Biofuels production by thermal cracking of soap from brown grease

The transformation of waste oils and fats into biofuels attracts great interest due to the low cost of these materials. The thermal and/or catalytic cracking of oils and fats is an alternative route to the classic transesterification process of biodiesel production when the raw material has low quality. In this work, thermal cracking of sodium soaps of residual fatty materials from Brazilian restaurants (brown grease mainly composed of fatty acids of soybean oil) was tested to assess the feasibility of yielding a high quality diesel-like product. The reactions occurred in a single stirred steel reactor of 300 ml at high temperatures (723 °K) at atmospheric pressure for 1h45 min. The organic liquid product was analyzed for acid and saponification value, thermogravimetric characteristics. The chemical composition of the liquid product diesel-like fractions was determined by FT-IR, Nuclear Magnetic Resonance Spectroscopy (NMR 1H and 13C) and GC-MS. The hydrocarbons obtained were very similar to diesel oil and suitable for use, in pure form or in mixtures, in diesel oil engines. Yields above 60% and very low acidity (0.5 mg KOH/g) were obtained, meeting the requirements of ANP (Brazilian National Petroleum Agency) Resolution No 51 de 25/11/15.