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1.
The effect of the support pore size on the membrane morphology was investigated for zeolite silicalite-1 membranes synthesized by pore plugging method on supports with zirconium oxide and/or titanium oxide active layer. Parameters including surface coverage, zeolite layer thickness, crystal size and shape, zeolite penetration depth were used to quantify the membrane morphology. Five supports with different pore sizes for their active layer in the range of 0.14–1.4 μm were investigated. The X-ray diffraction (XRD) analysis showed a typical silicalite-1 zeolite structure with a high internal crystalline order grown inside the pores as well as on top of all supports. The XRD results also showed that the silicalite-1 crystals in the synthesized membranes are not randomly oriented. The crystallographic preferred orientation (CPO) analysis revealed that the degree of orientation toward either the a-axis or b-axis perpendicular to the support surface, increased by decreasing the pore size of the support. The 0.45 μm support had the most preferably oriented zeolite layer for access of molecules entering into the membrane structure with the highest number of crystals oriented with the b-axis (the one with straight channels) perpendicular to the support surface. The scanning electron micrographs (SEM) analysis of the membranes revealed a dense and continuous surface morphology with the highest crystal size of silicalite-1 around 1.5 μm on the surface of the support with the 0.45 μm pore size. SEM micrographs also showed a continuous layer grown over four supports out of five supports with different pore sizes that were investigated, with no layer observed on the 1.4 μm pore size support. The average thickness of the zeolite layer was in the range of 0.7–1.4 μm, depending on the pore size of the support. The supports with 0.2 and 0.45 μm pore sizes had the most uniform zeolite layer thickness while the support with 0.8 μm pore size active layer had the least uniform zeolite layer thickness. The electron diffraction spectrometer (EDS) analysis confirmed the formation of pure silicalite-1 layer at the surface as well as inside the pores of all supports. The highest silicalite-1 crystal penetration was for the supports with 0.45 and 1.4 μm pore sizes. Single gas permeation experiments with He and N2 gases at 293 K illustrated that regardless of the pore size of the support, the He and N2 permeances were constant despite the change of the pressure across the membranes. The highest permeances were observed for the membrane prepared using the 0.45 μm pore size support, while the lowest permeances were for the membrane prepared using the 1.4 μm pore size support. These results confirmed the selective properties of the prepared membranes. No matter what is the pore size of the support or the feed pressure, N2 permeances were around three times higher than those for He.  相似文献   

2.
《分离科学与技术》2012,47(11):2483-2499
Abstract

The selective removal of water from ethanol through pervaporation was demonstrated in a microchannel device using a commercial membrane. Photolithography and dry etching techniques were employed for fabrication of the microseparator with hydraulic diameters of 30 µm to 80 µm. Experiments conducted at 90°C and 2–3 Torr, with Reynolds Numbers ranging from 8 to 91, resulted in an average water and ethanol permeance of 1.2×10?3 and 8×10?5 cm3/cm2 · s · cmHg respectively. A mass transfer analysis involving Sherwood correlations was used to calculate the theoretical boundary layer resistance. The comparison of overall mass transfer coefficient with the boundary layer coefficients suggests that the membrane was the dominant resistance for this system.  相似文献   

3.
《分离科学与技术》2012,47(5):1034-1064
Abstract

This work highlights the recovery of water from sewage effluents using alumina ceramic membranes with pore sizes of 0.2 and 0.45 µm respectively in dead‐end filtration mode. The work demonstrates the ability and advantages of alumina‐based microfiltration (MF) membranes in filtering microbes and other harmful pollutants normally present in sewage effluents in dead‐end filtration mode. The fouling behavior of the membranes in the filtration cycle is identified, which in turn helped to regenerate the fouled membranes for subsequent usage. Regeneration studies of fouled membranes also suggest that though chemical cleaning was effective in recovering membrane performance, the fouling had still been progressed slowly and the membranes showed the ability to perform at least five filtration cycles of highly‐contaminated sewage effluents. As expected, the filtration efficiency and flux characteristics at various transmembrane pressure (TMP) of the membranes varies with the pore size of the membrane and is explained in light of Darcy's and Poiseuille's laws of filtration. The results show that alumina ceramic membrane with disc geometry having a pore size of 0.2 µm is more effective in filtering the total suspended solids, turbidity and microbes of the sewage effluents as compare to that of 0.45 µm membrane to a level in which the permeate water appears to be benign for discharging into the surface thereby offering the possibility of recycling or reusing the recovered water from the sewage effluents for suitable purposes.  相似文献   

