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Ferric sulphate catalysed esterification of free fatty acids in waste cooking oil

Gan, Suyin, Ng, Hoon Kiat, Ooi, Chun Weng, Motala, Nafisa Osman, Ismail, Mohd Anas Farhan
Bioresource technology 2010 v.101 no.19 pp. 7338-7343
biodiesel, catalysts, cooking fats and oils, esterification, ferric sulfate, free fatty acids, hydrolysis, ions, metals, methanol, temperature
In this work, the esterification of free fatty acids (FFA) in waste cooking oil catalysed by ferric sulphate was studied as a pre-treatment step for biodiesel production. The effects of reaction time, methanol to oil ratio, catalyst concentration and temperature on the conversion of FFA were investigated on a laboratory scale. The results showed that the conversion of FFA reached equilibrium after an hour, and was positively dependent on the methanol to oil molar ratio and temperature. An optimum catalyst concentration of 2wt.% gave maximum FFA conversion of 59.2%. For catalyst loadings of 2wt.% and below, this catalysed esterification was proposed to follow a pseudo-homogeneous pathway akin to mineral acid-catalysed esterification, driven by the H⁺ ions produced through the hydrolysis of metal complex [Fe(H₂O)₆]³⁺ (aq).