Kinetic Modeling of the Hydroconversion of Carboxylic Acids into Biofuels

Hydrotreatment of vegetable oils is a technology that has shown its effectiveness in the production of biofuels in a large scale; nevertheless, few companies are capable of performing this process. Since it involves a complex mixture in the feedstock as well as a huge amount of reactions, it is not an easy task to achieve the modeling, design and optimization of industrial reactors when adequate data is not provided. This work is presented as a first attempt to establish a rigorous kinetic modeling able to describe the hydrotreatment of vegetable oils considering that carboxylic acids are either intermediates or components in the feedstock to be processed. To reach this goal,  the reaction network is generated on the basis of the molecular reactions and elementary steps performed in both functions of the catalyst, calculating heats of formation, entropies, symmetry and gas phase heat capacities for all the species generated in the reaction network. To obtain the global rate equation, species obtained are classified in groups of isomers (GOI) according to the number of carbons and branches of each species. The GOI’s rate equation is calculated for each elementary step defined in terms of the sum of the single rate equations. To reduce the amount of independent kinetic parameters, the concept of the “single event” is introduced. Meanwhile the Evans-Polanyi relation is used to calculate the activation energies. Experimental data obtained from a 100 ml batch reactor using a model carboxylic acid (dodecanoic acid), were used to calculate the independent kinetic parameters. This theoretical model is applied to analyze the behavior of the process when temperature and pressure are modified.