fuel is diluted and it shows less toxicity compared to other hydrocarbon fuels.
Concerning the environmental aspects, the use of bio-ethanol (alcohol from biomass) brings advantages due to its by-products sustainability. Regarding to the overall reaction (Reaction 1), the carbon dioxide produced is re-absorbed by the sugar cane in the subsequent crop, since it is part of the photosynthesis process and the carbon cycle.
In fact, this renewable hydrogen source can decisively contribute towards the hydrogen economy insertion in the developing countries, which are the major sugar-cane suppliers in the world, and to increase the trade opportunities for them.
There are essentially three different processes to reform hydrocarbon fuels:
2. Autothermal reforming;
3. Partial Oxidation.
Applying these for ethanol, the follow reactions are reached:
C2H5OH + 3H20 6H2 + 2C02 (1)
C2H5OH + 1,784H20 + 0.60702 4.784H2 + 2C02 (2)
C2H5OH + 1.502 -► 3H2 + 2C02 (3)
The Eqs. (1-3) correspond to each global process and only lead to a first approximation. The experimental reactions for steam-reforming case will be presented later.