Catalyst Deactivation Rate Research Articles

Pilot Plant Studies on Accelerated Deactivation of Commercial Hydrotreating Catalyst

In petroleum refineries, estimation of rate of catalyst deactivation is important in order to evaluate and compare the performances of different hydrotreating catalysts. However, in hydrotreating operation, catalyst deactivation is slow due to coke formation at normal operating conditions and usually catalyst activity drops significantly after 12 to 18 months period. In the present work, a testing method is developed and employed to a commercial hydrotreating catalyst for a period of 300 hrs in a pilot plant with diesel as a feedstock and by using accelerated deactivation technique. Kinetic parameters of hydrodesulfurization reaction are estimated by measuring the product sulfur before deactivation level and at the end of 100 hrs, 200 hrs and 300 hrs of deactivation. It is found that the value of kinetic parameters decreases with increase in time on stream. The quality of products hydrotreated at different levels of deactivation is also studied in the present work. The value of saturates are found to decrease with time on stream, whereas the value of carbon residue and polyaromatic hydrocarbons found to increase with time on stream.

CO oxidation: Deactivation of Au/TiO2 catalysts during storage

In a study of the phenomenon of catalyst deactivation during storage, Au/TiO2 catalyst was stored under various conditions, viz. vacuum, nitrogen, air, refrigeration, dark, and light, and tested for CO oxidation activity at regular intervals. The data shows that the catalyst deactivates under all the storage conditions over 12 months and that storage in vacuum significantly enhances the rate and extent of deactivation. Storage in light accelerates the deactivation. The catalyst appears to deactivate through a combination of Au(III) reduction, Au nanoparticle agglomeration, loss of surface hydroxyl groups, loss of surface moisture, and accumulation of surface carbonates and formates. The rate and extent of catalyst deactivation can be limited by storing the catalyst in the dark at sub ambient temperature (refrigerator) and under inert atmosphere.

Parametric study of the decomposition of methane using a NiCu/Al 2O 3 catalyst in a fluidized bed reactor

CO 2-free production of hydrogen via catalytic decomposition of methane (CDM) was studied in a fluidized bed reactor (FBR) using a NiCu/Al 2O 3 catalyst. A parametric study of the effects of some process variables, including catalyst particle size, reaction temperature, space velocity and the ratio of gas flow velocity to the minimum fluidization velocity ( u o/ u mf), was undertaken. A mean particle size of 150 μm allows optimization of results in terms of hydrogen production without agglomeration problems. The operating conditions strongly affect the catalyst performance: hydrogen production was enhanced by increasing operating temperature and lowering space velocity. However, increases in operating temperature, space velocity and the ratio u o/ u mf provoked increases in the catalyst deactivation rate. At 700 °C, carbon was deposited as carbon nanofibers, while higher temperatures promoted the formation of encapsulating carbon, which led to rapid catalyst deactivation.

Influence of Metallocene Type on the Order of Ethylene Polymerization and Catalyst Deactivation Rate in a Solution Reactor

AbstractThe solution polymerization of ethylene using rac‐Et(Ind)2ZrCl2/MAO and (Dimethylsilyl(tert‐butylamido)(tetramethyl‐ cyclopentadienyl)titanium Dichloride)(CGC‐Ti)/MAO was studied in a semi‐batch reactor at 120 °C under different monomer pressures and catalyst concentrations. The kinetics of ethylene polymerization with rac‐Et(Ind)2ZrCl2/MAO can be described with first order reactions for polymerization and catalyst deactivation. When (CGC‐Ti)/MAO is used, however, second order kinetics are observed for catalyst decay and the order of polymerization changes from 2 to 1 with increasing ethylene pressure.

Metal (IV) Phosphates as Solid Catalysts for Selective Dehydration of Sorbitol to Isosorbide

Metal (IV) phosphates of tin, zirconium and titanium were used as catalysts for selective dehydration of sorbitol to isosorbide. Tin phosphate showed the highest selectivity to isosorbide with a moderate conversion. The deactivation rates of catalysts were fitted by an empirical Voorhies equation and the results showed tin phosphate had the lowest deactivation rate with the least values of m and n. Thermal analysis showed deactivation rate was in accordance with coke deposition. The acidity caused by functional groups of the catalysts was the direct factor for catalyst lifetime, which was evidenced by NH3-TPD, XRD, IR and Raman characterizations.

Effect of hydrogen on the synthesis of carbon nanofibers by CO disproportionation on ultrafine Fe3O4

AbstractCarbon nanofibers (CNFs) are grown by catalytic CO disproportionation over ultrafine Fe3O4 catalyst at a hydrogen concentration of 0–29.17%, and the time‐depending rates of CNFs growth are continuously monitored and the morphologies of the as‐synthesized CNFs are analyzed. Increasing H2 concentration will lower CO dissociation energy and assist catalyst reconstruction so as to shorten the induction period and increase the growth rate of CNFs, but it will also increase the rate of catalyst deactivation because carbon hydrogasification is not possible and carbon diffusion in the catalyst particle is rate limiting. As a result of H2‐induced catalyst reconstruction and carbon deposition, the morphology of the CNFs changes from twisty to helical and to straight and becomes less entangled when the H2 concentration is increased. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd.

