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Large Scale Growing of Energy Crops.
Hydrocarbon (energy) producing plants include a large number of Euphorbia and Asclepias species.
These species bear latex and 35% of their dry weight can be obtained as organic extracts. After the water is removed, the latex gives rise to a liquid oil.
Chemical analyses of extracts from E. lathyris show that 5% of its dry weight is a mixture of terpenoids and 20% is a simple sugar (hexose).
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The terpenoids can be converted into a gasoline like product and hexoses may be fermented to ethanol. The conversion of certain biomass derived gasoline-like materials into high quality transformation fuels has also been demonstrated.
Consequently, 8-12% of its dry weight can be obtained as oil, giving 20 barrels of oil/acre/year. Similarly, E. tirucalli can give upto 5-10 barrels of oil/acre/year. Sugar crops (like sugarcane and sugar beet) and starch crops (like corn) are also valuable as solar energy converters.
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An effective use of these renewable resources leads to conversion in several products that can be used as fuels, chemicals and other products.
These crops not only give sugar which may be used directly or converted into ethanol (liquid fuel), but also give valuable by-products such as bagasse, which can be used as solid fuel.
we described in some detail the methods of conversion of sugar and starch into ethanol. Technology has been developed to utilize this ethanol as fuel alcohol in motor cars.
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In Brazil, motorists fill their tanks with alcohol (95% pure) instead of petrol (motor engine can be modified at a small price, so that it can use alcohol). In other cases, a mixture of petrol and alcohol called gasohol can be used, without altering the engines.
The gasohol programme in Brazil, which started in 1975, showed tremendous success and is the world’s largest single biotechnology programme. ‘Short rotation forestry’ is another approach used for biomass production. It involves growth of forest species (e.g. Eucalyptus, Populus, Pinus), which give rapid juvenile growth and can be regrown from harvested stumps.
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This type of biomass production is suited to a variety of climates and gives a very high yield. In recent years micropropagation using tissue culture techniques has proved very useful in propagation of these tree.
Cellulose as a source of energy. Cellulose is the most abundant organic material on the earth and is a major component of all plants. If fuel alcohol can be devived from cellulose, this will be a very flourishing industry.
Each cellulose molecule consists of a few hundred to several thousand glucose units linked together.
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If cellulose can be degraded into glucose, the latter can be easily used for the production of fuel alcohol. Several fungi are known which possess the enzyme cellulase and, therefore, can degrade cellulose into glucose.
However, cellulose in woody plants is intimately asociated with lignin in the form of lignocellulose. An enzyme ‘ligninase’ has also been discovered, which can degrade lignin. Biotechnologists, therefore, are busy in developing the following two steps process for converting cellulose (from trees, weeds, shrubs, straw. etc.) into fuel alcohol :
(i) lignocellulose may be degraded with the help of certain fungi into sugars (action of ligninase and cellulose) and
(ii) sugars may be fed to yeasts for fermentation to alcohol. Studies in several countries including USA and Sweden have shown great promise in this approach.
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