Hydrodemetallization Activity Research Articles

Guard-bed catalyst: Impact of textural properties on catalyst stability and deactivation rate

An effects of the hierarchical pore structures or pore type on guard bed catalyst during heavy oil hydroprocessing. • FeMo/Carbon-Al 2 O 3 supported catalysts with different texture were investigated for HDM. • An increase in porosity leads to higher HDM and metal retention capacity. • HDM relationship has been established with the type of pores. • Correlation between pore size distribution and HDM activity has been established • Micro- and mesopore showed a negative impact on HDM activity while macro-pores have a positive effect The hydrodemetallization (HDM) activity and the stability of FeMo supported catalysts have been investigated during the hydroprocessing of heavy crude oil. The prototype FeMo catalysts were developed in this study as guard-bed catalysts. Such type of front catalyst is frequently used in complex hydrotreatment to protect the more vulnerable subsequent catalysts. Various prototype supports were synthesized in this study to produce different textural properties. Such textural properties were generated and optimized by using different support compositions (0−75 wt.% activated carbon in alumina) and following a certain support pretreatment methodology for pore expansion. Both the support composition and the pretreatment methodology have significantly contributed in developing an optimized HDM catalyst with a large pore volume and a distinctive bimodal pore structure. The large pore volume substantially improved the metal retention capacity, while the bimodal pore structure remarkably reduced the diffusion limitation, allowing the large hydrocarbon molecules ( i.e. , asphaltene) to reach the inner catalytic sites to enhance their conversion rates. The presence of carbon in the catalyst support, even after calcination, considerably reduced coke and metal depositions on pore-mouths and catalytic sites. The textural and the mechanical properties of support indicate that the optimum composition is attained when the carbon-alumina ratio is 1:1 (50/50 wt.%). The role of textual properties on catalyst stability was investigated by comparing fresh and spent catalysts. The characterization of spent catalysts indicates that the bimodal type of pore has stable performance with time-on-stream (TOS).

Texture Evolution of Hard-Templated Hierarchically Porous Alumina Catalyst in Heavy Oil Hydroprocessing

The study is devoted to the deactivation behavior of alumina “guard-type” mesoporous and hierarchical catalysts in long-term 800 h hydroprocessing of heavy oil under conditions close to industrial ones. The purely mesoporous sample had only 10–15 nm mesopores by Hg porosimetry whereas the hierarchical catalyst possessed a bimodal pore size distribution with maximum at 15 nm (55 vol%) and 40 nm (45 vol%, related to the mouths of 200 nm spherical macropores). Both catalysts had similar activities for the first 200 h of hydroprocessing. The mesoporous catalyst underwent the rapid deactivation in hydrodesulfurization (HDS) and hydrodemetallization (HDM) of V after 200 h on stream, and the remarkable decrease in hydrodeaspaltenization (HDAs) and Ni removal after 300–400 h on stream due to the intensive mesopore plugging by 55% of the total volume. The hierarchical catalyst did not show any decline in HDS and HDAs during the 800 h experiment, though its HDM activity also reduced due to the surface poisoning and coke deposition, albeit to a lesser extent. The intrinsic mesopores of the hierarchical alumina were shown to narrow down to 10 nm but did not experience substantial blocking observed for the mesoporous catalyst. Hierarchical texture seems not only to provide wide macro- and mesopores less prone to plugging by coke species, but to ensure effective transport of reaction products out of the small pores which prevents them from blockage.

The Influence of Metal Deposits on Residue Hydrodemetallization Catalysts in the Absence and Presence of Coke

Spent hydrodemetallization (HDM) catalysts were collected from pilot-scale reactors with different time-on-stream, and they were treated with an extraction or regeneration method for further investigation. The fresh, spent, and regenerated samples were characterized systematically. Their catalytic performances were assessed using model molecules and Kuwait atmospheric residue as the reactants. Compared with conventional NiMo/Al2O3 catalysts, deposited metal sulfides had a notable increase in their HDM activity but an obvious decrease in their naphathelene hydrogenation activity. With short contact time, metal deposits accelerated residue HDM activity, and they were also involved in the loss of hydrodesulfurization (HDS) activity. At the initial stage of operation, HDM activity was reduced significantly due to the formation of coke. However, coke and metal deposits together contributed to the loss of HDS activity and the rapid fall of long period on-stream HDM activity.

