Porous Pellets Research Articles

Coadsorption of gaseous xylene, ethyl acetate and water onto porous biomass carbon foam pellets derived from liquefied Vallisneria natans waste

AbstractBACKGROUNDOnly a few studies have focused on the purification of waste gas containing a mixture of volatile organic compounds (VOCs) with engineered biochar. The adsorption behaviors of gaseous xylene and ethyl acetate (EA) individually and in binary mixture onto porous biomass carbon foam pellets (BCFPs) were studied by static headspace gas chromatography.RESULTSThe removal efficiency nearly reached 100% for 17.32 mg L−1 xylene and 18.02 mg L−1 EA within 120 min at a BCFP dosage of 0.2 g L−1, a temperature of 40 °C and a relative humidity of 30%. The adsorption behavior followed the pseudo‐second‐order kinetic model for single and binary mixtures of xylene and EA. The coexistence of xylene had considerable influence on the adsorption performance of EA, whereas the coexistence of EA exhibited minimal effect on the adsorption performance of xylene. The monolayer adsorption capacities of sole xylene and EA were 250.63 and 206.61 mg g−1 respectively. The total adsorption capacity reached 322.36 mg g−1 for the binary mixture, but the adsorption capacity for sole xylene and EA decreased because of competitive adsorption. The adsorption process was spontaneous and endothermic. Pore filling was involved in the adsorption of xylene and EA onto BCFPs. Meanwhile, xylene adsorption was involved in the hydrophobic interaction and π–π electron dispersion interaction.CONCLUSIONBCFPs are an effective adsorbent for VOC adsorptive removal from waste gas. Competitive adsorption between xylene and EA on BCFPs was determined. Results indicated that the physicochemical properties of VOCs had an effect on the adsorption performance. © 2019 Society of Chemical Industry

Selection About Molten Salts Used For The Electrochemical Reduction of Porous TiO2 pellets

Diagrams of the equilibrium potential E (relative to the standard chlorine electrode) against the activity of oxide ion ( expressed as its logarithm, pO2−) in systems of Ti-O-Cl-M (M=Li, Na, Mg, Ca, Sr and Ba) were plotted to investigate the electro-deoxidation of porous TiO2 pellets in different chloride molten salts, including LiCl, NaCl, MgCl2, CaCl2, SrCl2 and BaCl2. From the diagrams, the reduction pathways of TiO2 in different molten salts are similar; and the applied potential (vs Cl−/Cl2) on the cathode and O2− ion activity influence greatly on the reduction pathway of TiO2 and the deoxidation limit. To test and verify the results of the thermodynamic analysis, electro-deoxidation experiments in different molten salts were done to determine the actual pathways in the electrochemical reduction of TiO2 and the possible deoxidation limits in the molten salts. The results indicated that the thermodynamic analysis is helpful in predicting and understanding the electrochemical reduction process of titanium oxides though the experimental results differ slightly from the thermodynamic analysis in some systems. Low-oxygen Ti can be obtained only in molten CaCl2.

The corrosion behaviors of thermal barrier material of M-YTaO4 attacked by CMAS at 1250 °C

The corrosion of YSZ TBCs attacked by calcium–magnesium–aluminosilicate (CMAS) is a serious problem. Yttrium tantalite (YTaO4), a new kind of potential thermal barrier ceramic material, was expected to replace the YSZ to manufacture the TBCs because of its great thermophysical characteristics. In this study, porous YTaO4 ceramic pellets, instead of actual TBCs, were used to investigate the CMAS corrosion resistance at 1250 °C. Results indicated that CMAS couldn't cover the whole surface of YTaO4 pellets homogeneously because of low wettability between liquid CMAS and YTaO4, in addition, there was almost no reaction layer after 4 h reaction. The XRD results showed that M-YTaO4, M′-YTaO4, Ca2Ta2O7 and Y2Si2O7 were the main four phases after reaction and there was no phase containing the elements of Mg and Al. Compared with YSZ TBCs, this new kind of potential thermal barrier ceramic material showed well resistance to CMAS corrosion.

