Alumina Extrudates Research Articles

Design and Synthesis of a Novel Catalytic System Based on Pd Supported on Alumina Extrudates for Hydrotreating of PAO Lubricants

ABSTRACTThe development of hydrogenation processes for polyalphaolefin (PAO) lubricants, which hold commercialization potential, is a challenging endeavor. Here, we synthesized and characterized rod‐shaped γ‐alumina supported Pd catalyst for PAO hydrofinishing, comparing it with γ‐alumina supported Ni catalyst. Results indicated that Pd/Al2O3 catalyst efficiently promoted PAO hydrofinishing, whereas Ni‐based catalyst exhibited lower activity. Optimization of reaction variables using the one‐factor‐at‐a‐time method revealed that hydrogenated polyalphaolefin could be achieved with a 90% yield using a 5 wt.% catalyst, a hydrogen pressure of 12 bar, at 130°C after 7 h. The superior performance of the fabricated catalysts, coupled with the use of rod‐shaped alumina suitable for large‐scale hydrogenation reactors, suggests the versatility of the process for potential commercialization. Additionally, the higher performance of Pd/alumina compared to Ni/alumina catalyst was computationally assessed at the molecular level using DFT methods.

Enhancing mechanical strength and porosity of alumina extrudates through composite processing

Industrial alumina supports need to possess both high mechanical strength and porosity, but these requirements often conflict with each other. In this work, differences in powder properties such as particle shape, flowability, and peptizability were utilized to composite for extrusion. When globoid pseudo-boehmite was composited with sheet-like alumina at a mass ratio of 3:1, the extrudate exhibited a mechanical strength of 183 N·cm−1 and a porosity of 62.24%, representing a 46.4% and 4.5% increase, respectively, when compared to using globoid alone. Multiscale characterizations revealed that the composite extrudate possessed rich and interconnected mesopores and macropores. The outcome of DEM indicated that the composited extrudates had higher porosity and particle average coordination numbers than the single powder extrudates. This study revealed a correlation between powder properties and extrudate structures, providing design insights for the targeted control of mechanical strength and pore structure.

Enhancing interfacial synergies for the preparation of high mechanical strength and interconnected porosity of alumina extrudates through pre-wetting method

The forming of catalyst supports is a crucial step in the application of industrial catalysts. Alumina, a widely employed catalyst support, is often shaped using nitric acid as a peptizer to enhance mechanical strength. However, the use of large amounts of nitric acid typically results in a decrease in specific surface area and damage to the pore structure due to chemical corrosion. In this work, we present a more practical approach that is pre-filling the open pores of pseudo-boehmite powder with water instead of directly filling them with nitric acid solution. The binder with a small quantity of nitric acid plays a synergistic role in functioning as a glue on the particle surfaces. And through this method, high-strength (231 N cm−1) alumina support can be prepared more efficiently through extrusion. Besides, the pore structure of the extrudates was characterized by multi-scale methods, including nitrogen physical sorption and XRM (X-ray microscopy), which revealed abundant interconnected hierarchical pores deriving from the pre-wetting shaping process. This proposed approach enables the attainment of high mechanical strength and interconnected porosity for alumina extrudates with less use of acid, which holds a significant practical application value.

Adsorption of Nickel Ions on the γ-Alumina Surface: Competitive Effect of Protons and Its Impact on Concentration Profiles.

Mesoporous γ-alumina is used as an adsorbent in the decontamination of water from heavy metals (e.g., nickel and cobalt) and as a support for heterogeneous catalysts prepared by impregnation. In these cases, alumina extrudates are in contact with aqueous solutions containing precursors of the active metal phase to be deposited. The proton concentration (or pH) in the metal solution in contact with alumina can impact the adsorption efficiency of decontamination processes and the activities of catalysts. Yet, it is difficult to quantify the effect of the pH inside the pores since protons are not detected by classical imaging techniques. In this article, the effect of protons on nickel adsorption on alumina is evaluated using a novel technique coupling liquid analysis (pH, conductivity, and UV/vis) and laser-induced breakdown spectroscopy (or LIBS) analysis of concentration gradients inside the solid. Both methods are in excellent agreement. The results show a slow diffusion of protons inside alumina pores (diffusion continues even after 940 min), yielding high proton concentration gradients. On the other hand, the nickel species penetrate the extrudates faster but are slowly displaced by protons under certain operating conditions. As a result, different metal concentration profiles are obtained, depending on the initial pH and contact time. These findings are interesting in catalysis since they prove the possibility of controlling the deposition of the active metal on catalysts by regulating the operating conditions of impregnation. For typical industrial impregnation times (a few minutes to 1 to 2 h), protons do not have enough time to deeply penetrate inside extrudates, so the initial pH of the metal solution will have nearly no effect on the metal distribution. Conversely, decontamination processes have much longer contact times; therefore, lower initial pH values should have negative impacts on the adsorption efficiency due to the protons displacing the adsorbed nickel.

