The dynamics of propagating liquid pulsations generated via various cyclic operation strategies in trickle beds was monitored through electrical capacitance tomography (ECT) for gas and liquid Superficial velocities in the range of trickle flow regime. The characteristics of ON-OFF liquid, ON-OFF gas, and gas/liquid alternating cyclic operations were compared in terms of mean liquid holdup, pressure drop, pulsation intensity, pulsation propagation velocity, and spatial maldistribution maps of liquid holdup and liquid Pulsation propagation velocity. The morphological features of liquid holdup pulsation,, as I function of cycle frequency were characterized in terms of breakthrough, plateau, and decay times. Gas/liquid alternating cyclic strategy was shown to produce long-lived liquid Pulsations under the applied operating conditions and thus could be viewed as a new process intensification means to achieve uniform phase holdup and velocity distributions. In ON-OFF liquid cyclic operation, Pulsation velocity did not increase along the bed unlike the ON-OFF gas and gas/liquid alternating cyclic modes where increased pulsation velocities were able to give rise to Pulse flow regime. The gas/liquid alternating cyclic operation resulted in the shortest breakthrough and decay times and the longest plateau time, thus approaching the ideal square-shaped inlet pulsations for symmetrical splits. ECT imaging Was also used to scrutinize the dynamics of local deposition of fines in trickle beds fed with kaolin Suspensions Under the three cyclic operations. Data revealed that applying ON-OFF gas and gas/liquid alternating cyclic methods resulted in significant reduction of fines deposition. This suggests new practical subject for possible industrial implementation of self-cleaning modulation strategies of trickle beds SUN to Unwanted filtration during suspension flows.

Sodium A-zeolite with different platinum contents were prepared by directly incorporating platinum precursor (Pt(NH3)4Cl2) into the zeolite during synthesis. Pt/KA-zeolite was then obtained by ion-exchange with KCl solution. The effect of platinum concentration on the crystal morphology and platinum dispersion was investigated by hydrogen chemisorption, scanning electron microscopy (SEM), X-ray diffraction (XRD), and time-of-flight secondary ion mass spectrometer (TOF-SIMS). SEM results revealed a bimodal crystal size distribution for NaA-zeolite with low platinum concentration (<1wt%). Chamfered edges were found for all the larger cubic crystals (∼4μm). Two types of cubic crystals, smooth surface cubes with chamfered edges and rough surface cubes, were observed for the smaller crystals (∼400nm). The proportion of the rough surface nanosized cubes increased as the platinum content increased. At about 4wt% platinum, only nanosized rough surface cubic crystals were obtained, which were transformed into nanocrystals of KF-zeolite after ion-exchange with KCl, as indicated by X-ray diffraction results. TOF-SIMS data taken before and after sputtering the surface layers revealed that platinum was distributed homogeneously inside of the zeolite, which was supported by hydrogen chemisorption results, indicating that platinum particles were confined in the zeolitic cages for both the microsized and nanosized cubic crystals. A mechanism was proposed to elucidate the role of platinum precursor on the nucleation and growth of nanosized zeolite, which is consistent with all of the characterization results.

This paper presents the contribution of hydrogen spillover to the hydrogenation of naphthalene over Pt/RHO catalysts. Platinum supported on RHO zeolite was prepared by adding a Pt precursor to the synthesis gel of RHO zeolite. Pt/RHO catalysts were characterized by XRD, TEM, TPR and XPS. The hydrogenation activity was tested using 1-hexene, 1-cyclohexene and naphthalene as model compounds. XRD and TEM results indicated that incorporating Pt precursors into the synthesis gel did not affect the crystal structure and the morphology of the RHO zeolite. TPR, XPS and hydrogenation tests revealed that Pt particles were located in both RHO cages and intrazeolite spaces. In Pt/RHO containing lower levels of cesium, a small amount of Pt was also located on the external surface of the zeolite. The contribution of hydrogen spillover over hybrid Pt/RHO_H-Y zeolite catalysts was examined in naphthalene hydrogenation. Naphthalene conversion increased from 21% over a Pt/RHO catalyst to 91% over Pt/RHO diluted with H-Y zeolite, clearly demonstrating the positive effect of hydrogen spillover on the hydrogenation reaction.

