Backgrounder on ethanol
30 October 2004
What is 'Ethanol'?
Ethanol is the chemical name for commonly used alcohol, also known as ethyl alcohol, also known as spirit, rectified spirit, extra neutral alcohol. Two routes are used to produce ethanol - synthetic manufacture and bio fermentation. Synthetic manufacture involves chemical reaction of petroleum substances. Ethanol produced through this route has high propanol content
Bio fermentation involves fermenting sugar-bearing or starchy substrates using yeast. The fermented wash contains ethanol with other impurities. Distilling a fermented wash containing ethanol produces rectified spirit.
Rectified spirit has usually about 95 per cent by volume ethanol, the remainder being water, and some trace impurities. This is because ethanol forms azeotrope with water at around 95 per cent v/v concentration and cannot be separated from water above that point by simple distillation.
What is 'Fuel-Ethanol'?
Ethanol (Ethyl alcohol) used as an additive to fuel, by blending with petrol, for motor vehicle is called fuel-ethanol. Fuel ethanol can be used as an oxygenate in petrol. It reduces emission of carbon monoxide by taking combustion to completion. It replaces oxygenates like tetraethyl lead which leads to poisonous lead-fumes polluting the atmosphere. It is also a replacement for other oxygenates like MTBE (methyl tert-butyl ether) and ETBE (ethyl tert-butyl ether) - which can cause surface water pollution.
It maintains the 'carbon cycle' of nature, reducing the 'greenhouse effect'. It is made from renewable sources of material like agricultural products and prevents depletion of limited and precious resources like fossil fuels. It employs renewable source of energy like solar energy through a natural route. It is a material readily available within our country and need not be imported from outside.
Ethanol could be blended in various proportions in petrol. Ethanol is usually added 5 to 10 per cent by volume of petrol for such application. In Brazil, ethanol is added 24 per cent by volume in gasoline (petrol).
Ethanol is also added to diesel. Usually, 3 per cent by volume is added. Tests have been conducted satisfactorily with up to 10 per cent by volume addition.
Ethanol added to petrol is also referred to as absolute alcohol, anhydrous alcohol, dehydrated alcohol, power alcohol, etc.
The specifications of fuel-grade ethanol for blending in petrol are defined as per ASTM D 4806 as follows:
| Ethanol, volume per cent, min. | 92.1 |
| Methanol, volume per cent, max. | 0.5 |
| Solvent-washed gum, mg/100 mL, max. | 5.0 |
| Water content, volume per cent, max. | 1 (Note1) |
| Denaturant content, volume per cent, min. | 1.96 |
| Volume per cent, max. | 4.76 |
| Inorganic Chloride content, mass ppm (mg/L), max. | 40 (32) |
| Copper content, mg/kg, max. | 0.1 |
| Acidity (as acetic acid CH3COOH), mass per cent (mg/L), max. | 0.007 (56) (Note 3) |
| PH | 6.5 to 9.0 |
| Appearance | Visibly free of suspended or precipated contaminants (clear and bright) |
Notes:
1. In some case, a lower content may be necessary to avoid phase separation of gasoline-ethanol blend at very low temperatures. This reduced water content, measured at the time of delivery, shall be agreed upon between the supplier and purchaser.
2. If denatured fuel ethanol is prepared by the addition of denaturants to undenatured fuel ethanol after fuel ethanol after it has been produced rather than during the dehydration process, the 15.56/15.56o C (60/60 o F) specific gravity in air of the undenatured fuel ethanol shall be in the range from 0.7937 - 0.7977.
3. Denatured fuel ethanol may contain additives such as corrosion inhibitors and detergents that may affect the titratable acidity (acidity as acetic acid) of the finished fuel ethanol. Although the base fuel ethanol may meet the acidity specification, the effect of these additives may produce an apparent high titratable acidity of the finished product. Contact the ethanol supplier if there is a question regarding the titratable acidity of your denatured ethanol to verify that the base ethanol meets the acidity requirements of section 4.1
Specifications of Absolute Alcohol as per IS : 321 - 1964
| Component | Unit | Content |
| Specific gravity at 15.6 °C, max | - | 0.796 |
| Ethanol content at 15.6 °C, min | per cent volume | 99.50 |
| Miscibility with water | - | Miscible |
| Alkalinity | - | Nil |
| Acidity (as acetic acid, CH3COOH), max., | per cent w/w | 0.006 |
| Residue on evaporation, max., | per cent w/w | 0.005 |
| Aldehyde content (as CH3COOC2H5) max | g/100 ml | 0.10 |
| Copper (as Cu), max | g/100 ml | -- |
| Lead (as Pb), max | g/100 ml | -- |
| Methyl alcohol content | - | To satisfy the requirement of test |
| Fusel Oil | - | To satisfy the requirement of test |
| Ketones, isopropyl, tertiary butyl | - | To satisfy the requirement of test |
| Sulphur compounds | per cent w/w | -- |
| Sulphur dioxide (as SO2) | per cent w/w | -- |
In order to make fuel-ethanol unsuitable to drink (before blending with petrol), it is denatured by adding another substance.
Fuel-ethanol has following functions:
- Octane enhancement / anti-knocking agent
- Oxygenating agent
- Fuel extender / fuel replacement.
