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Fats and Oils - Why the Fuss?
Dr B.B. Marvey
 Fats
and oils to the rescue
In recent years a lot of interest has developed around the industrial
application of feedstock from renewable resources. It is for this reason that
naturally occurring fats and oils could become one of the major players in the
chemical industry for the near future. This might then result in a new economic
order, placing the agricultural industry in the economic forefront as one of the
largest wealth-generating sectors. These materials (fats and oils) are not
chemically very different from petroleum, which explains why crude oil is a
fossil fuel. There is, therefore, no reason why they cannot replace the
gradually diminishing crude oil in the near future.
Fats and oils are obtained from vegetable and animal sources. Their main
constituents are mixed triglycerides (esters of glycerol) having long-chain
carboxylic acid moieties. A large proportion of the vegetable oils such as
coconut, palm and palm kernel oil come from countries with tropical climates.
Soybean, rape seed and sunflower oils come from moderate climates. Animal fat is
obtained from the meat industry with beef tallow being the most abundant fat.
Fish oil comes from the fishing industry.
In 1997, the total world production of fats and oils was estimated to at 100
million tons (Mt), of which 80 Mt was of vegetable origin and only 20 Mt of
animal origin. Almost 75% of plant oils are derived from four major crops, viz.
soybean, rapeseed, palm and sunflower oil. Of the total world
production of fats and oils, more than 80% is used for human consumption. Half
the remaining part is used in the animal feed industry and about 14% goes to the
chemical industry.
Fats and oils in manufacturing
 Although
fats and oils do not presently command a wide industrial application like
petroleum, they are nevertheless a significant feedstock, used in manufacturing
a number of products including lubricants, surfactants, surface coatings,
polymers, pharmaceuticals, cosmetics, to name a few. In fact, most scientists
already see the potential in field crops as drivers for our economy in the next
few decades. By developing more industrial processes that utilise fats and oils,
it may be possible to significantly lessen global dependence on petroleum. In
any case, before World War II, most products like paints, coatings and adhesives
were made from vegetable oils or other plant products. Henry Ford, for example,
made everything from clothing to automobile bumpers from vegetable oils. It is,
therefore, not just wishful thinking that in the near future, some of these
products will go back to using vegetable oils instead of petroleum. Already
there are latex paints in the market, and Dow chemical Co. and Cargill Inc. are
producing new plastics from corn.
"Green Chemistry "
Besides, fats and oils have a number of advantages over their petroleum
counterpart, for example, they are produced from renewable resources, they are
easily biodegradable, and their processing does not result in the production of
large amounts of CO2, which is an environmental problem. Therefore,
chemical processes involving natural fats and oils are largely "Green
Chemistry" processes. On the other hand, the use of petrochemical feedstock
has several disadvantages, namely, the resources are limited, they contribute to
the net CO2 emissions on combustion, and they are poorly
biodegradable.
In recent years biodiesel has also been gaining worldwide popularity as an
alternative energy source. It comes from transesterification of vegetable oil,
and it is basically a mixture of methyl esters. It is very light oil, less
viscous, very lubricating, and can be used in any Diesel engine including
trucks, generators, boats, trains, busses, and cars. With few or no real
modifications it can just be poured straight into the fuel tank of Diesel
engines. Tests done in the US and Europe have also shown that engines running on
biodiesel have minor, if any differences, in torque, horse power, range, and top
speed to those running on petroleum-based diesel. In fact, the engines running
on biodiesel were generally found to idle smoother and accelerate more smoothly.
Furthermore, biodiesel is biodegrable, non-toxic, and essentially free from
sulphur and aromatics.
Overcoming its limitations
Although there is so much that can come out from fats and oils, there are
still some limitations that need to be overcome and that is, most of them
contain predominantly C16 and C18 fatty acids. This tends to make these oils
suitable for edible use and only of limited value as oleochemicals. This
limitation is serious since the synthesis of most other industrial products
requires fatty acids and derivatives with shorter and longer chain-lengths.
Genetic Modification
To overcome this limitation scientists must exploit options for varying the
chain-length of the available fatty acids to produce a wide variety of useful
products. The possibilities include genetic modification of existing oil crops
and chemical methods. For example, the seed oil of many Umbelliferae
species including the spice plant coriander contains 70-80 per cent petroselinic
acid, an isomer of oleic acid (C18) with the double bond in the C6 rather than
the C9 position. This can be converted to hexane-1,6-dioic (adipic) acid through
oxidative ozonolysis. Adipic acid, in turn, can be used for the manufacture of
polymers:
Since the coriander plant is not a high-yielding oilseed crop, attempts have
been made to transfer its genes to the rapeseed plant for reasons of producing a
high-petroselinic oil crop. When adipic acid is manufactured from petroleum,
huge amounts of ozone depleting nitrous oxide, N2O, are produced.
Therefore, the method for producing adipic acid through biosynthesis coupled
with chemical synthesis has environmental advantages over the currently used
method, which involves petroleum. Other chemical methods for transforming fatty
acids and their derivatives include hydrogenation, isomerization, epoxidation,
hydroformylation and dimerization.
Alkene alternatives
Recently there has also been a growing interest in utilising what is known as
the alkene metathesis reaction for altering chain-lengths of "oils" to
form new compounds. Alkene  metathesis
is primarily a catalyst-driven reaction and involves the cleavage of
carbon-carbon double bonds. Basically two alkene molecules come into contact
with each other and swap partners (alkylidene moieties) as shown to the right.
This reaction has become synthetically useful since the discovery of various
well-defined transition metal carbene complexes which can catalyse alkene
metathesis. There are also several industrial processes based on alkene
metathesis reaction. The Phillips Triolefin Process makes propene by reacting
ethene and 2-butene metathetically. Propene is then used to make the polymer
polypropylene, which in turn is used to make films, fibres, and plastic moulding
materials. The Shell Higher Olefin Process (SHOP) also uses metathesis
technology to convert ethene to detergent range molecules.
Good news for the continent
Fats and oils containing carbon-carbon double bonds can undergo
transformation by metathesis reaction to form intermediates, which could then be
used for the synthesis of a wide range of reaction products ranging from
pharmaceuticals and cosmetics to polymers and fine chemicals. In South Africa,
interest in alkene metathesis research is growing. The good news also is that
most active metathesis catalysts are derived from platinum group metals PGMs
(Platinum, Palladium, Rhodium, Ruthenium, Iridium, Osmium) of which South Africa
has the privilege of being in the forefront as world producer of PGMs. Africa
also has hectares of lands and favourable climate for the production of oil
crops and for stock farming. This must be good news for the continent that is
currently positioning itself to take a more proactive role in the global
economy.
For more information: B.B. Marvey, PhD
Department of Chemistry, University of North-West, P/Bag X2046, Mafikeng, 2735.
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