Alumina Pellets Research Articles

Metal-doped alumina pellets catalyze the quick degradation of humic acid using oxygen as the oxidant at low temperatures

Low-temperature catalytic air oxidation (LTCAO) is a promising technique that utilizes oxygen to oxidize humic acid (HA) at low temperatures. Still, the fine catalyst particles are difficult to recover and reuse, hindering the actual application of this technique. This study developed a new catalyst pellet by coating Fe or Cu on small Al2O3 balls. The pellet exhibited exceptional treatment efficiency and remarkable durability. HA was adsorbed on the catalyst surface, reacted with the •O2− and •OH species generated in oxygen activation, and finally degraded into CO2 and H2O. The total organic carbon in the HA solution was removed by 92.5 % within 90 min. During HA degradation, the primary intermediates included 2,4-dimethyl-benzaldehyde, 2,4-bis(1,1-dimethylethyl)-phenol, and hexanoic acid ethyl ester. The results provided a new type of catalyst that can be used in actual bed or tower reactors, taking a big step of LTCAO toward application.

Investigating the behaviour of NaCl brines and hydrocarbons in porous alumina using low-field NMR relaxation and diffusion methods.

The behaviour of multiple fluid phases within a porous medium is hard to predict. NMR measurements offer an excellent tool to probe such systems in a fast and non-invasive way. Such systems can be relevant to hydrocarbon recovery, catalysis, and CO2 and H2 geo-storage, among others. Since electrolyte solutions are always present in subsurface reservoirs, understanding their behaviour within porous media is highly important. In this study, we use NMR relaxation and diffusion methods to investigate the diffusion coefficients and strength of interactions between alumina surfaces and brines at various NaCl concentrations, focusing on the effect of salt concentration on transport and interactions within the porous structure. Furthermore, we study the spontaneous displacement of dodecane, a model hydrocarbon, from the same alumina pellets using the same brine solutions. Results show that brines of lower salinity consistently displace more dodecane in total, after soaking dodecane-saturated pellets in a brine solution for several days. This indicates that increased salt concentrations can reduce wettability towards the aqueous phase in simple metal oxide surfaces and highlights the capabilities of NMR to efficiently study such systems.

Influence of the acrylamide-based monomer on the sintering of ceramics shaped by gelcasting

Alumina ceramics were prepared by gelcasting, based on an in-situ polymerization that promotes the formation of homogeneous green ceramic parts and allows the preparation of complex shapes and/or large-size ceramics. The influence of the monomer on the sintering behaviour of alumina pellets has been studied by considering three acrylamide-based monomers, i.e. acrylamide (AM), methacrylamide (MAM) and dimethylacrylamide (DMAA). Slurries with an alumina solid content of 50 vol% have been cast and pre-sintered pellets (1000 °C) with relative densities around 55% were obtained. These presintered pellets exhibit different granular packing, depending on the initial monomer used, as demonstrated by X-ray tomography, SEM and Hg porosimetry analyses. This results in significant differences in sintering behaviour, giving rise to very different final densities after 1 h sintering at 1530 °C: from 88% to 98%. This behaviour is described in terms of shrinkage rate, linked to the granular packing induced by the gelation process.

Developing Versatile Contactors for Direct Air Capture of CO2 through Amine Grafting onto Alumina Pellets and Alumina Wash-Coated Monoliths.

The optimization of the air-solid contactor is critical to improve the efficiency of the direct air capture (DAC) process. To enable comparison of contactors and therefore a step toward optimization, two contactors are prepared in the form of pellets and wash-coated honeycomb monoliths. The desired amine functionalities are successfully incorporated onto these industrially relevant pellets by means of a procedure developed for powders, providing materials with a CO2 uptake not influenced by the morphology and the structure of the materials according to the sorption measurements. Furthermore, the amine functionalities are incorporated onto alumina wash-coated monoliths that provide a similar CO2 uptake compared to the pellets. Using breakthrough measurements, dry CO2 uptakes of 0.44 and 0.4 mmol gsorbent-1 are measured for pellets and for a monolith, respectively. NMR and IR studies of CO2 uptake show that the CO2 adsorbs mainly in the form of ammonium carbamate. Both contactors are characterized by estimated Toth isotherm parameters and linear driving force (LDF) coefficients to enable an initial comparison and provide information for further studies of the two contactors. LDF coefficients of 1.5 × 10-4 and of 1.2 × 10-3 s-1 are estimated for the pellets and for a monolith, respectively. In comparison to the pellets, the monolith therefore exhibits particularly promising results in terms of adsorption kinetics due to its hierarchical pore structure. This is reflected in the productivity of the adsorption step of 6.48 mol m-3 h-1 for the pellets compared to 7.56 mol m-3 h-1 for the monolith at a pressure drop approximately 1 order of magnitude lower, making the monoliths prime candidates to enhance the efficiency of DAC processes.