Adsorption of asphaltenes on multiscale porous alumina

Alumina catalysts are frequently used in refineries for the hydrotreatment of heavy petroleum fraction that are enriched in asphaltenes. The transport of real and model asphaltenes molecules through powder and alumina’s extrudates treated or not at 150 °C to remove or not surface-adsorbed water was studied. The kinetics and isotherms of adsorption at 298 K were obtained by the solution depletion method. Calorimetric experiments were also investigated. The kinetic is faster on the powder than on the alumina extrudates where the equilibrium is reached after 24 h (against 1 h for the powder) due to mass transfer limitation. The capacity of adsorption of model asphaltenes on untreated powder and extrudates is comparable around 1.1 and 1.2 mg.m− 2 and increases with the heat treatment due to water removal. Both adsorption strength and capacity of real asphaltenes on alumina is lower compared to the model asphaltene molecule which could be explained by the strong interaction between the acidic function of the model molecule and the alumina surface. The calorimetric study in absence of alumina shows the dimerization of model asphaltene molecules. In presence of alumina, the enthalpy of adsorption of model and real asphaltenes on alumina is determined. The enthalpy of adsorption of model asphaltenes on treated powder is higher than on untreated powder meaning that more energetic sites are available (probably due to the release of water-occupied sites) and the curve obtained for treated powder suggests different adsorption sites. The enthalpy of adsorption of model asphaltene is higher for the treated extrudates but these results must be taken carefully because the kinetic of adsorption is very slow (24 h) for extrudates. The effect of flow rate was studied by saturating an extrudate column with model asphaltene molecules. The adsorption increases as the flow rate decreases which could be explained by higher friction in the macropores leading to the release of weakly retained asphaltenes as the flow rate increases or by less intermediate pore blocking by asphaltenes as the flow rate and thus the pressure increases. This study shows that the transport of asphaltenes through porous alumina supports is a complex process depending on many parameters.

Transport in multiscale porous extrudates

When considering porous materials that are shaped under a specific form for a given application, a possible anisotropy of structure, that could be created by the synthesis procedure, have to be considered. This anisotropy may have consequences on the transport properties. To evidence such anisotropy, several methods are proposed here in the case of extrudates of alumina used as catalysts supports. The simplest one seems to be the release of probes, here a salt, in controlled geometry. Electrical measurements are also simple in principle but limited to aqueous solutions and to pore size ranges where the double layer can be screened. NMR is a very powerful tool, but the porous domain that is analyzed is often questionable. Finally, approaches such as band spreading analysis of chromatographic peak are also interesting in their ability to explore various pore domains by changing probe size, but a modeling is needed and the preparation of adapted columns is sometimes itself a difficult task. The tortuosity of the material, analyzed here in longitudinal and transverse directions, is used as an intercomparing parameter. Tortuosity measurements: Anisotropy of alumina extrudates. • Anisotropy due to the synthesis method is evidenced by simple experimental methods. • Tortuosities determined by diffusion and conductivity in all directions. • Transversal tortuosity of alumina extrudates higher than longitudinal one.

Zeolites in a good shape: Catalyst forming by extrusion modifies their performances

Chemical interactions occurring between zeolites and alumina binders during the critical steps of catalyst forming are the focus of this study. Three widely used and commercially significant variants of FAU zeolite, covering a wide range of Si/Al ratios, micro-and mesoporosity and acidic properties (Y [LZY-64, Si/Al = 2.3] and USY [CBV 720 and CBV 760 with Si/Al = 16 and Si/Al = 28, respectively]) were shaped by extrusion with pseudoboehmite to produce bound extrudates. These extrudates were characterized by conventional techniques (XRD, 27 Al NMR and IR spectroscopy, N2 physisorption...) and compared to their parent powders activated under the same conditions. The catalytic performances of the zeolite powders, their derived alumina extrudates and physical zeolite/ γ-Al2O3 mixtures were also evaluated employing two different reactions: i) n-octane hydroisomerization, to probe all catalytic sites and ii) 1,3,5 tri-isopropyl benzene dealkylation to probe only the external/mesoporous surfaces. The bound zeolites systematically displayed catalytic performance superior to their parent powders or physical mixtures, especially in the dealkylation of 1,3,5 tri-isopropyl benzene. Infrared spectroscopy measurements of the number, nature and strength of the acid sites were consistent with these catalytic results demonstrating that new catalytic sites are created and located on the external or mesoporous surface of the zeolites, i.e. at the zeolite-binder interface. The work reported here clearly illustrates that binding and subsequent thermal treatment of zeolite powders to produce commercially representative forms can significantly alter the quality and quantity of active sites creating active centers not usually present in pure powders which are typically studied and reported in much of the open literature. Such a study is also a blueprint for other catalytic phases, other forming processes (spray-drying, oil-dropping, pelletizing…) and could also be applied to the shaping of adsorbents.

