Acceleration and simplification of separation by addition of inorganic acid in biodiesel production

This paper describes a new approach to transesterification stopping and separation improving by the addition of inorganic acid, hydrochloric and phosphoric, to the whole reaction mixture after the reaction. The transesterification of oil was carried out by methanol and potassium hydroxide as the catalyst. The inorganic acid neutralises methoxide ions (formed from methanol and potassium hydroxide) and transforms soaps (formed by oil saponification) to fatty acids, which increases the acid number. The principle of stopping is the neutralization of the methoxide ions only. Best results are achieved by concentrated phosphoric acid with a ratio of 0.25 wt% to oil. The advantage is that separation is relatively fast (5 h) and the biodiesel conforms to EN 14214 without any other purification processes such as centrifugation, wet and dry washing and drying of the ester phase. Moreover, the content of glycerol in the formed glycerol phase is approximately 75%. This method of biodiesel production, which uses neutralization of methoxide ions after the transesterification followed by separation, saves energy because no purification processes are needed and no waste is formed. The biodiesel is more environmentally friendly because less energy is consumed. (C) 2018 Elsevier Ltd. All rights reserved.