Experiments were carried out to monitor the evolution of the deposition of fine particles in trickle-bed reactors during the flow of nonpolar hydrocarbon oil-like liquid suspensions using electrical capacitance tomography (ECT) imaging. The accuracy of the ECT rendition was validated in the pristine (i.e., deposit-free) bed state by comparing the liquid holdup measurements from ECT with the liquid holdup from residence time distribution (RTD) measurements. The pulse-flow characteristics (pulse velocity and frequency) estimated from the ECT signals were in agreement with existing literature data. For filtration experiments, the effects of the initial liquid suspension distribution, the gas and liquid superficial velocities, and single-phase flow (i.e., zero gas velocity) on the structure of the deposition in the bed were studied. ECT imaging successfully tracked the unsteady-state progression of bed plugging throughout the trickle bed. It was found that increasing the liquid or gas superficial velocity resulted in increased local deposition. The transition, due to deposition, from trickle to pulse flow was also determined from ECT. In the case of stagnant gas, a filter cake formed on top of the bed.

PIONA (paraffin, isoparaffin, olefin, naphthene, aromatic) is a widely used characterization method for petroleum fractions boiling below 200 degrees C, while a gas chromatography-field ionization mass spectrometry (GC-FIMS)characterization method developed at the National Centre for Upgrading Technology (NCUT) provides a reliable hydrocarbon type distribution by carbon number (#C) for middle distillates boiling between 200 degrees C-360 degrees C. This article proposes an integrated approach to combine the results from both PIONA and GC-FIMS measurements, resulting in detailed hydrocarbon-type distribution between the initial and end boiling points of the middle distillate. Furthermore, summing up the mass in each boiling point (BP)interval (e.g., 10 degrees C) generates an equivalent simulated distillation (SimDis) curve that needs to be reconciled with the SimDis measured by the ASTM D2887 method. This article also discusses a simple data reconciliation approach that allowed us to use the three separate pieces of information (PIONA, GC-FIMS, and SimDis) as an internally consistent basis for the derivation of molecular representation of materials characterized in such a way.

Monolith reactors have been widely used as catalytic converters in the automobile industry. Their applications in other fields, such as environmental pollution abatement and hydrocarbon processing for fuel cells, have also received much attention because of the unique advantages they can offer compared to packed-bed reactors. Detailed modeling and simulation can help understand the complexity of interactions between various physical and chemical processes occurring within monolith channels and in the channel walls. In this review, first a general monolith reactor model for gas phase reactions is proposed and discussed for various modeling applications. In the following sections, the recent published studies on modeling and simulation of gas; phase monolith reactors were reviewed with the focus on mass and heat transfer in monoliths, transient/dynamic modeling, gas flow uniformity and chemical kinetics effects on monolith reactor performance. Suggestions on future work were provided. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.

One W–Ni catalyst supported on hydrothermally treated zeolite Y and two W–Ni catalysts supported on chemically treated zeolite Y were prepared. The catalysts were characterized by NH3-TPD, pyridine-IR, TEM, BET, and XPS. Their performance of hydrodesulfurization, hydrodenitrogenation, and hydrodearomatization were compared using light cycle oil (LCO) as the feed. The results showed that the hydrothermal treatment promotes HDS activity whereas the chemical approach favours the HDA activity. The HDN activity of the three catalysts was similar. Addition of zeolite Y with high proportion of Brønsted acidity in the catalysts helps to enhance the hydrodearomatization activity.

Experiments were carried out to investigate the evolving hydrodynamics of trickle-bed reactors as altered by the concomitant filtration of a flowing suspension containing micrometer-scale fines. The filtration efficiency, two-phase pressure drop, and bed specific deposit (mass of deposited fines per unit of reactor volume) were monitored using flows of air and a kaolin-containing kerosene suspension to clarify the roles of packing (smooth vs porous collectors), bed height, bed entrance distribution of the suspension, makeup addition in recirculation mode, gas superficial velocity, and flow regime transition. It was observed that deposition did not exhibit a seamless pattern but rather consisted of scattered mesoscale islands of deposits, several collector-diameters in size, separated by relatively large plug-free multiple interconnected pores. These corridors favored the in situ development of bed maldistribution that favored short-circuiting of the flow and leveling off of the bed pressure drop. Contrary to expectation, the transition from trickle flow to pulse flow due to progressive bed obstruction was not systematic, and to occur, it required a minimum clean-bed starting liquid holdup value.

