A. Stanislaus

Kinetics and Modeling of Petroleum Residues Hydroprocessing

Several factors must be taken into consideration while interpreting data on kinetics of reactions occurring during hydroprocessing of petroleum residues, i.e., the origin of feed, properties of catalysts and related diffusion phenomena, catalyst deactivation, form of kinetic model, and experimental system employed. Among the operating parameters, temperature, H2 pressure, H2S/H2 ratio, H2/feed ratio, and contact time have a pronounced effect on kinetic data as well. Moreover, although of the same distillation cut point, residues may vary widely in composition. For example, the content of metals (vanadium+ nickel) may range from few ppm for residues derived from a sweet crude to more than 1000 ppm for one derived from a heavy crude. The content of asphaltenes and CCR may exhibit a similar variability. For the most part, significant discrepancies among reported values of kinetic parameters can be reconciled by closely examining the conditions of experiment used for determination of kinetic data. Kinetic data are incorporat ed in mathematical models used for predicting the life of catalyst during hydroprocessing operation. Good predictions can be made if reliable kinetic data are used for modeling. In this regard, the selection of experimental conditions for determining kinetic results is crucial to ensure their reliability. Thus, properly designed tests for accelerated aging of catalyst may be the source of a valuable information. Otherwise, erroneous conclusions could be reached.

Preparation of a large pore alumina-based HDM catalyst by hydrothermal treatment and studies on pore enlargement mechanism

The changes occurring in the alumina phase during hydrothermal treatment of γ-alumina in the presence and absence of additives such as P, F, phenol and acetic acid, were investigated with a view to understand the mechanism of pore widening in γ-alumina under hydrothermal conditions. The results showed that the formation and growth of boehmite into large crystallites by rehydration of γ-alumina was responsible for pore enlargement. As a part of the study, a wide pore Ni-Mo/γ-alumina was prepared by hydrothermal treatment procedure and its performance in vacuum residue hydroprocessing was evaluated. The catalyst showed a remarkably high activity for hydrodemetallization and asphaltenes conversion reactions in vacuum residue hydroprocessing. Distribution of the deposited metals within the catalyst pellet was more uniform for this catalyst compared to that of a conventional HDM catalyst.

Heavy oil hydrotreating catalyst rejuvenation by leaching of foulant metals with ferric nitrate-organic acid mixed reagents

Abstract Much effort has been devoted in recent years to develop processes for the rejuvenation of metal fouled spent catalysts from residue hydroprocessing units. In this paper we report the influence of adding ferric salts to some organic acids in selective extraction of foulant metals from the spent catalyst prior to decoking. Leaching experiments were carried out using two different organic acids, namely, oxalic acid and tartaric acid with and without ferric nitrate addition. The spent and the treated catalysts were characterized and the improvements in surface area, pore volume and HDS activity as a result of leaching with different reagents compared. The studies revealed that in the absence of ferric salts, the acids showed very poor activity for leaching foulant metals from coked spent catalyst. Addition of ferric nitrate enhanced the leaching efficiency of each acid to a different degree. The selectivity for the removal of the major metal foulant (vanadium) was different for different leaching reagents. The enhanced leaching by the ferric nitrate-organic acid system has been explained in terms of a synergistic mechanism involving oxidizing and complexing reactions. The improvements in surface area and pore volume recovery was found to be related to the extent of vanadium removal from the catalyst. The HDS activity of the catalyst also increased significantly by leaching of the deposited metals. The study showed that oxalic acid-ferric nitrate reagent was superior to other reagent systems in terms of selectivity for vanadium leaching as well as for surface area, pore volume and activity recovery.

