Microporous Powder Research Articles

Preparation and enhanced mechanical properties of novel Al2O3‐C ceramic filter reinforced by microporous powder and SiC whiskers

AbstractIn present work, the novel Al2O3‐C ceramic filter fabricated by using microporous corundum‐spinel powder instead of dense Al2O3 powder and reinforced by SiC whiskers is proposed. The effects of Si powder content (0, 3, 6, and 9 wt. %) on the microstructures and mechanical properties of the filters were studied. After replacing the α‐Al2O3 micro‐powder with microporous corundum‐spinel powder, the in situ spinel whiskers were formed inside the filter skeleton under the reducing atmosphere. The rough surface structure of the microporous powder increased the interface contact area with the small‐sized carbon particles, resulting in a compact interface bonding in the filter skeleton and a higher cold compressive strength of the filter. When the Si powder content increased to 6–9 wt. %, the in‐situ SiC whiskers were formed not only between the microporous powder, but also inside the pores near the surface of it by vapor‐solid reaction mechanism in the filter skeleton. The SiC whiskers synergized with the microporous powder to form a more compact interface structure, thus remarkably enhancing their cold compressive strength and thermal shock resistance. Overall, the mechanical properties of the filters were significantly improved by the addition of 9 wt. % Si powder. The filter skeleton had an apparent porosity of 36.2% and a bulk density of 1.93 g/cm3. The filter also exhibited a high cold compressive strength of 1.59 MPa and a superior thermal shock resistance. It has the potential for better purification efficiency on molten steel in the future due to a rougher skeleton surface structure compared to existing Al2O3‐C filters.

All-Nanoporous fiber sorbent with a Non-Sacrificial polymer of intrinsic microporosity (PIM) matrix

Microporous materials are highlighted with regard to low-energy and low-carbon adsorptive separation processes, where the interests have evolved simple microporous powders into a structured sorbent platform of fiber sorbent to tackle the technical challenges of large-scale applications. However, the challenge of sorption capacity loss in a limited footprint due to the addition of non-adsorbing binder materials still remained. Polymers of intrinsic microporosity (PIMs) are promising advanced materials for gas separation and capture due to their unique textural properties and processability. This article reports an efficient but straightforward blend of organic and inorganic materials, PIM-1 and zeolite NaY, forming “all-nanoporous” fiber sorbents. The combination of the two nanoporous materials resulted in a structured platform for a sorption-based separation system for volatile organic compounds (VOCs). It is differentiated from other sorption platforms as it presents minimal volumetric sorption loss from the “binder” material by allowing the microporous substrate to work as a VOC sorbent. The “all-nanoporous” fiber sorbent of NaY/PIM-1 shows feasible sorption performance capabilities under both dry and humid conditions while maintaining a minimal pressure drop due to its hierarchical porous structure.

Phenanthroline-Based Polyarylate Porous Membranes with Rapid Water Transport for Metal Cation Separation.

The selective separation of ions in terms of extremely similar size and properties remains an important challenge in water purification. We innovated a kind of porous nanofilm via interfacial polymerization using rigid heterocyclic ligands to achieve high valent cation selectivity and rapid water/ion transport. The interconnected microporosity and uniformly distributed cation-affinitive sites of the ultrathin membranes enabled water permeation (7.5 L m-2 h-1 bar-1), ion permeance of Na+ (1.5 mol m-2 h-1 bar-1), and Mg2+/Na+ permselectivity (2.1) during nanofiltration. The forward osmosis exhibited a prominent water flux of 95 LMH at 1 M NaCl draw solution, which expanded various applications. The polyarylate membranes comprising 4,7-diphenyl-1,10-phenanthroline showed a higher water permeation and ion selectivity than the planar monomers, e.g., resorcinol. A distinct fluorescence responsiveness existed between membranes and cations for the interaction characterization. Host-guest nuclear magnetic resonance (NMR) spectroscopy and solid-state nuclear magnetic resonance spectroscopy characterized the preferential affinitive of divalent/high-valent cations in the interconnected microporous powders; an ultraviolet spectrophotometer characterized the light responsiveness of the porous nanofilms. Such an active membrane has potential applications in selective separation and adsorption of cations, photocatalytic materials, photosensors, and other fields.