Catalytic Performance and Synergetic Effect of Mo-V/Al2O3 in Residue Hy-drotreatment

Mo-V/Al 2 O 3 catalyst samples with different atom ratios of Mo/(Mo+V) were prepared by pore volume impregnation. The catalyst samples were characterized by Raman spectroscopy, H 2 temperature-programmed reduction, and high resolution transmission electron microscopy. The catalytic performance of Mo-V/Al 2 O 3 samples for model molecules (naphthalene) and for real feedstock (Kuwait atmosphere residue) was measured after sulfidation. Hydrogenation (HYD), hydrodemetallization (HDM), and hydrodesulfurization (HDS) were assessed. It can be concluded that Mo and V exhibited a synergetic effect in model molecules HYD and residue HDM reactions. Because the metals and sulfurs exist in different forms in residue and the V–S and V–Mo–S phases are more active for HDM than HDS, it is observed that the Mo-V/Al 2 O 3 catalyst exhibited higher HDM activity and lower HDS activity compared with the Ni-Mo/Al 2 O 3 catalyst.

Hydrodemetallation (HDM) of nickel-5,10,15,20-tetraphenylporphyrin (Ni-TPP) over NiMo/γ-Al2O3 catalyst prepared by one-pot method with controlled precipitation of the components

In this work, a series of NiMo/γ-Al2O3 catalysts is prepared by one-pot method with controlled precipitation of AlCl3·6H2O, (NH4)6Mo7O24·4H2O and NiCO3·2Ni(OH)2·4H2O using urea and ammonium carbonate as additives. The molar ratio of urea to Al varied from 4.1 to 17.2 and the influence of this parameter on the surface and structural properties of the catalysts and HDM activity was studied. HDM of Ni-TPP was carried out in a batch reactor. The catalysts were characterized by BET, XRD, H2-TPR, DRS, XPS, EDS, FT-IR, TG–DTA and NH3-TPD. The results show that urea employed as additive not only improves the solubility of Mo and Ni salt, but also adjusts the hydroxyl concentration and facilitates the formation of molybdate and polymolybdate. The existence of residual chlorine may improve the dispersion of the particles containing Ni and Mo on the surface of porous Al2O3, enhance hydrogen spillover and the acidity of the catalyst. HDM activity varied with the amount of urea to a maximum at urea/Al of 12.3 with activity of 98%. The highest activity occurred at this ratio is mainly due to better porosity, well dispersed active particles, increased octahedral molybdenum/nickel oxides and proper acidity.

Early stage deactivation of heavy crude oil hydroprocessing catalysts

Four different CoMo catalysts supported by alumina, alumina–titania, alumina–silica and carbon were used to study the early stage of deactivation. Hydrodemetallization (HDM) and hydrodesulfurization (HDS) activities of these catalysts have been tested in high pressure, high temperature micro-plant by using heavy crude oil as feed. Thiophene activity of the spent catalysts was compared with the fresh and regenerated catalysts. The results show that the alumina and alumina–titania supported CoMo catalysts exhibit high and stable performance for both HDM and HDS activities. Though the initial activities of alumina–silica supported CoMo catalyst are high, the activities decrease rapidly with time-on-stream. Having higher acidic sites may cause this rapid deactivation. Thermogravimetric analysis results also support that the nature of deposited carbon on this catalyst is different from the coke deposited on the other three catalysts. SEM-EDX results show that vanadium sulfides are more preferably deposited at the outer surface of carbon catalyst. Thiophene HDS activity of fresh, spent and regenerated results suggest that the deactivation of alumina catalyst is cause of coke deposition whereas both metal sulfides and coke depositions are responsible for CoMo/Al2O3–TiO2 and CoMo/Al2O3–SiO2 catalysts deactivation, particularly at the early stage of hydroprocessing of the heavy oil.

