Simulation of the soybean oil hydrotreating process for green diesel production

Abstract

Renewable diesel, or green diesel, is the biofuel with the fastest growing use in the world. Its use as a replacement for fossil diesel is important to reduce the impact of carbon emissions. Green diesel is formed by a mixture of hydrocarbons with a chemical composition similar to that of fossil fuel, making it a drop-in biofuel. Commercial processing employs hydrotreatment of vegetable oil, which, in addition to producing green diesel, can also be used to produce biofuel for aviation, bionaphtha and biopropane. The present paper proposes a model for the hydrotreatment of soybean oil for the production of green diesel. The process was simulated in Aspen Plus® v10; the decarboxylation, decarbonylation and hydrodeoxygenation reactions were carried out in a stoichiometric reactor in the presence of an NiMo/Al2O3 catalyst. In addition to the cracking reactions and fractionation, the fuels produced green diesel, aviation biofuel, and light gases. Brazilian soybean oil was used as the raw material to produce the green diesel. Sensitivity analyses were performed to adjust the best fractionation conditions, considering the composition of the product and the distillation column energy. The best results were chosen when the distillation column was configured with 22 stages, feed at stage 12 and reflux ratio equal to 0.8. The hydrogen/soybean oil ratio was 0.031. The energy used in the process was 1181 kW/h. More than 80% of the soybean oil was converted to renewable fuels, with approximately 65% to green diesel. In addition, a prediction of the simulated physical chemical properties was made and compared with the current Brazilian legislation for green diesel obtaining values within the established specifications. The ASTM D86 distillation curve was compared with simulated results from green diesel obtained from experimental data and fossil diesel. The experimental and simulated distillation curves agreed, showing only a small difference between curves up to 25% of recovered volume. This can be explained by the lighter components present in the experimental green diesel. The proposed simulation supported the potential of Brazilian soybean oil for the production of quality renewable fuels.