Esterification of rosin with methyl alcohol for fuel applications

Oleoresin is obtained via tapping of living pine trees and as a byproduct of Kraft process in the pulp industry. Its low cost of production becomes it in an attractive source for biofuels. Oleoresin is composed mainly by rosin (around 80%, a solid mixture of isomeric abietic acids), and cannot be used directly as fuel in engines. Conversely, the methyl ester of rosin has lower boiling and melting points than rosin and posseses high solubulity in hydrocarbons. Esterification of rosin with methyl alcohol was evaluated over acid and basic heterogeneous catalysts in the presence of several solvents. In contrast to acid catalysts, basic materials were active in the reaction. In particular, a low-cost calcium-based material showed the best performance. Conversion of rosin of 55% with a complete selectivity to methyl esters was obtained with 40% wt. loading of the calcium-based material (respect to rosin) and mild conditions (atmospheric pressure, 64 °C and 3.5 h) and without solvent. Other catalysts, such as magnesium oxide, titanium dioxide and alumina, achieved up to 30% conversion. The calcium carbonate and calcium hydroxide were the main phases in the calcium-based material, suggesting that the strength of basic sites can be an important property of the catalyst activity. Calcium-based material was reused in five reaction cycles, obtaining a significant reduction in the activity that was attributed to catalyst poison and insufficient after treatments.