New Mo–V based oxidic precursor for the hydrotreatment of residues

In order to understand the role of vanadium and its interaction with molybdenum atoms in the catalysts used for the hydrotreatment of residues, mixed heteropolyanion (HPA) precursors PMo(12−x)VxO40(3+x)− have been prepared and deposited by incipient wetness impregnation on an alumina support. The evolution of the compounds in the impregnating solutions till their deposition on the support has been analysed using various spectroscopic techniques such as Raman, 31P and 51V NMR, XPS as well as TEM. Activity measurements on model molecules (toluene and cyclohexane) and on real feedstock (vacuum residue) have been performed after activation step (ex situ sulphidation). Hydrogenation (HYD), isomerisation (ISOM), hydrodemetallation (HDM), hydrodesulphurisation (HDS), hydrodeasphaltenisation (HDAsC7) were assessed. During tests (2h) on a Safaniya vacuum residue feed, interesting HDM activity was observed compared to reference promoted and unpromoted catalysts (NiMo and Mo/Al2O3). It can be concluded that the use of vanadium in the impregnating solution may promote HDM and HDAsC7 (increase of vanadium removal rate around 15% compared to Mo-catalyst without vanadium). Furthermore HDM and HDAsC7 catalytic performances turned out to be close to the ones of NiMo catalyst. The increase in HDM/HDAsC7 activity may be related to the improvement of hydrogenation and/or isomerisation, the latter being improved by the presence of vanadium.

Catalyst Deactivation during Hydrotreating of Maya Crude in a Batch Reactor

The deactivation of a hydrotreating catalyst is investigated in a batch reactor by using Maya heavy crude as a feed. A reference catalyst NiMo supported on gamma alumina having wide pore diameter is used to evaluate hydrodemetallation (HDM) and hydrodesulfurization (HDS) activities. It is found that, with increasing contact time, the conversion and deposits increase. The pore size distribution results show that surface area and total pore volume significantly reduce on the spent catalysts due to coke deposits. However, loss of these properties is reversed upon regeneration of the spent catalysts. It is observed from SEM study that coke preferably deposits on the pore mouth whereas vanadium is more evenly distributed throughout the catalyst particles. These deposits cause the deactivation of HDM activity; however, the reason for the loss of HDS activity is only the presence of metal deposits which may cover active sites.

Hydrodesulfurization, Hydrodenitrogenation, Hydrodemetallization, and Hydrodeasphaltenization of Maya Crude over NiMo/Al2O3 Modified with Ti and P

The effect of adding Ti (4.5 wt%) and P (∼1.0 wt%) by several routes to a NiMo/ab Al2O3 catalyst on the hydrodesulfurization (HDS), hydrodenitrogenation (HDN), hydrodemetallization (HDM), and hydrodeasphaltenization (HDAs) of heavy Maya crude was investigated. The results show that not all the catalyst functionalities respond equally well to the addition of Ti and P to the catalyst formulation. There is not a single catalyst formulation that can achieve optimum performance in all the catalyst functionalities. For HDS, Ti incorporation increases activity but the route by which P is added afterwards can improve or be detrimental to HDS activity. For HDN, the incorporation of P to the catalyst can lead to significant improvements in catalytic activity and catalyst stability. Ti increases HDM activity but the addition of P to the catalyst is detrimental to this functionality. For the elimination of asphaltenes, the catalyst supported on pure alumina is the best. So for HDAs, no benefit is obtained by the addition of Ti or P to the catalyst. Textural properties are important and HDM and HDAs increase with catalyst average pore diameter. Hydrodemetallization activity increases with the acidity of the catalyst.