Life cycle environmental impact assessment of lab-scale preparation of porous alumina pellets as substrate for hydrogen separation metal layer-based membranes

PurposeThe study aimed to identify the environmental hotspots of lab-scale preparation of high purity porous Al2O3 pellets with suitable feature to work properly as metal layer-based deposition substrates for hydrogen separation membranes. The work intention was providing hints that may help the designing of upscaled systems, fundamental for the development of a possible future industrial production of hydrogen separation metal layer-based membranes technology.MethodsThe goal of this study was achieved assessing and analyzing environmental impacts of Al2O3 pellet production at lab scale. Primary data were collected in Padua laboratories of National Research Council of Italy. Secondary data were retrieved from Ecoinvent 3.7 database. Life cycle assessment (LCA) was performed using Environmental Footprint 3.0 method employing SimaPro 9.3 as software. Moreover, the CML LCIA method v. 4.7 was used to verify the robustness analysis of characterized results.ResultsLife cycle impact assessment highlighted as the main driver of environmental impacts was mainly associated to the pellet consolidation process and their morphological characterization stage. In particular, the impact of the first energy consuming process resulted strictly related to the peculiar energy mix used (linked to the laboratory geographical location). Conversely, morphological characterization stage was found to affect mainly the mineral resource depletion category due to the Au coating used for performing scanning electron microscope (SEM) analyses.ConclusionsThe study identified the environmental hotspots related to lab-scale preparation of porous alumina pellets as substrate for hydrogen separation metal layer-based membranes. The optimization strategies evaluated in this work were addressed to improve the environmental profile of experimental activities considering several scenarios, in view of a possible industrial scale-up.

Effect of olivine as MgO-bearing flux on low- and high-alumina iron ore pellets

In the present study, the effect of MgO in the form of olivine flux on low- and high-alumina iron ore pellet mineralogy and pellet quality was studied. Green pellets were prepared by varying the MgO content from 0 to 1.5% with a basicity (CaO/SiO2) of 0.30. The pellets were tested for green pellet properties, cold crushing strength (CCS), and reduction degradation index (RDI) and fired at temperatures between 1300 and 1320 oC. An optical microscope with an image analyzer, SEM-EDS, was used to assess the mineralogical phases present in the pellets and the chemical analysis of the mineralogical phases, respectively. The laboratory tests showed that with increasing MgO addition in both low and high alumina pellets, magnesio-ferrite & silicate melt phases increased and the porosity and hematite phases decreased. The decrease in porosity was due to increase in silicate melt formation from the silica in the olivine. With increasing MgO addition, the CCS value of the pellets increased up to an MgO content of 0.9 to 1.1%. Thereafter, the CCS value of the pellets decreased with increasing MgO addition for both low and high alumina pellets. At an MgO content of 0.9 to 1.1%, the CCS value was higher due to the formation of a low melting point magnesio-ferrite phase, which imparted strength to the pellets. For pellets with an MgO level of >1.1, the RDI was within the control limit for both low- and high-alumina pellets. This may be due to a reduction in the porosity of the pellet and a better distribution of the silicate melt phase. Low-alumina pellets showed better physical and metallurgical properties compared to high-alumina iron ore pellets.

Optimization of Pellet Plant Straight Grate Induration Furnace Firing Cycle for High Alumina and High LOI Iron Ore Pellet

Optimization of Pellet Plant Straight Grate Induration Furnace Firing Cycle for High Alumina and High LOI Iron Ore Pellet

Wake flow and flame characteristics in the porous media with different surface combustion states: An experimental study

• A porous burner formed by SiC foam ceramic and alumina pellets is designed. • The packed bed surface flame characteristics are captured by the high-speed camera. • The wake flow fields under different combustion are analyzed by the PIV system. • Combustion zone map as a reference for the industrial application is obtained. A porous media burner composed of silicon carbide foam ceramic material and alumina pellets was developed to delve into the surface combustion. The surface flame characteristics under lean-burn conditions were captured with the high-speed camera. With the K-type thermocouples and the particle image velocimetry (PIV) method, the temperature distribution and the wake flow field in different combustion cases were analyzed. Moreover, by accurately regulating the inlet flow and the premixed equivalence ratio, the wide variety of flame forms are classified (e.g., the centered blue flame, the tiled blue flame, the tapered dark red flame and the tapered bright red flame). Lastly, the combustion zone map was generated to classify the mentioned variety of flame forms, which could be referenced to assess thermal characteristics for surface combustion.

