Used frying oils as a source for supercritical FAME preparation.

Triglycerides of vegetable oils and fats are becoming increasingly important as alternatively fuels for diesel engines due to the diminishing petroleum reserves. However, their high viscosities and low volatilities do not permit their direct use or in oil/petrol blends in any engine diesel engine type. Nowadays the main process development to overcome this drawback is the methanolysis transestrification reaction to produce a mixture of FAME (Fatty Acid Methyl Esters) called biodiesel (BDF) which is a biodegradable, non-toxic diesel fuel substitute that can be used in unmodified diesel engines. It has a significant added value compared to petro-diesel because of its higher lubricity, which extends engine life and reduces maintenance costs and environmental benefits as well as contribution to fuel economy.

Although the alkaline catalyst transestrification method with methanol has the benefit of using moderate reaction conditions, several aqueous washings are needed to remove the catalyst after the reaction. Moreover, the oils and fats used, especially the waste ones, may contain water and free fatty acids. The presence of water reduces the catalytic activity, while free fatty acids react with the catalyst to produce saponified products, risking a reduction in the yield of FAME. Therefore, manufacturing biodiesel from waste cooking oils by the alkaline catalyst method is not necessarily easy.
Moreover biodiesel produced by transesterification with alcohols of vegetable oils presents glycerol as the major side-product. Due to the growning production rate of biodiesel, the availability of glycerol has also been rapidly increasing in recent years. Because the high costs due to its purification, glycerol from biodiesel is not economically suitable.
Non-catalytic biodiesel production methods with supercritical fluids have been, therefore, developed in order to resolve these various problems.

The aim of our project is the production of biodiesel using waste frying vegetable oils and different supercritical fluids as methanol, ethanol or carbon dioxide in order to reduce or eliminate the glycerol production.
All experiment were carried out batchwise in a 100 ml supercritical reactor. The sampling system was designed to monitor the reaction at various times. A GC-FID system was used to measure the fatty acid methyl esters composition of the produced biodiesel.