Deactivation of a Zn/TiO2 catalyst in the course of methanol steam reforming in a microchannel reactor

The service life tests of a Zn/TiO2 catalyst deposited on the microchannel plates of copper foam, nickel foam, and corrugated brass foil in the process of methanol steam reforming demonstrated that the catalyst stability and operation time depend on microchannel plate material. The rate of catalyst deactivation correlated with the thermal conductivity of the microchannel plate material. It was found that catalyst deactivation resulted from the decomposition of zinc titanates, which are active components, and it was accompanied by the appearance of a zinc oxide phase. The best results in the service life tests were obtained with the microchannel plates of copper foam. A microchannel reactor containing 16 copper plates continuously operated at 400°C for 150 h; in this case, the conversion of methanol decreased by 8%. The subsequent microreactor operation for 500 h caused a decrease in the methanol conversion by 26%. It was found that the loss of the catalyst activity was a reversible process, and the activity can be restored by annealing in air.

Influences of Water and Syngas Partial Pressure on the Kinetics of a Commercial Alumina-Supported Cobalt Fischer−Tropsch Catalyst

The influences of the water partial pressure and the syngas pressure on the reaction kinetics of a commercial alumina-supported cobalt Fischer−Tropsch (FT) catalyst were investigated. Both a fresh catalyst, as well as an aged catalyst from a demonstration reactor, were employed in the study. It was concluded that water has a negligible influence on the overall FT reaction rate but lowers the methane selectivity and increases the CO2 selectivity. Longer term exposure to higher water partial pressures did not lead to step changes in the catalyst activity but may have increased the rate of gradual irreversible catalyst deactivation. Increasing the syngas pressure at constant H2/CO ratio significantly increased the FT reaction rate and decreased the methane selectivity, suggesting a substantial incentive to explore higher pressure operation of commercial cobalt−FT processes.

Catalytic Vapor Decomposition of Methane over Nickle Catalyst: Growth Rate and the Corresponding Microstructures of Carbon Nanofibers

Time-resolved intrinsic reaction rate of catalytic vapor deposition of methane into carbon nanofibers (CNFs) and hydrogen on supported Ni catalysts was determined under different reaction temperatures (773–973 K) and feed compositions (PH2 = 0–0.29 atm, PCH4 = 0:28–0.71 atm) and the microstructure of the produced CNFs was characterized by Raman and TEM. The results showed that, increasing the reaction temperature, methane partial pressure and decreasing hydrogen partial pressure increased the initial reaction rate but generally led to fast catalyst deactivation. A high carbon yield per unit catalyst was obtained as a compromise between initial reaction rate and catalyst deactivation rate. The microstructures of the produced CNFs had a close relationship with the initial reaction rate. The CNFs produced with high initial rate tended to have a small angle between the graphene layers and the growth axis, thin diameter and a hollow core. This phenomenon can be used for monitoring and controlling the CNFs synthesis process.

Effects of reaction conditions on hydrogen production and carbon nanofiber properties generated by methane decomposition in a fixed bed reactor using a NiCuAl catalyst

In this paper, the results obtained in the catalytic decomposition of methane in a fixed bed reactor using a NiCuAl catalyst prepared by the fusion method are presented. The influences of reaction temperature and space velocity on hydrogen concentration in the outlet gases, as well as on the properties of the carbon produced, have been investigated. Reaction temperature and the space velocity both increase the reaction rate of methane decomposition, but also cause an increase in the rate of catalyst deactivation. Under the operating conditions used, the carbon product is mainly deposited as nanofibers with textural properties highly correlated with the degree of crystallinity.

Influence of reaction products of K-getter fuel additives on commercial vanadia-based SCR catalysts: Part I. Potassium phosphate

Commercial vanadia-based full-length monoliths have been exposed to aerosols formed by injection of K3PO4 (dissolved in water) in a hot flue gas (T>850°C) from a natural gas burner. Such aerosols may form when burning fuels with high K- and P-content, or when P-compounds are mixed with biomass as a K-getter additive. The formed aerosols have been characterized by using both a SMPS system and a low pressure cascade impactor, showing a dual-mode volume-based size distribution with a first peak at around 30nm and a second one at diameters >1μm. The different peaks have been associated with different species. In particular, the particles related to the 30nm peak are associated to condensed phosphates, whereas the larger particles are associated to potassium phosphates. Two monoliths have been exposed during addition of 100 and 200mg/Nm3 K3PO4 for 720 and 189h, respectively. Overall, deactivation rates up to 3%/day have been measured. The spent catalysts have been characterized by bulk chemical analysis, Hg-porosimetry and SEM-EDX. NH3-chemisorption tests on the spent elements and activity tests on catalyst powders obtained by crushing the monoliths have also been carried out. The catalyst characterization has shown that poisoning by K is the main deactivation mechanism. The results show that binding K in K–P salts will not reduce the rate of catalyst deactivation.