Enhancing the abrasion resistance of hydrophobic coatings by flower bush-like micro rough structure of alumina

The anti-fouling design of ceramics is of great significance in improving their effectiveness and range of applications. Generally, constructing a micro rough structure coated with a low surface energy polymer substance is an effective strategy for creating a super-hydrophobic layer on ceramic surfaces. However, to be operated under certain wear conditions, the abrasion resistance of hydrophobic materials constructed by conventional methods is far from the requirements for application. Inspired by the multi-scale porous structure of the flower bush, a flower bush-like multi-scale micro rough structure (FMMS) has been constructed on ceramics using alumina pellets as petals. Compared with single-scale micro rough structures and non-connected pore micro rough structures, this structure enabled hydrophobic coatings which accelerated failure once worn, to attain an excellent contact angle (CA) of 143° and a sliding angle (SA) of 8.7° after a 100th abrasion test, demonstrating that the FMMS can significantly improve the mechanical stability of the coating. The hydrophobic model designed for the FMMS indicates that the excellent performance of the structure was achieved by a multi-scale protection mechanism for the hydrophobic material and a multi-scale pore-forming mechanism for the surface, and this provides a new idea for the design of highly abrasion-resistant super-hydrophobic surfaces on ceramics.

Inhomogeneous packed bed burner for improving the utilization of low‐concentration methane

AbstractHomogeneous packed bed was usually assumed in the study of porous media combustion. However, the absolute homogeneous structure was impossible in the actual application. In this article, an experimental system was established to study the inhomogeneity of porous media with different diameters and materials of pellets. The effects on the burner temperature, pollutant emissions and start‐up characteristics were investigated. Results indicate that the mixed pellets of the three‐diameter and four‐diameter combinations improved the flame temperature and moved the flame location to the downstream. The CO emission decreased with the increasing of inlet velocity significantly, but the NOx emission increased. For the mixing of zirconia and alumina pellets, the flame temperature was increased and the flame location was close to the outlet with more zirconia pellets. In addition, an orange submerged flame appeared finally compared with the blue flame during the initial ignition of the gas at the surface.

A performance analysis of the spray-type packed bed thermal energy storage for concentrating solar power generation

The concept of spray-type packed bed thermal energy storage (medium and high temperature thermal energy storage, from 200 °C to 350 °C, Alumina pellets+T66 fluid) has been proposed in our previous investigation. Its low-cost and high-efficiency shows its promising application prospect. Further investigation of the new concept is carried out both numerically and experimentally in this paper. First, the “charging-standby-discharging” cycle of a pilot spray-type packed bed is investigated experimentally. Second, the dynamic liquid holdup of the spray-type packed bed is correlated with the experiment data and is applied to build the mass balance equations. Based on the energy balance equations and mass balance equations, a three-phase one-dimensional transient model for the spray-type packed bed is established. Results from the experiment confirms the correctness of the numerical model. Based on the model, the liquid holdup of the packed bed during the “charging-standby-discharging” cycle is studied. At last, sensitivity analysis was carried out to study the influence of the parameters of the “charging-standby-discharging” process on the thermal performance of the spray-type packed bed. Values of these parameters can be found to achieve the best thermal performance of a spray-type packed bed.

Long-acting CoAl2O4 spinel catalyst developed on activated alumina pellets by facile synthesis to activate peroxymonosulfate: Controllable cobalt leaching and environmental adaptability

A novel composite catalyst prepared by fixing cobalt aluminate (CoAl2O4) spinel on formed alumina carrier by impregnation-calcination route is reported, which can be used to efficiently activate peroxymonosulfate (PMS) to degrade p-nitrophenol (PNP). The internal laws of phase composition and preparation conditions are explored in detail, and the results show that the introduction of additional aluminum ions in the preparation process changes the coordination environment and the electronic state of cobalt ions, which leads to the transformation of spinel/inverted spinel in the composition, and further affects the activity and stability of the catalyst. The selected CoAl-Aaps-600 catalyst has high CoAl2O4 content, showing good cycle performance and low cobalt leaching, and has great catalytic degradation performance at different temperatures and a wide pH range. Most notably, a fixed bed reactor packed with 20 g of CoAl-Aaps-600 exhibits excellent capacity to continuously treat 60 L of PNP solution with acceptable PNP removal ratio and low cobalt leaching content. Sulfate radical and singlet oxygen are identified as the main reactive oxygen species produced in CoAl-Aaps-600/PMS system, and the reaction mechanism is reasonably inferred. This work provides a potential application material and process for the treatment of continuous organic wastewater.

