Making Biodiesel (transesterification)
As mentioned earlier, biodiesel can be made using vegetable oils or animal oils and fats. There are three basic methods for making biodiesel using oils and fats:
- Base catalysed transesterification of oil
- Direct acid catalysed transesterification of oil
- Converting oil to its free fatty acids and then to biodiesel
The first option is the most commonly used because it is the most economical of the three and requires only low pressures and temperatures and gives a good conversion yield (about 98%). Making biodiesel with this method basically involves turning oil into biodiesel, and is carried out by a process called transesterification. Despite the long and scientific sounding name, this simply requires adding a commonly found catalyst to alcohol (collectively called the reactants), which are then added to the oil. The end result is transesterified oil, or biodiesel. In fact this process really results in two products - biodiesel (also called methyl esters) and glycerine, a valuable by-product used in the production of soap.
Making Biodiesel:
| (Reactants) Catalyst + Alcohol | + | Vegetable Oil | = | Biodiesel |
|---|
The Catalyst
A catalyst is any substance that changes the rate of a chemical reaction without being consumed by the reaction itself. There are two choices for the catalyst for making biodiesel:
- Sodium hydroxide - NaOH (otherwise known as caustic soda or lye)
- Potassium hydroxide - KOH (otherwise known as potash)
Sodium hydroxide is the cheaper option, but potassium hydroxide is easier to use and mixes better with alcohol. The process is much the same using either catalyst but more potassium hydroxide will be needed than when using sodium hydroxide.
The Alcohol
Unfortunately simply buying some cheap wine or lager will not be suitable for making biodiesel because the alcohol content will need to be almost 100%. There are also two choices for the alcohol:
- Methanol (wood alcohol)
- Ethanol (absolute alcohol)
Methanol is easier to use than ethanol and tends to produce more consistent results with less effort. Ethanol is the greener choice for producing fossil free fuel but it needs to be very dry, can be expensive and needs oil that is very low in free fatty acids. Making biodiesel using ethanol is certainly not for beginners.
The Reactants
When using methanol, sodium hydroxide is normally used as the catalyst and this mixture produces sodium methoxide. Potassium hydroxide can be used instead but around 1.4 times more will be required. When using ethanol, potassium hydroxide is normally used as the catalyst because sodium hydroxide takes too long to dissolve in ethanol. This mixture creates potassium ethoxide. In either case, making biodiesel safely should always be your first priority so please make sure you read the section on health and safety.
The Oil
A variety of oils can be used in the production of biodiesel, including various vegetable oils, animal fats, and algae. When using the most common choice, vegetable oil, there are also choices here:
- Straight vegetable oil (SVO)
- Waste vegetable oil (WVO)
Straight vegetable oil is generally new, unused cooking oil, whereas waste vegetable oil is oil that has already been used and is traditionally dumped into landfill sites once finished with. Either type of oil can be used for making biodiesel, however; straight oil will be more costly, and waste oil will require more processing to remove debris and to deal with the increased presence of free fatty acids.
Is it Legal?
The goalposts have moved somewhat over the years, but currently making biodiesel for personal use is perfectly legal; the government permits the production of 2,500 litres of biodiesel a year TAX FREE. Visit HM Revenue & Customs website for more information (4.2.1. Exempt producers/users). Also, The Environment Agency provides details about the regulations surrounding biodiesel production.
A note on Home Insurance
As well as noting the safety implications regarding making biodiesel, consideration must be given as to whether your home insurance policy will cover any damage caused if say an explosion occured. Most insurers policy wordings state that policyholders are required to ensure that 'reasonable precautions' are adhered to. If you intend to make biodiesel, check first with your insurance company to confirm that cover will be provided against any damage caused to your home. In any case, it is advisable that the manufacturing process is carried out as far from your house as possible, and in an area that should the worst happen, the impact of any damage would hopefully be reduced. Detached outbuildings or worksheds would be ideal. Integral garages or utility rooms would not.