Modeling of Catalyst Activity Profiles in Fixed-Bed Reactors with a Moment Transformation Method

A model for pseudo-steady-state catalyst activity profiles in a fixed-bed reactor is presented. It is based on conservation of moments of the exact catalyst activity profile, as calculated from the catalyst deactivation rate. These moments are then transformed analytically into a polynomial approximation of the activity profile for each time step. Then temporal and spatial evolution of the catalyst activity can be followed, and correspondingly accurate predictions of reactor performance with partly deactivated catalyst can be carried out. The present model is especially suitable for situations where the observed reaction rate is not solely determined by kinetics of a catalytic reaction, but also by heat or mass transfer limitations, or if the pressure drop in the reactor affects reaction rates. A further important class is when multiple reactions are taking place with different mechanisms so that the dominant mechanism changes as catalyst is deactivated. It can also be used in catalyst lifespan design, since measured temperature gradients can be followed by the model and transformed into information regarding catalyst activity profile. Also optimization of reactor operation with partly deactivated catalyst can be improved.

Glow Discharge Plasma-Assisted Preparation of Nickel-Based Catalyst for Carbon Dioxide Reforming of Methane

A plasma-assisted method was employed to prepare Ni/-Al2O3 catalyst for carbon dioxide reforming of methane reaction. The novel catalyst possessed higher activity and better coke-suppression performance than those of the conventional calcination catalyst. To achieve the same CH4 conversion, the conventional catalyst needed higher reaction temperature, about 50C higher than that of the N2 plasma-treated catalyst. After the evaluation test, the deactivation rate of the novel catalyst was 1.7%, compared with 15.2% for the conventional catalyst. Different from the characterization results of the calcined catalyst, a smaller average pore diameter and a higher specific surface area were obtained for the plasma-treated catalyst. The variations of the reduction peak temperatures and areas indicated that the catalyst reducibility was promoted by plasma assistance. The dispersion of nickel was also remarkably improved, which was helpful for controlling the ensemble size of metal atoms on the catalyst surface. The modification effect of plasma-assisted preparation on the surface property of alumina supported catalyst was speculated to account for the concentration increase of absorbed CO2. An enhancement of CO2 adsorption was propitious to the inhibition of carbon formation. The coke amount deposited on plasma treated catalyst was much smaller than that on the conventional catalyst.

Deactivation studies of bifunctional Fe-HZSM5 catalyst in Fischer-Tropsch process

A physical mixture of alkali-promoted iron catalyst with binder based on Fischer-Tropsch synthesis and an acidic co-catalyst (HZSM5) for syngas conversion to hydrocarbons was studied in a fixed bed micro reactor. Deactivation data were obtained during the synthesis over a 1400 h period. The deactivation studies on iron catalyst showed that this trend followed the phase transformation Fe 2.2C (ɛ) → Fe 5C 2 (χ) → Fe 3C (θ), and the final predominant phase of the catalyst was Fe 3C (θ). Deactivation of zeolite component in bifunctional catalyst may be caused by coking over the zeolitic component, dealumination of zeolite crystals, and migration of alkali promoters from iron catalyst under synthesis conditions. The deactivation rate of iron catalyst was also obtained.

Study on deactivation of hybrid catalyst for dimethyl ether synthesis in slurry reactor

Deactivation of composite catalyst for one-step dimethyl ether (DME) synthesis in slurry reactor was studied under reaction conditions of 260°C and 5.0 MPa. It was found that instability of Cu-based methanol synthesis catalyst led to rapid deactivation of the composite catalyst. Deactivation rate of the Cu-based catalyst in slurry reactor was compared with that in fixed-bed reactor. The results indicated that harmfulness of water, which is formed in the synthesis of DME, caused the Cu-based catalyst to deactivate at a high rate in slurry reactor. Techniques of TPR, XRD, and SEM-EDS were used to characterize the reduction behaviors, crystal structures, and surface properties of the catalyst. The results showed that carbon deposition and grain growth of Cu were important reasons for the rapid deactivation of the Cu-based catalyst, and no obvious metal loss of Cu was found.

