Kinetic analysis and modeling of hemp seed oil methanolysis over quicklime

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Hemp (Cannabis sativa L.) is a versatile crop used across multiple industries, and its seed oil has potential application as a renewable raw material for biodiesel production. This study investigates the kinetics of biodiesel production via quicklime-catalyzed methanolysis of hemp seed oil (HSO). Owing to the moderately high concentration of free fatty acids, HSO was first subjected to esterification. The methanolysis of the esterified HSO was performed at methanol-to-HSO molar ratios of 6:1, 9:1, and 12:1, with quicklime amounts of 3%, 5%, and 7% of HSO mass, at 60 oC under atmospheric pressure. The kinetics of the methanolysis reaction was evaluated using two different kinetic models: a pseudo-first order model and a model involving a changing reaction mechanism coupled with triacylglycerol (TAG) mass transfer limitations. The pseudo-first order model effectively described the reaction kinetics within two distinct regimes, initially controlled by TAG mass transfer, followed by a chemical reaction-controlled regime. The second model provided a continuous description of the reaction kinetics over the whole reaction course. The volumetric TAG mass transfer coefficient and the parameter defining the affinity of TAG to the active sites of the catalyst were found to be independent of methanol concentration but increased with catalyst amount. Both models yielded the same apparent reaction rate constant (0.155 min-1) and demonstrated very good agreement with experimental TAG conversion degree data (MRPD = ±10.8%, 81 data points). Despite comparable accuracy, the model involving the changing reaction mechanism and TAG mass transfer limitations is recommended due to its computational simplicity and consistent applicability.