Biomedical Engineering Reference
In-Depth Information
enriched by distillation/rectification and dehydration. The CO
2
liberated dur-
ing its combustion was first fixed from the atmosphere by the crops during
their growth, and thus the use of bioethanol in place/addition of fossil fuels
would then reduce the net release of greenhouse gases in the atmosphere. The
potential impact of this strategy is large if we consider that road transport ac-
counts for 22% of all greenhouse gas emissions (http://:www.foodfen.org.uk).
Bioethanol would have a positive environmental impact also because it is
biodegradable and not toxic for living organisms as fossil fuels. A further
advantage is that bioethanol can be easily integrated into the existing fuel
distribution system. In fact, as mentioned, in quantities up to 5%, bioethanol
can be blended with conventional fuel without the need of engine modifica-
tions and adaptation of forecourts and of transportation system.
Finally, its increased use would also have positive a socio-political impact,
by reducing the dependence from the oil producing countries and boosting
the rural economy.
2.1.2 Biodiesel
Biodiesel is an alternative fuel, which can be produced from vegetal resources.
It is made by the
trans
-esterification of vegetal lipids generating lipid methyl
esters (the chemical name for biodiesel) and glycerine, which is a valuable
by-product used in soaps and other products.
In USA, biodiesel is mainly produced from soybean oil, while in Europe
from rapeseed oil. In addition to these crops, biodiesel can be produced using
some microalgae, which are able to accumulate large amount of triglycerides
in their cells. Biodiesel contains no petroleum oil, but it can be blended at
any level with petroleum diesel, and in this form it can be used in recent
compression-ignition (diesel) engines with little or no modifications. Thus its
introduction, even if massive, would not need modification in the fuel dis-
tribution systems. It also shares other advantages with bioethanol. As it is
produced from vegetal sources, its utilization would have no net impact on
the concentration of carbon dioxide in the atmosphere. Furthermore, biodiesel
is also biodegradable, nontoxic, and essentially free of sulphur and aromatics.
2.1.3 Biofuels Still Present Limitations Preventing Their Massive
Utilization
Although bioethanol and biodiesel present big advantages for the environment
and they could rather easily substitute at least partially fossil fuels, there are
still two major limitations to the massive use of biofuels: energetic yield and
costs.
First, the energetic yield is calculated as the ratio between all the energetic
inputs (used for the cultivation of the crop, transport, and transformation)
and all the outputs (fuel, but also all the by-products, as glycerine in the
case of biodiesel). The energetic yield of biodiesel from soya, for example, is
