Liquid biofuels
Practical Action
The raw feedstock, such as sugar cane residues, is ground up to a small size and the active
ingredients in the feedstock react with dilute sulphuric acid, breaking down into a mixture of
simple sugars, cellulose and cellulose enzymes which are grown at this stage (or they can be
bought in). The cellulose is further reacted with the cellulose enzymes to form glucose. Both
the simple sugars and the glucose are fermented with yeasts or bacteria, forming ethanol, with
carbon dioxide as a by-product. The non-reactive parts of the sugar cane remain as a woody
waste which can be used as a fuel to drive the process.
Plant oils for energy
Plant oils can be extracted using hand tools, such as the Approtech oil expeller shown on the
left (Approtech), or the motorised Sundhara-type oil presses, such as the one shown on the
right (http://www.jatropha.de/expellers/ ).
These methods are similar to those used for food oil extraction. Practical Action has extensive
information on these types of extraction, including a technical brief specifically on oil
extraction.
Biodiesel
Raw m aterial
(e.g.Plant oil)
M ixed with m ethanol and a
catalyst at low tem perature
and pressure
G lycerine
D is tilla tio n
W ashing
Biodiesel
The raw oil is reacted with an excess of alcohol (often methanol or ethanol) in the presence of
a catalyst (often potassium or sodium hydroxide). The products of this reaction are crude
biodiesel and crude glycerine, with an excess alcohol, which is recovered and re-used.
Uses of biofuels
The main use of biofuels globally is within the transport sector, with bio-ethanol replacing
petrol (gasoline) and bio-diesel replacing diesel. Governments have been keen to promote the
use of such fuel for transport purposes as they can draw increased revenue from taxing its
sale as motor fuel. In the longer term, unregulated planting of energy crops for the transport
sector is likely to lead to land degradation, social unrest and famine.
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