Studies on the rejuvenation of spent catalysts: effectiveness and selectivity in the removal of foulant metals from spent hydroprocessing catalysts in coked and decoked forms

Abstract Two routes were used to rejuvenate spent residue hydroprocessing catalysts by leaching foulant metals. In the first, deoiled spent catalyst containing coke and deposited metals in sulfide form was chemically treated to remove the metal foulants. In the second, deoiled spent catalyst was decoked by controlled combustion of coke and the resultant coke-free catalyst containing metals in oxide form was subjected to leaching. Oxalic acid, a chelating agent which is able to form soluble metal complexes, was used for metal leaching in both routes. The influence of adding an oxidizing agent such as H 2 O 2 to oxalic acid in particular its effect on the leaching efficiency was examined in both routes. The spent and treated catalysts were characterized and the improvements in surface area, pore volume and hydrodesulphurization-activity of the catalysts were compared. The selectivity for leaching of the major metal foulant (vanadium) was better, and activity recovery was higher for the catalyst rejuvenated by metal leaching prior to decoking.

Effect of acidic and basic vapors on pore size distribution of alumina under hydrothermal conditions

Abstract The development of wide pore catalysts, with surface areas and mechanical strengths for application in, for example, the hydroprocessing of petroleum residues, has received increased attention in recent years. In the present paper, we have investigated the influence of acidic and basic vapors on pore enlargement of γ-alumina supports under low-temperature hydrothermal conditions. γ-Alumina in the form of 1.5 mm extrudates was subjected to hydrothermal treatment in an autoclave in the presence of acetic acid and ammonia for various time intervals in the temperature range 150–300 °C. The treated catalyst samples were characterized for surface area, pore size distribution and crushing strength. The samples were also examined by scanning and transmission electron microscopes and X-ray diffraction to assess the extent of sintering and possible changes in the alumina phase. The results of the studies revealed that ammonia enhances, whereas, acetic acid suppresses pore enlargement of γ-alumina under hydrothermal conditions. Surface area loss for samples treated under different atmospheres were of the order: ammonia + water > water > acetic acid + water. In the presence of ammonia, selective widening of pores in the 100–250Arange with improved side crushing strength was noticed at low or moderate temperatures (e.g. 150°C). The contrasting effects of ammonia and acetic acid vapors on the sintering and pore enlargement of γ-alumina under hydrothermal conditions is discussed on the basis of the influence of these reagents on hydroxylation of Al-O-Al bonds and the subsequent formation of boehmite and its recrystallization.

Performance comparison of alumina-supported Ni-Mo, Ni-W and Ni-Mo-W catalysts in hydrotreating vacuum residue

Abstract In the present work we report the performance of a Ni-Mo-W γ-Al 2 O 3 catalyst in comparison with conventional Ni-Mo and Ni-W catalysts for promoting various reactions that occur during residual oil hydroprocessing. The performance evaluation tests were conducted in a high pressure fixed bed reactor system using Kuwait vacuum residue as feed. The reactions that were monitored included hydrodesulfurization (HDS), hydrodenitrogenation (HDN), hydrodemetallation (HDM), hydroconversion to distillates (HC), asphaltenes removla, and CCR reduction. The results revealed that the Ni-Mo-W catalyst was more active for various conversions than either the Ni-Mo or Ni-W catalyst. The activity improvement was particularly higher for HDN, HDM, HC, asphaltene conversion and CCR reduction. The addition of W to Ni-Mo Al 2 O 3 enhanced the hydrogenation function of the catalyst.

Studies on rejuvenation of spent residue hydroprocessing catalysts by leaching of metal foulants