The hydrogenation and hydrocracking performances of a series of MoNi/Al2O3 catalysts were evaluated with 4,6-dimethyl dibenzothiophene (4,6-DMDBT), 1-methylnaphthalene, pyridine, and hexadecane as model compounds. Different materials which involved amorphous silica-alumina, and hydrothermally treated zeolite beta and zeolite Y were introduced as part of the catalyst supports. The catalysts were characterized by BET, NH3 temperature programmed desorption (NH3-TPD), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The addition of zeolites in the catalysts could greatly improve the hydrodesulfurization and hydrodenitrogenation activities, but it had have little enhancement in the hydroconversion of 1-methylnaphalene. The comparison among zeolite beta containing catalysts with various zeolite content (5-20 wt%) indicated that the optimum hydrogenation activity was achieved by the catalyst containing 10 wt% zeolite beta. A considerable amount of hexadecane was hydrocracked on zeolite containing catalysts. The hydrocracking of hexadecane proportionally increased with the zeolite content. Zeolite Y appeared to be more effective in enhancing the hydrotreating activity than zeolite beta. The high hydrogen pressure not only considerably increased hydrodearomatization activity, but also greatly suppressed the cracking of hexadecane in the feed. (c) 2006 Elsevier B.V. All rights reserved.

The hydrodynamic behavior of trickle bed and monolith reactors experiencing deposition from fines-contaminated feed flows was studied to assess the potential aptitude of monolith to be an alternative for disability of trickle bed reactors under filtration condition. Beds with equal collection surface area were subjected to single-pass kaolin+kerosene suspension and air flows to study the influence of filtration for different gas and liquid superficial velocities. It was found that for equivalent gas and liquid velocities, specific deposits in trickle bed are up to two times more than in monolith.

The hydrodynamics of a trickle-bed reactor subjected to fines-contaminated feed flows was studied under cyclic operation to assess whether or not periodic flows are able to reduce fines deposition and hence to extend reactor operational life under filtration conditions. The bed was subjected to single-pass kaolin+kerosene suspension and air flows to study liquid–, gas– and alternating liquid–gas cyclic operation policies. It was found that fast- and slow-mode liquid cyclic operation policies were not be able to decrease either the pressure drop or the specific deposit; however, with adjusting carefully the parameters of liquid cyclic operation it would be possible to prolong the trickle-bed cycle life. The alternating gas–liquid cyclic feed was also found useful to reduce the levels of pressure drop and bed specific deposit and exhibited the same efficiency for both short and tall beds.

Selective ring opening of decalin over the catalysts comprising of Ir in combination with Pt supported on mesoporous material, Zr–MCM-41 was studied in a trickle bed reactor. The Zr substituted MCM-41 (Si/Zr=5) support was synthesized by hydrothermal method and characterized by BET surface area measurement, XRD, FTIR, TPD of ammonia. XRD showed hexagonal nature of MCM-41. TPD of ammonia and DRIFTS of ammonia adsorption spectra, respectively, showed moderate acidity and presence of Lewis and Brønsted acid sites. Zr–MCM-41 catalysts loaded with Ir and Pt in the range of 0–1.5wt.% were prepared and characterized by DRIFT spectroscopy of CO adsorption, DRIFT of NH3 and TEM. The activity and selectivity of Ir/Pt-loaded Zr–MCM-41 were investigated in the ring opening of decalin in the temperature range of 300–400°C at 5MPa in the presence of hydrogen. Increase in Ir loading significantly increased the ring opening products yield and selectivity. Maximum conversion of 55wt.% obtained at 400°C. In the range of operating conditions studied, the optimum loading for better ring opening yield of 15wt.% was 1.5wt.% Ir and 0.75wt.% Pt.

