Structural and morphological study of metal deposition on an aged hydrotreating catalyst

The results of NiMo/γ-Al₂O₃ hydrodemetalation catalyst deactivation in a long-term test are presented. A residue from Maya crude has been processed in a continuous hydroprocessing unit provided with a trickle-bed reactor (TBR) at 648 K, 10 MPa H₂ pressure, 1 l/h g_cat LHSV and 0.2 kg/kg ratio H₂/oil. Samples of catalyst from 100, 1100, 2100 and 3100 h on-stream have been characterised by Ni, V and Mo determination and the evolution of the structural and morphological characteristics of these samples has been followed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) using electron backscattering detector and microanalysis by dispersion of energies (EDS). XRD and XPS results have confirmed the presence of sulphide phases with a stoichiometry close to (V, Ni, Fe)₃S₄. Metal deposition profiles of vanadium have shown high concentrations in the edges while nickel deposition profiles have been more uniform. The shape of these profiles has indicated that for vanadium removal reactions, the metal deposition process becomes more diffusion rate limited, resulting in a less deep penetration into the catalyst pellet.     

Isobutane alkylation with C4 olefins on a sulfonic solid acid catalyst system based on laminar clays

Natural clays were modified by means of the controlled attack of strong Brönsted acids in aqueous solution. The variations of the surface acidity of the solids, followed by IR of adsorbed pyridine and hammett indicators, indicated a population of Brönsted type sites above 800 μ mol/g, while the surface area increased from 23 up to 105 m²/g. A series of solids (ATZ-L, ATZ-A and ATZ-G) was activated using trifluoromethanesulfonic acid (CF₃SO₃H), then evaluated at the bench scale in a fixed bed reactor, both in liquid and gas phase, using an iC₄/C₄⁼ molar ratio, which led to 5.5% trimethylpentanes (TMP) against 35.9% of C₈⁼ and 53.4% of heavier C₉⁺ products for the catalysts (ATZ-L) having higher acid strength, i.e. Ho≈−9.3. For the solids having a moderate surface acid strength (Ho≈−4.4) the activation rate after 12 h runs was about 70%, but the solids having a higher acid strength, i.e. Ho=−5.6 and −9.3, showed a deactivation rate almost null after 24 h runs.     

THE FLAT LAMINAR OPPOSED JET DIFFUSION FLAME:A NOVEL TOOL FOR KINETIC STUDIES OF TRACE SPECIES FORMATION

The flat laminar opposed jet diffusion flame was used to determine net rates of formation and destruction of nitric oxide under a wide range of temperatures and local fuel concentrations. In order to accomplish this the theoretical model of this flame was first validated with respect to experimental data on major species and temperature. Then the measured NO and temperature profiles were utilized in conjunction with the species conservation equation to obtain the desired result.     

Nanostructured Ni-containing spinel oxides for the dry reforming of methane: Effect of the presence of cobalt and nickel on the deactivation behaviour of catalysts

Nanostructured Ni-containing spinel oxide catalysts were obtained using a nanocasting method. Analyses by XRD, TEM, TPD-CO₂ and TPR showed that Ni^o and/or Co^o entities with high accessibility to CH₄ and CO₂ were responsible for high catalytic performance in the dry reforming of methane. The NiCo (Co^o and Ni^o dispersed on NiAl₂O₄) and NiAl (Ni^o dispersed on NiAl₂O₄) species were highly active for CH₄ conversion, whereas Ni^o dispersed on either Fe₃O₄–Co₃O₄ or CeO₂–NiAl₂O₄ provided a lower catalytic performance due to active phase degradation. The higher activity exhibited by NiAl compared to NiCo was related to the higher activity of nickel for CO₂ decomposition, while its remarkable stability seemed to be due to the presence of well dispersed nanoparticles involved in long-term conversion because they produced non-deactivating carbon deposits, as suggested by Raman analyses.     

Deactivation of a Fe-ZSM-5 catalyst during the selective catalytic reduction of NO by n-decane: An operando DRIFT study

The selective catalytic reduction (SCR) of NO by n-decane was investigated on a Fe-ZSM-5 prepared by the FeCl₃ sublimation method. NO conversion profiles versus temperature were followed in both temperature programmed surface reaction (TPSR, 10 °C min⁻¹) and steady state experiments. A higher NO conversion with a maximum of ca. 80% at 400 °C is observed in the course of the TPSR tests. This phenomenon has been attributed to strong adsorption of n-decane which protects the active sites against the poisoning. Indeed, in steady state experiments at 390 °C the strong decrease of activity as a function of time on stream is due to the polymerisation of conjugated nitriles. This study indicates that long chain alkanes are not the most adequate reductants of NO for high temperature SCR applications. Moreover, due to an easier polymerization of conjugated nitriles on iron zeolites (stronger Fe Lewis sites), this type of catalyst seems less attractive than Cu-zeolite catalysts for the SCR of NO by hydrocarbons in this respect.     

