Dynamics of Silicon Sorption on the NiMo/Al2O3 Guard Bed Catalyst During Hydrotreating of Diesel

The dynamics of the silicon sorption on the NiMo/Al 2 O 3 guard-bed catalyst containing ~2.0 wt % Ni and ~6.0 wt % Mo during hydrotreating of diesel was studied. The catalyst bed was divided into five equal sections separated by perforated metal partitions permeable to the feed. Four series of experiments were performed; their time was varied in the range 48–200 h, and the temperature was 340°C. A diesel fraction containing ~1.0 wt % sulfur, 130 ppm nitrogen, and 200 ppm silicon introduced in the form of decamethylcyclopentasiloxane was used as the feed. The specific surface area of all the spent samples was 170–190 m 2 /g, the pore volume was 0.35– 0.43 cm 3 /g, and the average pore diameter was 8–9 nm. The sorption on a catalyst grain 2.5 mm in diameter is diffusion-controlled. The effective mass transfer coefficient and the catalyst capacity under the experimental conditions (5 wt %) were estimated using the equation describing the sorption process.