Mathematical Model of Extraction from a Body with Bidisperse Porous Structure

A mathematical model is proposed to describe extraction from a semi-infinite body with pores of two types, namely, large pores extending to the surface and small pores communicating with the large pores. The effective transfer coefficients in the two types of pores are assumed to be different. By the fractional differentiation method, the time dependence of the extractant flux through the body surface is described. The theoretical results are compared with experimental data.     

Mathematical model of impregnation and extraction for a bidisperse porous material

A model for analyzing the process of impregnation (and, in a sense, the inverse process of extraction) for a porous solid with two types of pores is considered that is suitable for describing the process at large values of time. A solution to the problem with the most typical additional conditions is obtained, and the kinetic function of impregnation (extraction) and the flux density of a substance from a solid are found. A set of equations of the problem is reduced to a single equation. The issues associated with the applicability of this equation and the possibility of its generalization are discussed.     

Description of the initial stage of impregnation and extraction processes using a bidisperse model

A model for analyzing the process of impregnation and the inverse process of extraction for a porous solid with two types of pores is considered. The model is suitable for describing the process at small values of time. A solution to the problem with under most typical additional conditions has been obtained, and the kinetic function of impregnation (extraction) and the flux density of matter from the solid have been found.     

Characterisation of intra- and inter-C–S–H gel pore water in white cement based on an analysis of NMR signal amplitudes as a function of water content

¹H nuclear magnetic resonance (NMR) relaxation analysis of water in progressively dried white cement paste is used to estimate the width and relative specific area of intra-C–S–H sheet pores and inter-C–S–H particle gel pores. The measurement is based on the ratio of solid echo to free induction decay signal amplitudes and the observation that as water is removed, so the surface fraction contributing to the solid echo increases. The intra- and inter-C–S–H pores are found to be 1.5 nm and 4.1 nm thick respectively. The total specific area and volume ratio is 2.4 and 0.88 respectively. The volume ratio of readily evaporable water within the pore types is 0.63. Hence, the sheet porosity is 47% of the total or 38% if based solely on evaporable water. The method is distinct from NMR analyses based on the relaxation time. There is good agreement between the measured widths by the two methods.     

Surface compatibility in a carbon-alloy composite and its influence on the electrochemical performance of Li/ion batteries

Carbon-alloy composites were prepared by coating carbon materials with different surfaces with Sn, Sb or SnSb. The SnSb-hard carbon spherule (HCS) composite electrode shows the best cycling performance. The matching of crystalline parameters between SnSb and the carbon ensures a good dispersion of SnSb alloy on the surface. The high density of the nucleation centers on the HCS surface leads to a small SnSb crystallite size. Open pores on the surface of HCS, into which the alloy crystals are allowed to grow, act as pinning centers, which further stabilize the composite. These three factors are supposed to be responsible for the best cyclic performance of SnSb-HCS composite. The latter two factors also result in a large BET surface area, which leads to a large initial irreversible capacity loss, because more solid electrolyte interface film is formed. It seems that the best cyclic performance and the highest initial efficiency are paradoxical in the SnSb-carbon composite. Further surface modification should be conducted to obtain better electrode materials.     

Dilatation of Porous Glass

A porous body dilates when its surface energy changes, either by adsorption of a gas or by immersion in a liquid. A new equation is derived to describe the resultant strain and is shown to agree better with experiment than the equation proposed by Yates. The physical properties needed for the calculation include Young's modulus and surface area. Measurements are presented for a commercial porous glass that show that the modulus increases by a factor of ∼2, with negligible accompanying shrinkage, upon heating to 800°C. The increase is attributed to the presence of hydroxyls (nonbridging oxygens) in the solid phase that condense on heating. The surface area contains a large contribution from gel that precipitates in the pores during acid leaching. It is concluded that the gel is rigidly bound to the solid network, and therefore contributes to the dilation of the body Porous glasses show an anamolously large expansion when immersed in water, which is attributed to absorption of water into the solid phase. Diffusion of water into the solid phase is expected to be enhanced by the large concentration of nonbridging oxygens.     

