Deactivation Of Hydrodesulfurization Catalysts Research Articles

Deactivation of hydrodesulfurization catalysts during reactor startup

AbstractMetal sulfide catalysts for ultra‐deep hydrodesulfurization of diesel generally lose a fraction of their catalytically active sites during reactor startup. The underlying mechanisms are discussed. A laboratory diagnostic tool consisting of three probe molecules is developed for testing metal sulfide catalysts' start‐of‐run (SOR) activity maintenance. It is found that a significant fraction of the active sites on a commercial supported catalyst are deactivated permanently, but this is not the case with a bulk metal sulfide catalyst. The SOR deactivation of the bulk catalyst is completely reversible, while that of the supported catalyst is partially reversible. The diagnostic tool may provide a basis for developing a high‐throughput approach for evaluating and enhancing catalyst SOR stability, thereby increasing plant productivity.

Deactivation of Hydrodesulfurization Catalysts in Two-stage Resid Desulfurization Process. (Part 5). Characterization of Asphaltenes after Hydrodemetallization and Subsequent Hydrodesulfurization Reactions.

Hydrodemetallization (HDM) and subsequent hydrodesulfurization (HDS) of Arabian light (AL) atmospheric residues were performed with a bench-scale unit, and the structure of the asphaltenes obtained from each reaction was characterized. The HDM reaction caused a decrease in the number of aromatic rings, an increase in aromaticity, and a decrease in the number of alkyl side chains, but no formation of naphthenic rings. In contrast, HDS reaction formed naphthenic rings, but their number decreased with an increase of HDS temperature, thus leading to an increase of aromaticity. Using the structural parameters obtained by using a computer program based on the SAAH system developed by Katayama et al., we modeled the structure of asphaltenes after HDM and HDS reactions and found that the aromatic unit structure of AL asphaltenes became coronene-type as hydrotreatings proceed.

Deactivation of Hydrodesulfurization Catalysts in Two-stage Resid Desulfurization Process. (Part 4). Deactivation in a Long-term Aging Test under Constant Reaction Temperature.

The long-term aging tests involving hydrodesulfurization catalysts were done at 380°C. The used catalysts were then characterized to investigate the deactivation mechanism. The amount of coke on the catalyst peaked around 30 days, and then decreased. This decrease in coke was due to the hydrogenation reaction with Ni-sulfide deposited on the catalyst. Elemental analysis, measurement of pore size distribution, and activity tests of the used catalysts revealed that the catalyst deactivation at start and middle of a run (MOR) was caused by coke and by metal deposits, respectively. In addition, calculations revealed plugging of pore mouths and the presence of sealed space of pores at MOR, resulting in the catalyst deactivation.

Deactivation of Hydrodesulfurization Catalysts in Two-stage Resid Desulfurization Process. (Part 6). Characterization and Activity of Used Hydrodesulfurization Catalysts.

The activity tests of used HDS catalysts, which were prepared during 30 days of aging under various HDS reaction conditions, were performed and their characterization was performed to understand the initial deactivation of the HDS catalysts. The pore volume measurements revealed that the sealed space of pore increased with aging, resulting in HDS catalyst deactivation. Laser Raman and 13C-NMR analysis showed that aromaticity of coke was the highest at the center of the catalyst pellet and was influenced more by reaction temperature than by reaction pressure. Comparison of HDS activity of the used catalysts with real feed to that with a model compound (thiophene) showed that the effect of reactant diffusion on HDS activity was negligible. A good correlation was observed between HDS activity and coke content, suggesting that coke deactivation was predominant at the start of run, regardless of HDS reaction conditions involved.

Deactivation of Hydrodesulfurization Catalysts in Two-stage Resid Desulfurization Process. (Part 7). Influence of Reaction Conditions at the First Stage on Deactivation Mechanism.

Aging tests of hydrodesulfurization (HDS) catalysts were performed in the operation mode of constant sulfurremoval using product oils derived from hydrodemetallization (HDM) of Kuwait atmospheric residue under vanous reaction conditions. The used catalysts obtained were characterized to clarify the effects of HDM reaction conditions, focusing on reaction temperature, at the first-stage on the deactivation mechanism of the HDS catalysts at the second-stage. A good correlation occurred between the fouling rate of HDS catalysts and the content of hard-coke (insolubles in light gas oil) on the used HDS catalysts when the HDM and HDS temperatures were below 400°C, indicating that coke formation causes the HDS catalyst deactivation. When the HDM temperature at the first-stage was increased from 400 to 430°C, the HDS catalysts showed an increase in the fouling rate, despite a decrease in hard coke and metal deposits. This unusual phenomenon could be explained by introducing the concept of soft coke (solubles in light gas oil), which was removed during the preparation of used catalysts. Furthermore, details about the effect of HDM temperature on the deactivation mechanism of HDS catalysts were discussed.

Deactivation of Hydrodesulfurization Catalysts in Two-stage Resid Desulfurization Process (Part 3). Influence of Asphaltene Content of Feedstock and Hydrodesulfurization Temperature at Second-stage.

Aging tests of a hydrodesulfurization (HDS) catalyst in a two-stage resid desulfurization process, which consisted of hydrodemetallization (HDM) and HDS, were carried out on a small-scale pilot plant. The purpose was to determine the influence of asphaltene content of feedstock and that of HDM temperature in the first stage on HDS catalyst deactivation in the second stage under various reaction temperatures (HDS temperature). As feedstocks, resids of various asphaltene content were prepared by adding propane deasphalted (PDA) asphalt to atmospheric residue of Arabian light crude. Results show that at HDS temperatures below 400°C, an increase either in asphaltene content or in HDM temperature gradually increased the fouling rate, and at HDS temperatures above 400°C, this increase rapidly increased the fouling rate. These results suggest that, at lower HDS temperatures, coke precursor formed in the HDM reaction plays a key role in the HDS catalyst deactivation, and at higher HDS temperatures, coke precursor formed in the HDS reaction also significantly affects the HDS catalyst deactivation. The results also suggest that in the deactivation mechanism of HDS catalyst in the second stage, coke had a stronger effect on the HDS catalyst deactivation than did metal deposits.

Deactivation of Hydrodesulfurization Catalysts under Coal Liquids. 2. Loss of Hydrogenation Activity Due to Adsorption of Metallics

Deactivation of Hydrodesulfurization Catalysts under Coal Liquids. 2. Loss of Hydrogenation Activity Due to Adsorption of Metallics

Deactivation of Hydrodesulfurization Catalysts under Coal Liquids. 1. Loss of Hydrogenation Activity Due to Carbonaceous Deposits

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