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Biological agents as fuels: Bio fuels
#1
Fuels obtained from biological sources are known as bio fuels.
The branch of biotechnology dealing with the exploitation of biological agents to convert it into sources of energy is known as fuel biotechnology. The bio fuels produced should be portable in large quantities in vehicles, should be able to burn in internal combustion engines of vehicles and should be approximately equivalent to petrol in energy content.

Biogas: It is one of the early and largely produced sources of energy. It is produced from biomass by simple burning or using sophisticated technologies of breakdown. It can be produced by small scale production units, recovery and conditions of production is not costly. But the product released is of low yield and some times pure gases are not evolved.

Bio ethanol: Bio ethanol is produced from biomass by the action of various microbes. The production of bio ethanol occurs from two different raw materials.

(i) From sugar and starch crops: The raw materials is acted upon by microbes like Saccharomyces cerevisia, Bacillus licheniformis, Zymomonas

(ii) From cellulosic materials: This involves two method by enzymatic hydrolyses and by chemical hydrolysis. Organisms like Trichoderma reisei, Saccharomyces cerevisiae, Clostridium etc., break down the biomass or rather the cellulose present in the biomass by the production of enzyme cellulase. The cellulose gets converted to sugars which are broken down by any S. cerevisiae into ethanol. In certain cases, the pentose is formed as an intermediate and only genetically modified E. coli can break down this into simple sugars.

The ethanol so produced is recovered from the water-ethanol mixture by distillation utilizing the difference in boiling points of water and ethanol.
Advantages of bio ethanol as a fuel include: The heat of vaporization is much higher than petrol resulting in less heating up of cylinders. The higher octane number than petrol results in higher power production and no pre-ignition of bio ethanol over commercial petrol. Since it is burnt completely, hydrocarbon residue is not released forming a much cleaner fuel. It has comparatively less chances of catching fire during accidents. In commercial market, petrol is mixed with ethanol to produce ‘gasohol’ which yields good energy and high octane number.
It also include negative aspects like it absorbs moisture, the downstream recovery is high, and the engines under ethanol utilizes more fuel than petrol.

Biobutanol:
This is produced from Clostridium acetobutylicum by anaerobic fermentation. The substrate used is molasses. The production has not met with much success as the cost incurred was too high and application of genetic engineering techniques by modifying the organism resulting in high expression; high substrate utilization is being considered.

Bio diesel
Bio diesel is produced mainly by two ways- from lipids and from hydrocarbons by plants and algae

Bio diesel from lipids:
Lipids are source of energy and can be utilized to release the same. Many plants store lipids in their seeds and this can be processed to produce esters of lipid fatty acids. The product seems to resemble diesel hence known as bio diesel. Bio diesel can be used in the natural form without much modification directly as a fuel.

Bio diesel from hydrocarbons:
Certain plants have the ability to accumulate hydrocarbons which can be utilized to produce fuels. The plants that accumulate hydrocarbons do it as latex. The plant species of family Euphorbiaceae, some milk weeds like Asclepias species, and a tree called as C. multijuga has the above said ability.

Plants of the family Euphorbiacae produce latex which has hydrocarbons emulsified in water. Separation or removal of water yields necessary hydrocarbons. The milk weeds also store latex which can be removed and utilized. The tree C. multijuga is a native of Brazil and it fixes nitrogen in its roots and produces a liquid large in volume and which is quite similar to diesel oil. This can be utilized as an efficient source of bio diesel production. Some freshwater and marine algae are also known to deposit hydrocarbons. This also acts as a source of diesel.

Positive features of bio fuel:
The source from which the bio fuel is produced is biological which is renewable in nature resulting in unlimited production without fear of depletion of resources as in the case of conventional sources like oil, petrol etc. The carbon dioxide emission by burning of bio fuels is much less comparatively. The other polluting gases like sulphur dioxide are not released helping in keeping environment clean. They burn completely and so the energy released is high. The left over residue can be used as manure.

Negative points:
Larger volumes of raw material are required to produce a good quantity of bio fuel and the cost of production is also high.
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#2
Biomass can be converted into liquid fuels known as bio fuel.Two types of bio fuels are ethanol and bio diesel.
1) Ethanol produced by a process called Gasification. Gasification uses high temperature and a low oxygen environment to convert biomass into synthesis gas.This gas can be chemically converted into other fuels.
2) Bio diesel is made by combining alcohol with vegetable oil and animal fat.It can be used as an additive to reduce vehicle emission and renewable alternative fuel for diesel engine.
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#3
Ethanol produced by microorganisms, e.g., Saccharomyces cerevisae, from biomass is called bioethanol. It is the most widely used biofuel used for transport purposes, especially in Brazil and USA. At present, bioethanol is not cost competitive as compared to petrol but is being used for transport due to government subsidies.

Any biofuel proposed to be used for transport purposes should have the following features:

1. It should be portable in sufficient quantities in the vehicle

2. It should burn in the internal combustion engines

3. It should be roughly equivalent to petrol in energy content

Ethanol has certain features, which make it more desirable than petrol, but it also has some undesirable features.

Advantages of bioethanol over petrol:

1. Ethanol has a much higher latent heat of vaporization (855MJ/kg) than petrol (293kJ/kg). This energy is obtained from the air in the carburetor. As a result, the fuel mixture entering the cylinder is much cooler and hence denser in case of ethanol than in case of petrol. Even though ethanol has only 61.8% (27.2 kJ/kg) energy content of petrol (44 kJ/kg), the energy produced by combustion of ethanol during each stroke is only slightly lower than that released from petrol.

2. Ethanol has a higher octane number (99) than petrol (80-100). As a result, preignition does not occur when ethanol is used in engines set for petrol. Preignition denotes ignition before the piston has reached the correct position during compression cycle. It leads to power loss and damage to valves and piston.

3. Higher octane rating of ethanol allows the compression ratio of the engines to be increased; this results in increased production of power.

4. Ethanol is burnt more completely so that hydrocarbon emission is drastically lower as compared to that in case of petrol.

5. Ethanol has a much higher flash point (45 degrees C) than petrol (13 degrees C).

6. It can be mixed with petrol; this increases the octane rating of petrol. However, in these cases the ethanol has to be 100% pure otherwise it won’t mix properly with petrol.
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#4
The natural toxin ricin is isolated from endosperm of castor. It consists of two polypeptide chains called as A and B where the polypeptide A accounts for its toxicity. The immunotoxin formed as a conjugate between an antibody and ricin A chain results in specific binding to tumour cells and irreversible enzymatic modification of ribosomes preventing protein synthesis is such cells.
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