Solid‐state modification of isotactic polypropylene (iPP) via grafting of styrene. I. Polymerization experiments

Grafting of vinyl monomers onto isotactic polypropylene (iPP) in the solid state, that is, below the melting point, displays several advantages over melt or solution grafting processes, such as negligible degradation of the iPP and absence of any solvent. The final properties of such iPP modifications or actually compatibilized PP blends are dependent on the dispersion of the new polymer into the iPP matrix, which is controlled to a large extent by the degree of grafting versus the amount of free homopolymer formed. In the present work, the solid‐state modification of iPP by styrene has been investigated from the point of view of the monomer polymerization behavior. In order to determine the styrene conversion and the distribution of the newly formed PS phase along the radius of the iPP powder particles, the reaction products were characterized by infrared (FTIR) and Raman spectroscopy. Fractionation of the reaction products via selective solvent extraction allowed the determination of the grafting efficiency (Φ). It was shown that besides the grafted PS two additional types of PS are formed, that is, free PS homopolymer in the pores of the PP powder and free PS in the amorphous PP phase. Phi shows an optimum as a function of the feed peroxide composition and the feeding rate. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3279–3291, 2003     

Modeling of Matter Extraction from a Capillary Porous Particle with a Bidisperse Capillary Structure

A model is suggested for a particle with a bidisperse capillary structure. A numerical analysis of the model demonstrates that, for the liquid extraction of a desired substance from the particle, there exists an optimum range of oscillation frequencies of the liquid in large pores.     

微生物浸出反应硫化铜矿石表面形态特征显微分析

通过光学显微镜和电子显微镜分析了硫化铜原矿样和经摇瓶浸出反应后的矿样表面形态变化特征.结果表明:两个矿样的铜的浸出率、TFe离子质量浓度均随着浸出逐渐上升,粒径较小的矿样浸出率较大.未经浸出反应的原矿样表面比较平整,微观尺度上的孔隙、孔洞很少;浸出反应后,矿石表面吸附有大量细菌,表面变得凹凸不平,大量目的金属元素被浸出.     

Carl Hanson Medal

ABSTRACT

Nondispersive equilibrium separation of citric acid from an aqueous solution by reversible chemical complexatlon with trioctyl amine in a diluent of methyl isobutyl ketone is achieved in a microporous hydrophobic hollow fiber extractor. The extractor had a shell-and-tube configuration : a total of 102 hydrophobic polypropylene (Celgard X-20, 240 μm id, 290 μm od, Hoechst Celanese) hollow fibers potted in epoxy in a stainless steel tube of 0.46 cm id. The effective fiber length vas 18.5 cm and surface area/volume was 46.8 cm. Theoretical models have been developed to predict the rate of extraction of citric acid in such systems. It essentially considers diffusion of solute molecules through the boundary layers of the two phases, in addition to the diffusion through the organic liquid occupying the membrane pores, and reversible chemical equilibrium at the phase interface. Conventionally in an aqueous-organic system having a high distribution coefficient for small solutes with a hydrophobic fiber and organic in pores, the aqueous boundary layer resistance controls. Here that is true also except when the membrane resistance of the large citric acid-amine complex diffusing through the organic-filled pores is higher than the aqueous phase boundary layer resistance. Experimental observations show further that the back extraction rate of citric acid present in the solvent (amine-organic diluent) into aqueous sodium hydroxide is much lover than the extraction rate for such a system in the sane hollow fiber extractor.     

Preparation of alumina–silica bimodal pore catalysts for Fischer-Tropsch synthesis

The bimodal pore structure support has excellent advantages in solid catalysis reaction because the large pores provide pathways for rapid molecular transportation and small pores provide a large active surface, contributing to high diffusion efficiency and high dispersion of supported metal simultaneously, A multi-functional bimodal pore catalyst support, alumina-silica bimodal pore support, was prepared from polymer complex solution and silica gel. The obtained bimodal pore support had two kinds of main pores, decreased pore volume and enlarged specific surface area, comparing the original silica gel. This kind of bimodal pore support was applied in slurry phase Fischer-Tropsch synthesis, where cobalt was supported as active metal. Alumina-silica bimodal pore catalyst exhibited high catalytic activity and favorite selectivity, due to the spatial effects of bimodal pore structure and chemical effects of coexisting alumina, which formed the new small pores of bimodal pore support.     

