Question

Please explain the science behind fuel alternatives; biodiesel, ethanol and MTBE.

Answer 1

Fuel Alternatives -

Looking to the draw backs of conventional petroleum fuels and also its limited sources , alternative sources of fuels are being sought out. The significant ones are :

1) Biodiesel - Biodiesel is a diesel fuel made from vegetable oils, animal fats , or recycled restaurent greases. It can be used in its pure form (B100), or blended with petroleum diesel. Common blends include B2 ( 2% biodiesel ), B5 , & B20

A comparision of Biodiesel vs. Petroleum- based Diesel is noteworthy as follows-

...............................Advantages......................................................Disadvantages.....................

• Domestically produced from renewable..............Use of blends above B5 is .............................................................................liable to damage
• resources..............................................................engine.
• Can be used in most diesel engines,.....................Lower fuel economy and ................................................................................power ( 10% lower
• especially newer ones.............................................for B100, 2% for B20 )
• Less air pollutants ( other than NO_x )......................Currently more expensive.
• Less green house emissions .................................( e.g., B20 &..B100 generally .................................................................................not suitable for use at low
• reduces CO₂ by 15% )............................................temperatures.
• Biodegradable.........................................................Concerns about B100 impact .................................................................................on engine
• ..................................................................................durability.
• Non- toxic......................................................................................................
• Safer to handle.......................................................Slight increase in nitrogen ...............................................................................oxide emissions.

Biodiesel cost more than petroleum diesel.

MTBE ( Methyl tert- butyl ether ) or 2-Methoxy -2 - methylpropane with molecular formula(CH3) 3 CO CH3

is a volatile, flammable, colorless liquid organic compound . It is preferred over lead tetra -ethyl as an antiknocking agent. It is actually a gasoline additive , used as an oxygenate ( ie. component which increase oxygen content of gasoline ) to raise the octane number. Therefore, it helps gasoline to burn more completely, reducing tailpipe emissions.

MTBE is is manufactured via chemical reaction of methanol ( derived from natural gas) and isobutylene from butane ( derived from crude oil or naturalgas ). Thus MTBE is derived from fossil fuels.

Further , MTBE has a water solubility of 4.3% at 25^o C. It is, therefore , sufficiently soluble to have a detectable unpleasent odor. Also because of its relatively high water solubility it tends to diffuse rapidly through ground and surface water from the site of contamination, and many remedial measures are not effective in removing it from environment in comparision with other gasoline additives.Hence, it is harmful for agriculture.

Alcohol or ethanol as a fuel - Ethanol has been found to be a safe alternative to MTBE. It doesn't damage agricultural lands. However it happens to be costlier as compared to MTBE.

There are both great advantages and great disadvantages associated with the use of ethanol as an alternative fuel to petroleum.

Advantages

1. Unlike petroleum ethanol is a renewable source.
2. Ethanol burns more cleanly in air, producing less carbon (soot) and carbon mono-oxide.
3. The use of ethanol as opposed to petroleum could reduce carbon-di-oxide emissions, provided that a renewable energy source was used to produce crops required to obtain ethanol and to distil fermented ethanol.

........Disadvantages

(i) Ethanol has lower heat of combustion .(ii) Large amounts of arable lands are required to produce the crops needed to obtain ethanol. (iii) Major environmental problems would arise out of disposal of waste fermented liquors. (iv) Typical current engines would require modifications to use high concentration of ethanol.