Page 33 - Biofuels Refining and Performance

16 Chapter One

by electrical discharge and gets into soil by rainwater in the form of
nitrites and nitrates. These are reduced to ammonia by the biological
nitrogen fixation of symbiotic organisms or by blue-green algae.

In Escherichia coli and Bacillus subtilis, NO 3 is reduced to NH 3

[NO 3 → NO 2 1 → N O 2 → NH OH → NH ]
2
2
2
3
and an oxidation reduction potential of 0.96 V (pH 7.0) is utilized by
these systems to convert other materials to a more oxidized state.
3
NH O → NO 2 H O H 36,500 cal
2
2
3
2
1

NO 2 O 2 → NO 3 17,500 cal
2

2e 2e 2e
N ≡ N ⎯⎯→ HN NH ⎯⎯→ H NNH ⎯⎯→ 2NH 3
2
2
Via Mo-protein complex
Hydrogen is made available from reduced coenzymes, and the energy
is available from ATP produced by the oxidation of general metabolites.
In some systems, H becomes the by-product, and this could be an ideal
2
fuel or it can be used in a suitable chemical cell for the production of energy.
1.6 Chemical Cell
Two different metals in contact with a polar or ionic fluid generate the
flow of electrons. When touched simultaneously by two different metal-
lic rods, muscles contract, a pioneering observation that gave birth to
the study of galvanic, voltaic, and Daniel cells.
The potential generated depends on the energy of sublimation, the ion-
ization potential, the electronic work function, and the energy of solva-
tion of ions. The nature of the solvent influences the last factor. The
electronic work function also includes several other conditions of ionic
activity. As a result, a potential difference will arise out of a simple con-
centration gradient, provided that anionic and cationic stoichiometry is
maintained. A review of the existing knowledge is worthwhile here.
If two small baths, each having either Zn or Cu metal and correspond-
2 2
ing dilute solutions of Zn and Cu salts, are in electrical continuity—
say through a capillary of a U tube or a Pt wire—then current will flow
in the two metals when connected outside, with Cu behaving as a cathode
and Zn as an anode (see Fig. 1.3). The setup can also be designed by sep-
arating the two systems by a semipermeable membrane.
A similar experience is the cylindrical design of the commonly avail-
able dry cells, where a graphite rod at the center serves as a reference