Studies on recycling and utilization of spent catalysts: Preparation of active hydrodemetallization catalyst compositions from spent residue hydroprocessing catalysts

Spent catalysts form a major source of solid wastes in the petroleum refining industries. Due to environmental concerns, increasing emphasis has been placed on the development of recycling processes for the waste catalyst materials as much as possible. In the present study the potential reuse of spent catalysts in the preparation of active new catalysts for residual oil hydrotreating was examined. A series of catalysts were prepared by mixing and extruding spent residue hydroprocessing catalysts that contained C, V, Mo, Ni and Al2O3 with boehmite in different proportions. All prepared catalysts were characterized by chemical analysis and by surface area, pore volume, pore size and crushing strength measurements. The hydrodesulfurization (HDS) and hydrodemetallization (HDM) activities of the catalysts were evaluated by testing in a high pressure fixed-bed microreactor unit using Kuwait atmospheric residue as feed. A commercial HDM catalyst was also tested under similar operating conditions and their HDS and HDM activities were compared with that of the prepared catalysts. The results revealed that catalyst prepared with addition of up to 40wt% spent catalyst to boehmite had fairly high surface area and pore volume together with large pores. The catalyst prepared by mixing and extruding about 40wt% spent catalyst with boehmite was relatively more active for promoting HDM and HDS reactions than a reference commercial HDM catalyst. The formation of some kind of new active sites from the metals (V, Mo and Ni) present in the spent catalyst is suggested to be responsible for the high HDM activity of the prepared catalyst.

Modelling of hydrodesulfurization catalysts: II. Effects of catalyst pore structures on deactivation by metal deposits

A mathematical model, previously developed to describe deactivation by metal deposition, has been applied to catalyst with macro-, micro- and random pore structures. Simulation results showed that effectiveness factor reduces progressively with the increasing age of the catalyst. For the macropore system, catalyst lifetime was found to be over 1 year and it is the highest in comparison with both micropore and random pore models. It was revealed that a pore structure in which the pore diameter is enlarged increases hydrodemetallization activity and will be very effective for improving metal resistance because pore-mouth plugging can be curtailed. Predicted catalyst lifetimes matched plant data very closely. The need to develop catalysts of optimum pore structure to achieve desirable goals has been validated.

Characteristics of Maya crude hydrodemetallization and hydrodesulfurization catalysts

Hydrotreating of Maya crude is carried out under conditions close to the industrial operation. Various catalysts are prepared in the laboratory and the results are compared with a reference catalyst. Catalysts for such hydrotreating process are designed with high porosity and low active metal content considering metal deposition during the reaction and consequently the stability. Information regarding the activity and deactivation of the catalyst is discussed on the basis of catalyst porosity and deposited metal characterization. It was found that supports prepared by ammonium carbonate and urea hydrolysis methods have macro pore size distribution (PSD) as well as comparatively higher pore volume. The hydrodemetallization (HDM) activity increases while the hydrodesulfurization (HDS) activity decreases with increasing the average pore diameter (APD). The results of HDM and hydrodeasphaltenes (HDAs) activities of catalyst protrude distinct contribution of macro PSD of support which has more capabilities to retain metal deposition and better diffusion of complex organo-chelating metals. The spent catalysts are characterized by PSD, temperature-programmed reduction (TPR), in situ Fourier transform infrared (FT-IR), and transition electron microscopy (TEM). The spent and fresh catalysts characterization results are in well agreement with the activity. It has also been proposed that deposited vanadium sulfide may act as auto-catalytic activity for HDM and HDAs instead of being poison. It is also found that the deposition of metal depends on the porosity and surface area of the catalyst.

Effect of alumina preparation on hydrodemetallization and hydrodesulfurization of Maya crude

Hydrodesulfurization (HDS) and hydrodemetallization (HDM) of Maya crude were carried out in a high pressure (5.4 MPa) micro-reactor close to industrial practice. The effect of support preparation (γ-alumina) was compared using different preparation techniques. The different support preparation methods leading to a variation in textural properties of the supports and its characterization provides important information about their applicability for Maya crude processing. Ammonium carbonate prepared supports provide improved pore size distribution as well as high pore volume. The prepared catalysts are effective for HDS and HDM, having less formation of deteriorating substances such as Ni and V with more stable behavior against time-on-stream. The HDM activity increases while the HDS activity decreases with increasing average pore diameter. Laboratory prepared catalysts showed comparable performance as well as stability in comparison with commercial catalysts against hydrotreating of heavy Maya crude feed. Among all prepared catalysts, better porosity containing catalysts represent higher and stable activity for HDM as a function of time-on-stream. The comparison of catalyst activity was carried out with commercial one which contains TiO 2 and higher amount of molybdenum. The results of activity and stability of catalyst protrude distinct contribution of pore size distribution of support which has more capabilities to retain metal deposition as well as better diffusion of complex organo-chelating metals (V, Ni, etc.).