External Wetting Efficiency in a Three-Phase Fixed Bed Loaded with Porous and Non-Porous Packings

Films and rivulets are the two basic forms of dynamic liquid in a three-phase fixed bed (trickle bed), which determines the wetting efficiency of the catalyst. This paper is devoted to the conflicting wetting performance observed between non-porous glass beads and less wettable porous alumina, and a parallel zone model is applied to resolve the complex liquid flow texture. It shows in both cases of glass beads and aluminium pellets, the pressure drop, film flow and rivulet flow fractions all display pronounced multiplicities along with the liquid flow rates in increasing and decreasing branches, although the rivulet flow fraction is reduced to 0 in the liquid decreasing branch started from pulsing flow in both cases. Different from the glass beads, there is almost no wetting efficiency difference for the alumina pellets with respect to liquid flow rate increasing or decreasing, which is in agreement with the dynamic liquid holdup measurements. The liquid is significantly more uniformly distributed over the crosssection in the Al2O3 bed since rivulet flow is much reduced than in the case of glass beads.

Preparation of Eggshell-Type Ru/Al2O3 Catalysts for Hydrogen Production Using Steam-Methane Reforming on PEMFC

Ru-based eggshell-type catalysts, in which Ru is located at the outer region of the pellet, were prepared by the impregnation method, using spherically shaped γ-Al2O3 pellets for steam-methane reforming (SMR). Ru was only supported on the external region of the pellet because of the strong interaction between its precursor and the alumina pellet. The Ru precursor penetrated the inside of the pellet by adding nitric acid to the impregnation solution. The distribution and thickness of the Ru layer in the catalyst can be controlled using the HNO3/Ru molar ratio and contact time at the impregnation step. Among the catalysts, the graded eggshell-type catalyst showed the highest activity and long-term stability in the SMR reaction. In addition, in the daily startup and shutdown (DSS) operation, similar to the hydrogen production environment for domestic polymer electrolyte membrane fuel cells (PEMFC), the graded eggshell-type catalyst showed high activity and stability after multiple cycles. Based on the experimental studies, it was confirmed that Ru-based catalysts are suitable for steam-methane reforming for PEMFC.

Combustion characteristics of a low calorific gas burner with ceramic foam enclosed by alumina pellets

Combustion characteristics of a low calorific gas burner with ceramic foam enclosed by alumina pellets

Numerical Investigation of Effect of Porosity and Fuel Inlet Velocity on Diffusion Filtration Combustion

Methane-air diffusion filtration combustion in a radiative round-jet burner was numerically investigated in this work. The purpose of this study was focused on the effects of porous media porosity and gas velocity on temperature distribution and CO and NOx emissions. Reduced chemical kinetics was used where air and methane were assumed to be at their stoichiometric ratio, while thermo-physical properties were varied per the solid matrix porosity variation. Combustion characteristics were evaluated based on conduction and radiation as the two primary heat transfer modes within the solid matrix. Numerical simulations were carried out based on a packed bed with 3 mm alumina pellets. Results show that combustion temperature increases while the temperature gradient decreases with the increase in porosity, yielding higher NOx, and lower CO emissions. Furthermore, the combustion temperature is the lowest and most uniformly distributed with 1 m/s and 3 m/s gas velocities, wherewith 3 m/s gas velocity, combustion occurs outside of the porous zone. The corresponding NOx and CO emissions are the lowest with 1 m/s gas velocity and increase with the increase in gas velocity from 1 m/s to 10 m/s.

