Porous Pellets Research Articles

Immobilization of the metagenomic lipase, LipG9, on porous pellets of poly-hydroxybutyrate produced by the double emulsion solvent evaporation technique.

This work aimed to produce porous poly-hydroxybutyrate (PHB) pellets in order to evaluate the pellets as a support for immobilization of the metagenomic lipase, LipG9. Four types of pelletized PHB particles with different morphological characteristics were obtained using the double emulsion and solvent evaporation technique (DESE). The micropores of these PHB pellets had similar average diameters (about 3nm), but the pellets had different specific surface areas: 11.7 m2 g-1 for the PHB powder, 8.4m2 g-1 for the control pellets (Ø<0.5mm, produced without the pore forming agent), 10.0m2 g-1 for the small pellets (Ø<0.5mm), 9.5m2 g-1 for the medium pellets (0.5 < Ø<0.8mm) and 8.4m2 g-1 for the large pellets (Ø>1.4mm). Purified LipG9 was immobilized by adsorption on these pellets, and the results were compared with those obtained with PHB powder. The highest immobilization yield (83%) was obtained for the medium PHB pellets, followed by large (76%) and small (55%) PHB pellets. The activity of LipG9 immobilized on the pellets, for the synthesis of ethyl oleate in n-hexane, was highest for the medium pellets (22Ug-1 ). The immobilization yield was high for PHB powder (99%) but the esterification activity was slightly lower (20Ug-1 ). These results show that pelletized PHBbeads can be used for the immobilization of lipases, with the advantage that pelletized PHB will perform better than PHB powder in large-scale enzyme bioreactors.

Processing Temperature Impact on TiNb2O7 Thick All Active Material Lithium-Ion Battery Electrodes

Lithium-ion batteries have become a widespread energy storage technology, and research continues towards improving battery properties. One route to increase electrode areal active material loading and decrease relative volume fractions of inactive components is to increase electrode thickness, but increasing thickness can impact mechanical stability for conventional composite electrodes. All active material (AAM) electrodes, including those in this work, can mitigate mechanical and transport limitations for very thick lithium-ion electrodes. Such electrodes are free of polymer binders and conductive additives, and processed by pressing electroactive material powder into a porous pellet followed by mild sintering to improve mechanical properties. This study investigated the processing of a more recent material processed into AAM electrodes, TiNb2O7, which has relatively high volumetric capacity among reported materials processed into AAM electrodes. The anode material was characterized in AAM electrodes where different processing temperatures were used, resulting in different titanium and niobium containing phases being present. This manuscript provides insights and electrochemical consequences for fabricating AAM electrodes with multicomponent oxide phases.

Modelling and simulation of chemical reaction of porous MgCl2 pellets with NH3 by including impact of heat and mass transfer and structure change.

The MgCl2-NH3 reactive system is investigated in terms of heat and mass transfer coupled with chemical reaction through numerical simulation. The reversible nature of the chemical reaction is captured by including adsorption and desorption terms in the rate expression simultaneously. The kinetic coefficients of the adsorption are directly adopted from the literature, while those for the desorption reaction are calculated based on the thermodynamic relations. The impact of changing pressure and pellet porosity are also investigated in the simulations. The initial temperature of the pellet is 300 K in all simulations. Temperature, NH3 pressure, and conversion distributions in the pellets, along with pellet swelling are obtained and presented as a function of time. The results indicated strong effects of heat transfer resistances in the pellets.

Effect of binder ratio on the physical properties of porous carbon pellet for CO2 capture

The purpose of this work was to investigate the effect of binder ratio on the physical properties of carbon-based pellets in capturing CO2. The influence of the binder materials was also examined to compare the pellet quality. To make good-quality carbon pellets, tapioca starch (TS) and xanthan gum (XG) were used as organic binders and mixed with activated carbon to form pellets. The physical properties of the carbon pellets were analyzed using different analytical methods: Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX), Thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR). In addition, the CO2 adsorption performance of the carbon pellets was investigated by evaluating their adsorption capacity and CO2 breakthrough characteristics. The results revealed no significant changes to the pore development of the carbon pellets after the CO2 adsorption. However, the EDX results for the carbon pellets using the starch binder showed an increase in the oxygen content after the CO2 adsorption. With the addition of water and the binder, both types of carbon pellets (TS-AC and XG-AC) still produced high carbon content. Interestingly, the carbon pellets using the low-cost binder (tapioca starch) shows high performance than xanthan gum binder due to has numerous functional groups, longer breakthrough time and high CO2 adsorption capacity. The TS-AC carbon pellets exhibited a remarkably high breakthrough time and CO2 adsorption capacity of 16.2 min and 21.84 mg/g at 25 ˚C.

