(624b) Mechanistic Study of the Conversion of Dodecanoic Acid into Hydrocarbons

Hydrotreatment of vegetable oils is technology with increasing interest for the production of renewable transportation fuels. The triglycerides in the vegetable oils are converted by means of high temperature, high hydrogen pressure and a bifunctional catalyst into hydrocarbons. The development of a kinetic model for the global reaction is important for the design and optimization of industrial reactors. However as many elementary steps and molecular reactions are involved, it results very complex. As a first attempt to tackle this problem, this work focuses on the study of the conversion of a model carboxylic acid, i.e. dodecanoic acid, mainly into jet fuel, gasoline and LP gas. The scope of this work is to obtain a detailed mechanistic model able to describe the treatment of the carboxylic acid by means of the generation of a reaction network, calculating the thermodynamic properties from the products and intermediates involved and obtaining rate equations which are based on the single event concept. The reaction network takes into account the carbenium ion chemistry as well as a mechanism on a bifuncional catalyst. The reaction network thus generated is the basis for the development of a complex kinetic model as it can be applied for the hydroconversion of larger carboxylic acids into hydrocarbons. Heats of formation, entropies and gas phase heat capacities for all species involved are calculated using Benson's group contribution method. In order to reduce the amount of species and elementary steps involved in the reaction, it is introduced the single event concept. Rate equations are obtained by considering metal and acid steps while the Evans-Polanyi relationship is used to calculate activation energies.