A simple plug-flow model was developed to study the deactivation mechanisms of hydroprocessing catalysts in atmospheric residue desulfurization (ARDS) units. The three stages of catalyst deactivationsat the start of the run, middle of the run, and end of the runsare considered. The catalyst deactivation is mainly due to metal and coke deposition. The model parameters considered are the unit temperature, fluid velocity, reaction rate constant, catalyst combination, catalyst bed length, and feed concentration of sulfur, metals, and asphaltenes. The simulated results compared very well with our laboratory data for a long catalyst life test operated under constanttemperature mode. The model is further applied to a parametric study that examines the effects of space velocity, unit temperature, and maximum metal capacity on the performance of catalyst systems. A constant-sulfur-mode simulation is also given.

A hydroprocessing multicatalyst deactivation and reactor performance model was originally developed to predict the life and performance of atmospheric residue hydroprocessing catalysts in a pilot-plant long-life test. The model has been subsequently applied to predict catalyst and reactor behavior in an accelerated life test using Boscan crude oil as the feedstock. Simulations from the original model did not compare well with accelerated test run data. Because Boscan crude oil has very high metal and asphaltene contents, mass balance terms that emphasized noncatalytic hydrothermal reactions in the model were needed, especially when catalysts were severely deactivated. Excellent comparisons were obtained after including hydrothermal reaction terms to refine the model. The model was then used to simulate the Boscan crude oil hydroprocessing in constantsulfur-mode operations, and it was found that it would be more beneficial to operate the atmospheric residue desulfurization unit at a lower initial temperature.

Atmospheric residue desulfurization (ARDS) is one of the major processes installed in refineries worldwide for upgrading petroleum residues to more-valuable clean products. Because of the importance of the process, research and development related to the process and its associated catalysts has gained increasing attention internationally. Hence, it is necessary to develop a reliable testing methodology for evaluating ARDS catalysts in a relatively short time. From our experience, it has been determined that, within 2-3 months, an ARDS catalyst system consisting of 3-5 catalysts can be evaluated and their performance in an industrial unit can be predicted. This requires generating quality data related to the initial activities, kinetic parameters of individual catalysts, the deactivation behavior, and maximum metal capacity in the catalyst system. Using the proposed catalyst evaluation methodology, values of the apparent reaction kinetics and catalyst life can be determined. These data are fed into an in-house developed mathematical model, which enables the prediction of the performance of the same catalyst system in an industrial scale. Very satisfactory results, from both pilotplant test and commercial plant prediction, are realized from the developed methodology. When conducting long-life tests using the same feedstock and catalyst system, but under different operation modes, such as the constant-sulfur mode or the constant-temperature mode, the catalyst deactivation behaviors between the two life tests are significantly different, However, their respective values of the maximum metal-on-catalyst (MMOC) of the total catalyst system are very similar.

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