Volume 8, Issue 2 (February 2011)
Potentiometric Titration as an Alternative Technique for the Determination of the Iodine Value in Biodiesel Matrix from Palm Oil
The specification of biodiesel is related to factors associated with its quality as a fuel. The iodine value as one of those quality parameters measures the degree of unsaturation present in a biodiesel composition. The unsaturated fatty acids (existence of double bonds) are susceptible to the oxidation reactions that can lead to the formation of polymeric compounds by heating. Moreover, these polymeric compounds can produce gum formation, which is detrimental to the vehicle engine due to its corrosive actions. For determining the iodine value in biodiesel, the standardized procedures use volumetric titration—with starch as an indicator—as the main technique for iodine value measurement. Some of these procedures also mention potentiometric titration as an alternative technique. This work aims to show the results of the iodine value obtained from an experimental design based on 23 factorial designs at two levels. It was performed on a biodiesel matrix from palm oil in order to indicate major trends as well as a direction to choose the best alternative to determine the iodine value for developing certified reference materials by Inmetro, the Brazilian Metrology Institute. Three variables were studied: two qualitative variables—the titration techniques (volumetric and potentiometric) and the solvent used to dilute the biodiesel—and one quantitative variable, the temperature. There were no significant differences between the two techniques used, though it was not the case for variables such as solvent and temperature. Therefore, the potentiometric technique has shown better quality in the determination of the iodine value when compared to the volumetric technique. The relative standard deviations presented by the potentiometric titration were from 0.04 % to 0.32 %. On the other hand, the volumetric titration presented relative standard deviations ranging from 0.25 % to 1.03 %.