Kinetic model of synthetic diesel production from stearic acid using MATLAB

Abstract

Hydrodeoxygenated vegetable oil is a second-generation alternative diesel. Oxygen in vegetable oil is removed through hydrodeoxygenation (HDO), decarbonylation (DCO), and decarboxylation (DCO₂) as the other main reactions in synthetic diesel production. The final products are hydrocarbon compounds with C15-C18 carbons, similar to traditional petroleum diesel. This study investigated the reaction mechanism and a kinetic model of synthetic diesel production from stearic acid (SA) with an NiMo/Al₂O₃ catalyst in the temperature range 270-300°C under excessive H₂. The kinetic model consisted of mass balance equations and rate law equations based on pseudo-first-order reactions. A MATLAB program was used for calculations. The results from the simulation demonstrated the %distribution of hydrocarbon products based on the proposed model was in good agreement with the experimental data. Furthermore, the results showed that the initial H₂ pressure greatly affected the composition of the hydrocarbon products and the reaction time. Therefore, the suggested conditions for synthetic diesel production from SA were an initial H₂ pressure of 75-80 bars, a reaction temperature of 300°C, an SA concentration of 5% wt, and a reaction time of 1.5 hours. These conditions produced an average low heating value of synthetic diesel of 44.22 Megajoule (MJ)/kg.