Novel boehmite transformation into γ-alumina and preparation of efficient nickel base alumina porous extrudates for plasma-assisted CO2 methanation

Homogeneous low pressure cold plasma glow discharge was used for both boehmite to gamma alumina transformation as well as for catalytic CO2 conversion into methane.Novel plasma-assisted boehmite transformation into alumina was successfully achieved at lower temperature (80°C less) and shorter period of time (1h less) than the classical transformation. The final alumina structure properties were improved. The mechanism of the novel plasma-assisted boehmite transformation was addressed. Nickel alumina porous extrudate preparation was optimized and fully characterized. The amounts of binder and nitric acid used during the preparation of extrudates were studied. The concentration of nitric acid presented a major role in the catalytic properties of these catalysts leading to the improvement of the active phase dispersion and reducibility. As a result, methane yield was also improved with support acidity. A simulation study was performed in order to evaluate the influence of the extrudates dimensions on the pressure developed inside the reactor and on the glow discharge stability. It was demonstrated by simulation the need of shaping the nickel alumina catalysts for allowing the generation of a stable plasma discharge through the catalytic bed. Plasma-assisted CO2 hydrogenation under partial vacuum was carried out using the optimized nickel alumina extrudates. Formulation of efficient nickel alumina porous extrudates is provided for plasma or even industrial CO2 methanation reactors.

Influence of preparation method on dispersion of cobalt spinel over alumina extrudates and the catalyst deN2O activity

A series of supported catalysts of the Co3O4 spinel active phase dispersed over alumina extrudates (9×25mm) was prepared by several methods (incipient wetness impregnation with Co(NO3)2 and CoCl2, with glycerol-assisted impregnation with Co(NO3)2, combustion synthesis, and two variants of spray deposition with Co(NO3)2 on pristine and ammonia soaked extrudates). The catalysts were characterized by XRF, XRD, RS, UV–vis, SEM/TEM/EDX, and their catalytic deN2O activity was investigated in the temperature programmed surface reaction (TPSR) mode. The relation between the spinel active phase particle size and its radial dispersion over the alumina extrudate and the deN2O activity was revealed and quantified. For the assessment of the active phase utilization, the N2O concentration profile across the extrudates was calculated using Thiele modulus and compared with the radial distribution of the spinel. It was shown that the dispersion of spinel active phase exhibits optimal profile when the sample is obtained in the presence of the organic components of the precursor mixture (glycerol or urea). The obtained results were discussed in the context of practical implications for the development of an efficient, low-cost catalyst for the N2O abatement.

Effect of Wood Flour Addition on the Pore Volume and BET Surface Area Properties of the Prepared Gamma Alumina (ɤ-Al2O3) Extrudates Used in Catalyst Carriers

Effect of Wood Flour Addition on the Pore Volume and BET Surface Area Properties of the Prepared Gamma Alumina (ɤ-Al2O3) Extrudates Used in Catalyst Carriers