Synthesis gas production from dry reforming of methane over Ni/Al 2O 3 stabilized by ZrO 2

The effect of zirconia as a promoter and catalyst preparation method for Ni/Al 2O 3 on catalyst activity and coke inhibition was investigated for the reforming of CH 4 by CO 2. The performance of the promoted catalyst prepared by co-impregnation and sequential impregnation methods with different loadings of ZrO 2 was compared. The addition of ZrO 2 greatly improved the stability of Ni/Al 2O 3 catalyst in terms of coke inhibition by enhancing the dissociation of oxygen intermediates, which then react with carbonaceous species formed over the metal. The rate of catalyst deactivation due to coke deposition for the sequential impregnated catalyst was lower compared to the co-impregnated catalyst at the same promoter loading. For the co-impregnated catalyst, ZrO 2 loading did not substantially affect the catalyst stability, while the low promoter loading in sequentially impregnated catalyst was much more stable than the high loading. The 7% ZrO 2 loaded in Ni/Al 2O 3 by sequential impregnation yielded the most stable catalyst for a dry reforming reaction.

The usage of high metal feedstock for the determination of metal capacity of ARDS catalyst system by accelerated aging tests

For residue hydrotreating catalysts that are deactivated mainly by pore blockage due to deposition of metals, the capacity for accommodation of the deposited metals is an important parameter in determining its stability and life. The primary objective of the present work is to determine the maximum metal capacity of different catalysts that are used in different reactors of atmospheric residue desulfurization (ARDS) units by accelerated aging tests in a short duration. A feedstock with high metals content, namely, Boscan crude, was used for the tests in a multireactor pilot plant to cause complete deactivation of the catalysts by metal accumulation in a shorter period. The influence of operating temperature and LHSV on the rate of catalyst deactivation was also examined for the high metal feed. Catalyst deactivation rate was found to be more than five times faster for the high metal Boscan feed compared to the conventional atmospheric residue from Kuwait export crude. It was possible to determine MMOC of an ARDS catalyst system within 45–50 days by accelerated deactivation test using a high metal feed (e.g., Boscan crude).

The effect of sulfur compound on the hydrogenation of tetralin over a Pd–Pt/HDAY catalyst

A composite metal catalyst with a Pd/Pt of 4:1 and an H-form dealuminated Y zeolite support for the hydrogenation of tetralin was investigated. The materials were characterized by XRD, NH3-TPD, N2 adsorption, TPR and FTIR. The activity for the hydrogenation of tetralin was investigated with a high-pressure fixed-bed continuous-flow reactor operating at 4.0 MPa. The thiotolerance was tested with feeds containing 200 ppm sulfur in the form of 4,6-dimethyldibenzothiophene and thiophene, respectively. It was found that thiophene was more effective for deactivating the catalyst than the former one. The diffusion barrier of the pores for the sulfur compound is likely the major reason for the different deactivation rate of catalysts. The products other than decalins were mainly decalin isomers and ring-opened products. Selectivity of cracking products for the feed with thiophene was lower than that for the other feed, while that of ring-opened and ring-contracted products with the two feeds was similar. © 2007 Elsevier B.V. All rights reserved.

Catalytic Pyrolysis of High Density Polyethylene on a HZSM-5 Zeolite Catalyst in a Conical Spouted Bed Reactor

HDPE has been pyrolysed at 450 °C and 500 °C using HZSM-5 zeolite as a catalyst. Batch runs have been carried out at atmospheric pressure in a conical spouted bed reactor. Product analysis has been carried out by means of a GC, connected on-line with a thermostated line. The degradation rate of the plastic is slightly faster at 500 °C than at 450 °C and much faster than thermal pyrolysis in both cases. Products have been grouped into five lumps: the lump of light olefins, C2-C4; light alkanes, C1-C4; the gasoline fraction, C5-C11 compounds; C11+ hydrocarbons; and the coke deposited on the catalyst. An HZSM-5 catalyst is appropriate to obtain light olefins; about 55 wt% in both cases. The yield of gasoline fraction is also considerable and although its composition is not suitable for commercial gasoline, is interesting for its use in petrochemistry. The catalyst deactivation rate is low.

Dehydration of methyl phenyl carbinol catalyzed by modified active aluminum oxide

The effect of modification with metal salts and acids on the acid-base characteristics and the catalytic properties of active aluminum oxide in the reaction of methyl phenyl carbinol dehydration to styrene was studied using the IR spectroscopy of adsorbed base molecules. The surface treatment of γ-Al2O3 with chromium and nickel cations decreased the catalyst activity because of the occurrence of hydrogenation side reactions. The appearance of strong Bronsted and Lewis acid sites as a result of modification with sulfate, nitrate, and fluoride anions accelerated the deactivation of the catalyst. Upon modification with acetic acid solutions, additional Lewis acid sites with QCO = 33.5−34 kJ/mol were formed on the surface of aluminum oxide, and the concentration of strong basic sites with PA = 900 kJ/mol decreased; this facilitated an increase in the catalyst activity and a decrease in the rate of catalyst deactivation.