Bioethanol is ethyl alcohol, grain alcohol, or chemically C2H5OH or EtOH. It is a clear, flammable, colorless liquid that is miscible with water, as its hydrophilic hydroxyl group is capable of hydrogen-bonding with water molecules. Bioethanol refers to ethanol that is produced from biomass. It is the most widely used liquid biofuel produced from biological feed stocks that contain sugars or the materials that could be converted into sugars such as starch or cellulose.
Bio-ethanol and bio-ethanol/gasoline blends have a long history as alternative transportation fuels. It began with the use of ethanol in the internal combustion engine invented by Nikolas Otto in 1897. Brazil has utilized bio-ethanol as a transportation fuel since 1925. The use of bio-ethanol for fuel was widespread in Europe and the United States until the early 1900s. Because, it became more expensive to produce than petroleum-based fuel, especially after World War II, bio-ethanol’s potential was largely ignored until the oil crisis of the 1970s. Since the 1980s, there has been an increased interest in the use of bio-ethanol as an alternative transportation fuel. Countries including Brazil and the United States have long promoted domestic bio-ethanol production. In addition to the energy rationale, bioethanol/gasoline blends in the United States were promoted as an environmentally driven practice, initially as an octane enhancer to replace lead. Bio-ethanol also has value as oxygenate in clean-burning gasoline to reduce vehicle exhaust emissions. The ethanol production process, only uses energy from renewable energy sources. Hence, no net carbon dioxide is added to the atmosphere, making ethanol an environmentally beneficial energy source.
Advantages of Ethanol over Petrol
- Ethanol has a much higher latent heat of vaporization (855 MJ/kg) than petrol (293 kJ/kg). As a result, the fuel mixture entering the cylinder is much cooler and hence denser in case of ethanol than in the case of petrol. 2. Ethanol has a higher octane number (99) than petrol (80-100). As a result, ‘pre ignition’ does not occur when ethanol is used.
- 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 is much less likely to catch fire and explode in cases of fuel leakage, e.g., during accidents.
6. In can be mixed with petrol; this increases the octane rating of petrol. In USA a 20% ethanol: 80% petrol mixture is being marketed as ‘gasohol’.
Disadvantages of Ethanol
- Engines run on ethanol may give starting problems when the air is cool.
2. Ethanol is highly hydrophilic. As a result, it can absorb moisture from atmosphere, etc.
3. It reacts with metals used in the alloys of carburettors etc. It can be remedied by using nickel in the engine alloys.
4. The downstream processing for ethanol recovery is costly as it requires lots of energy.
5. Ethanol run engines use about 10% more fuel than petrol, which means a proportionately larger tank.
Ethanol Specifications for US, Brazil and EU
|D 4806||D 4806 Undenatured||Anhydrous||Hydrous|
|Color||Dye Allowed, but not mandated||Dye Allowed, but not mandated||Dye mandated for in country, but not for export.||Dye prohibited for in country||Dye Allowed, but not mandated|
|Ethanol Content, vol %, min.||92.1||93.9||99.6(3)||–||[96.8]|
|Ethanol + C3-C5 sat. alcohols, vol %, min||–||[98.4](2)||–||–||98.8|
|Total Alcohol, vol %, min.||–||[98.95]||99.6||95.1||[99.76]|
|C3-C5 sat. alcohols, vol %, max||–(1)||[4.5]||–||–||2.0|
|Water content, vol %, max||1.0||1.05||[0.4]||[4.9]||0.24|
|Density at 20C, kg/m3, max||–||–||791.5||807.6||–|
|Methanol, vol %, max||0.5||0.53||–||–||1.0|
|Denaturant, vol %, min/max||1.96 / 5.0||No Denaturant||No Denaturant||No Denaturant||Set By Country 0/1.3|
|Hydrocarbons, vol %, max||–||–||3(4)||3(4)||–|
|Solvent-washed gum, mg/100 mL, max||5.0||5.3||–||–||–|
|Gum or Resid by Evap, mg/100ml, max||5 (washed gum)||5.3 (washed gum)||–||5 (unwashed)(5)||10 (unwashed)(5)|
|Electrical Conductivity, uS/m, max||–||–||500||500||–|
|Sulfate, mg/kg, max*||4||4.2||–||4||Working|
|Inorganic Chloride, mg/kg, max||40.||42.1||–||1||25|
|Copper, mg/kg, max||0.1||0.105||0.07||–||0.1|
|Sodium, mg/kg, max||–||–||–||2||–|
|Iron, mg/kg, max||–||–||–||5||–|
|Acidity, mass % (mg/L), max||0.007 (56)||0.0074 (58.9)||0.0038 (30)||0.0038 (30)||0.007|
|pHe||6.5 – 9.0||6.5 – 9.0||–||6.0 – 8.0||Dropped|
|Phosphorus, mg/L, max||–||–||–||–||0.5|
|Sulfur, mg/kg, max.||30.||5||–||–||10|
|Appearance||Clear & Bright||Clear & Bright||Clear & No Impurities||Clear & No Impurities||Clear & Bright|
(1) Not specified by can be calculated for US. (Heavy alcohol content = 100 – ethanol content – methanol content – water content)
(2) Numbers in [ ] are calculated estimates and not specified limits
(3) Limit only applies to ethanol not produced by fermentation from sugarcane or ethanol contaminated by other types of alcohol
(4) Applies only to imported ethanol
(5) Procedures are likely different.
(courtesy: White Paper On Internationally Compatible Biofuel Standards, Tripartite Task Force Brazil, European Union & United States Of America)