Effective reduction of hydrogen consumption in ultra-deep hydrodesulfurization of diesel: Deep insights into the effect of thermodynamic limitations during hydrotreating

Abstract

Reducing hydrogen (H2) consumption massively while ensuring the ultra-strict product quality is the most critical and extremely challenging issue in diesel hydrotreating process. In this work, the effect of operating parameters (including reaction temperature, reaction pressure, hydrogen/oil (H2/oil) volume ratio and liquid hourly space velocity (LHSV)) on H2 consumption were systematically studied first. Most importantly, the reduction of H2 consumption caused by temperature elevation was calculated upon satisfying the requirements of content of sulfur (S) and polycyclic aromatic hydrocarbons (PAHs) in the diesel quality standards (S≯10 mg/kg, PAHs≯7%) using feedstock with different properties. Results showed that H2 consumption was reduced by 23.1% when the temperature reached 401 °C (compared with temperature being 365 °C) using a diesel feed whose S content, N content and density were 9759.1 mg/kg, 147.1 mg/kg and 0.8626 g/cm3, respectively, while the impact on the catalysts activity, structure and coke deposition behavior was relatively little which was proven by the XPS, TEM, CAT-CS and TG-MS studies on the fresh and spent sulfide catalysts. The significant reduction of H2 consumption was attributed to the different thermodynamic behavior of S and aromatic compounds at relatively high temperature which led to a slightly decrease in hydrodesulfurization (HDS) conversion while a significantly drop in hydrodearomatization (HDA) conversion. This is a promising method to effectively reduce H2 consumption which can greatly benefit the future industrial applications in producing ultra clean diesel products with ultra-low H2 consumption.