Influence of the boundary conditions on capillary flow dynamics and liquid distribution in a porous medium

After depositing a wetting liquid onto a porous medium surface, and under the influence of the capillary pressure, the liquid is imbibed into the porous medium creating a wetted imprint. The flow within the porous medium does not cease once all the liquid is imbibed but continues as a secondary capillary flow, where the liquid flows from large pores into small pores along the liquid interface. The flow is solved using the capillary network model, and the influence of the boundary condition on the liquid distribution within the porous medium is investigated. The pores at the porous medium boundaries can be defined as open or closed pores, where an open pore is checked for the potential threshold condition for flow to take place. In contrast, the closed pore is defined as a static entity, in which the potential condition for flow to take place is never satisfied. By defining the pores at distinct porous medium boundaries as open or closed, one is able to obtain a very different liquid distribution within the porous medium. The liquid saturation profiles along the principal flow direction, ranging from constant to steadily decreasing, to the profile with a local maximum, are found numerically. It is shown that these saturation profiles are also related to the geometrical dimension that is perpendicular to the flow principal direction, and changing the boundary type from open to closed allows the liquid distribution within the porous medium to be controlled. In addition to the liquid distribution, the influence of the boundary conditions on capillary pressure and relative permeability is investigated, where both parameters are not influenced by variation of the boundary condition types. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Effect of pores on dielectric breakdown strength of alumina ceramics via surface and volume effects

To investigate the effect of pores on the dielectric breakdown (DB) of alumina ceramics under AC voltage, we implant pores at different positions (surface, interior, and the whole body) of the ceramic samples by adding the polyvinyl alcohol solid particles at different positions in the green bodies. Meanwhile, two electrode setups are used to test the dielectric breakdown strength (DBS), in order to analyze the effect of pore distribution on the DB, and the morphology of the DB channels is characterized. The results reveal both the pores on the surface and in the bulk reduce the DBS, and the pore distribution affects the shape and position of the DB channel. Besides, pre-breakdown in a low-DBS layer is found when the voltage is not high enough to produce DB. It confirms that the effect of pores on the DB is a combination of the volume effect and the surface effect.     

Catalysis Over Pore-Expanded MCM-41 Mesoporous Materials

Pore-expanded MCM-41 (PE-MCM-41) silica was obtained via a two-step strategy consisting of synthesis of MCM-41 in the presence of cetyltrimethylammonium cations (CTMA⁺) followed by hydrothermal treatment in the presence of an aqueous suspension of dimethyldecylamine (DMDA). It is believed that the two surfactants self-organize into concentric cylinders comprised of an inverted DMDA micelle within a regular CTMA⁺ micelle. The amine head groups point towards the pore center, thus creating a hydrophilic channel within the pores. Selective extraction of DMDA afforded PE-MCM-41E, a highly porous material with hydrophobic surface. Calcination of as-synthesized PE-MCM-41 or PE-MCM-41E gave rise to PE-MCM-41C which exhibits a unique combination of large pores (up to 20 nm), large pore volume (up to 3.5 cm³/g) and large surface area, often exceeding 1000 m²/g. All three mesophases were used as starting materials for the development of innovative catalysts and adsorbents. Moreover, post-synthesis alumination of PE-MCM-41 and PE-MCM-41C led to novel large pore aluminosilicates with different Si/Al ratios, which provided new opportunities in acid and bifunctional catalysis. This contribution is an overview of the catalytic applications of pore-expanded mesoporous silica and aluminosilica.     

Analytical electron tomography mapping of the SiC pore oxidation at the nanoscale

Silicon carbide is a ceramic material that has been widely studied because of its potential applications, ranging from electronics to heterogeneous catalysis. Recently, a new type of SiC materials with a medium specific surface area and thermal conductivity, called β-SiC, has attracted overgrowing interest as a new class of catalyst support in several catalytic reactions. A primary electron tomography study, performed in usual mode, has revealed a dual surface structure defined by two types of porosities made of networks of connected channels with sizes larger than 50 nm and ink-bottled pores with sizes spanning from 4 to 50 nm. Depending on the solvent nature, metal nanoparticles could be selectively deposited inside one of the two porosities, a fact that illustrates a selective wetting titration of the two types of surfaces by different liquids. The explaining hypothesis that has been put forward was that this selectivity against solvents is related to the pore surface oxidation degree of the two types of pores. A new technique of analytical electron tomography, where the series of projections used to reconstruct the volume of an object is recorded in energy filtered mode (EFTEM), has been implemented to map the pore oxidation state and to correlate it with the morphology and the accessibility of the porous network. Applied, for the first time, at a nanoscale resolution, this technique allowed us to obtain 3D elemental maps of different elements present in the analysed porous grains, in particular oxygen; we found thus that the interconnected channel pores are more rapidly oxidized than the ink-bottled ones. Alternatively, our study highlights the great interest of this method that opens the way for obtaining precise information on the chemical composition of a 3D surface at a nanometer scale.     

