08-10-2012, 04:32 PM
Formation of Biodiesel
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What is Biodiesel?
Biodiesel refers to a non-petroleum-based diesel fuel consisting of short chain alkyl (methyl or ethyl) esters, made by transesterification of vegetable oil or animal fat (tallow), which can be used (alone, or blended with conventional petrol diesel) in unmodified diesel-engine vehicles. Biodiesel is distinguished from the straight-vegetable oil (SVO) (sometimes referred to as “waste vegetable oil” “WVO” “used vegetable oil” “UVO” “pure plant oil”, “PPO”) used(alone, or blended) as fuels in some converted diesel vehicles.”Biodiesel” is standardized as mono-alkyl ester and other kinds of diesel-grade fuels of biological origin are not included.
Uses of biodiesel
• Biodiesel fuel is a renewable energy source that can be made from soy beans grown for fuel, or from cooking oils recycled from restaurants. This means it is a renewable resource unlike petroleum-based diesel.
• There is an excess production of soybeans in the United States; therefore biodiesel is an economic way to utilize this surplus.
• Biodiesel is less polluting than petroleum diesel. Compared to petroleum diesel, biodiesel produces less soot (particulate matter), carbon monoxide, unburned hydrocarbons, and sulfur dioxide.
• The absence of sulfur in 100% biodiesel should extend the life of catalytic converters.
• Biodiesel fuel can also be used in combination with heating oil to heat residential and industrial buildings. This can reduce dependence on non-renewable and increasingly expensive heating oil.
• Biodiesel burns cleaner & is made of non-toxic chemicals so it does not give out poisonous fumes, unlike the ordinary fuel.
Reactions involved
Transesterification:
Animal & plant fats & oils are typically made of triglycerides which are esters of free fatty acids with the trihydric alcohol, glycerol. In the transesterification process, the alcohol is deprotonated with a base to make it a stronger nucleophile. Commonly, ethanol or methanol is used. As can be seen, the reaction has no other inputs than the triglyceride & the alcohol.
Normally, this reaction will precede either exceedingly slowly or not at all. Heat, as well as an acid or base are used to help the reaction more quickly.
Biodiesel is a much cleaner fuel than conventional fossil-fuel petroleum diesel
• Biodiesel burns up to 75% cleaner than petroleum diesel fuel.
• Biodiesel reduces unburned hydrocarbons (93% less), carbon monoxide (50% less) & particulate matter (30% less) in exhaust fumes, as well as cancer-causing PAH (80% less).
• Sulphur dioxide emissions are eliminated (biodiesel contains no Sulphur).
• Biodiesel is a plant-based & using it adds no extra CO2 greenhouse gas to the atmosphere.
Disadvantages of Biodiesel
• Biodiesel is currently about one and a half times more expensive than petroleum diesel fuel. Part of this cost is because the most common source of oil is the soybean, which only is only 20% oil. However, the costs of biodiesel can be reduced by making biodiesel from recycled cooking oils rather than from new soy beans, or by making it from plant matter with higher oil content.
• It takes energy to produce biodiesel fuel from soy crops, including the energy of sowing, fertilizing and harvesting.
• Biodiesel fuel can damage rubber hoses in some engines, particularly in cars built before 1994. You should check with the manufacturer before using biodiesel to see if you need to replace any hoses or rubber seals.
• Biodiesel cleans the dirt from the engine. This dirt then collects in the fuel filter, which can clog it. Clogging occurs most often when biodiesel is first used after a period of operation with petroleum diesel, so filters should be changed after the first several hours of biodiesel use.