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In the upgrading of heavy petroleum oils and residues by hydrotreating, multiple-reactor fixedbed units loaded with different types of catalysts are extensively used. Catalysts for such hydrotreating processes are chosen on the basis of activity, selectivity, and life. The performance of the overall hydrotreating process with regard to various reactions, such as hydrodemetallation (HDM), hydrodesulfurization (HDS), hydrodenitrogenation (HDN), asphaltenes cracking (HD-Asph), and conversion to distillate and catalyst life-on-stream, is clearly linked to the performance of the catalyst in different reactors. Information regarding the activity, selectivity, kinetics parameters, and deactivation of the individual catalysts are, therefore, highly desirable for optimizing reactor loading in a multiple catalyst system. In the present work, a comparative study was conducted on the kinetics of various reactions such as HDS, HDV, HDNi, HDN, CCR reduction, and asphaltenes conversion in hydrotreating Kuwaiti atmospheric residue (KU-AR) over three types of catalysts. The results showed diverse kinetics behavior of different hydrotreating reactions. The diverse kinetics behavior of the different reactions and the strong dependence of the kinetics parameters on catalyst type are consistent with the kinetic aggregation theory. The results are discussed in comparison with those available in published literature.

In the upgrading of heavy petroleum oils and residues by hydrotreatment, multiple-reactor fixed-bed units loaded with different types of catalysts are used extensively. Catalysts for such hydrotreatment processes are chosen on the basis of activity, selectivity, and life. The performance of the overall hydrotreatment process, with regard to various reactions, such as hydrodesulfurization (HDS), hydrodenitrogenation (HDN), hydrodemetallization (HDM), asphaltenes cracking (HDAsph), and conversion to distillates, as well as catalyst life-on-stream, are clearly linked to the performance of the catalyst in different reactors. Information regarding the activity, selectivity, kinetic parameters, and deactivation of the individual catalysts are, therefore, highly desirable for optimizing reactor loading in the multiple-catalyst system. This paper presents the performance tests for various reactions on two types of industrial hydrotreating catalysts: those used at the midsection and the tail-end of a graded catalyst system designed to hydrotreat atmospheric residual oils. The tests were conducted using straight-run Kuwait atmospheric residue, a demetallized residue, and a demetallized/desulfurized residue. The activity and kinetic parameters for different reactions that are typically occurring during the hydroprocessing of these feedstocks were determined. The results revealed significant changes in activity, depending on the feedstock used for the tests. Furthermore, apparent rate orders and rate constants for some reactions were significantly changed. The study demonstrates the importance of proper selection of the feedstocks used in the performance evaluation and screening of candidate catalysts for graded catalyst systems for residual-oil hydrotreatment.

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In this study, the effect of three different feedstocksnamely, straight-run atmospheric residue (AR), demetallized AR (DM-AR), and demetallized/desulfurized AR (DMDS-AR)on the coke formation on an industrial catalyst system consisting of a hydrodemetallization (HDM) catalyst (A), a hydrodemetallization/hydrodesulfurization (HDM/HDS) catalyst (B), and a hydrodesulfurization/hydrodenitrogenation (HDS/HDN) catalyst (C) were examined. The used catalysts, aged under the same operating conditions (catalyst A with atmospheric residue (AR), B with AR or demetallized atmospheric residue (DM-AR), C with AR or demetallized and desulfurized atmospheric residue (DMDS-AR)), were characterized by combining physical/chemical analyses with temperature-programmed oxidation/mass spectroscopy (TPO/MS) and solid-state 13C nuclear magnetic resonance (NMR). Special emphasis was made on finding a relationship between feed quality and the amount and nature of coke. The results revealed that hydrotreated feeds generate significantly more coke than straight-run AR. The higher propensity in coke formation using a demetallized feedstock is due to the bulky aromatic structure of the asphaltenes in DM-AR, along with a high H/C ratio of the feed (phase separation−precipitation−coke formation). In the case of DMDS-AR, coke generation is attributed to the nature of catalyst C (namely, high acidity and small pores), rather than to the quality of the feed. Concerning the coke properties, it was found that the coke generated from hydrotreated feeds is less aromatic than that from AR. Regarding other coke features, such as degree of condensation or degree of alkyl substitution, no obvious interplay between these structural parameters and the nature of feed or catalyst could be found.

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