Modeling of fuel-cladding stresses in porous UC/SIC fuel pins

Maximum stress development in nuclear fuel pins during their exploitation in the gas-cooled Gen-IV reactors is an important parameter for analysis of fuel-cladding compatibility, especially in the case of testing of new fuel or cladding materials. This article is devoted to the stress evaluation in the combination of uranium carbide fuel and silicon carbide cladding. Swelling fuel exerts the largest pressure on the cladding when initial gap between fuel and cladding has been already closed. Numerical modeling predicts rapid stress increase in this regime. To alleviate these stresses annular-shaped kernel-based bi-modal porous pellets have been designed in the General Atomics Co. with small pores in the spherical agglomerates (kernels) and comparatively large pores between kernels. A new numerical approach is developed to take into account specific features of the mechanical behavior of this new fuel. The modeling predicts stress decrease in direct proportion to porosity of the fuel, but the most significant stress reduction is expected with the upper bound increase of reactor power accompanied by the temperature increase in the pellet. Because of the temperature non-uniformity, stress relaxation in the pellet is sensitive not only to the mean value of porosity but also to its distribution along the pellet radius. Comparatively cold regions near the cladding must have higher porosity than high-temperature core regions for efficient stress relaxation.

Probing local diffusion and reaction in a porous catalyst pellet

In the present work, we report on the direct measurement of spatially resolved concentration profiles inside a single catalyst pellet under reaction conditions using a capillary sampling method. CO oxidation on a platinum-coated, porous alumina cylinder was chosen as test reaction system. CFD simulations were conducted to probe the invasiveness of the method, which turned out to be acceptable for practical application. Spatially resolved CO2 mole fraction profiles inside the particle are presented for different reaction conditions. Phenomena that result from the interplay between diffusion and reaction such as boundary layers, bifurcation, multiple steady states and kinetic oscillations are also shown. The method might allow the knowledge-based optimization of many industrial fixed-bed processes without requiring major changes to the process layout.

Recovery of gold from industrial wastewater by immobilized gold-binding proteins on porous silica carriers grafted with amino group

Our recent work demonstrated excellent gold biosorption potential of extracellular proteins obtained from a thermophilic bacterium Tepidimonas fonticaldi AT-A2. In this study, the gold-binding proteins were immobilized on amino-grafted porous silica carriers to further enhance the feasibility of using them for Au recovery from real industrial wastewater. The maximum protein immobilization capacity on the amino-grafted porous silica reached the highest level of 13.83 mg protein/g carrier when the protein loading concentration was 400 mg/L and the amino groups content on the silica carrier was 16%. The mechanical strength of the amino-grafted porous silica could be improved to 19.47 kg by converting the silica powder into pellet form using a calcination temperature of 700 °C. Continuous biosorption of Au (III) from prepared Au solution and from real industrial wastewater was carried out using fixed beds packed with the protein-loaded amino-grafted porous silica pellets. The maximum Au adsorption capacity of the fixed beds with a feeding rate of 0.12 ml/min was 1259 and 448 mg Au/mg protein from the prepared Au solution and an electroplating wastewater (Au concentration was approximately 40 mg/L), respectively. The maximum Au adsorption rate of the fixed beds when using the real wastewater was 33.4 mg/g/h, which is similar to the results of using the prepared Au solution.

High Porosity in Nanostructured n-Type Bi2Te3 Obtaining Ultralow Lattice Thermal Conductivity.

Porous structure possesses full potentials to develop high-performance thermoelectric materials with low lattice thermal conductivity. In this study, the n-type porous nanostructured Bi2Te3 pellet is fabricated by sintering Bi2Te3 nanoplates synthesized with a facile solvothermal method. With adequate sublimations of Bi2TeO5 during the spark plasma sintering, homogeneously distributed pores and dense grain boundaries are successfully introduced into the Bi2Te3 matrix, causing strong phonon scatterings, from which an ultralow lattice thermal conductivity of <0.1 W m-1 K-1 is achieved in the porous nanostructured Bi2Te3 pellet. With the well-maintained decent electrical performance, a power factor of 10.57 μW cm-1 K-2 at 420 K, as well as the reduced lattice thermal conductivity, secured a promising zT value of 0.97 at 420 K, which is among the highest values reported for pure n-type Bi2Te3. This study provides the insight of realizing ultralow lattice thermal conductivity by synergistic phonon scatterings of pores and nanostructure in the n-type Bi2Te3-based thermoelectric materials.