4.
《分离科学与技术》2012,47(3):477-491
Abstract

This investigation experimentally studied the penetration curve of particles that impact on a sintered stainless‐steel filter with various pore sizes, sampling flow rates and jet diameters. The penetration curves were compared to those with an aluminum foil substrate. Test data reveal that when the sintered stainless‐steel filter has larger pore sizes (100 µm or 40 µm), the particle penetration, P(%), is lower and the curve is less steep than that obtained from the aluminum foil substrate. The penetration curve of the sintered stainless‐steel filter with smaller pore size (5 µm) is close to that of the aluminum foil substrate. The dimensionless cutsize‐shift (the ratio of the dimensionless cutsize of sintered stainless‐steel filter to that of aluminum foil) falls as the pore sizes and the Reynolds number increase. Experimental data were then compared with theoretical results, and theory over‐predicted the dimensionless cutsize‐shift. Hence, a regression equation for the dimensionless cutsize‐shift is proposed by fitting the experimental data. The discrepancy between the experimental data and the regression prediction is within 4%. The regression equation can be used to predict the dimensionless cutsize for the size‐fractionated measurements of particles that impact on a sintered stainless‐steel filter with various sized pores and Reynolds numbers.  相似文献   

5.
Abstract

The preparation of ground low‐density poly(ethylene) (LDPE), high‐density poly(ethylene) (HDPE), and poly(ethylene terephthalate) (PET) materials suitable for use by inverse gas chromatography (IGC) experiments is described. Materials prepared showed a smaller and more uniform particle size, 83–86 µm (200 mesh), than commercially available Chromosorb® W solid chromatography support. In addition, the BET surface area of polymeric materials, 0.367–0.559 m2/cm3, was much greater than the surface area of 150‐ to 212‐µm‐diameter glass beads. The use of polymeric materials with uniform particle sizes and defined surface areas have several advantages over polymer coated Chromosorb® W and glass beads in IGC experiments.  相似文献   

6.
This study examines the effects of a graphene nanosheet (GNS) conductive additive on the performance of a highly packed (2.5 g cm?3) lithium-ion battery cathode containing 92 wt% Li1.1(Mn0.6Ni0.4)0.9O2 microspheres (approximately 6 μm in diameter). GNSs, approximately 2.0 nm thick and 0.5–1.0 μm in width, are introduced into an electrode slurry in the form of a dispersion in N-Methyl-2-pyrrolidone. They are substantially smaller than the oxide particles; therefore, their presence exerts no adverse influence on the packing density of the electrode. A small quantity of the GNS additive (≤200 ppm relative to the oxide mass) can significantly increase the overall electronic conductance and improve the conductance uniformity of the oxide electrode, leading to reduced polarization and enhanced specific capacity and rate performance. However, the GNS additive also promotes solid-electrolyte interphase formation, resulting in resistance buildup and capacity deterioration upon cycling. This study is the first to identify such an adverse effect caused by a graphene additive. The interplay between the positive and negative effects has led to an optimal GNS additive content of approximately 100 ppm, enhancing both the rate and cycle life performance.  相似文献   

7.
In order to prepare spherical salbutamol sulfate particles of adjustable size, a Nano Spray Dryer B-90 was employed. A 33 full-factorial design was used to investigate the influence of process parameters (mesh size, feed concentration, and drying air temperature) on particle size (median size and width of the particle size distribution), amount of product produced per time, and product yield. The median particle size was significantly influenced by all three factors of the statistical design. Within the design space studied, particle sizes of 1.0 to 6.4 µm were obtained. The width of the particle size distribution (span) increased with increasing mesh sizes. All particles with a particle size greater than 2.4 µm showed a bimodal particle size distribution. Generally, larger mesh sizes as well as higher concentrations led to an increase in the amount of product prepared per time. The corresponding values observed were from 0.4 to 75.8 mg/min. The product yield was independent of the process parameters studied. All products were amorphous after spray drying and were stable up to a relative humidity of 60% at a temperature of 25°C.  相似文献   