Effects of Asphaltene Content in Atmospheric Residue and Mean Pore Size of Catalyst on Initial Deactivation of Hydrodesulfurization Catalyst

Hydrodesulfurization (HDS) of atmospheric residue (AR) over Ni_Co_Mo catalysts supported on γ-alumina was carried out to examine the effect of alumina pore size on HDS activity, hydrodemetallization (HDM) activity and initial catalyst deactivation under deep hydrodesulfurization conditions. HDM activity slightly increased with alumina pore size, but HDS activity decreased due to the decrease in the surface area of the support. Deactivation of the HDS catalyst was greater on large pore size supports than on medium pore size supports. The combination of HDS catalyst with large pore size supports (40%) and medium pore size supports (60%) did not improve the catalyst life. HDS was carried out with the large pore size support catalyst at the upstream side in the first reactor and the medium pore size support catalyst at the upstream side in another reactor. Catalyst deactivation was greater in the former than in the latter reactor. These results suggest that HDS catalyst supported on alumina with medium pore size has a higher performance than HDS catalyst supported on alumina with large pore size for deep HDS. To examine the behavior of asphaltene (ASP) at the reaction temperature, adsorption of ASP was investigated on catalyst supports with different pore size. ASP was a large molecule at low temperatures, but the molecular size decreased at HDS reaction temperature caused by the dissociation of the molecular structure. Furthermore, ASP containing sulfur was preferentially adsorbed on the catalyst support. The chemical interaction between ASP and alumina indicates that alumina is a good support for the HDS reaction.

Alumina–titania binary mixed oxide used as support of catalysts for hydrotreating of Maya heavy crude

Three different methods are applied to prepare alumina–titania binary mixed oxide supports. These supports are used to prepare catalysts for hydrotreating of Maya heavy crude. Sequential incipient wetness and co-impregnation techniques were employed for preparation of catalysts. Ammonium heptamolybdenum was used as precursor for MoO 3. Catalysts are characterized by XRD, TPR and pore size distribution. Hydrodemetallation (HDM), hydrodesulfurization (HDS), hydrodenitrogenation (HDN), and asphaltene conversion (HDAsp) reactions are studied on these catalysts. One reference catalyst is also taken for comparison. Coke and metals depositions on spent catalysts are measured. Catalyst deactivation rate is also studied. A combined method of urea hydrolysis and pH variation is suitable to prepare bigger size of pore diameter and more pore volume support. XRD results indicate that prepared alumina–titania oxides are amorphous or very poor crystalline in nature. Very complex nature of TPR profiles is observed. Two catalysts (C and D) show very high activities and also give very good stability compared to reference catalyst. We observe an average correlation between pore diameter of catalyst with HDM and HDAsp conversions. It indicates that bigger pore diameter catalyst is suitable for removal of metals and asphaltenes, but bigger pore size is not only criterion to show good HDM activity. Total pore volume is also an important parameter in this regard. Enhancement of activities is observed on P containing catalyst. Coke is deposited on the catalyst pore mouth and it caused a drastic reduction of specific surface area of spent catalyst. Coke deposition is more on the catalyst having bigger pore diameter. We also observe that rate of V removal is higher than rate of Ni removal.