Polysaccharides from sunflower stalk pith: Chemical, structural and functional characterization

Polysaccharides from sunflower stalk pith (SSP) were extracted by hot water and sodium hexametaphosphate (SHMP). Chemical analyses suggested both fractions dominated in galacturonic acids with a small amount of neutral sugars, indicating their identity as pectins. The weight average molecular weight and intrinsic viscosity for water-extractable pectin (WEP) and SHMP-extractable pectin (SEP) were 57.2 kDa, 0.48 dL/g and 23.1 kDa, 0.50 dL/g, respectively. The degree of esterification (DE) was calculated to be 92% and 64%, respectively. Methylation analysis demonstrated that 1,4-GalpA residues dominated all the sugar linkages, while other linkage types including 1,2-Rhap, 1,2,4-Rhap, 1,4-Galp and 1,5-Araf were also present in WEP and SEP. NMR spectroscopy further revealed WEP and SEP mainly demonstrated homogalacturonan (HG) structure and a small fraction of rhamnogalacturonan-I (RG-I) structure. The microstructure and water- and oil-holding capacity (WHC and OHC) of SSP was also examined. SSP was a microporous powder. Both WHC and OHC increased with particle size of the SSP, reaching up to over 40 g liquid/g fibre at particle size of 30 mesh (0.595 mm). However, the oil-SSP mixtures showed oil loss after absorption on filter paper for 24 or 48 h. Oil loss increased with SSP particle size decrease. 30 mesh SSP reduced oil loss in peanut butter by 74% with 2.2% addition.

Flat Plate Collector for Process Heat with Full Surface Aluminium Absorber, Vacuum Super Insulation and Front Foil

A new flat plate collector is under development for economic process heat of temperatures between 80° and 150°C. A vacuum super insulation (VSI) with micro-porous powders (perlite or fumed silica) in an evacuated (0.1 mbar) stainless steel envelope has been developed for the rear side of the collector which replaces the mineral wool insulation of standard collectors. CFD simulations of the equivalent thermal conductivity of the VSI including losses via the powder and edge losses have been performed depending on geometry. Applying a 100μm thin VA foil as VSI cover, the collector losses can be reduced by about 0.6W/m2K. Between glass cover and absorber the collector will be equipped with a transparent ETFE foil reducing the loss coefficient further by about 1.2W/m2K. Additionally, a full surface aluminium absorber with a very high collector efficiency factor F’ of 0.97 is used, reaching maximum collector efficiencies of about 0.9. Up to a temperature difference of 110K, the new collector is estimated to have higher efficiencies than standard flat plate and vacuum tube collectors. In the temperature range of 80° and 150°C the efficiency is expected to lie between 65% and 35%. Four different and successively improved prototypes are under test and construction, respectively. The first prototype showed the principal feasibility of the concept and was the first VSI collector operated under outdoor conditions at temperatures up to 120K over ambient.

Storage of hydrogen in nanostructured carbon materials

Abstract Recent developments focusing on novel hydrogen storage media have helped to benchmark nanostructured carbon materials as one of the ongoing strategic research areas in science and technology. In particular, certain microporous carbon powders, carbon nanomaterials, and specifically carbon nanotubes stand to deliver unparalleled performance as the next generation of base materials for storing hydrogen. Accordingly, the main goal of this report is to overview the challenges, distinguishing traits, and apparent contradictions of carbon-based hydrogen storage technologies and to emphasize recently developed nanostructured carbon materials that show potential to store hydrogen by physisorption and/or chemisorption mechanisms. Specifically touched upon are newer material preparation methods as well as experimental and theoretical attempts to elucidate, improve or predict hydrogen storage capacities, sorption–desorption kinetics, microscopic uptake mechanisms and temperature–pressure–loading interrelations in nanostructured carbons, particularly microporous powders and carbon nanotubes.