8.
《分离科学与技术》2012,47(11-12):2981-3002
Abstract

This study examines the usefulness of the discrete element method (DEM) for studying particle motion in SPLITT fractionation. The method was tested against the conventional SPLITT theory and published experimental data for particle sizes 7, 10, and 15 µm at various run conditions and good agreement was achieved. Illustrative studies presented in this paper show that particle collisions occur at concentrations as low as 0.05%(v/v); and particle trajectory deviates from theory more notably for larger particles, 15 µm diameter and greater. The finding suggests the DEM can be useful in SPLITT calculations for modeling the influence of particle-particle interactions.  相似文献   

9.
ABSTRACT

The study aimed to develop chemically crosslinked poly(2-methoxyethyl methacrylate-co-acrylic acid) (p(MEMA-co-AA)) microhydrogels as carriers for pH-responsive oral targeted delivery of therapeutics. p(MEMA-co-AA) microgels were successfully synthesized by simple free radical suspension polymerization technique confirmed through Fourier transform infrared spectroscopy, thermogravimetic analysis, powdered x-ray diffractrometry, and scanning electron microscopy. Chemically crosslinked spherical microhydrogels with an average size in the range of 4.1 µm ± 2.21 to 9.7 µm ± 3.21 exhibited pH-dependent controlled release of the model drug. Maximum swelling, drug loading, and release were observed at pH 7.4. The optimal formulation achieved good delayed and sustained release features with decreased Cmax, prolonged Tmax, and mean residence time in comparison to oral drug solution.  相似文献   

10.
A supercritical assisted drying (SAD) process was employed to produce insulin submicroparticles from an ethanol/water solution. The effect of the processing conditions on the morphology, size, and thermodynamic activity of the produced particles was investigated. Insulin particles generated from the process were generally spherical with average sizes between 0.4 and 1.1 µm. FTIR, HPLC, the Lowry method, and DTA–TG were implemented to investigate the thermodynamic activity and solvent residue of the produced particles. Results showed that the ethanol content of the aqueous solution had a more sensitive effect on the thermodynamic activity of the insulin particles than other operating factors; a high content of ethanol tended to denature the insulin particles. A rapid expansion of supercritical solutions (RESS)–SAD combined process was proposed to produce insulin–tripalmitin composite particles. Results indicated that irregular composite particles with insulin content of 33.1%, having a bimodal particle size distribution with two peaks at 3.5 and 11.0 µm, were obtained at 50.0°C and 12.0 MPa. These particles revealed no initial burst with a sustained release of insulin of more than 400 min.  相似文献   

11.
The collection efficiencies of commonly used membrane air sampling filters in the ultrafine particle size range were investigated. Mixed cellulose ester (MCE; 0.45, 0.8, 1.2, and 5 μm pore sizes), polycarbonate (0.4, 0.8, 2, and 5 μm pore sizes), polytetrafluoroethylene (PTFE; 0.45, 1, 2, and 5 μm pore sizes), polyvinyl chloride (PVC; 0.8 and 5 μm pore sizes), and silver membrane (0.45, 0.8, 1.2, and 5 μm pore sizes) filters were exposed to polydisperse sodium chloride (NaCl) particles in the size range of 10–400 nm. Test aerosols were nebulized and introduced into a calm air chamber through a diffusion dryer and aerosol neutralizer. The testing filters (37 mm diameter) were mounted in a conductive polypropylene filter-holder (cassette) within a metal testing tube. The experiments were conducted at flow rates between 1.7 and 11.2 l min?1. The particle size distributions of NaCl challenge aerosol were measured upstream and downstream of the test filters by a scanning mobility particle sizer (SMPS). Three different filters of each type with at least three repetitions for each pore size were tested. In general, the collection efficiency varied with airflow, pore size, and sampling duration. In addition, both collection efficiency and pressure drop increased with decreased pore size and increased sampling flow rate, but they differed among filter types and manufacturer. The present study confirmed that the MCE, PTFE, and PVC filters have a relatively high collection efficiency for challenge particles much smaller than their nominal pore size and are considerably more efficient than polycarbonate and silver membrane filters, especially at larger nominal pore sizes.  相似文献   

