What is Biodiesel and How to Make it

The American Society for Testing and Materials (ASTM) defines biodiesel fuel as mono-alkyl esters of long chain fatty acids derived from a renewable lipid feedstock, such as vegetable oil or animal fat. Biodiesel is constructed from 2 words i.e.: “Bio” and “Diesel”. The word ‘‘Bio’’ represents renewable and biological source in con­trast to petroleum-based diesel fuel. The word ‘‘Diesel’’ refers to its use in diesel engines. As an alternative fuel, biodiesel can be used in neat form or mixed with petroleum-based diesel.

Biodiesel, as an alternative fuel, has many positive benefits. It is derived from renewable and domestic resources. The use of biodiesel thereby relieving reliance on petroleum fuel which Indonesia are now importing it. Biodiesel is also biode­gradable and non-toxic. Comparing with petroleum-based diesel, biodiesel has a more favourable combustion emission profile, such as low emissions of carbon mon­oxide, particulate matter and unburned hydrocarbons. Carbon dioxide produced by combustion of biodiesel can be recycled by photosynthesis, thereby minimizing the impact of biodiesel combustion on the greenhouse effect (Körbitz, 1999; Agarwal and Das, 2001).

Biodiesel has a relatively high flash point (150 °C), which makes it less volatile and safer to transport or handle than petroleum diesel (Krawczyk, 1996). It provides lubri­cating properties that can reduce engine wear and ex­tend engine life (Von Wedel, 1999). In brief, these merits of biodiesel make it a good alternative to petroleum-based fuel and have led to its use in many countries, especially in environmentally sensitive areas.

The most common way to produce biodiesel is by transesterification, which refers to a catalyzed chemical reaction involving vegetable oil and alcohol to yield biodiesel or fatty acid methyl esters and glycerol. Triacylglycerols (triglycerides) as the main compo­nent of vegetable oil consist of three long chain fatty acids esterified to a glycerol backbone. When triacyl­glycerols react with methanol, the three fatty acid chains are released from the glycerol skeleton and combine with the alcohol to yield fatty acid alkyl esters (e.g., fatty acid methyl esters or FAME). Glycerol is produced as a by-product which can be utilized later as soap raw material. Methanol is the most commonly used alcohol because of its low cost and easy to find in general chemical stores.

The very first process before putting used cooking oil into the plant is to screen the oil to separate it from debris. The screened oil is mixed with methanol and steered for about 45 minutes at 55 oC in the mixing tank. The liquid is then settled for about 30 minutes to separate biodiesel from glycerol. Biodiesel produced still needs to be washed by water to dissolve impurities such as glycerol, soap, catalyst, methanol and other remained chemical materials. The washing water is then removed by boiling it for about 45 minutes.