High-temperature esterification of fatty acids with methanol at ambient pressure

The article presents the results of the kinetic study of the acid-catalyzed esterification of free fatty acids (FFA) with methanol (MeOH) at elevated temperatures above the boiling point of MeOH, at ambient pressure, and at continual flow of liquid MeOH into the reaction mixture. Under these conditions, the reaction follows the rate equation valid for reactions of the first order. Beside temperature, the pseudo rate constant depends also on the flow rate of MeOH and on the concentration of a catalyst. At temperatures 50-60 degreesC higher than the boiling point of MeOH, the reaction rate is two to three times higher than at the temperatures close to the boiling point of MeOH. Apart from the temperature, the increase of the rate is facilitated also by a high local molar excess of MeOH in the input site with respect to FFA and by effective removal of water from the reaction mixture. The composition of the reaction mixture is then farther from the equilibrium composition. High conversion of FFA to methyl esters (above 99%) with low residual acidity of the product (acid value around 2-3 mg KOH/g) is achieved at short times of several tens of minutes and at a low total molar ratio of MeOH/FFA of around 3-4.