We all are aware of the world’s dependence on the fossil fuels such as coal, petroleum, diesel, natural gas etc. But these are non-renewable sources of energy and are prone to depletion in the near future. Further, these fuels also pollute the environment. This creates a need for renewable and more eco-friendly fuel, which can substitute these fossil fuels.
The most agreeable alternative of the fossil fuels is the biodiesel.
What is biodiesel?
The bio diesel is produced from either animal fats or from Vegetable fats like jatropha curcas, algae fuel, waste vegetable oil (WVO), soya, canola, sunflower seed, algae, etc.
Apart from being renewable, the pure biodiesel (B100) also emits up to 40% less carbon monoxide.
Bio Diesel Production Processes
- Direct use and blending
- Thermal cracking (pyrolysis)
- Micro emulsification
- Transesterification (alcoholysis)
Among these methods, the trans-esterification process is used to produce cleaner and environmentally safe biodiesel .Further it is also economically safe method as it can use used or waste oil as raw material and the glycerol produced as bi-product can be utilized.
Transesterification process of biodiesel production – Overview
It is the process of alcoholysis of high viscosity vegetable oil or animal fat (triglycerides) by methyl/ethyl alcohol to produce low viscosity methyl/ethyl ester or Bio Diesel.
The overall reaction of alcoholysis or Transesterification can be represented as follows:
Triglycerides (Vegetable/animal fat) + Methyl Alcohol ↔ Glyserol (Bi-Product) + Methyl Ester (Bio Diesel)
Glycerol is produced as bi-product of the process.
Image source: wiki
Trans-esterification process – detailed reaction mechanism
Pre-Step: This step involves the dissociation of the alkali catalyst (NaOH) in water to produce ions. These ions aide the alcoholysis process:
OH – + ROH ↔ RO – + H2O
NaOR ↔OR – + Na +
Step-1: The first step involves the attack of carbonyl group of the triglyceride by the alkoxide ion, resulting in the formation of tetrahedral intermediate:
Triglycerides (Vegetable/animal fat) +OR – ↔ Tetrahedral Intermediate
Step-2: In the second step, the tetrahedral intermediate reacts with the alcohol to form ion of alcohol (Methyloxide/ethyloxide):
Tetrahedral Intermediate ↔ Alcoholic Ion + Methyl/ethyl Ester (Bio Diesel)
Step-3: In this step, the rearrangement of the tetrahedral intermediate, results in formation of an acid ester and diglyceride:
Tetrahedral Intermediate + Alcoholic Ion ↔Diglyceride + Methyl/ethyl Ester (Bio Diesel)
Step-4: The diglycerides are further reduced to monoglycerides to glycerol and methyl/ethyl esters (Bio-diesel).
Catalyzed trans-esterifications are typically completed within one hour. Thus the trans-esterification process is performed on high viscous triglycerides and reduced to low viscous ethyl esters, which have similar properties of diesel and can serve as a renewable, eco-friendly, alternate fuel source to replace it. The byproduct glycerol can be used for pharmaceutical formulation. Thus further reduce the cost of biodiesel.
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