Design and testing of a monopropellant thruster based on N2O decomposition in Pd/Al2O3 pellets catalytic bed

The aim of the present paper is the investigation of a monopropellant engine based on the exothermic decomposition of nitrous oxide, as a “green” substitute of the most common but highly toxic hydrazine-based systems. First, a general procedure for the design of such a system, in terms of sizing of the catalytic chamber and of the nozzle for prescribed mission requirements, is defined. This procedure is applied for the design of an 800-mN-class thruster prototype, with catalysts based on palladium as active phase on alumina pellets support. Such prototype is experimentally tested highlighting first the nitrous oxide decomposition behavior and issues related to an optimization of system thermal insulation for reducing energy losses. Finally, the measured engine performance are presented and discussed, including a comparison with the results obtained with the same system in a cold-flow operation mode, showing the gain in terms of increased specific impulse and reduced propellant consumption due to the exploitation of the thermal energy obtained from nitrous oxide decomposition.

Two-Dimensional Numerical Study of Methane-Air Combustion Within Catalytic and Non-catalytic Porous Medium.

This study numerically investigates a two-dimensional physical model of methane/air mixture combustion in catalytic and non-catalytic porous media. The temperature distribution and flame stability of combustion in inert alumina (Al2O3) pellets and platinum (Pt) catalyst-supported alumina (Al2O3) pellets, were studied by changing the burner structure, operating parameters, and physical properties of alumina pellets. The simulation results indicated that the gas temperature in the inert porous medium is higher than that in a catalytic porous medium, while the solid temperature in an inert porous medium is lower than that in a catalytic porous medium. The flame moved toward the burner exit with the increasing diameter of the packed pellets at a lower equivalence ratio and moved toward upstream with the increased thermal conductivity of packed pellets. The flame location of the catalytic porous burner was more sensitive to the flame velocity and insensitive to thermal conductivity compared to the inert porous burner. The distance of the flame location to the burner inlet is almost constant with the increasing length of the porous media for both the catalytic and inert porous burner, while the relative position of the flame location moved toward the upstream.

Determination of Dose Distributions by High-energy Electrons in Alumina Pellets Using Monte Carlo Simulations

Electron beam accelerators are broadly used to study the effects of ionizing radiation on the properties of materials. These accelerators are also used to study radiation effects in some important ceramics such as alumina. The produced high-energy electrons at MeV energies will deposit doses that are typically non-uniformly distributed within the entire material. Such distributions provide valuable information regarding the degree of internal and surface changes owing to the irradiation. In the present study, the Monte Carlo (MC) method was used to obtain the dose distributions of high-energy electrons to alumina ceramic in pellet form. The distributions obtained via MCNP5 (Monte Carlo N-Particle version 5) were normalized by experimental values. For the energy of the simulated electrons, both monoenergetic and polyenergetic source electron energies were evaluated. The distributions of the depth-dose, depth-energy, and the top and bottom surface 2D dose mesh were obtained. Results showed that either assumption of monoenergetic or polyenergetic source electron energies resulted in similar depth-dose curves. The depth-energy results showed a larger spread in energy distributions for polyenergetic as compared to monoenergetic source electrons; nonetheless, the average doses for both were similar. The 2D dose maps showed a uniform dose distribution at the top pellet surface and a significantly non-uniform distribution at the bottom of the pellet. These results emphasize the effectiveness of the MC method in determining non-uniform doses within materials, which can be used in quantifying the changes in the material properties at each separate area of the electron irradiated object.

Role of surface coverage of alumina with Pt nanoparticles deposited by laser electrodispersion in catalytic CO oxidation

This work elucidates the role of surface coverage of alumina with Pt nanoparticles on the catalyst efficiency in CO oxidation. Size-selected Pt nanoparticles were deposited on the outer surface of alumina pellets by the laser electrodispersion technique. The alumina surface coverage with Pt varied from 0.04 to 3.5 nanoparticle layers and affected the Pt electronic state and catalyst efficiency. Even in the multilayer coatings nanoplatinum particles remained isolated. The catalysts were tested in CO oxidation at CO/O2 ratios of 0.2, 1 and 2 in the temperature-programmed and pulse reaction modes. At CO/O2 = 0.2 the temperature of 50% CO conversion increased with decreasing the surface coverage with Pt particles. At CO/O2 = 2 the decrease in the surface coverage enhanced the catalyst activity. Pt0 dominates only in multilayer catalysts, however, approximately half of platinum remained non-oxidized even at such a low metal loading as 0.01 wt%. The change in the electronic state of platinum under the thermal treatment in the reaction mixture affected the catalyst efficiency. The oxidation state of Pt depended on the metal loading, reaction temperature, CO/O2 ratio in the reaction mixture, mode of its feeding and surface coverage with Pt nanoparticles that influenced the interparticle and particle – support interactions.