膜特征对锂资源提取过程的影响

可再生能源领域的发展吸引了众多学者对锂电池行业的关注,高效绿色提锂技术成为研究的重点。膜分离技术由于在连续操作中具有操作方便、运行易控、耗能低等特点在锂资源提取中展现出广阔的应用前景。本文基于锂资源提取的膜分离技术,归纳并讨论膜孔和膜表面特征对锂离子分离的影响。文章指出,离子在膜孔中的传输是其分离的基础,离子尺寸和离子在膜孔中传输形态影响其传输速率。膜孔的尺寸和形态是影响锂离子分离的关键因素,不同尺寸、形态和膜孔内电荷在分离过程中表现出不同的分离效果。基于膜表面特征,文章概括了现有荷正电膜、荷负电膜及表面亲疏水性在锂离子分离中的性能差异。最后,文章探究了膜分离技术在锂资源提取中存在的挑战和机遇,推进膜分离技术在锂资源提取方向的理论研究和实际应用。     

SEM topography of twin fracture surfaces of Alite pastes 3 years old

The topography of fracture surfaces of some pastes of tricalcium silicate solid solutions hydrated for 3 years was studied by scanning electron microscopy. The symmetrical areas of the two halves arising from a single fracture operation were compared. Observations have been also made on the surfaces, one of which was partially attacked.Large amorphous C-S-H zones are abundant; acicular and subgrain forms in irregular pores are also present. Ca(OH)₂ masses both in large and very little areas for the typically lamellar morphology are recognizable. No visible porosity at the boundaries between C-S-H and Ca(OH)₂ solid phases in descernible.The fracture paths are transparticle in character. The results of the selective dissolution of the fracture surface of one half in respect to the other unattached are discussed.     

Ceramic membranes from reaction-sintered silicon nitride on nitride and oxide substrates

The gas permeability and pore sizes in membranes and porous materials from reaction-sintered silicon nitride (RSSN) are studied. The substrates for the RSSN membranes are highly porous (80% pores) silicon nitride with pores 50–80 μm in size and alumina-based ceramics with pores about 10 μm in diameter. Silicon powder with a specific surface of 1.4 g/cm² is deposited onto the substrates in the form of an aqueous dispersion by various methods including filtering and sintered in nitrogen at 1300–1400°C. The main difficulty of the process is in preventing the formation of defects at the places where the largest channel pores reach the surface of the substrate. Membranes with 0.5 -1 μm pores can be obtained on both types of substrate after a single deposition.     

Convective extraction from a porous particle under the effect of point pressure pulses

The recovery of an extractant from a porous particle under the effect of point pressure pulses on its surface is studied. It is assumed that the place of a pressure pulse is determined in a random manner. Different configurations of pores are considered: a single pore that runs through a particle and branched pores that have several mouths. Explicit relationships for the yield of the extractant at each sequential impact are derived. It is found that asymptotic regularities for extractant recovery from pores of various configurations at the final stage of the process differ only by a numerical factor that increases with an increase in the number of mouths and does not depend on the internal structure of pores.     

Mesoporous materials as host for an entrapped enzyme

Three mesoporous materials, silica, alumina and titania, were used as host for a lipase and the enzyme-loaded particles were employed as catalyst for esterification of caprylic acid using a mixture of glycerol and water as reaction medium. The reaction proceeded well with all three oxides but alumina gave considerably higher conversion than the other two. Hydrophobized silica gave an even higher degree of esterification. The degree of esterification obtained is believed to depend on the microenvironment of the enzyme. When alumina, which is positively charged under the conditions used, and hydrophobized silica are used as host material, the negatively charged lipase can be assumed to be adsorbed at the walls of the pores. The water activity is believed to be lower at the solid surface than in the middle of the pores, where the enzyme is situated when silica and alumina are used as host material. It is shown that the lipase is not irreversibly entrapped in the pores of the mesoporous materials. When the particles are removed by filtration after completed reaction and subsequently washed with an aqueous buffer, the enzyme is leached out. The lipase can be immobilized in the pores, however, by cross-linking in situ inside the pores using glutaraldehyde as cross-linking agent. Mesoporous materials loaded with cross-linked lipase can be reused several times with only marginal loss of activity.