Abstract Due to environmental concerns much effort has been devoted in recent years to the development of processes to rejuvenate and reuse metal-fouled spent catalysts from residue hydroprocessing units. As a part of an extensive research program on the subject, we report in this paper about the extraction of the deposited vanadium from the spent catalyst using ferric nitrate–oxalic acid reagent system and its effect on catalyst’s surface area and activity recovery. A comparative assessment of different modes of ferric nitrate addition to oxalic acid, namely, (i) continuous addition, (ii) batch addition, and (iii) successive addition, on the leaching efficiency was made. The results revealed that addition of ferric nitrate to oxalic acid enhanced its leaching activity remarkably, and continuous mode of addition was more effective than the others. The improvements in the surface area and pore volume of the catalyst were better and about 85% of the HDS activity was recovered for the catalyst leached with ferric nitrate–oxalic acid reagent system in a continuous addition mode. Removal of the coke from the leached catalyst increased the HDS activity further from 85 to 95% of fresh catalyst activity. The unleached vanadium remaining in the catalyst was not concentrated at pore mouths, but was well distributed within the pellet. The enhanced leaching of vanadium in the continuous addition mode of the oxidizing reagent was explained in terms of a synergistic mechanism involving oxidation and complex formation reactions of the low-valent vanadium sulfide species during treatment with the ferric nitrate–oxalic acid reagent system.

Effect of thermal treatment on the sintering and structural changes of cobalt—molybdenum/alumina and nickel—molybdenum/alumina hydrotreating catalysts

Abstract The effect of calcination temperature on the Co Mo/Al2O3 and Ni Mo/Al2O3 catalysts in their oxidic form has been studied by X-ray photoelectron spectroscopy, X-ray diffraction, differential thermal analysis and surface area and porosity measurements. Calcination up to 600°C produces no large changes in activity of the catalyst. Calcination at higher temperatures results in loss of surface area, in volatillisation of molybdenum species, in a reduction in the amount of molybdenum on the surface and in the formation of various aluminates. Significant differences in temperature sensitivity are noticed between Co Mo/Al2O3 and Ni Mo/Al2O3 with regard to the above changes. The change in catalytic activity with calcination temperature is related to the changes in the inorganic chemistry of the system induced by calcination. Optimal calcination involves treatment at up to 600°C (Ni-Mo/Al2O3) or 700°C (Co-Mo/Al2O3).

Effect of Diluents in Controlling Sediment Formation During Catalytic Hydrocracking of Kuwait Vacuum Residue

Abstract Conversion of low-value petroleum residues to high-value distillates by catalytic hydrocracking has gained considerable importance in recent years. One of the common operating problems encountered in the process is the formation of coke-like sediments in the products. The carbonaceous sediment materials usually deposit on the reactor and downstream vessels as well as on catalyst surface and cause both operability and rapid catalyst deactivation problems. Prevention or suppression of coke-like sediment deposition is highly desirable alleviate equipment fouling problems and to attain high conversions in residue hydrocracking operations. In the present work, the influence of adding some aromatics-rich gas oil streams, such as heavy cycle gas oil (HCGO) and light cycle oil (LCO), produced in the FCC units to vacuum residue on various conversions as well as on sediment formation was investigated. The results revealed that mixing aromatics-rich gas oils with vacuum residue feed was very effective in reducing sediment formation even at very high conversion levels (> 80%). The diluents, however, did not have any appreciable benefits in improving the yield of distillates and the extent of other hydrotreating reactions. The results are consistent with the asphaltenes phase separation mechanism. The addition of aromatics-rich diluents may improve the solubility of the asphaltene cores in the product oil medium and control the onset of their precipitation.

Rejuvenation of residual oil hydrotreating catalysts by leaching of foulant metals: modelling of the metal leaching process

Abstract Increasing emphasis has been paid in recent years on the development of processes for the rejuvenation of spent residual oil hydroprocessing catalysts, which are deactivated by deposition of metals (e.g. vanadium) and coke. As part of a research program on this subject, we have investigated selective removal of the major metal foulant from the spent catalyst by chemical leaching. In the present paper, we report the development of a model for foulant metals leaching from the spent catalyst. The leaching process is considered to involve two consecutive operations: (i) removal of metal foulants along the main mass transfer channels connected to the narrow pores until the pore structure begins to develop and (ii) removal of metal foulants from the pore structure. Both kinetic and mass transfer aspects were considered in the model development, and a good agreement was noticed between experimental and simulated results.