Flame spray synthesis of CoMo/Al 2O 3 hydrotreating catalysts

The first alumina supported and unsupported cobalt molybdenum hydrotreating catalysts have been prepared by one-step flame spray pyrolysis (FSP) by spraying and combusting tris(acetylacetonato)aluminum, cobalt 2-ethylhexanoate and molybdenum 2-ethylhexaoate dissolved in toluene. The oxide particles produced contained varying amounts of transition metals (8, 16, 24 and 32 wt.% Mo with atomic ratio Co/Mo = 1/3 and 16 wt.% Mo with atomic ratios Co/Mo = 2/3 and 1/1) with alumina constituting the balance. In addition, an unsupported reference catalyst (atomic ratio Co/Mo = 1/3) was produced. The particles obtained consisted mostly of γ-Al 2O 3 with some CoAl 2O 4, as evidenced by X-ray diffraction (XRD) and UV–vis spectroscopy. Bulk MoO 3 was not detected by XRD, except at the highest molybdenum content (32 wt.%) and in the unsupported sample, indicating that molybdenum is well dispersed on the surface of the support. The specific surface area as measured by nitrogen adsorption (BET) decreased from 221 to 90 m 2/g when going from the lowest loading supported catalyst (8 wt.%) to the unsupported reference. Transmission electron microscopy (TEM) images showed that at low molybdenum loadings nanoparticle agglomerates with 5–10 nm primary particles were produced. As the molybdenum loading on the alumina was increased from 8 to 32 wt.% and for the unsupported reference the primary particle size increased to up to 20 nm and the morphology became more irregular due to primary particle sintering and aggregation. After activation by sulfidation the activity of the catalysts were measured for the three hydrotreating reactions hydrodesulfurization, hydrodenitrogenation and hydrogenation using a model oil containing dibenzothiophene, indole and naphthalene in n-heptane solution. The best catalyst was the FSP-produced material containing 16 wt.% Mo (atomic ratio Co/Mo = 1/3), which did not contain crystalline MoO 3 and only small amounts of CoAl 2O 4. The hydrotreating activity was approximately 75% of that of commercial cobalt molybdenum catalysts prepared by wet impregnation of pre-shaped alumina extrudates. Since the commercial catalyst is the product of years of development, this shows the potential of the flame spray pyrolysis technique. The Co–Mo–S phase, active for hydrotreating, is formed upon sulfidation of the flame made oxide precursor. TEM images of the spent catalysts showed that as the metal loading was increased from 8 to 32 wt.% Mo the average length of supported MoS 2 entities increased from 3 to 4 nm (for the unsupported catalyst it was 8.5 nm), while the average number of MoS 2 layers per particle increased from 1.1 to 2.5. The increase in MoS 2 particle size resulted in lower activity.

Effect of Mixing on the Pore Structure of Alumina Extrudates

AbstractThe mixing conditions have a direct impact on the pore structure of alumina extrudates. We study the pore structure of samples prepared with two mixers: a standard Eirich mixer and a smaller yet more severe Fukae mixer, which operates at 1500 rpm. We present the development of a bimodal pore size distribution within the range of 25–150 Å produced by using the Fukae mixer. The pore structure consists of larger pores that grow at the expense of the smaller ones and can be tuned as a function of mixing time.

Effect of Particle Porosity on Hysteresis in Trickle-Bed Reactors

Hydrodynamics in trickle-bed reactors (TBRs) is quite complex because of the coexistence of gas−liquid−solid phases. Recent past hysteresis have been the subject of investigation to improve the understanding of the flow features at the microlevel, aiming to demystify the complex hydrodynamics. The purpose of the present study is to identify the role of particle porosity on hysteresis by choosing particles of different pore density (nonporous, semiporous, porous) but prepared from same material with identical shape and sizes. Experiments were carried out with industrial relevant-sized alumina extrudates in a 150 mm ID column using both a dry- and a wet-bed startup procedure. Comprehensive pressure drop hysteresis data were generated in increasing and decreasing modes of water flow in the presence of a constant flow of air at ambient condition. Pronounced but different magnitudes of pressure drop hysteresis were observed with all three types of particles at first cycle as well at subsequent cycle of operation. A deviation in pressure drop up to 90% was found between increasing and decreasing modes of operation, even after prewetting the bed. The same amount of hysteresis was observed for all the subsequent cycles, but the value is higher for particles with higher porosity. This confirms that particle porosity plays a major role in the existence of different flow texture at the microlevel in the trickle flow regime. This observation is reported here for the first time, and we believe that there is no such experimental data available in the literature. The genesis of this different hysteretic behavior of porous particles lies in the different ways liquid spreads/retracts over porous and nonporous particles. A conceptual framework of hysteresis proposed by Maiti et al. (2005), which is based on the concept of participating and nonparticipating particles and principles of liquid spreading on porous and nonporous substrates, is found to explain successfully the various features of hysteresis observed with all three types of particles. This study is expected to be useful to the TBR researcher and practitioner in enhancing the understanding further to demystify the complex hydrodynamic phenomena in TBRs.

