Biodiesel is made from a combination of any vegetable or animal fat, and an alcohol, usually methanol. Quality biodiesel that is made to fuel specifications will run any diesel engine. Feedstock is assessed on it’s energy content, purity and water content. Most biofuel crops are annuals, which bring about a food vs fuel debate, with oil seed bearing trees the better option.
Vegetable oil is a fat that is liquid at 20ᵒc. Examples of biodiesel feedstocks include:
Used cooking oil (UCO)
UCO is the cheap and most environmentally friendly biodiesel feedstock available. The trade off is that it typically has 2 – 4% free fatty acid content, chips, water, cigarette buts, engine oil, rubber gloves, etc thatis required to be filtered out.
UCO can contain any fat.
Jatropha biodiesel is primarily used in India and Sri Lanka where the plant is native and cheap labour is available to harvest it. Jatropha can be hedged and used as a fence as it is spiky and deters animals. Trials in South Africa found that plantations of it created a wildlife desert as the berries make animals constipated. Jatropha is listed as a noxious weed in some states in Australia and is only considered an appropriate plantation in its native environment.
Pongamia is the biodiesel tree of the future. Pongamia is in the pea family, it does not like frost, it is drought tolerant and fixes nitrogen, and it is native to most of the tropical world including Australia. Pongamia produces a pod that contains oil. It has been estimated from realistic yields that Australia could meet its entire petrol, diesel, kerosene and LPG consumption with a 200km x 200km square paddock of Pongamia. This is smaller than many farms in Australia. In practice, you would not plant it all in one paddock it would be dispersed through appropriate climates as wind breaks on a farm for example. This provides shade for animals and another income stream for the farmer.
Canola biodiesel is the most common biodiesel in Europe.
Sunflower biodiesel is the most common biodiesel in France.
Moringa is another very promising biodiesel feedstock. It is an oil-producing tree.
Some bioenergy businesses assert that Mustard biodiesel has potential application, though it’s yields are lower than that of canola. The promise is that it will give better yields in dry conditions.
This was investigated in 2006 during a dry year, when mustard should have out preformed canola side by side, crops of mustard and canola were assessed. It was discovered that the canola crop had twice the yield of seed than the mustard crop.
Tallow biodiesel makes superior biodiesel unless you live in cold areas. Tallow biodiesel has a higher energy content than fossil diesel but it gels at higher temperatures. Regardless, tallow biodiesel can be used down to +2ᵒc or distilled to achieve lower operating temperatures.