Corrosion resistance and thermal-mechanical properties of ceramic pellets to molten calcium-magnesium-alumina-silicate (CMAS)

Because gas turbine engines must operate under increasingly harsh conditions, the degradation of thermal barrier coatings (TBCs) by calcium-magnesium-alumina-silicate (CMAS) is becoming an urgent issue. Mullite (3Al 2 O 3 ·2SiO 2 ) is considered a potential material for CMAS resistance; however, the performance of mullite in the presence of CMAS is still unclear. In this study, mullite and Al 2 O 3 –SiO 2 were premixed with yttria stabilized zirconia (YSZ) in different proportions, respectively. Porous ceramic pellets were used to conduct CMAS hot corrosion tests, and the penetration of molten CMAS and its mechanism were investigated. The thermal and mechanical properties of the samples were also characterized. It was found that the introduction of mullite and Al 2 O 3 –SiO 2 mitigated the penetration of molten CMAS into the pellets owing to the formation of anorthite, especially at 45 wt% mullite/55 wt% YSZ. Compared with Al 2 O 3 –SiO 2 , mullite possesses a higher chemical activity and undergoes a faster reaction with CMAS, thus forming a sealing layer in a short time. Additionally, the thermal expansion coefficient, thermal conductivity, and fracture toughness of different samples were considered to guide the architectural design. Considering the CMAS corrosion resistance, thermal and mechanical performance of TBCs systematically, a TBC system with a multilayer architecture is proposed to provide a theoretical and practical basis for the design and optimization of the TBC microstructure.

Ethylene Hydrogenation in Pellets with Different Pore Structures, Measured in a One-Sided Single-Pellet Reactor

Abstract The ethylene hydrogenation reaction was investigated in a kinetic turbo reactor and a one-sided single-pellet reactor. An empirical kinetic expression was fitted to experimental results taken from the turbo reactor, and the gas compositions at the catalyst centers were measured for three different pore structures by means of the single-pellet reactor. A bimodal pore model was developed and applied to the computation of the gas composition profiles inside the three pore structures. The calculated results were compared to the measurements. A distinct influence of the pore structures on the gas fluxes and concentration profiles inside the pores could be detected which demonstrates that the proper choice of the pellet pore structure is of importance for a high conversion.

Modeling of Multiprocess Behavior for Feedstock-Mixed Porous Pellet: Heat and Mass Transfer, Chemical Reaction, and Phase Change

Insight into the complicated energy-mass transfer and hierarchical reaction in metallurgical industry is of particular value in improving productivity and reducing energy consumption. This work pro...

Electromagnetic wave absorption properties of carbon black/cement-based composites filled with porous glass pellets

Cement-based composites filled with carbon black (CB) and porous glass pellets(GPs) were prepared, and the electromagnetic wave absorption properties (EMAPs) were investigated with the arch method in 1.7–18 GHz. Results indicate that introducing of GPs into cement-based materials enhances the EMAPs significantly. The larger the particle size is, the lower the impedance of the composite is. The number of absorption peaks increases, the reflectivity curve becomes flat, and the EMAPs increase first and then decrease. The GPs with the size of 0.25–1.0 mm contribute most to the EMAPs with the same content. Graded GPs produce high mechanical strength, and the synergistic effect of particles with different sizes on the enhancement of EMAPs is not obvious. The optimal content of GPs and composite thickness are 50 vol% and 20–30 mm, respectively. The composite reaches the lowest average reflectivity at − 9.67 dB, and the bandwidth below − 10 dB is 7.47 GHz when CB is 1.5 g/L, the thickness is 20 mm and the filling ratio is 50 vol%.

Porous spherical calcium aluminate-supported CaO-based pellets manufactured via biomass-templated extrusion-spheronization technique for cyclic CO2 capture.

Calcium looping has been proposed as one of the most promising technologies for CO2 capture to mitigate the growing problem of global warming. However, the loss in capacity and attrition are two issues lying on the way to practical application for calcium looping process. To improve CO2 capture performance and mechanical strength of CaO sorbents, a biomass templated extrusion-spheronization palletization technique was employed to manufacture porous calcium aluminate-supported CaO-based pellets. For the first time, this work investigated the granulation of calcium aluminate-supported CaO-based sorbents and also the effectiveness of three novel biomass-based pore-creating materials of straw, willow, and wheat. The results indicated that the incorporation of calcium aluminate-based supports could effectively enhance cyclic performance and stability. Besides, the 5 wt.% addition of pore-creating materials could further promote the cyclic CO2 capture capacity of calcium aluminate-supported CaO-based pellets. The pellets added with 25 wt.% calcium aluminate-based supports and 5 wt.% straw still held a good carbonation conversion of 46.45% after 50 cycles even tested under CO2-rich calcination atmospheres. In addition, the anti-attrition ability tests by friability tester (FT) demonstrated that all the prepared pellets owned an excellent degree of attrition (less than 1%). The good CO2 capture performance and mechanical strength endowed biomass-templated calcium aluminate-supported CaO-based pellets with promising prospects for practical CO2 removal.