Catalytic wet oxidation of phenol in a trickle bed reactor

Catalytic liquid phase oxidation of aqueous phenol was studied in a pilot plant trickle bed reactor using a copper oxide catalyst supported on alumina. Catalysts were prepared by impregnating CuO on alumina extrudates and on computer designed shape (CDS) alumina pellets. Phenol oxidation was carried out in a 2.54 cm diameter reactor with a catalyst bed length of 60 cm and in the pressure range of 1–15 atm and temperature range of 373–403 K Compared to alumina extrudates higher phenol conversion was achieved over CDS pellets under identical conditions. Phenol oxidation reaction was strongly affected by the temperature and pressure, however, pressure had less effect. Hydrodynamics of the reactor had strong influence on phenol oxidation reaction. A one dimensional axial dispersion model was proposed to simulate the experimental results. The model satisfactorily explains the experimental results with a deviation of ±15%.

RTD studies in trickle bed reactors packed with porous particles

AbstractThe residence time distribution (RTD) for liquid phase in a trickle bed reactor (TBR) has been experimentally studied for air‐water system. Experiments were performed in a 15.2 cm diameter column using commerical alumina extrudates with D/dp ratio equal to 75 to eliminate the radial flow differences. The range of liquid and gas flow rates covered was 3.76 < ReL < 9.3 and 0 < ReG < 2.92. The axial dispersion model was used to compute axial dispersion coefficient. The effect of liquid and gas flow rates on total liquid holdup and axial dispersion was investigated. The total liquid holdup has been correlated to liquid and gas flow rates.

Hydrodynamics and solid—liquid contacting effectiveness in an upflow multiphase reactor

Experimental runs were carried out in a fixed bed upflow pilot reactor to investigate the hydrodynamics of the liquid phase. Three kinds of packing were used: 3 × 3 mm glass cylinders, 3 × 4 mm alumina cylinders and 1.7 × 4 mm alumina extrudates. A tracer injection technique was used and the dynamic responses were interpreted using three different models: the axial dispersion model (PD), the stagnant zones model (PE) and the axial dispersion and stagnant zones model (PDE). Solid—liquid contacting effectiveness was evaluated by measuring the apparent intraparticle diffusivities of porous particles in the presence of the gas—liquid flow. The experimental results led to the following conclusions: (a) the axial dispersion model (PD) is not able to give a satisfactory interpretation of liquid hydrodynamics; (b) the flow map of upflow multiphase reactors is not yet well enough defined, especially for small size packings; (c) the estimate of the pressure drop by correlations in the literature is sufficiently good; (d) solid—liquid contacting effectiveness is higher, on average, than in trickle-bed reactors, but it decreases with an increase in gas flow rate.

On the fracture toughness of extrudates and its relationship to rates of bulk particle attrition

In the course of systematic studies of the bulk attrition of three well-characterised cylindrical alumina extrudates of about 3 mm dia. and 3 mm length, a desirable goal was to relate the attrition to fundamental material parameters. From the standpoint of fracture mechanics, a logical basic parameter is K IC, the stress intensity factor at failure. The three grades of extrudate were also cast in the form of rectangular bars, which are particularly useful for obtaining K IC. However, the extrudates are brittle and porous, making it not possible to introduce a crack of known length into a specimen prior to testing. None the less, a recently developed method employing a chevron notch cut into the bars has been employed; three calculational techniques are deployed that yield consistent and logically related values of K IC . Utilisation of the values of K IC for unification of attrition data was not entirely successful, better correlation being achieved by use of estimates of the material tensile failure stress probably because the flaw structures of the three extrudates are not the same. It remains logical that the parameters K IC and flaw size are important variables for attrition and these can be usefully considered independently.

975. Problems and factors influencing metallization of various substrates: R Holland,Proc Soc Vac Coaters Conf, 23–24 February 1965, Society of Vacuum Coaters, POB 3095, Cleveland 17, Ohio

A series of supported catalysts of the Co3O4 spinel active phase dispersed over alumina extrudates (9 × 25 mm) was prepared by several methods (incipient wetness impregnation with Co(NO3)2 and CoCl2, with glycerol-assisted impregnation with Co(NO3)2, combustion synthesis, and two variants of spray deposition with Co(NO3)2 on pristine and ammonia soaked extrudates). The catalysts were characterized by XRF, XRD, RS, UV–vis, SEM/TEM/EDX, and their catalytic deN2O activity was investigated in the temperature programmed surface reaction (TPSR) mode. The relation between the spinel active phase particle size and its radial dispersion over the alumina extrudate and the deN2O activity was revealed and quantified. For the assessment of the active phase utilization, the N2O concentration profile across the extrudates was calculated using Thiele modulus and compared with the radial distribution of the spinel. It was shown that the dispersion of spinel active phase exhibits optimal profile when the sample is obtained in the presence of the organic components of the precursor mixture (glycerol or urea). The obtained results were discussed in the context of practical implications for the development of an efficient, low-cost catalyst for the N2O abatement.