The effects of particle size, steam pressure, temperature, and duration on the hydrothermal stability of zeolite beta were studied using the Taguchi orthogonal design. The particle size, crystallinity, textural properties, acidity, and framework structure of the zeolite beta were compared before and after hydrothermal treatment. The results showed that the hydrothermal stability of zeolite beta increased with particle size decrease, and decreased with increase of steam pressure and temperature. No significant changes in particle sizes and morphologies were observed for zeolites with particle sizes between 100nm and 500nm, while an obvious aggregation was identified for the nano-sized sample. The total surface areas and acidity of all treated zeolites were reduced by hydrothermal treatment. After hydrothermal treatment, obvious realumination was observed for all zeolites.

The interactions of H2 and H2S molecules with Pt–Pd bimetallic catalysts were investigated at the molecular level using a DFT (density functional theory) approach to better understand the structures and properties of active sites, and the relations between structural changes and sulfur resistance. It was found that when alloying the Pt catalyst with a small amount of Pd at a particular surface atomic ratio range, both H2 and H2S showed different adsorption properties compared to those on monometallic Pt or Pd catalyst. The adsorptions of both H2 and H2S were enhanced, but the adsorption energy of H2 increased more than that of H2S, indicating that the adsorption of H2S became less favorable compared with H2 on the bimetallic Pt–Pd catalyst surface. The desorption energy of hydrogen from monometallic Pt or Pd, as well as bimetallic Pt–Pd supported on zeolite, were calculated by temperature-programmed desorption (TPD), the values were compared against the DFT results to explain experimentally and theoretically why the bimetallic Pt–Pd catalyst has better sulfur resistance than monometallic Pt catalyst.

Pt supported on a carbon molecular sieve (Pt/CMS) was prepared by pyrolysis of polyfurfuryl alcohol containing pre-reduced Pt particles. The catalysts were characterized by hydrogen chemisorption, XRD, N2 adsorption/desorption and TEM. Hydrogen chemisorption showed that not all the Pt particles were exposed to H2 molecules. Oxidation treatment made Pt particles more accessible to H2. Catalyst activity was evaluated by hydrogenation of 1-hexene. Hydrogen spillover was demonstrated by diluting Pt/CMS with activated carbon or hydrogen type zeolite Y. The initial conversion of 1-hexene was increased from 86.5% to 98.5% and to 100% when Pt/CMS was diluted with activated carbon and hydrogen type zeolite, respectively. The high initial conversion was sustained for 6h in the presence of diluents while the conversion decreased quickly for Pt/CMS alone.

The present work studies the effect of organic chelating agents on the solution-support interfacial process during the catalyst preparation. EDTA-Ni(II)-Mo(VI)-gamma-Al2O3-H2O is used as a representative catalyst synthesis system. It has been found that Ni(II) adsorption increases with pH value starting from pH 6 and reaches a maximum at pH 8 without EDTA, whereas the adsorption vs pH is reversed (maximum at pH 3.5 and no adsorption at pH 9) when EDTA is introduced into this system with a molar ratio of EDTA/Ni(II)= 1. According to ion-exchange theory, Ni(II) possibly forms a surface ternary complex with the alumina surface sites through EDTA acting as a bridge. It has also been found that Mo(VI) adsorption decreases with pH (maximum at pH 3 and no adsorption at pH 9) in the absence of EDTA. EDTA suppresses the adsorption of Mo(VI), although the adsorption of Mo(VI) vs pH remains the same. EDTA has a higher coordinating constant with the surface Al3+ than do Mo(VI) anions. Free EDTA competes with Mo(VI) on the alumina surface sites. Because EDTA has a preference to chemically bond with Ni(II), which forms a stable complex, Ni-EDTA could be selectively adsorbed on the alumina surface. On the basis of these experimental results, it can be rationalized that EDTA promotes the dispersion of both Ni(II) and Mo(VI) on alumina. Meanwhile, EDTA also limits strong interactions between the metal ions and alumina, thereby contributing to the formation of more vigorous sites.