Structure reinforcement of porous hydroxyapatite pellets using sodium carbonate as sintering aid: Microstructure, secondary phases and mechanical properties

Porous HAP pellets suitable for loading therapeutic agents were prepared using microcrystalline cellulose (MCC) as pore former and sodium carbonate as sintering aid (SAID). The effect of sintering temperature on the microstructure, mechanical properties and disintegration of pellets prepared at different SAID content was studied. Pellets were characterized by SEM, image analysis, porosimetry and surface area. Secondary phases were identified by PXRD, ATR-FTIR and Raman spectroscopy. Increasing the sintering temperature decreased the diameter, porosity, surface area and friability of the pellets but increased the pore size, tensile strength and disintegration time. The effect of SAID was dependent on sintering temperature. With 5% SAID, a secondary β-tricalcium phosphate (β-TCP) phase was formed, indicated by FTIR peak at 980 cm−1 and characteristic PXRD reflections, whereas with 10%, a secondary B-type carbonated hydroxyapatite phase (CHA) formed, indicated by FTIR peaks at 878 and 1450 cm−1, a broad Raman peak in the region 1020 to 1050 cm−1 and PXRD reflections. Pellets prepared with SAID showed high strength and also porosity. The biphasic HAP/β-TCP pellets exhibited remarkably great strength (4.39 MPa) at the high sintering temperature, while still retaining 43.9% porosity. Relationships were established between the mechanical properties or disintegration time of the porous pellets and the microstructural parameters.

Modeling fixed-bed reactors from metal-foam pellets with detailed CFD

Open-cell metal foams are a promising alternative to conventional solid pellets for the application as structured catalyst support. Pellets made from metal foams can be used in fixed-bed reactors instead of ceramic pellets. In this contribution, a comprehensive and detailed computational fluid dynamics (CFD) model is presented for fixed-bed reactors consisting of metal foams. The inner structure of the foams, i.e. pores, struts, and nodes, is not resolved. Instead, a pseudo-homogeneous model is applied to describe pressure drop and heat transfer inside the foam pellets. The fixed-bed structure is particle-resolved. The bed is generated synthetically with the discrete element method (DEM) and the results are in great agreement with µCT data. The experimental pressure drop for two different porous pellet shapes can be reproduced reasonably with CFD simulations. In an illustrative heat-transfer study, the performance of a state-of-technology solid-pellet bed and a porous cube bed is compared. Whereas the heat transfer is similar in both cases, the pressure drop is lower in the bed of porous cubes. A residence-time distribution analysis reveals that the porous pellet shape should be optimized to obtain a better mixing behavior. The presented fixed-bed model can be applied for such tasks, since it is valid for almost any pellet shape.

Lattice Boltzmann simulation of intraparticle diffusivity in porous pellets with macro-mesopore structure

Intraparticle diffusion inside porous pellets plays a controlling step in most reactive transport processes. In order to investigate microscopic diffusion process in porous pellets with macro-mesopore structure, a three-dimensional lattice Boltzmann method (LBM) approach with multi-relaxation-time (MRT) collision operator was utilized to calculate the intraparticle diffusivity. With respect to the hierarchical pore structure, the modified random generation of macro-meso pores (RGMMP) algorithm was proposed to obtain pore structure of porous pellets. In this work, a resin catalyst that has macro-mesopore structure was selected as a validation example. Based on the LBM approach, the effects of four geometrical parameters of the modified RGMMP algorithm on the intraparticle diffusivity, namely the total porosity, the ratio of mesopore porosity to macropore porosity, the ratio of average macropore diameter to mesopore diameter and the macropore growth direction were investigated, so as to elucidate the mass transfer mechanism in porous pellets with macro-mesopore structure. These theoretical findings are useful for the pore structure optimization design of porous pellets with macro-mesopore structure.

Improvement of aqueous solution coexisting with arsenite and arsenate using iron mixed porous clay pellets in batch and fixed-bed column studies

Abstract Arsenic-polluted water is a global concern and puts millions of people at risk of developing cancer. The improvement of aqueous solution coexisting with arsenite and arsenate using iron mixed porous clay pellets was investigated in batch and fixed-bed column systems. Batch studies showed that the removal rate occurred in two main phases with an equilibrium time of 52 h. The pseudo-second-order model well described the experimental data. Isotherm data were well fitted by the Langmuir–Freundlich model. The removal efficiency was significantly reduced in alkaline solution and the presence of phosphate ions. The column study revealed that the breakthrough time and saturation time increased with lower feeding flow rate, higher bed height, and lower initial adsorbate concentration. The Thomas model provided good performance for predicting the column experimental data.