Experimental Apparatus for Characterizing the Internal Diffusivity of Microporous Powders

Abstract The characterization of the micropore range in porous powders requires sophisticated apparatuses, which limits their thorough characterization to large laboratories. We describe a modification of a BET adsorption apparatus, in which the key instrument is a high precision differential pressure sensor, which even small laboratories can afford, that can be used to measure the internal diffusivity and micropore size distribution (mPSD) of microporous powders. The apparatus is based on the conventional gas uptake rate measurement and adsorption manometry for measuring diffusivity and mPSD, respectively. Numerical simulations of the measurement and uptake rate were used to analyze the apparatus.

Solid‐state compaction and drawing of nascent reactor powders of ultra‐high‐molecular‐weight polyethylene

AbstractThe continuous production of ultra‐high‐molecular‐weight polyethylene (UHMWPE) filaments was studied by the direct roll forming of nascent reactor powders followed by subsequent multistage orientation drawing below their melting points. The UHMWPE reactor powders used in this study were prepared by the polymerization of ethylene in the presence of soluble magnesium complexes, and they exhibited high yield even at low reaction temperatures. The unique, microporous powder morphology contributed to the successful compaction of the UHMWPE powders into coherent tapes below their melting temperatures. The small‐angle X‐ray scattering study of the compacted tapes revealed that folded‐chain crystals with a relatively long‐range order were formed during the compaction and were transformed into extended‐chain crystals as the draw ratio increased. Our results also reveal that the drawability and tensile and thermal properties of the filaments depended sensitively on both the polymerization and solid‐state processing conditions. The fiber drawn to a total draw ratio of 90 in the study had a tensile strength of 2.5 GPa and a tensile modulus of 130 GPa. Finally, the solid‐state drawn UHMWPE filaments were treated with O2 plasma, and the enhancement of the interfacial shear strength by the surface treatment is presented. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 718–730, 2005

Solution‐Processed, Organophilic Membrane Derived from a Polymer of Intrinsic Microporosity

A polymer with a rigid, randomly contorted molecular structure (see Figure), incorporating fused rings connected by spiro‐centres, may be precipitated or cast from solution to give microporous powders and membranes stable up to temperatures of 350 °C, with apparent surface areas > 600 m2 g–1. Organophilic membranes may be formed, as demonstrated by the separation of phenol from water by pervaporation.

Silicon Chemical Vapor Deposition (CVD) on microporous powders in a fluidized bed

The fluidized bed Chemical Vapor Deposition (CVD) process constitutes today one of the most efficient techniques to modify the surface properties of dense (nonporous) powders. The success encountered in this field is the reason why this process has been extended to the treatment of microporous powders, for which there are very important industrial interests. The article presents an experimental analysis of the influence of the main operating parameters on the spatial localisation and the nanostructure of silicon deposits from silane on microporous powders. The first results obtained show that uniform deposits appear on all the surfaces of the pores in the form of discontinuous rafts. These results, which will be coupled with a theoretical predictive model, prove that the control at the nanometric scale of the organization of CVD materials on microporous powders today has become possible.

Immobilization of a Soluble Metal Complex in an Organic Network. Remarkable Catalytic Performance of a Porous Dialkoxyzirconium Polyphenoxide as a Functional Organic Zeolite Analogue

Treatment of anthracenebisresorcinol 1 (a tetraphenol) with Zr(OtBu)4 in THF results in polycondensation to give an O−Zr−O network and affords a poly(dialkoxyzirconium phenoxide), 14-·2[Zr(OtBu)2] (Zr host), in quantitative yield as an insoluble, amorphous, microporous powder with a particle size of ∼0.7 μm, a pore size of ∼0.7 nm, and a specific surface area of ∼200 m2/g. The powder exhibits reversible Langmuir-type adsorption/desorption of N2 at 77 K and hexane at 298 K. Adsorption and coadsorption of ethyl acetate, benzene, and other polar and apolar guests also occurs readily at 298 K. The Zr host catalyzes the Diels−Alder reaction of acrolein with 1,3-cyclohexadiene in a remarkable manner. As a solid metal−organic catalyst, it has a formula-based turnover rate constant of 40 h-1, which far exceeds those of its components, i.e., the soluble Lewis acid Zr(OtBu)4 (0.1 h-1) and the hydrogen-bonded insoluble organic network 1 (0.3 h-1). The solid catalyst can be easily separated from the organic product, ...

