CHEMISTRY 1000
Topics of Interest #6:
Biofuels, Cellulose and Wood
Where Do Biofuels Come From?

Biofuels can be produced in a number of different ways, including:




Chemical breakdown of used cooking fats
Extraction from crops with naturally high oil content (e.g. oil palm)
Fermentation of sugars from crops grown specifically for that purpose
(e.g. sugar cane, sugar beet). Starchy crops (e.g. corn) can be used
too but are highly inefficient.
Little of the sugar in biomass is actually present as free sugar or
even starch. Most of it takes the form of cellulose. Like starch,
cellulose is a polymer made of sugar units (one unit = glucose).
Unlike starch, cellulose is more difficult to break down because of
the way the sugar units are attached.
R. Rinaldi, R. Palkovits and F. Schuth Angewandte Chemie International Edition
(2008) 47, 8047-8050.
Where Do Biofuels Come From?

Starch
CH2OH
O
O
H
HO
HO
O
CH2OH
one sugar unit
(“monomer”)
O
H
HO
HO
O
CH2OH
O
H
HO
HO
O
CH2OH
H
HO

HO
n

O
O
maltose unit
Cellulose

CH2OH
O
HO
O
H
H
OH
O
HO
O
O
HO
HO
CH2OH
OH
O
CH2OH
H
O
O
O
O
HO
H
H
CH2OH
n
cellobiose unit
R. Rinaldi, R. Palkovits and F. Schuth Angewandte Chemie International Edition
(2008) 47, 8047-8050.
Cellulose and Biofuels


If it were possible to more easily break down cellulose into its
constituent sugars (or even shorter chains of sugars), the more
abundant cellulose could also be used as a source of biofuels.
Cellulose and wood dissolve
alkylmethylimidazolium salts:
ionic
liquids
(!)
called
carbon chain
H
N+
C
C
H
in
large anion-
C
N
H
CH3
You can see why this ionic compound might not form a solid lattice
like the ionic solids we’ve looked at this term.
R. Rinaldi, R. Palkovits and F. Schuth Angewandte Chemie International Edition
(2008) 47, 8047-8050.
Cellulose and Biofuels


After the cellulose has been dissolved in the ionic liquid, the
solution can be passed over a solid acid catalyst which breaks it
down to shorter chains of sugars that could potentially be
fermented to give biofuels from a wider variety of sources than is
currently feasible.
This process even works on wood!
R. Rinaldi, R. Palkovits and F. Schuth Angewandte Chemie International Edition
(2008) 47, 8047-8050.