Some people do make their own biodiesel. Many people think that it is just a case of getting some vegetable oil and putting it in a car but it needs more than this.
Firstly if you are using second hand vegetable oil, such as some from a restaurant which has already been used to cook with, you will need to filter it to remove any food debris. You then need to add methanol to the oil. This is to extract the glycerol and you will need to add some sort of a catalyst such as sodium hydroxide or potassium hydroxide. The catalyst is used to aid the chemical reaction because it is not strong enough without.
If the vegetable oil has been used for cooking or has already been heated in some way, it needs further treatment. The reheating of the oil will cause some of the fatty acid bonds in the glycerol to break away and these need to be removed. They can either be esterified or removed by adding extra catalyst. The first option tends to be used in commercial production but the second in domestic or smaller scale production as it is simpler. One the glycerol is separated it is left to settle so that it is in layers. The biodiesel is then removed and washed and filtered and then dried.
It can be a very slow process as the filtering can take time as well as all of the other aspects. This means that you will need to have a supply in stock for when you run out or else you may have to wait quite a long time for some more.
It is also worth bearing in mind that if you make a mistake somewhere in the process then there is a risk that you might cause damage to the vehicle or machine that you are running with the biodiesel. This means that you need to completely sure of what you are doing.