CHARACTERIZATION OF SEVERAL GENERATIONS OF NiMo HYDROPROCESSING CATALYSTS EMPLOYED IN THE SAME HYDROTREATER

Abstract

employed to perform hydrodesulfurization (HDS) of diesel fractions in the same hydrotreater of a Brazilian refinery. The basic differences are the quality of the feedstocks and the HDS experimental conditions. Samples were characterized by X-ray fluorescence, X-ray diffraction, 13 C CP-MAS NMR, elemental analysis, loss of volatiles, specific surface area and average pore volume. The amount and variety of foreign elements deposited on the catalyst increased in the most recent generations due to the higher amounts of impurities in the processed feedstocks. Coke became more aromatic and loss of textural properties was more prominent in these samples as expected from the more drastic HDS conditions and the quality of the crude diesel. On the other hand, loss of volatiles was lower due to the low carbon content, partial oxidation of sulfur to sulfate species and oxidation of some elements deposited on the catalyst. Coke tended to ignite as it became more aromatic. For this reason, leaching of decoked samples from the most recent generations by sulfuric acid presented very low yields due to the formation of refractory oxides that are insoluble in the leachant.

Catalyst Stacking Technology as a Viable Solution to Ultralow Sulfur Diesel Production

“…The name of specific hydrotreating is determined based on the impurity to be removed: hydrodesulfurization (HDS) aims to remove sulfur, hydrodenitrogenation (HDN) aims to remove nitrogen; hydrodeoxygenation (HDO) aims to remove oxygen, and so on. Hydrotreating catalysts are mostly made of Ni, Co, Mo, and W sulfides, and they represent approximately one-third of the total worldwide catalyst consumption . Most commercial HDS units use trickle-bed reactors, where the feedstock and the hydrogen stream flow concurrently.…”

“…The phenomena of deactivation of hydrodesulfurization catalysts are well known. − Some studies focused on accelerated deactivation useful for the estimation of catalyst lifetime can be found in the literature. − Some general trends in the deactivation of hydrodesulfurization catalysts are included next. Catalysts containing an acid function are more prone to deactivation by coke deposition, catalysts with high hydrogenation capacity show higher endurance to coke buildup, high metal content catalysts are prone to sintering, tailored pore structure may attenuate pore-clogging deactivation, and the deactivation rate is dependent on the operating temperature and the feedstock’s specific gravity and contaminant content. ,,,, Accordingly, it is expected that catalysts with different textural properties, metal content, and acidic properties show differences in the deactivation rate. Therefore, the determination of an optimal configuration of catalysts in a multibed approach to reach deep HDS to ultralow sulfur levels must also consider the convergence of catalyst lifetime of the whole catalytic system.…”

“…Hydrotreating catalysts are mostly made of Ni, Co, Mo, and W sulfides, and they represent approximately one-third of the total worldwide catalyst consumption. 8 Most commercial HDS units use trickle-bed reactors, where the feedstock and the hydrogen stream flow concurrently. HDS conditions depend on many factors like feedstock quality, product specifications, catalyst activity, number of reactors, reactor internals, hydrogen purity, etc.…”

“…When sulfur is present, sulfur oxides (SO x ) are produced during diesel combustion; this contaminant creates serious respiratory problems, causes acid rain, and poisons the oxidation catalysts in the engine emission control system, increasing other contaminant emissions. , Therefore, one of the main objectives of oil refining is sulfur removal; however, changing production from low sulfur diesel (50–500 ppm) to ULSD (>15 ppm) in pre-existing hydrodesulfurization (HDS) units represents a tough challenge because of the higher content of refractory sulfur compounds in middle distillates in contrast to lighter fractions. ULSD production can be achieved by hardening operating conditions (i.e., increasing reactor temperature and hydrogen partial pressure and lowering liquid hourly space velocity (LHSV)), process optimization, and using catalysts with higher activity and less prone to deactivation . Nevertheless, any of these solutions augment the overall operating costs, and usually revamping of pre-existing HDS units is needed to overcome operating constraints, which implies significant capital investments aiming to reduce sulfur to concentrations below 15 ppm.…”

“…ULSD production can be achieved by hardening operating conditions (i.e., increasing reactor temperature and hydrogen partial pressure and lowering liquid hourly space velocity (LHSV)), process optimization, and using catalysts with higher activity and less prone to deactivation. 8 Nevertheless, any of these solutions augment the overall operating costs, and usually revamping of pre-existing HDS units is needed to overcome operating constraints, which implies significant capital investments aiming to reduce sulfur to concentrations below 15 ppm. For these reasons, governments, universities, institutes, and companies devoted to research and development of new technologies for the oil refining industry are working on developing new highly active HDS heterogeneous catalysts, process optimizations, more efficient configurations for HDS units, and alternative desulfurization techniques to lower capital investments, operating costs, and, therefore, ULSD market prices.…”