Give Properties of Biodiesel and Power Alcohol

Power alcohol

Introduction

Alcohol used for the generation of power is called power alcohol.
Absolute acohol ( $100%$ ethyl acohol) and rectified spirit ( $93-95%$ ethyl alcohol) are not used as prime fuels but they are only used as additives to petrol.
Generally , power alcohol has petrol and alcohol in the ratio of $4:1$ .
If about 20-25% ethyl alcohol is blended with petrol and is used as a fuel, it is known as power alcohol for internal combustion engine.
It is important to note that rectified spirit mixes well with petrol only in presence of benzene, tetralin or ether. Hence whenever it is used as power alcohol, either of the solvent must be used.

C 2 H 5 OH CH 3 CH 2 OH

Manufacture of ethyl alcohol ( $93-95%$ ethyl alcohol)

1.Dillution:

Since the high concentration of sugars is undesirable for the fermentaion raction, molasses is first of all diluted with water to get about $8-10%$ solution of sugars

2.Addition of dilute sulphuric acid

The diluted molasses is acidified with small amount of dilute shulpuric acid. Dilute sulphuric acids check the growth of undesirable bacteria which would otherwise form lactic acid and acetic acid

3.Addition of yeast (alcoholic fermenation)

In this process sugars (e.g.glucose, fructose, manenoseand galctose), genearlly, glucose are decomposed by certain yeast to ethyl alcohol and carbon dioxide.

C₆H₁₂O₆→ 2C₂H₅OH + 2CO₂ + energy

For use in internal combustion engine, $100%$ alcohol should be prepared. Hence $100%$ alcohol is obtained by distilling alcohol in the presence of benzene or any dehydrating agent.

Advantage of Power alcohol

It has a high “octane” rating, which prevents engine detonation (knock) under load.
It burns clean.
An alcohol burning engine tends to run cooler thus extending engine life and reducing the chance of overheating
It has less starting problems.
Alcohol removes all traces of moisture in the petrol.
Use of ethyl alcohol in petrol reduces our dependence on foreign countries for petrol and saves foreign considerably.
Power alcohol is cheaper than petrol.
Ethyl alcohol contains ‘ $O$ ‘ atoms, which helps for complete combustion of power alcohol and the polluting emissions of $CO$ , hydrocarbon, particulates are reduced largely.

Disadvantage of Power alcohol

It lowers the calorific value of petrol.
Ethyl alcohol may undergo oxidation reaction to form acetic acid, which corrodes engine parts.
Ethyl alcohol has high surface tension and its atomization, especially at lower temperature, is difficult causing starting trouble.

Biodiesel

Biodiesel is an alternative diesel fuel. It, is a natural and renewable domestic fuel made from vegetable oils, mostly soy and corn and animal fat. It holds no petroleum, is biodegradable and nontoxic. It is viewed as an alternative for diesel engines.
Bio-diesel also refers to a vegetable oil- or animal fat-based diesel fuel which comprises of long-chain alkyl esters and is typically made by reacting lipids with an alcohol chemically.
Biodiesel is most commonly a mono-ester of methanol but other alcohols like ethanol can also be used.
It is also known as a mono-alkyl methyl ester or methyl ester for short.

Vegetable oil using problems

Vegetable oil is too thick to flow through modern diesel engines
These oils contain very large amounts of biologically active fats called Omega-6 polyunsaturated fatty acids, which are harmful in excess.

Properties of Biodiesel

Biodiesel has better lubricating properties.
It has higher cetane number.
It give complete combustion thus increase engine energy output.
It is slightly miscible with water.
Its flash point is high.

Manufacture

The Transesterification process is the reaction of a triglyceride (fat/oil) with an alcohol to form esters and glycerol.

Transesterification is the chemical process which replaces one type of alcohol for another in an ester.

A triglyceride has a glycerine molecule as its base with three long chain fatty acids attached. The nature of the fatty acids can in turn affect the characteristics of the biodiesel. During the esterification process, the triglyceride is reacted with alcohol in the presence of a catalyst, usually a strong alkaline like sodium hydroxide. The alcohol reacts with the fatty acids to form the mono-alkyl ester, or biodiesel and crude glycerol.

The products of the reaction are the biodiesel itself and glycerol.

A successful transesterification reaction is signified by the separation of the ester and glycerol layers after the reaction time. The heavier, co-product, glycerol settles out and may be sold as it is or it may be purified for use in other industries, e.g. the pharmaceutical, cosmetics etc.

The simplest biodiesel recipe is:

Mix 5 grams of $NaOH$ with $200ml$ of methanol.
Stir until the $NaOH$ is completely dissolved.
Heat 1 liter of new vegetable oil to $55°C$ .
Mix the methanol with the vegetable oil.
Continue to stir for 15 minutes while the transesterification reaction takes place.
Allow the glycerin to settle out for 2 hours.
The stuff on top is raw biodiesel. It needs to be cleaned before it can be used.

Advantages of biodiesel fuel

Biodiesel fuel is a renewable energy source.
It is less polluting than petroleum diesel.
The lack of sulfur in $100%$ biodiesel extends the life of catalytic converters.
It can also be blended with other energy resources and oil.
It can also be used in existing oil heating systems and diesel engines without making any alterations.
The lubricating property of the biodiesel may lengthen the lifetime of engines.

Disadvantages of biodiesel fuel