(576f) Kinetics of Free Fatty Acid Esterification On Sulfated Zirconium Oxide

Biodiesel has emerged as a promising renewable and clean energy alternative to petrodiesel. While biodiesel has traditionally been prepared through homogeneous base catalysis, heterogeneous acid catalysis has been investigated recently due to its ability to convert cheaper but high free fatty acid content oils such as waste vegetable oil while decreasing production cost. In this work, the reaction mechanism of palmitic acid over sulfated zirconia (SO₄/ZrO₂) and activated acidic alumina (AcAl₂O₃) were studied experimentally in a batch reactor. The models of the reaction over the catalysts were developed in two parts. First, a kinetic study was performed using a deterministic model to develop a suitable kinetic expression and the related parameters were estimated. Second, a stochastic model was developed to further confirm the nature of the reaction at the molecular level. The esterification of palmitic acid obeyed the Eley-Rideal mechanism in which palmitic acid and methanol are the adsorbed species on the surface of SO₄/ZrO₂ and AcAl₂O₃ respectively. The coefficients of determination of the deterministic model were 0.98, 0.99 and 0.99 for SO₄/ZrO₂ at 40, 60 and 80^oC respectively and 0.99, 0.96 and 0.98 for AcAl₂O₃ at the same temperature. The deterministic and stochastic models were in good agreement.