SEPARATIONS AND CHARACTERIZATIONS OF FRACTIONS FROM MAYAN, HEAVY ARABIAN, AND HONDO CRUDE OILS

ABSTRACT Mayan, Heavy Arabian, and Hondo crude oil resids have been separated with a modified, extended ASTM D2007 procedure. The fractions obtained have been characterized with various analytical techniques. Chemical properties, hydrodesulfurization, and hydrodemetallation activities of the resids have been correlated with the chemical properties of the separated fractions. Many correlations were indicative of the overall bulk properties of the resids and the broad chemical classes obtained from the separation schemes. Other correlations reflected the unique chemical nature of each crude oil resid. Some potentially important correlations were found between hydrodesulfurization activity and sulfur concentration in polars and asphaltenes, and between hydrodemetallation activity and nitrogen concentration in the acid and bases fractions.

EFFECT OF SILICON ON HYDROTREATING OF PETROLEUM RESIDUA

ABSTRACT Catalyst life in residual oil hydrotreating is dependent on the deposition of coke and metals in the catalyst pores. Although silicon naturally occurs in relatively small amounts in crude oils, recent analysis in this laboratory of used catalyst from a commercial unit showed silicon deposits of one to six percent inside catalyst particles. Laboratory reactor tests simulating commercial operations showed that silicon deposition reduced both catalyst hydrodesulfurization and hydro-demetallization activity. Electron microprobe analysis demonstrated that silicon deposition influenced deposition profiles of metals, sulfur, and carbon.

HYDRODEMETALLATION CATALYST DEACTIVATION—EFFECT OF METALS ACCUMULATION ON HYDROGENATION AND HYDROGENOLYSIS ACTIVITIES

The deactivation of hydrodemetallation catalyst was investigated in diffusion-free conditions using a model oil system. The hydrodemetallation activity of a CoMo/γ-alumina catalyst was studied using nickel or vanadyl etioporphyrins as model compounds and the hydrodesulfurization and hydrogenation activity using dibenzothiophene and naphthalene. The experiments were carried out over sulfided catalysts at 320°C and 4.83 MPa total pressure. The catalyst activity for nickel etioporphyrin hydrodemetallation was maintained at least up to 50% metal loading. The hydrogenolysis activity decreased with increasing nickel and vanadium on the catalyst but the hydrogenation activity increased. The changes in activity were attributed to the different activities of the various sulfide phases present in the catalyst system.

Laterite as a catalyst for the hydrotreatment of heavy Oil. II. Influence of chemical and thermal treatments on the HDS and HDM activity

AbstractEffects of thermal treatment and iron extraction by the dithionate method (DCB) on the pore size distribution of laterite, and influence of iron and molybdenum impregnation on hydrodesulfurization (HDS) and hydrodemetallization (HDM) of natural DAO Morishal feedstock, were investigated. Thermal treatment up to 400°C noticeably improves pore size distribution and surface area. Higher temperatures drastically decrease the specific surface area, although the total pore volume remains constant. Iron extraction of laterite calcined at 550°C decreases HDS activity, but improves HDM activity. On the contrary, iron and molybdenum impregnation noticeably increases HDS activity and does not improve the HDM function.

The role of transition metal sulfides in hydrotreatment. III. Acidity, XPS and catalytic activity

Although, recently, most of the research on catalysis has been devoted to hydrotreatment, attention has been paid to hydrodesulfurization (HDS) but very little has been done on hydrodemetallization (HDM). This article is part of a systematic study directed towards defining the role of transition metal sulfides in hydrotreatment reactions [1,2]. We have considered catalysts supported on silica or alumina. Acidity has been evaluated using pyridine as probe molecule. This property can be attributed to the sulfide phase of the catalysts. The alumina supported catalysts were more acid than the silica supported catalysts. Since the acidity might exclusively be of Lewis type, the pattern observed through the first row transition metal sulfides reflects the trend of the electron-aceptor character of these sulfides. The XPS results indicate that catalysts are partially sulfided (at 400°C). At the same time, the results corroborate a better Me-support interaction on alumina than on silica. The HDM and HDS intrinsic activities, using a desalphalted (DAO) Morichal as feed were evaluated normalizing conversion in terms of the surface metal sites per surface area. The intrinsic activity patterns obtained for the first row transition metal sulfides, were very similar to those mentioned of acidity, reaffirming the importance of the electronic structure of the sulfide phase on its catalytic activity.