Analytical solutions of reaction–diffusion phenomena by porous cylindrical pellets with finite length

AbstractAnalytical solutions were derived to predict transient change of intra‐particle concentration inside cylindrical pellets with finite length immersed in an infinitely large medium. After the derivation of steady‐state concentration by eigenfunction expansion, a transient solution was obtained by the separation of variables. Effects of the Thiele modulus (Φ) and aspect ratio of the pellet (H/R) were studied by calculating the average intra‐particle concentration at a stationary state. The effectiveness factor (η) was also affected by H/R and Φ, since irreversible first order kinetics was assumed. As Biot number (Bi) increased, both intra‐particle concentration and η increased due to the decrease of the mass transfer resistance of the surrounding film. Good agreement between analytical and numerical solutions was confirmed for both steady‐state and transient solution by comparing the analytical results with the numerical solutions by finite element method. To extend the results to a batch reactor with finite volume, Duhamel's theorem was applied by assuming time‐dependent boundary conditions to reflect the change in bulk concentration as a function of time. A method was proposed to measure intra‐particle diffusivity for batch adsorber by setting Φ = 0. To investigate the effect of H/R, η could be included in material balance of batch, continuously stirred tank reactor (CSTR), and fixed bed reactors to predict reactor performance assuming a pseudo‐steady state. First‐order reaction by egg‐shell catalysts as well as nonlinear reaction with two reactants could be solved numerically assuming finite cylindrical pellets. By solving coupled differential equations of material and energy balances, dynamic catalysis was confirmed from the enhancement of conversion, assuming forced oscillation of inlet temperature in CSTR.

Experimental assessment of Fe-doped CaMnO3 porous pellets in a bench-scale packed-bed reactor for thermochemical energy storage

Thermodynamic cycles requiring high operating temperatures (≥750 °C up to 1200 °C) are currently being explored to improve the sun-to-electricity conversion efficiency of Concentrating Solar Power (CSP) plants. This is calling for the design of new efficient high-temperature (≥750 °C) Thermochemical Energy Storage (TCES) systems, which are fundamental for supplying power on demand during off-sun periods. Recently, Fe-doped CaMnO3 oxides have been proposed as TCES candidate materials, and the determination of their thermodynamics properties via thermogravimetric (TG) analysis allowed evaluation of their heat storage capacity at a very small scale (mg scale). A 10 % Fe-doped CaMnO3 composition (CaMn0.9Fe0.1O3-δ – CMF91) emerged as optimum candidate material for TCES application due to its large heat storage capacity complemented by enhanced thermal stability over multiple oxidation/reduction cycles. To advance in the thermal characterization of these materials at a multigram scale, here we carried out bench-scale reactor tests using CMF91 under conditions considered representative of future CSP plants. The redox-active material has been extruded in the form of porous pellets through a simple production method that required the use of carboxymethylcellulose as a removable binder and water. With the bench-scale reactor tests, the CMF91 pellets showed fully reversible reduction-oxidation in cycles between 500 and 1100 °C under relevant operating pO2 conditions without any deterioration of the pellet's structural integrity. Remarkably, the material exhibited the same δ(T, pO2) profile at this significantly larger scale (~40 g) than the one derived from thermodynamics. Nevertheless, slight differences in oxygen release/uptake profiles between cooling and heating branches can be tracked down to an excess heat generation in the perovskite bed not efficiently extracted by the carrier gas. These results demonstrate that CMF91 oxide is ideally suited for thermal energy storage applications with a large total (thermochemical and sensible) heat storage capacity (~ 916 kJ/kgABO3 or ~ 400 kWh/m3) and good scalability.

