Method for Quantification of Methanol and Sulfuric Acid Required for Esterification of High Free Fatty Acid Oils in Biodiesel Production

Abstract

Trasesterification of oils and fats using base catalyst is the common method of biodiesel production.  However, free fatty acids (FFA) in oils form soap with the base catalyst and hence FFA is converted into esters by acid esterification prior to transesterification.  Acid esterification is a reversible reaction and therefore high amount of alcohol (methanol) is required to promote the forward reaction.  However, use of large amounts of excess methanol and the catalysts (acid) increases the production cost. Therefore, in this work, a method to quantify feasible amounts of alcohol and acid required for acid esterification of high FFA oils was established. This method is fast, required to estimate only the FFA present in the oil by measuring the acid value and the reactant quantities were estimated based on the weight of FFA.  It was shown by using high FFA rubber seed oil that the optimum FFA conversion could be obtained when methanol concentration was 2.5 g/g of FFA, H₂SO₄ concentration was 0.05 g/g of FFA and the reaction time was 30 min. Further, quantification of reactants and reaction parameters were validated with Neem (Azadirachta indica) and waste cooking oils at different scales of operation.