Environmental Engineering Reference
In-Depth Information
The extraction of lipids molecules can traditionally be carried out using
conventional organic solvents such as hexane, dichloromethane and chloroform,
which pose a number of toxicological and environmental problems [28]. The use
of alternative green solvents and technologies is necessary for the safe and sus-
tainable extraction of waxes. One such solvent is supercritical carbon dioxide
[29]. Carbon dioxide is an ideal supercritical solvent for a number of applications
ranging from extraction processes to pharmaceutical applications [30]. This is
because the critical temperature is only 31.1°C; the benefits of near-critical oper-
ation can therefore be exploited at temperatures below 35°C. In addition, carbon
dioxide is non-flammable, has minimal toxicity and is widely available. It is
relatively inexpensive, recyclable and is an unregulated solvent. One slight disad-
vantage is the relatively high critical pressure of carbon dioxide (73.8bar).
However, operating at such pressures has become fairly routine in industrial-scale
extraction processes in which supercritical carbon dioxide is used, such as in the
extraction of hops and decaffeination of coffee [30, 31].
The extraction of waxes from biomass using supercritical carbon dioxide
has been previously carried out [28, 32-35]. Supercritical carbon dioxide was
found to be an ideal solvent for the extraction of plant lipids. The advantage
of using supercritical carbon dioxide as a solvent is that the extraction of non-
polar compounds can be made selective by fine-tuning the solvent power, which
is done by varying the temperature and pressure [31, 36-39]. Furthermore, the
extraction yields can be improved by adding polar modifiers (e.g. methanol,
ethanol) which increases the solvent polarity; however, this results in a decrease
in selectivity towards plant lipids as a higher proportion of polar compounds
are extracted [40, 41].
Successful extraction of lipids from bagasse wax has been carried out and the
extraction process was optimised by carrying out a factorial experimental design,
whereby the effect of temperature and pressure on the extraction yields was
modelled using a dimensionless factor coordinate system (Figure 2.1). These opti-
mised conditions yield a complex mixture of lipids that can be utilised in a wide
variety of applications.
The range of interesting molecules that have been identified in the wax extracts
of sugarcane bagasse are summarised in Table 2.3. Applications of these waxes
include use in nutraceuticals and ingredients for cleaning products, flavours,
degreasers, cosmetics and lubricants. Further discussion of potential applications
is provided in the following section.
Each class of hydrophobic compounds present in the bagasse wax has several
properties which make them ideal for a variety of applications.
Long-chain hydrocarbons have been shown to display semiochemical properties,
where they play a role in plant-insect interactions [44]. Work has been carried out
on the 'pseudocopulatory' behaviour of male bees,
Andrenanigroaena
, towards
the flowers of
Ophryssphegodes.
Results have shown that this orchid synthesises
a variety of chemical compounds which are present in the sex pheromone of
