What is Biodiesel?
Biodiesel A fuel comprised of mono alkyl esters (typically methyl or ethyl esters) of long chain fatty acids derived from vegetable oils or animal fats. Vegetable oils is chemically different from the biodiesel. Biodiesel need to meet standard set by ASTM. Vegetable oil and Mixtures or emulsions of vegetable oil and alcohol are not biodiesel. Main difference between biodiesel and vegetable is its viscosity.
Problem created by vegetable oil in diesel engine:
- High viscosity and poor combustion lead to carbon deposition, poor lubrication, engine wear and cold starting problems.
- Natural gums lead to problem in plugging filters and plugging injectors.
- It also causes engine knocking.
Biodiesel production from vegetable oil and animal fats:
- Mix Alcohol & Chemical Catalyst (Usually Base: NaOH, KOH): Methyl alcohol or ethyl alcohol is mixed with sodium hydroxide or potassium oxide to form methoxide or ethoxide. Usually methyl alcohol is preferred to ethyl alcohol because they are cheaper.
- Transesterification: Catalyst initiates the reaction and allows the fatty acid chains to detach and react with methanol (methoxide) to form new fatty acid esters. Typically, strong base catalyst is used however we also can use acid catalyst. Temperature of around 85 degree Celsius or 65 degree Celsius is used. For 65 degree less than 1-hour heating is required whereas for 30 we need 8 hr. heating. Besides this we need higher molar ratio of methoxide and oil because transesterification is reversible process. Only 90% conversion is feasible.
- Separate glycerol byproduct: Soap and water along with glycerol is formed as by product during transesterification. Glycerol need to be separated from biodiesel formed. Soap is formed as side reaction. Typically, decantation is used but larger plant use centrifugation. Glycerol contain methanol and catalyst.
- Biodiesel cleanup/processing: Washing is used to remove soap and methanol. Hot water is used and also acid also used to break soap. Washing option are top spray and water bubbling. And then drying is performed using vacuum to remove water.
Properties of Biodiesel:
- Lubricity
- Low Sulphur content
- Low CO and Hydrocarbon emission
- Poor cold properties: Cloud point and Pour point and Cold Soak filtration
Why Biodiesel ?
Biodiesel is a much better solvent than petro-diesel. Biodiesel loosens carbon deposits, varnishes, etc. from using petro-diesel causing fuel filter plugging. Cetane Number is considered as important properties for diesel engine. Cetane number is a measure of how well suited a fuel is for a diesel engine; higher cetane numbers indicate ease of ignition. Most biodiesels have higher cetane numbers of 46-60. And another important thing to remember about biodiesel is their Carbon emission reduction. B100 biodisel has around 80% of HC emission reduction. So mixing biodiesel with petro-disel reduce HC and CO emission.