Enhancement of ionic conductivity and fracture toughness by infiltrating porous Li0.33La0.56TiO3 pellets

Although solid-state lithium electrolytes have the potential to reduce the safety issues associated with organic liquid electrolytes, disadvantages such as low total conductivity, large interface impedance, and delamination of the interface due to cyclic stress still need to be addressed. The solid-state lithium-ion conductor Li0.33La0.56TiO3 (LLTO) was prepared via a hydrothermal route by using CTAB as templates in this paper. Perovskite LLTO with micro-porous channels was obtained and the total conductivity is comparable to the non-porous LLTO. Porous LLTO pellets are infiltrated with the non-porous LLTO precursor solution, and the total conductivities of the infiltrated porous LLTO are all higher than those without infiltration. After infiltration, the porous LLTO calcined at 600 °C achieves the highest total conductivity, 7.88 × 10−5 S/cm. The fracture toughness of the infiltrated LLTO is higher than that of the non-porous LLTO. The results demonstrate a new way to prepare solid-state lithium-ion conductors with high ionic conductivity and great tolerance to cyclic stress.

Porous BaTiO3 ceramic with enhanced piezocatalytic activity for water cleaning application

Using any piezocatalyst in powder form results in after-treatment problems in piezocatalysis process. Introducing porosity as a physical method in ceramic pellets will reduce both after-treatment problems as well as enhances the piezocatalytic activity. The present study reports the dependence of piezocatalytic activity on porosity level in BaTiO3 ceramic for the degradation of Methylene blue (MB) dye. The porosity from 0 to 30 wt % in BaTiO3 ceramic pellet/sample was introduced by using a pore former polymethyl methacrylate (PMMA). The synthesized pellets were analyzed through X-ray diffraction (XRD), Raman spectroscopy, Scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS). Further, the size of pores was computed through Barret-Johner-Halenda (BJH) pore size distribution analysis. The degradation of MB dye achieved through piezocatalyis process using non-porous and 30% porous BaTiO3 ceramic pellets were ∼55 and ∼88% in 330 min of ultrasonication. Thus, by introducing 30% of porosity in the synthesized pellet, piezocatalytic activity for degrading MB dye increased by 1.6 times.

Hollow microspheres formed by nanograins of Cr[formula omitted]Ti[formula omitted]O[formula omitted] synthesized by ultrasonic spray pyrolysis for acetone detection

The (Cr,Ti)2O3+z system, with corundum structure, has been studied due its technological application as gas or volatile compound detector. In this work we studied Cr1.8Ti0.2O3+z (CTO) particles grown by ultrasonic spray pyrolysis technique. The sample consists on hollow microspheres with a mean diameter of 12.8 μm, and the walls of the spheres are constituted by nanograins. Magnetic susceptibility studies and electron spin resonance spectroscopy showed a para- to antiferromagnetic transition at (306 ± 1) K. The acetone detection experiments were performed on compressed CTO forming a porous pellet. The CTO fabricated by spray pyrolysis detected very well acetone vapours with a linear response with the acetone concentration. This demonstrates that CTO particles produced by ultrasonic spray pyrolysis technique present high potentiality as volatile organic compounds detector. This synthesis route is economical and allows producing a great quantity of material in a short time, making this method adequate for large scale production.

Microstructure evolution of Cr2AlC MAX phase under a graphite bed between 1100 °C and 1500 °C

Thermal decomposition behaviors and microstructure evolution of porous Cr2AlC pellet samples in a graphite bed (65% N2 and 35% CO) between 1100 °C and 1500 °C were investigated to explore its potential slag-contact application. A walnut-like structure made of a porous chromium carbides core and Al2O3 shell was confirmed on the original Cr2AlC particle because of the formation of Al-depleted Cr2Al1-xC in the graphite bed atmosphere. After heat treatment at 1300 °C, depletion of Al within the Cr2AlC particle caused to generate a ∼650 μm thickness CrCx-enriched layer on the sample's surface and a highest Vickers hardness of 13.7 GPa. When the temperature rose to 1500 °C, cracks occurred in the sample because of the volumetric expansion from further decomposition. The degradation mechanism of fine-Cr2AlC particles in the range from 1100 °C to 1500 °C was proposed in detail.

