Trans-Esterification Between Citric Acid and Peanut Oil at Low pH and Ambient Temperature Catalyzed by Citric Acid and Sulfuric Acid Protonic Acid-H+

Abstract

The reason of this manuscript was to study the trans-esterification between the peanut oil and alcohol of citric acid molecules at ambient temperature with low pH and peanut oil was in excess in comparison with citric acid using two types of protonic acid-H+ catalyst such as the unattached protonic acid-H+ of reagent citric acid molecules at pH=1.66 with citric acid catalyst-unattached protonic acid-H+/peanut oil-fatty acids ratio [mol./mol.%]=1.21% and the unattached protonic acid-H+ of sulfuric acid molecules at pH=-3.76 with sulfuric acid catalyst-unattached protonic acid-H+/peanut oil-fatty acids ratio [mol./mol.%]=1.05%. Thus, biodiesel has been synthesized and basically characterized. Also, citric acid conversions evolutions with reaction-time and evaluation of reacted and unreacted peanut oil fatty-acids evolutions with reaction-time has been done following a protocol which allowed the quantification of the unreacted citric acid molecules. In the same time, the used protonic acid-H+ catalysts were characterized by their activities and turnovers evolutions. All these results helped the comprehension of the very probable mechanisms of this trans-esterification catalyzed by these protonic acids-H+. Particularly, it was noticed that the initial catalysts’ activities and turnovers were all the time very important but decreased in a sizeable way from 1mn reaction-time until obtaining generally a yellow biodiesel after 60mn reaction-time. These results allowed to consider that at these previous experimental conditions, molecules steric size influenced the catalysts’ activities and turnovers; and the first step was composed not only by the trans-esterification reaction between citric acid’s alcohol organic function and peanut oil but also the dehydration of citric acid molecules to form the white citric acid monomer, it could be transformed to another great molecules like yellow citric acid monomer or to another more great molecules composed with new alkene-unsaturated organic function which concentration increased and/or decreased with reaction-time according to the protonic acid-H+ nature as molecules and influenced the color of biodiesel in this case yellow or imperial yellow. Indeed, it was noticed that even if all catalysts activities and turnovers decreased globally, the citric acid protonic acid-H+ catalyst became clearly more active than the sulfuric acid protonic acid-H+ catalyst with time certainly because of the decrease of its alkene -unsaturated organic function concentration with time and still confirmed the alkene-unsaturated organic function effects as efficient support for protonic acid-H+ catalyst mobility.