Effect of Water On Esterification of Palmitic Acid Using ZSM-5 and Faujasite Zeolite Catalysts

Our research group has demonstrated the production of fatty acid methyl esters (biodiesel) using activated sludge generated from a wastewater treatment facility.  One of the main operating costs of this process is drying of the sludge prior to oil extraction and reaction.  A method of generating biodiesel from oil without transesterification is to convert the lipids to free fatty acids via hydrolysis, followed by esterification to obtain the fatty acid methyl esters (FAME). Thus, we have conducted a study to determine the maximum concentration of water that the esterification reaction would tolerate using zeolite catalysts.

This alternative method employs a solid acid to catalyze the esterification of the free fatty acid.  Since the silica:alumina (SiO₂:Al₂O₃)of the zeolites affects its acidity and hydrophobicity, the influence of the SiO₂:Al₂O₃ ratio in these catalysts on the reactions will be analyzed. These catalysts were screened for highest activity in conversion of fatty acid to FAME and water tolerance. The effect of water on the reaction was examined at volume compositions of 5 %, 10%, 20%, and 50%.

Esterification was completed using palmitic acid to represent the free fatty acids present in the oils. Two types of zeolite catalysts – ZSM-5 and Faujasite (Y) zeolites with SiO₂:Al₂O₃ ratios of 80:1 and 30:1 were tested and compared. The reactants included 0.5 g fatty acid, 10 ml methanol, and 10 mass % catalyst, with reaction temperature of 65°C, and a duration of 3 hours. The effect of various concentrations of water on the esterification of palmitic acid using these catalysts, and the reaction kinetics were evaluated to determine their activity and usability in the presence of water. Reaction parameters such as rate constants, rates, and activation energy were obtained.

Preliminary results on the ZSM-5 catalyst with SiO₂:Al₂O₃ ratio of 30:1 shows the activation energy to be 37.5 KJ/mol which is comparable to literature results for strong acids on a similar system. The yield of FAME shows nonlinear dependency on water concentration.