Integration of multi-scale porosimetry and multi-modal imaging in the study of structure-transport relationships in porous catalyst pellets

The forming process for heterogeneous catalyst pellets impacts on reactor performance. In order to intelligently optimise the product formulation and manufacturing procedure, the impact of fabrication options on the resultant pore structure and mass transfer properties must be fully understood. In this work, the more direct information possible from multi-modal imaging methods has been combined with the more statistically-representative, multi-scale data from porosimetry, including the rarely-used gas overcondensation technique, to characterise batches of methanol synthesis catalyst tablets made using different feed types. Despite the hierarchies of complexity of the porous pellets revealed by the computerised X-ray tomography and FIB-SEM images, the impact on mass transfer of controlled modifications to the void space, achieved through mercury porosimetry, could be modelled using a relatively simple random pore-bond network. The characteristic parameters for the model were obtained from a percolation theory-based analysis of the overcondensation data. A quantitative relationship was thereby obtained between the structural information contained within the overcondensation isotherms and the rate of mass uptake of gas into the porous pellets. This revealed the differential importance to mass transfer of particular sets of pores, associated with certain pellet structural features, and the impact on tortuosity of pellet fabrication parameters such as particle feed size.

One-step synthesis of porous Li4SiO4 pellets by polyvinyl alcohol (PVA) method for CO2 capture

Li4SiO4 has shown great prospects for cyclic high-temperature CO2 capture due to its excellent stability, high capacity and low regeneration temperature. However, dense morphology and attrition problem are the main obstacles that lie in its way to the practical applications. This work, for the first time, proposed a simple polyvinyl alcohol (PVA) technique for the one-step preparation of porous spherical Li4SiO4 pellets. The produced pellets exhibited a uniform diameter distribution of 2.5–3.5 mm and high capacity of 0.320 g CO2/g sorbent. Besides, the PVA method-derived Li4SiO4 pellets also presented excellent cyclic stability in the extended sorption/desorption operations of 30 cycles. It has been indicated that the enhancement of CO2 sorption capacity is ascribed to the formation of abundant pore channels and cavities resulted from the burning out of the well-dispersed polyvinyl alcohol. Moreover, the influence of CO2 presence at desorption stage on the sorbent performance was also investigated. It was indicated that the existence of CO2 at desorption stage caused sintering, which in turn resulted in the reduction of CO2 sorption capacity. In addition, the mechanical property of the pellets was tested. The weight loss was lower than 9 wt% over 2400 rotations in the anti-attrition ability test. In general, the high CO2 sorption capacity and satisfying mechanical property of the Li4SiO4 pellets via PVA route endows this method with promising prospects for the granulation of Li4SiO4 sorbents for realistic CO2 removal.

Novel Efficient Reduction Route for Magnesium Production Using Silicothermic Process.

A novel efficient reduction route was developed for preparing porous pellets to enhance mass transfer during magnesium production, which can improve the reactivity of pellet reaction to improve the reduction efficiency. A porous pellet precursor was prepared at 150 MPa using NH4HCO3 as a pore-forming agent, and the reaction characteristics of the pellets with 0, 5%, 10%, 20%, and 30% pore-forming agents were measured under a high vacuum of approximately 10 Pa heat-treated from 100 °C to 1400 °C. The results showed that the instantaneous maximum reduction rate first increased and then decreased with the increase in pore-forming agents. When the reduction conversion was 80%, the reduction efficiency of pellets with 5% pore-forming agent was 36% greater than that without pore-forming agent pellets. When the reduction conversion was 90%, the reduction efficiency of pellets with 5% pore-forming agent was 29% greater than that without pore-forming agent pellets. The results indicate that the diffusion rate of magnesium vapor in pellets is significantly increased; the time of chemical reaction reaching equilibrium is shortened; the chemical reaction rate and the magnesium production efficiency are increased by adding a proper ratio of NH4HCO3 compared to that obtained without NH4HCO3 at the identical reduction temperature.