12.
Waste tire dust (WTD) of mechanically reclaimed scrap tires was blended with polypropylene (PP) in five different compositions to prepare PP/WTD blends. Three series of blends with three different sizes of WTD (250–500 µm, 500–710 µm, and 710 µm–1 mm) were prepared in a Haake Rheomix Polydrive R 600/610 at a temperature of 180°C and a rotor speed of 50 rpm for 9 min. The results show that at the same blending composition, the PP/WTD blends with fine WTD size require higher equilibrium torque and exhibit higher values of tensile strength, Young's modulus, and elongation at break (Eb) than that of blends with coarser WTD size. The swelling index of the PP/WTD blends reveals that the blends with fine WTD size have better swelling resistance in both oil and toluene than all blends with coarser WTD. Scanning electron microscope (SEM) observation indicates that the PP/WTD blends with the finest WTD size exhibit better PP/WTD adhesion than blends with coarse WTD sizes.  相似文献   

13.
《分离科学与技术》2012,47(15):3506-3537
Abstract

The performance of ceramic membranes with pore sizes of 0.05 and 0.10 µm in purifying limed and partially clarified sugar cane juice was investigated under different operating conditions. From various operating conditions and strategies, switching off the permeate for 5 seconds for every 5 minutes (S5sT5 m) by an automated control valve provided higher flux. From the three pH experiments conducted on the 0.05 µm membrane, the best performance was observed at a pH of 7.5. Amongst the four fouling models tested, the cake filtration model fitted the performance of both membranes with higher accuracy at a transmembrane pressure of 0.5 bar. Filtering the cane juice through the membrane reduced the turbidity by 99.7%, color by 15%, and the starch concentration by 80% as well as increased the purity by 1.4%. The effective cleaning chemical composition from experimental results showed that 1% NaOH and 3000 ppm NaOCl solution performed the best but only for the experiments that were treating limed and partially clarified juice at pH 7.5.  相似文献   

14.
A non-surfactant-based synthesis approach to mesoporous hollow spheres through the use of colloidal silica is presented. Based on nanoparticle assembly chemistry developed previously for silica/polymer hybrid microcapsules, the room-temperature preparation follows a two-step sequence: (1) the electrostatic reaction of cationic polymer with an anionic salt solution, resulting in a suspension of salt-bridged polymer aggregates; and (2) the electrostatic reaction between this suspension and an aqueous suspension of nanoparticles (NPs). As a specific example, 13-nm silica particles, combined with polyallylamine and sodium citrate, gave silica/polymer hollow spheres with a mean diameter of 2.1 μm and a BET surface area of 4 m2/g. After calcination at 600 °C, the resulting silica-only microcapsules had a BET surface area of 259 m2/g, a modal pore size of 4.0 nm, and a pore volume of 0.38 cc/g, values that exceeded those of calcined silica NPs. This colloidal silica-based material is an example of the simultaneous control of pore size (at the nanometer scale) and particle morphology (at the micrometer scale) that is possible through charge-driven NP assembly.  相似文献   

15.
A facile and highly efficient route to produce simultaneously porous and reduced graphene oxide by gamma ray irradiation in hydrogen is here demonstrated. Narrowly distributed nano-scale pores (average size of ∼3 nm and surface density >44,900 pore μm−2) were generated across 10 μm thick graphene oxide bucky-papers at a total irradiation dose of 500 kGy. The graphene oxide sheet reduction was confirmed to occur homogeneously across the structures by Fourier transform infrared spectroscopy and Raman analysis. This one-step, catalyst-free, high penetration and through-put technique, offers great promises potential for the mass production of reduced graphene oxide from cheap graphene oxide.  相似文献   

16.
ABSTRACT

Three different SiC powders with average particle sizes of 0.45, 3.5 and 10?µm were used to prepare ZrC-20vol.-% SiC ceramics by hot pressing. The effects of SiC particle size on the densification, microstructure, mechanical properties and thermal properties of ZrC–SiC ceramics were studied. Ceramics prepared from SiC with finer particle sizes exert higher bending strength, hardness and lower thermal conductivity. The ZrC–SiC ceramics with a starting SiC particle size of 3.5?µm has relative high fracture toughness than others. Analysis indicates that SiC grain size and the grain boundaries control the thermal conductivity ZrC–SiC ceramics. Ceramics prepared from SiC with the particle size of 10?µm exhibits the highest thermal conductivity due to the larger grains and less grain boundaries.  相似文献   

