Chemistry Reference
In-Depth Information
incoming water with conventional chemical addi-
tives (anti-scaling, anti-corrosion, anti-redeposition,
anti-algae and biocidal agents).
6 Large-scale Sonochemistry
The progress of sonochemistry in green and sustain-
able chemistry is dependent upon the possibility of
scaling up the excellent laboratory results for indus-
trial use. There are currently several systems avail-
able commercially, with configurations to suit most
applications [7,126-129].
The first step in the progression of a sonochemical
process from laboratory to large scale is to determine
whether the ultrasonic enhancement is the result
of a mechanical or a truly chemical effect. If it is
mechanical then ultrasonic pretreatment of slurry
may be all that is required before the reacting system
is subjected to a subsequent conventional type of
reaction. If the effect is truly sonochemical, however,
then sonication must be provided during the reac-
tion itself. The second decision to be made is whether
the reactor should be of the batch or flow type.
Whichever type is to be used, there are only three
basic ways in which ultrasonic energy can be intro-
duced to the reacting medium (Table 16.3). Several
different types of ultrasonic reactors are currently
available.
5 Enhanced Extraction of Raw Materials
from Plants
The use of plants not only as food but also as flavour-
ing, colouring or in medicine has a long history. The
interest in aromatic and medicinal plants has
declined over the last half-century, mainly due to the
tremendous developments in the production of syn-
thetic substitutes. Nowadays, however, there is a
resurgence of interest in natural remedies, which is
in part due to some disillusionment with modern
medicines and the hope that new treatments can be
resurrected from ancient remedies.
Medicinal and aromatic plants provide an inex-
haustible resource of raw materials for the pharma-
ceutical, cosmetic and food industries and, more
recently, in agriculture for pest control. People have
learned to increase the power or usefulness of herbs
by preparing medicinal compounds from them, by
preserving them so that they are always available
and by finding new ways to release their active
constituents.
Increased efficiency in extraction leads directly to
a reduction in material wastage and power ultra-
sound has been shown to improve extraction from
plant materials. The classical techniques for extrac-
tion are mainly liquid-solid extraction by means of
steam and/or organic solvents. All such techniques
use relatively high temperatures and thus the energy
consumption is very high and decomposition of
some compounds also may occur. The use of ultra-
sound avoids these high temperatures and can result
in enhanced component extraction at lower temper-
atures and in a faster time [123-125].
Plants are a source of raw chemicals and there are
real possibilities for the growing of crops for specific
extracts. One of the best-known examples is the
rubber tree. It is also well known that oil plants like
sunflower, rape and castor could be not only a source
of food material but also a bulk source of chemicals
for the cosmetic and chemical industries. Some
examples are: linalool from coriander, limonene and
carvone from dill seeds, anethole from fennel seeds
and a-pinene that can be separated from turpentine
oil extracted from coniferous trees in quite large
amounts.
6.1 Batch systems
The obvious batch treatment processor is the ultra-
sonic cleaning bath, which is a readily available
source of low-intensity ultrasonic irradiation, gener-
ally at a frequency of around 40 kHz. A reactor based
on this design might require adaptation to provide
chemically resistant walls, a sealed lid for work
under an inert atmosphere and mechanical stirring.
Using this system for large-volume treatment, the
acoustic energy entering the reaction would be quite
small and any stirrer and fittings in the bath would
cause attenuation of the sound energy.
An alternative configuration would involve using
a submersible transducer assembly, which has been
used for many years in the cleaning industry. It con-
sists of a sealed unit within which transducers are
bonded to the inside of one face and can be designed
to fit into any existing reaction vessel.
6.2 Flow systems
Flow systems are generally regarded as the best
approach to industrial-scale sonochemistry. The
general arrangement would consist of a flow loop
