Change in the Apparent Order at Different Temperatures and Catalyst Volumes: Hydrodesulfurization of KEC-AR

This paper tackles the effect of reaction temperature on the apparent order of the hydrodesulfurization (HDS) reactions of an atmospheric residue (KEC-AR) derived from Kuwait Export Crude (KEC). Testing was carried out using a pilot plant consisting of five identical fixed-bed reactors arranged in series. A moderate-HDS-activity catalyst was used under a 120 bar (total) operating pressure, a feed flow rate of 120 mL per hour (mL/h), and a hydrogen-to-feed ratio of 1000 mL/mL. The liquid hourly space velocity (LHSV) varied by 4.0, 2.0, 1.0, 0.5, and 0.25 relative to the catalyst accumulative volumes in the five reactors. Testing was conducted between 360 and 420 °C with a temperature increase of 10 °C each time. Product samples were collected between the reactors using customized inter-reactor sampling systems that operate under the pilot plant's total pressure. The results showed that the HDS apparent order decreases with an increase in reaction temperature. The order dropped from 4.9 at 360 °C to 1.62 at 420 °C. Using the least-squares method (LSM), we demonstrated that the apparent overall orders are aggregates of several first-order reactions occurring consecutively at different rates and dependent on sulfur total disappearance. On the other hand, we showed that the apparent overall orders are aggregates of several reactions of different orders occurring simultaneously and independently of sulfur total disappearance. The first-order reactions' activation energy was found to be 22.1 kcal/mol and in total agreement with that reported in the literature for the sulfur removal from KEC-AR.