India imported about 2/3rd of its petroleum requirements last year, which involved a cost of approximately Rs. 80,000 crores in foreign exchange. Even 5% replacement of petroleum fuel by bio-fuel can help India save Rs.4000 crores per year in foreign exchange.
It is important that the options for substitution of petroleum fuels be explored to control this burgeoning import bill. The degrading air quality in our cities further warrant the quest for alternative, cleaner fuels. With the stock of fossil fuels diminishing throughout the world and demand for energy based comforts and mobility ever increasing, the time is ripe to strike a balance between energy security and energy usage. Having reached current levels of engineering excellence, reverting back to the ages of the bull carts will be next to impossible, compelling us to search for a basket of alternative fuels to derive energy that caters to our needs.
Several sources of energy, especially for driving the automotives are being developed and tested. This report presents detailed information on Biodiesel together with its emission benefits. The prospect of biodiesel as an alternative to conventional fuels like gasoline and diesel and the experience of other countries is also outlined.
1.0 Biodiesel
Biodiesel is the name for a variety of ester-based oxygenated fuels derived from natural, renewable biological sources such as vegetable oils. Biodiesel operates in compression ignition engines like petroleum diesel thereby requiring no essential engine modifications. Moreover it can maintain the payload capacity and range of conventional diesel. Biodiesel fuel can be made from new or used vegetable oils and animal fats. Unlike fossil diesel, pure biodiesel is biodegradable, nontoxic and essentially free of sulphur and aromatics. The concept of using vegitable oil as a fuel dates back to 1895 when Dr. Rudolf Diesel developed the first diesel engine to run on vegetable oil.
1.1 Production
Vegetable oils can be chemically reacted with an alcohol (methanol is the usual choice) to produce chemical compounds known as esters. Biodiesel is the name given to these esters when they are intended for use as fuel. Currently biodiesel is produced by a process called transesterification where the vegetable oil or animal fat is first filtered, then processed with alkali to remove free faty acids. It is then mixed with an alcohol (usually methanol) and a catalyst (usually sodium or potassium hydroxide). The oil’s triglycerides react to form esters and glycerol, which are then separated from each other and purified. Much of the current interest in biodiesel production comes from soybean producers faced with an excess of production capacity, product surpluses and declining prices. Methyl soyate, or soydiesel, made by reacting methanol with soyabean oil, is the main form of biodiesel in the United States. Waste animal fats and used frying oil (known as “fellow grease”), peanuts, cottonseed, sunflower seeds and canola are some of the potential feedstocks for biodiesel. Esters made from all the above feedstocks can be used successfully as automotive fuel, although they may differ slightly in terms of energy content, cetane number and other physical properties.
Oil from rapeseed is also a raw material of choice for biodiesel production and is leading with a share of over 80% as a raw material source with highly suitable properties. Sunflower oil takes second place with over 10% share mostly in Italy and Southern France. Percentage shared of some feedstocks for biodiesel in various countries is given in Table-1.
Table-1: Feedstock for biodiesel in some countries
Feedstock | % Share | Countries |
Rape seed | 80% |
|
Sunflower | 10% | Italy, Southern France |
Soya bean |
| U.S.A. |
Palm Oil |
| Malaysia |
Linseed&Olive oil |
| Spain |
Cotton Seed Oil |
| Greece |
Jatropha Curcas Oil |
| Nicaragua |
Beef Tallow |
| Ireland |
Used frying Oil |
| Australia |
The general process of biodiesel production is depicted in Figure-1. A fat or oil is reacted with an alcohol (methanol) in the presence of a catalyst to produce glycerine and methyl esters or biodiesel. The methanol is charged in excess to assist in quick conversion and recovered for reuse. The catalyst is usually sodium or potassium hydroxide, which has already been mixed with the methanol.
<?xml:namespace prefix = v ns = "urn:schemas-microsoft-com:vml" /?>
|
Reactor |
Settler |
Washing |
Purification |
Evaporation |
Alcohol Recovery |
Neutralization Distillation |
Settler |
Evaporation |
Alcohol |
Vegetable Oil |
Catalyst |
Mineral Acid |
Fatty Acid |
Glycerin |
Biodiesel |
Fig-1: General Process of Biodiesel Production
2.0 Characteristics of Biodiesel
Biodiesel as automotive fuel has similar properties to petrodiesel and as such can be directly used in existing diesel engines with no or minor modifications. It can be used alone or mixed in any ratio with petrodiesel. The most common blend is B20, a mix of 20% biodiesel with 80% petroleum diesel. Biodiesel has 11% oxygen by weight and essentially contains no sulphur or aromatics.
2.1 Physical Properties
Some of the physical characteristics of biodiesel are given in Table-2.
Table-2: Physical properties of Biodiesel
Properties | Values |
Specific gravity | 0.88 |
Viscosity @ 20 Ċ (centistokes) | 7.5 |
Cetane Index | 49 |
Cold filter Plugging Point (Ċ) | -12 |
Net Heating Value (Kilojoules/Liter) | 33,300 |
3.0 Emission Characteristics
Biodiesel is the only alternative fuel to have a complete evaluation of emission results and potential health effects submitted to the U.S.EPA under the Clean Air Act Section 211(b). These programs include the most stringent emissions testing protocols ever required by EPA for certification of fuels in the U.S. Emission results for pure biodiesel (B100) and mixed biodiesel (B20-20% biodiesel and 80% petrodiesel) compared to conventional diesel are given in Table-3.
Table-3: Biodiesel Emissions Compared to Conventional Diesel
Emissions | B100 | B20 |
Regulated Emissions | ||
Total Unburned Hydrocarbons | -93% | -30% |
Carbon Monoxide | -50% | -20% |
Particulate Matter | -30% | -22% |
NOx | +13% | +2% |
Non-Regulated Emissions | ||
Sulphates | -100% | -20%* |
Polyciclic Aromatic Hydrocarbons (PAH)** | -80% | -13% |
NPAH (Nitrated PAHs)** | -90% | -50%*** |
Ozone Potential of Speciated HC | -50% | -10% |
Life-Cycle Emissions | ||
Carbon Dioxide (LCA) | -80% | |
Sulphur Dioxide (LCA) | -100% | |
*Estimated from B100 results. **Average reduction across all compounds measured. ***2-nitroflourine results were within test method variability.
The use of biodiesel in a conventional diesel engine results in substantial reduction of unburned hydrocarbons, carbon monoxide and particulate matter. Emissions of nitrogen dioxides are either slightly reduced or slightly increased depending on the duty cycle or testing methods. Biodiesel decreases the solid carbon fraction of particulate matter (since the oxygen in the fuel enables more complete combustion to CO2), eliminates the sulphur fraction (as there is no sulphur in the fuel), while the soluble or hydrogen fraction stays the same or is increased.
Comments