The effect of dry heating of synthetic 2-line and 6-line ferrihydrite: II. Surface area, porosity and fractal dimension

AbstractNitrogen adsorption isotherms were measured on synthetic 2-line and 6-line ferrihydrites heated to 400 K, 500 K, and 600 K under dry conditions for different times ranging from 4 to 3000 h. Evaluation of specific surface area, microporosity and fractal dimension revealed that 2-line and 6-line ferrihydrites are highly microporous powders consisting of aggregates with corrugated interior and exterior surfaces. Furthermore, the surfaces of the single particles forming the aggregates have a smaller fractal dimension, i.e. a smoother appearance, than those of the entire aggregate. The diffusion of water lost during the heating process is influenced by the size of the micropores. The initial stage of the dehydration of the ferrihydrites can be described as similar to the process of Ostwald ripening.

Fiber Glass for Use in Evacuated Thermal Insulations

Various forms of glass fibers arc available which provide advantages over microporous powders in evacuated thermal insulations. The main advantage is that evacuated thermal insulation made from glass fibers can provide thermal resis tivities well in excess of 50 (F.ft2.h/Btu.in.) as compared to microporous powders which are typically limited to maximum resistivities of 35.

Lipase immobilized on a hydrophobic, microporous support for the hydrolysis of fats

AbstractEnzymatic hydrolysis of triglycerides has been studied as a low energy‐consuming alternative to the present steam (Colgate‐Emery) process. Cost analysis of the enzymatic process indicates that use of immobilized lipase compares favorably with the present steam process. This paper discusses the search for an adsorbent to use as the support material for the lipase. Hydrophobic microporous powders, membranes and fibers were found to give the best performance, as little of the lipase's activity was lost upon immobilization. Lipase immobilized on Accurel powder has been studied in various reactor configurations for the hydrolysis of triglycerides. Reactor designs studied include cocurrent and counter‐current fixed beds, continuous stirred tank reactors, and the diaphragm reactor. Productivities of the latter two reactor types were 1100 and 1700 kg fatty acid per kg immobilized lipase.

Study of “Non-Fickian” Diffusion Anomalies through Time Lags. V. Simple Distance-Dependent Anomalies in Laminated Media

The investigation of distance-dependent “non-Fickian” time-lag behavior is here extended to a laminated (multiple) membrane consisting of n laminations at right angles to the flow coordinate X, each lamination also exhibiting a continuous variation in diffusion properties along X. The results obtained in Paper II of the present series are valid here also. In addition, the “non-Fickian time-lag increments” characterizing such a multiple membrane can be analyzed into components arising from the variation of diffusion properties within each lamination and also from the differences between the over-all diffusion properties of the individual laminations. The relative importance of these contributions as a function of n is considered, with particular reference to the time-lag properties of microporous powder compacts formed by stepwise compression.

Study of “Non-Fickian” Diffusion Anomalies through Time Lags. III. Simple Distance-Dependent Anomalies in Microporous Media

The time-lag treatment developed in Paper II is here applied to a microporous medium with porosity varying with position in the direction of flow. It is assumed that diffusion in such a medium can occur in both pore and adsorbed phases without sensible disturbance of the adsorption equilibrium and that the relevant diffusion and distribution coefficients are constant. The case of gaseous Knudsen diffusion through microporous powder compacts formed by uniaxial compression is then considered in some detail. It is found that the time-lag anomalies, which characterize many experimental systems of this kind, can plausibly be ascribed in large part to distance-dependent “non-Fickian” diffusion behavior and interpreted qualitatively or semiquantitatively in terms of the present treatment.

Venting of high pressure fixed‐bed catalytic reactors

AbstractA semi‐quanlitative analysis is presented of the pressures arising in catalyst pellets during the rapid venting of a typical high pressure fixed‐bed reactor. It is shown, for both macroporous pellets and the microporous powder particles within them, that the pressures will not exceed those of the surroundings by more than a few atmosphers. It is concluded that a rapid release of pressure may be effected without risking damage to the catalyst pellets.