Revolutionizing Biodiesel Synthesis: Kinetic and Thermodynamic Insights with Carbonized Doum-Shell Catalyst

Abstract

Background: Conventional methods of biodiesel (FAME) synthesis often involve transesterification processes that are catalysed by homogeneous catalysts, which present challenges in terms of catalyst recovery, environmental impact, and production cost. Heterogeneous catalysts, particularly those derived from agricultural waste, have emerged as promising alternatives due to their reusability, environmental friendliness, and cost-effectiveness. Objectives: The study aims to bridge gaps by providing a comprehensive kinetic analysis of biodiesel production using a synthesized and novel, doum-shell catalyst. It incorporates first, second, and third-order rate model kinetics, alongside the determination of some energy parameters. Methods: Doum palm shell (DPS) was characterized by Fourier Transform Infrared (FTIR) and Atomic Force Microscope (AFM), and then carbonized, ground, and sulfonated to create a biochar catalyst, which was then used in the esterification of palmitic acid (PA) with methanol. Kinetic modelling of the esterification process was performed, followed by deriving thermodynamic parameters using Arrhenius and Eyring-Polanyi equations. Results: Kinetic modelling identified the First-Order reaction as the most appropriate for describing the esterification process at an optimum performing temperature of 55 °С, 180 min reaction time and rate constant, k = 7 · 10-4 min-1. Thermodynamic parameters were derived from the Arrhenius and Eyring-Polanyi equations, providing a deeper understanding of the energy changes involved in the esterification reaction. The activation energy, pre-exponential factor, entropy, enthalpy and free energies obtained for the First-Order, describe the catalysing of the synthesis process by DPS as robust, reversible, non-spontaneous, feasible and energy efficient. In both kinetics and thermodynamics carried out, the Second- and Third-Order of reaction analysis described the experimental data poorly due to lower R2 values comparative to the First-Order rate at 45, 55 and 65 °С. FTIR analysis confirmed the successful conversion of feedstock to biodiesel, with distinct ester functional groups such as, –OH, –SO3H and –COOH groups, identified in the DPS catalyst. Conclusions: This research lays the groundwork for future studies and large-scale implementation of this catalyst in biodiesel production, particularly in regions with abundant doum palm resources. Through comprehensive experimentation and analysis, the carbonized doum-shell catalyst was demonstrated to be a viable and efficient option for FAME synthesis from PA and methanol.

Keywords

• doum palm shell
• biodiesel production
• esterification
• palmitic acid
• sulfonation