17.
A novel forming method for preparing porous alumina ceramics using alumina fibers as raw materials by direct coagulation casting (DCC) combined with 3D printing was proposed. Porous fibrous alumina ceramics were fabricated through temperature induced coagulation of aqueous-based DCC process using sodium tripolyphosphate (STPP) as dispersant and adding K2SO4 as removable sintering additives. The sacrificial coated sand molds was fabricated by 3D printing technology, followed by the infiltration of silica sol solution for the subsequent suspension casting. Stable alumina suspension of 40 vol% solid loading was obtained by adding 2.0 wt% STPP and 40 wt% K2SO4. The controlled coagulation of the suspension could be realized after heating at 90 °C for about 35 min. The ceramic sample sintered at 1450 °C for 2 h showed the highest compressive strength of 24.33 MPa with porosity of 57.38%. All samples sintered at 1300–1450 °C had uniform pore size distributions with average pore size of 7.2 µm, which indicated the good structure stability when sintered at high temperature.  相似文献   

18.
ABSTRACT

The purpose of this study is to investigate the physical characteristics of pantoprazole-loaded enteric microparticles produced in different spray dryers and operational conditions. In all conditions tested it was possible to obtain powders that presented spherical shape microparticles, with mean sizes from 6.7 to 24.5 µm. The size was affected mainly by initial feed concentration (2.2 or 6.6% w/w). The integrity of microparticles affected surface area (24 to 113 m2/g)and drug release (71 to 98%). All powders presented very poor flow. The powder that presented higher release was produced with 6.6% solution and a rotating disc atomizer.  相似文献   

19.
Mo–MoSi2 functionally graded materials were prepared by a liquid phase siliconizing method. The microstructure, phase constitution, cross-section elemental distribution, grains size, and coating thickness of these materials were investigated with scanning electron microscopy (SEM), back scattered electron (BSE), energy dispersive spectroscope (EDS), glow discharge spectrum (GDS) and X–ray diffraction (XRD). The results indicate that the Mo–MoSi2 functionally graded materials have a dense multi-layer structure, mainly composed of surface layer (Si–MoSi2 layer, 1–10?µm), intermediate layer (MoSi2 layer, 22–40?µm), transitional layer (Mo5Si3 and Mo3Si layer, 2–3?µm) and Mo substrate. Moreover, the silicon concentration, grains size, and coating thickness increase gradually with the increasing temperature. The surfaces silicon concentrations are about 68–75?wt%, the average grains sizes of MoSi2 columnar crystals are about 7.1–9.4?µm, and the coating thicknesses are about 28–35?µm.  相似文献   

20.
Pyrrole monomer was polymerized by a chemical oxidative route in the presence of graphene oxide (GO), reduced GO (rGO), and graphene nanoribbons (GNR) separately to prepare composites of polypyrrole (PPy) as PPy–GO, PPy–rGO, and PPy–GNR, respectively. The morphological, chemical, and structural characterization of the as‐synthesized products was carried out using scanning electron microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy. Field emission studies of the PPy–GO, PPy–rGO, and PPy–GNR emitters were performed at the base pressure of 1 × 10?8 mbar in a planar “diode” configuration. The turn‐on field values, corresponding to an emission current density of 1 µA/cm2, are observed to be 1.5, 2.2, and 0.9 V/µm for the PPy–GO, PPy–rGO, and PPy–GNR emitters, respectively. The maximum emission current density of 2.5 mA/cm2 is drawn from PPy–GO at an applied electric field of 3.2 V/µm, 1.2 mA/cm2 at 3.6 V/µm from the PPy–rGO, and 8 mA/cm2 at 2.2 V/µm from the PPy–GNR emitters. All of the composites exhibit good emission stability over more than 2 h. The results indicate the potential for a facile route for synthesizing composites of conducting polymers and graphene‐based materials, with enhanced functionality. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45170.  相似文献   

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