A study on the conversion of trona to sodium bicarbonate

The deactivation model was used to explain kinetics underlying the conversion reaction of trona to NaHCO₃ (sodium bicarbonate). The model showed good agreement with the experimental data obtained from the conversion reaction of trona to NaHCO₃. It gave the value of 0.94 as an average correlation coefficient with the experimental data. However, at lower temperature, the model was in poor agreement with the data. This would be related to the structural variation of trona particles at the lower temperature. A trona particle is initially nonporous and then it begins to crack. This structural variation creates more surface area for the reaction with CO₂ and water vapor. However, at the lower temperature, the fissures on the surface of the particles are not fully developed during the beginning of the reaction. As a consequence, the level of the conversion of trona at the lower temperature is low during the beginning of the reaction and the time to approach the complete conversion is shorter as temperature increases. However, since the deactivation model does not include the term articulating the degree of the structural variation during the reaction, it does not fit well to the experimental data at the lower temperature. The deactivation rate constant, k_d is strongly temperature dependent and the change of the slope suggests the reaction mechanism changes as the reaction temperature increases.     

渣油加氢创新失活模型的应用

This article reports a new catalyst deactivation model for residue hydrotreating technology(RHT) with three adjustable parameters, named as "active-region-migration model". The active-region-migration model is proposed to describe the catalyst deactivation of RHT where the catalysts are deactivated due to metal loading. Along with the lumped reaction kinetics, the deactivation model can be applied to simulate the hydrogenation reaction performance in RHT. Industrial data from a commercial RHT unit show reasonably good agreements with the model calculations. Essentially, the active-region-migration model can separately simulate the catalytic-activity-change of each hydrogenation reaction during the whole run of RHT, with a single curve.     

Transformation of levoglucosan over H-MCM-22 zeolite and H-MCM-41 mesoporous molecular sieve catalysts

Catalytic transformation of levoglucosan (1-6-anhdyro-??-d-glucopyranose) was carried out in a fixed bed reactor at 573 K over zeolite and mesoporous material catalysts. Proton forms of MCM-22-30 and MCM-41-20 catalysts were tested in the conversion, changing also the residence time. The yield of the transformation product phases was substantially influenced by the structures, at the same time the formation of the different compounds were dependent on the structures of the acidic zeolite catalysts. Oxygenated species were the main liquid product, consisting mainly of aldehydes and furfurals (glycolaldehyde, formaldehyde, acetaldehyde, furfural, 5-methylfurfural, acetic acid). The formation of the liquid products was higher over MCM-41-20 than over MCM-22-30 for all the oxygenated species except acetic acid, indicating larger formation of non-condensable products over the microporous material. By increasing the residence time the formation of acetic acid increased in transformations over MCM-22, however, such increase also led to generation of more gases with both catalysts. The deactivation due to coking was more severe over the zeolite compared to the mesoporous material. It was, however, possible to successfully regenerate the spent zeolites without changing the structure.     

Water tolerance of DeNOx SCR catalysts using hydrocarbons: Findings, improvements and challenges

The recent developments on the effect of H₂O on deNO_x performance of a variety of SCR catalysts selectively removing NO_x by hydrocarbons in excess oxygen have been reviewed. In particular, the water tolerance of the catalyst is summarized to illustrate a common deactivation behavior of SCR catalyst for the reduction of NO by hydrocarbons under wet feed gas mixture. Earlier proposals elucidating the possible cause of the catalyst deactivation under wet conditions are discussed, focusing mainly on the catalyst characteristics. A promising way, which can improve the water tolerance and the hydrothermal stability of zeolite-based SCR catalyst, is also described.     

Catalytic wet air oxidation with a deactivating catalyst analysis of fixed and sparged three-phase reactors

A comparative analysis is made for a trickle-bed reactor, a packed-bubble column, a three-phase fluidized bed and a slurry-bubble column with an active and moderately deactivating catalyst for the wet oxidation at high pressure and temperature of organic-containing aqueous wastes. Compared to other mature industrial sectors where multiphase reactors are prevalent, the design of three-phase catalytic reactors for wet air oxidation processes is still at an emerging stage. This paper discusses, from a multiphase reactor engineering perspective, the design of such contactors by setting an exhaustive modeling framework of catalytic wet oxidation in which the molecular, particle and reactor scales are integrated. The simulation results indicate that when wet oxidation is liquid-reactant limited, packed-bubble columns outperform trickle beds, whereas slurry-bubble columns are the most vulnerable to “coke” deactivation.