Preparation of high-purity straight silicon nanowires by molten salt electrolysis

Silicon nanowires of high purity and regular morphology are of prime importance to ensure high specific capacities of lithium-ion batteries and reproducible electrode assembly process. Using nickel formate as a metal catalyst precursor, straight silicon nanowires (65–150 nm in diameter) were directly prepared by electrolysis from the Ni/SiO2 porous pellets with 0.8 wt% nickel content in molten CaCl2 at 900 °C. Benefiting from their straight appearance and high purity, the silicon nanowires therefore offered an initial coulombic efficiency of 90.53% and specific capacity of 3377 mAh/g. In addition, the silicon nanowire/carbon composite exhibited excellent cycle performance, retaining 90.38% of the initial capacity after 100 cycles. Whilst further study on the charge storage performance is still ongoing, these preliminary results demonstrate that nickel formate is an efficient and effective metal catalyst precursor for catalytic preparation of high purity straight silicon nanowires via the molten salt electrolysis, which is suitable for large-scale production.

Photocatalytic degradation of gaseous trichloroethylene on porous titanium dioxide pellets modified with copper(II) under visible light irradiation

Porous titanium dioxide pellets modified with copper(II) ion (Cu-TiO2) were synthesized by sol-gel method with dialysis for photocatalytic degradation of gaseous trichloroethylene (TCE) under visible light (VL) irradiation. TCE was completely degraded by passing the gas stream (mole fractions of oxygen and TCE were 0.2 and 1.75 × 10−4, respectively) at the flow rate of 25 mL min−1 through 0.2 g of the Cu-TiO2 pellets (Cu content: 0.1 atom%) calcined at 200 °C. TCE was converted mainly to carbon dioxide, dichloroacetic acid (DCAA), and inorganic chlorine species. Relatively small quantities of pentachloroethane (PCA) and trichloroacetaldehyde (TCAH) were detected as products on the Cu-TiO2 surface. Comparison with porous TiO2 pellets under ultraviolet irradiation revealed that more chlorinated products and less carbon dioxide were formed on Cu-TiO2 under VL irradiation. The mineralization of TCE to carbon dioxide was calculated to be only ca. 30.0%. It is noted that DCAA, PCA and TCAH were accumulated on the surface and were extracted with ethyl acetate. The porous Cu-TiO2 pellets show promise as the photocatalyst acting under VL irradiation for converting TCE gas to chlorinated compounds which can be used in industries.

Three dimensional thermal conduction of randomly packed beds of porous cylindrical ceria pellets immersed in carbon dioxide with effects of deviations of pellet porosities and sizes

Structures of randomly packed beds of cylindrical shape porous pellets composed of tiny ceria (CeO2) particles with wide ranges of pellet porosities and number density probabilities are generated by an improved controllable structure generation scheme (CSGS) including deviations of both pellet porosities and sizes. Three dimensional (3D) mesoscopic scale thermal conduction through the structures immersed in carbon dioxide (CO2) gas is simulated by a parallel non-dimensional lattice Boltzmann method (P-NDLBM). Effective thermal conductivity (ETC) in each direction and 3D temperature distributions with effects of pellet number density probabilities, porosities, and deviations are illustrated. Although the pellet number density probability and pellet porosity are equivalently important for changing of macroscopic global porosity, they have different effects on temperature distribution patterns and the overall ETC. A new form of ETC correlation related to the pellet number density probability and pellet porosity is proposed. The present ETC correlation based on the two pellet parameters shows a slight improvement comparing to conventional forms based on the macroscopic global porosity.

Micrograded ceramic-metal composites

The article shows new designed cermets and processes concerning primary to applications as thermal insulation materials with low emissivity. A new projected microstructure was obtained where dense regions (micropellets) rest inside the main porous pellet. The feature resembles a frozen hypercube, therefore such architecture is called hyper-pellet/ cermet. The processing method to obtain the hyper-cermet is based on sequential tape castings and sintering techniques. Ni-zirconia lamellae were prepared by a special mechanochemical process followed by sintering, which remain inside the main pellets as a dense region. The whole pellet is turned to be porous by employing pore-forming additives. All the constituents and porosity shapes are aligned along the disc/ flake planes. Thermal conductivity is estimated for the materials up to 800 °C by a flash diffusivimeter. Ceramographic analyses show graded density regions with directional constituents and pores. Applications of such materials are foreseen as temperature insulation materials and thermal radiation shields.