Our approach being the most ecological possible, the oil used for making biodiesel is used cooking oil collected from all sorts of eating establishments. In order to collect the best sort of oil, talk to the owner of the restaurant as well as the chef so you can explain the purpose of your approach. Collecting oil without permission can be qualified as an offence. Furthermore, make sure you check the quality of the oil collected. Used oil contains free fatty acids. They appear when oil is left in the open air over a certain period of time and becomes rancid or when heated in the presence of water. Frying food (that contains water) therefore causes FFAs to appear in oil. During transesterification, these FFAs react with the catalyst (strong base) and create an unwanted soap. The soap stops the products of the reaction, biodiesel and glycerol, from separating correctly, which creates an emulsion that is difficult to work with.
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