Synthesis free‐template highly micro‐mesoporous carbon nanosheet as electrode materials for boosting supercapacitor performances

Porous carbon 2D nanosheets (CNSs) with micro-mesopores interconnected are indispensable for energy conversion systems and storage applications. Herein, we synthesize free-template highly micro-mesoporous carbon nanosheet as electrode material for boosting supercapacitor performances. The activated carbon nanosheets derived from bio-waste were prepared by chemical impregnation followed by high-temperature pyrolysis without hard/soft/salt template-assisted and free-binder adhesives. Garlic skin wastes were selected as a precursor. Furthermore, activated carbon was designed in pellet/coin solids without the addition of binder materials. The porous carbon pellets exhibit a thin 2D nanosheet structure of 15 nm followed by unique wooden labyrinth-like and rod-like structures. The result showed that the impregnation of different chemical concentrations increases the surface area to 273% as high as 1002.920 m2 g−1 with a total volume of 1.3270 cm3 g−1. Moreover, the mesoporosity dominated 66.4%, followed by sub-ultra-micropores. In the symmetric supercapacitor, the carbon nanosheet boosted the specific capacitance almost 3-fold to 320.95 F g−1 in the aqueous electrolyte of 1 M H2SO4. The supercapacitor cell has a high energy density of 43.12 Wh kg−1 and power density of 161.99 W kg−1 at a constant current density of 1.0 A g−1. This work proposes a more effective, green, efficient, and controlled approach to obtain bio-waste-based porous carbon 2D nanosheet with a controlled pore structure for energy conversion and storage systems. Novelty Statement The novelty of this study is a green synthesis has possessed highly micro-mesopores nanosheet bio-waste. 2D nanosheet was prepared free-template and free-binder. Sub-ultra-micropores were confirmed with dominated mesoporosity of 66.8%. Carbon nanosheet boosted specific capacitance almost 3-fold to 320.95 F g−1.

Green hydrogen production based on the co-combustion of wood biomass and porous media

The production of green hydrogen by utilizing wood pellets is an effective way to solve the problem of energy shortage and environmental pollution. In order to improve the hydrogen production efficiency of biomass, a co-combustion system of inert porous media and wood pellets was built, and the combustion characteristic of wood pellets was studied with different porous media structures. The results demonstrated that the increasing of air velocity was beneficial to increase the combustion temperature, and hydrogen production reached the maximum value at v = 4 cm/s. Meanwhile, the hydrogen production increased with the increasing of inert bed length due to the intensification of heat circulation. When the length ratio of the hybrid to inert bed was 6: 3, the lower heating value of syngas was 3.69 MJ/Nm3 and the molar fraction of hydrogen increased by 69 % compared to the single wood pellets combustion. Moreover, the decreasing of pellets diameter was conducive to increase syngas production. The co-combustion of inert porous media and wood pellets realized the efficient utilization of biomass, and maximum growth rate of hydrogen reached 142 %.

Considerations when determining Counter-diffusion constants in liquid phase catalytic reactions using the Zero Length column (ZLC) method

The confusion with diffusion: In heterogeneous catalysis often, the catalytic material is housed within a porous support structure. It is important therefore to determine whether this support structure exerts limiting behaviors. In this paper, desorption and diffusion effects are separated under reactions conditions, to provide accurate effective diffusion constants in swelling and gate-opening catalysts. • A Zero Length Column (ZLC) method was developed using liquid chromatography. • Diffusion in porous catalyst pellets as small as 5 mg can be directly characterised. • Reactant counter-diffusion coefficients were determined for the Heck reaction. • Clear differences in diffusion rates for reactants versus non-reactant species. A Zero Length Column (ZLC) method was developed using a liquid chromatographic system to calculate reactant counter-diffusion coefficients in porous, solvent swollen catalytic pellets and gate-opening support materials. Reactant diffusivities within these porous materials were determined at the reaction conditions of 80 °C and 0.3–0.75 mL min −1 . For all materials, molecules of a similar size to the pore apertures, or molecules with strong interactions with the material surfaces, catalysts, were observable by the ZLC method, with both micro and macropore diffusion observed. Differences between Pd(II) and Pd(0) forms of the EnCat30 catalyst were examined to determine the effects of catalytic deactivation. The deactivated catalyst showed iodobenzene macroporous diffusion constants similar to the relatively inert toluene molecules. Finally, pulse field gradient NMR was utilised to compare and validate ZLC diffusion measurements for solvent swollen reaction systems. This study presents much needed novel findings on diffusivity data for liquid phase catalytic systems.

