Kinetics of Oxidation Decomposition on Jatropha Curcas Biodiesel

Abstract

High free fatty acid jatropha curcas oil was use as a feedstock of biodiesel through two step esterification, first by reaction of Jatropha curcas oil with methanol catalyzed by sulfuric acid, and second step is transesterification process with methanol catalyzed by sodium hydroxide. After purification step, 120 ppm pyrogallol was introduced into Jatropha curcas biodiesel. Accelerated controlled oxidation process was performed using rancimat test equipment with the dry airflow to the reaction tube is 10 L/min. Assuming that oxygen only reacts with double bond of the compound that compose biodiesel, measurement the quantity changes of double bond on biodiesel by the changes of the value of iodine number will brought to the rate of reaction. While reaction rate constant determine by Arrhenius law was calculated from the data of time to reach induction period in a certain temperature. It was found that total rate of oxidation process was determined by chemical reaction rate rather than mass transfer rate of oxygen to the body of biodiesel, both on biodiesel with or without pyrogallol. While in a presence of 120 ppm pyrogallol on jatropha curcas biodiesel, Arrhenius constant was determined by the value of frequency factor (A) = 28.47 x 106/sec and activation energy (E) = 97,31 kJ/mol. This mean that on the ambient temperature 30 oC, Jatropha curcas biodiesel in a presence of 120 ppm pyrogallol will decrease their iodine value 3.4% after 2.3 years.