Batch Heterogeneous Catalytic Selective Hydrogenation of Vegetable Oils Over Lindlar Catalyst: Kinetic Modeling Supported by Reaction Mechanisms

Heterogeneous catalytic selective hydrogenation (HCSH) of vegetable oils is a reactive pathway to maximize the fraction of monounsaturated oleic acid, a component of industrial interest, thanks to its stability and low-temperature properties. Kinetics of HCSH is usually interpreted by pseudo-first order laws, as previously done by this research group with data from batch tests on canola oil (Lindlar catalyst, 120-180 °C, 0.4-1.2 MPa): the pseudo-first order kinetics could interpret the observed phenomenon only by variable selectivities (i.e., ratios of kinetic constants). The present work proposes a refined modeling by Hougen-Watson approach. Detailed reaction mechanisms were hypothesized, challenging the following alternatives: (i) H₂ adsorption on the catalyst occured (Hinshelwood-Langmuir) or not (Eley-Rideal), (ii) H₂ adsorption was molecular or dissociative, (iii) H₂ adsorption was competitive or not with fatty acids adsorption, and (iv) reaction intermediates were formed or not. Six reaction mechanisms were developed with related kinetic rate laws for HCSH. Their kinetic parameters were regressed for the abovementioned experimental data by a purposely developed MATLAB script. The best mechanism was chosen based on the highest explained variance ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msup><mml:mi>R</mml:mi> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msup> </mml:mrow> <mml:annotation>$R^{2}$</mml:annotation></mml:semantics> </mml:math> ) and the lowest number of parameters. Chemical-physical meaningfulness of regressed parameters for the best model was checked by comparison with the literature.