Co-Application of Porous Polysulfide Pellets with Acidithiobacillus thiooxidans Improves Sulfate Availability in Soil

Co-Application of Porous Polysulfide Pellets with Acidithiobacillus thiooxidans Improves Sulfate Availability in Soil

Succinic acid-assisted modification of a natural zeolite and preparation of its porous pellet for enhanced removal of ammonium in wastewater via fixed-bed continuous flow column

Inspired by the development of adsorption techniques, an adsorbent for ammonium (NH4+-N) removal, featuring high selectivity towards NH4+-N, high adsorption capacity, simplicity of use, low cost and environmental friendliness, have attracted great attention in recent years. During this work, a natural zeolite with a lower nSi/nAl ratio of 4.2 was selected as the modified substrate. Various modification agents including NaOH, succinic acid (SA) and NaCl were performed to modify the zeolites successively. Due to succinic acid-assisted modification, plenty of carboxylate groups were distributed on the surface of zeolite as active adsorption sites. The modified zeolite (CMZ) shows a significant NH4+-N adsorption capacity which is much higher (10-fold) than that of natural zeolites. Moreover, CMZ also shows high selectivity for NH4+-N among several cations including Na+, Ca2+ and Mg2+. The NH4+-N adsorption kinetics and isotherms of CMZ fit the pseudo-first-order and Langmuir model, confirming a chemical monolayer adsorption process. After ten regeneration times, CMZ maintained the high NH4+-N adsorption capacity of around 14.55 mg g−1 showing outstanding stability and reusability when reused for water treatment. In addition, a modified porous zeolite pellet (MPZP) was further prepared. MPZP holds a relatively lower wear rate of 0.1% at the continuous flow rate of 50 BV h−1, suggesting high flushing resistance and long service life.

Catalytic Conversion of Hydrocarbons and Formation of Carbon Nanofilaments in Porous Pellets

Catalytic conversion of hydrocarbons occurring at metal nanoparticles in porous pellets is often accompanied by the formation of coke in the form of growing heterogeneous film-like aggregates or carbon nanofilaments. The latter processes result in deactivation of metal nanoparticles. The corresponding kinetic models imply the formation and growth of film-like coke aggregates. Herein, I present an alternative generic kinetic model focused on the formation and growth of carbon nanofilaments. These processes are considered to deactivate metal nanoparticles and reduce the rate of reactant diffusion in pores. In this framework, the kinetically limited reaction regime is described by simple analytical expressions. The diffusion-limited regime can be described as well but only numerically. The model presented can be used for interpretation of experimental results.Graphical

Investigation of the Electrochemical Reduction of Porous CaTiO3 Pellets in CaCl2%–0.5%CaO Molten Salt

The formation of CaTiO3 during the electro-reduction of TiO2 pellets in CaCl2-based molten salts is unavoidable. So in present paper, the electro-deoxidation of porous CaTiO3 pellets was investigated. Cyclic voltammetry and constant potential electrolysis experiments were conducted to gain insight into the electro-deoxidation mechanism. From the results, two new reduction pathways of the porous CaTiO3 pellets were determined. The main factor influencing the reduction pathways is the porosity. When the porosity is low, CaTiO3 is directly reduced into TiO. With the porosity increases, some CaTiO3 will firstly be reduced into CaTi2O4 and then the CaTi2O4 is further reduced into TiO. The effect of the potential applied on the cathode on the possible reduction limit of the sample was discussed. The results indicated that the more negative the potential is, the faster the deoxidation rate is and the lower the deoxidation limit is. Only when the applied potential is more negative than −1.6 V vs Ag+/Ag, low-oxygen titanium (the oxygen content is lower than 1%) can be obtained in our experimental conditions. In addition, the microstructural kinetics of phase transformations during reduction of the CaTiO3 pellets were also discussed.