Modeling and optimization of a trickle-bed reactor with hydrogen quenching for cost-effective hydrotreated biodiesel production

Abstract

The increasing global demand for sustainable energy and the need to reduce greenhouse gas emissions have driven interest in renewable fuels such as biodiesel. However, conventional biodiesels commonly exhibit limitations in oxidation stability and low-temperature operability, which restrict their blendability with petroleum diesel. Hydrotreated biodiesel (HBD), produced by hydrotreating vegetable oils, offers improved fuel properties, making it a promising alternative. This study addresses challenges in cost-effective industrial-scale HBD production by developing a modeling and optimization framework for a trickle-bed reactor (TBR) equipped with quench zones. Specifically, a kinetic study was conducted to identify the most suitable reaction rate model, followed by the construction of a pilot-scale hydrotreating TBR model based on the selected kinetics, validated against experimental data. Among the kinetic models evaluated, the A3 kinetic model demonstrated robust accuracy, with R-square values of 0.9889. To manage the exothermic heat of hydrotreatment reactions, quench zones utilizing hydrogen were strategically introduced between reactor beds to prevent hotspot formation. Then, economic optimization was performed, considering hydrogen recovery and utility usage in the entire production process, including units such as three-phase separator, H${}_2$-pressure swing adsorption, and multistage compressors. The results demonstrated that the optimal quench zone design and operating conditions could effectively enhance the economic feasibility by significantly reducing the required amount of quenching hydrogen while maintaining high HBD yield. Specifically, HBD revenue increased by 5.01%, electricity costs decreased by 4.36%, and chilled water costs were reduced by 2.86%. Overall, the optimal case achieved a 25.17% improvement in profitability compared with the base case.