Average pore diameter

Assuming that the external surface of a porous substrate is negligible, and that the pores are cylindrically shaped, the average pore diameter of a substrate can be calculated by the Wheeler formula 21 

Pore diameter and pore radius are expressed in nm. Vp is the volume (ml/g) of liquid adsorbate, and can be calculated from the volume of adsorbed gas (VJ by means of the Gurvitsch rule22 

The average pore radii of Kieselgel 40, 60 and 100, degassed for 17 h at room temperature were 2.14, 3.59 and 6.22 nm respectively. 

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Fig. XVII-27. Nitrogen adsorption at 77 K for a series of M41S materials. Average pore diameters squares, 25 A triangles, 40 A circles, 45 A. Adsorption solid symbols desorption open symbols. The isotherms are normalized to the volume adsorbed at Pj = 0.9. (From Ref. 187. Reprinted with kind permission from Elsevier Science-NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands.)...

Fig. 3. Microporous membranes are characterized by tortuosity, T, porosity, S, and their average pore diameter, d. (a) Cross-sections of porous membranes containing cylindrical pores, (b) Surface views of porous membranes of equal S, but differing pore size.

Fig. 25. Reverse osmosis, ultrafiltration, microfiltration, and conventional filtration are related processes differing principally in the average pore diameter of the membrane filter. Reverse osmosis membranes are so dense that discrete pores do not exist transport occurs via statistically distributed free volume areas. The relative size of different solutes removed by each class of membrane is illustrated in this schematic.

Characterization. When siHca gel is used as an adsorbent, the pore stmcture determines the gel adsorption capacity. Pores are characterized by specific surface area, specific pore volume (total volume of pores per gram of solid), average pore diameter, pore size distribution, and the degree to which entrance to larger pores is restricted by smaller pores. These parameters are derived from measuring vapor adsorption isotherms, mercury intmsion, low angle x-ray scattering, electron microscopy, gas permeabiHty, ion or molecule exclusion, or the volume of imbibed Hquid (1). 

Material and uses Shape"of particles Size range, U.S. standard mesh f Internal porosity, % Bulk dry density, kg/L Average pore diameter, nm Surface area, kmVkg Sorptive capacity, kg/kg (dry)... 

Metal Oxide - Since metals are less electrophilic than silicon, metal oxide adsorbents show even stronger selectivity for polar molecules than do siliceous materials. The most commonly used metal oxide adsorbent is activated alumina, used primarily for gas drying. Occasionally, metal oxides find applications in specific chemisorption systems. For example, several processes are under development utilizing lime or limestone for removal of sulfur oxides from flue gases. Activated aluminas have surface areas in the range of 200 to 1,000 ftVft Average pore diameters range from about 30 to 80 A. 

Figure 20 A typical scanning electron micrograph of the macroporous uniform poly(styrene-divinylbenzene) late> particles. Magnification 1200 x, (particle size = 16.0/rm average pore diameter = 200 nm).

A research group in Lehigh University has extensively studied the synthesis and characterization of uniform macroporous styrene-divinylbenzene copolymer particles [125,126]. In their studies, uniform porous polymer particles were prepared via seeded emulsion polymerization in which linear polymer (polystyrene seed) or a mixture of linear polymer and solvent were used as inert diluents [125]. The average pore diameter was on the order of 1000 A with pore volumes up to... 

The average pore diameter (APD) of a catalyst can be calculated from the E-cat analysis sheet by using the following equation ... 

In 1971, Hiatt et al. found that polyethylene oxide (PEO) of molecular weight about 100000 prevented the adsorption of rabies virus to porous glass with an average pore diameter of 1250 A. The support was modified by passage of one void volume of 0.4% solution of the polymer in water, followed by 5 or more volumes of distilled water or buffered salt solution. The virus was effectively purified from the admixtures of brain tissue fluid by means of size-exclusion chromatography on the modified glass column [28]. 

The heat transfer and pressure drop in a rectangular channel with sintered porous inserts, made of stainless steels of different porosity, were investigated. The experimental set-up is shown in Fig. 2.9. Heat fluxes up to 6MW/m were removed by using samples with a porosity of 32% and an average pore diameter of 20 pm. Under these experimental conditions, the temperature difference between the wall and the bulk water did not exceed AT = 55 K at a pressure drop of AP = 4.5 bars (Hetsroni et al. 2006a). 

BET surface area, pore volume and average pore diameter calculated from N2 adsorption-... 

Sample BET sur ce area(m2g-l) Pore volume Micropore volume (cm3g-l) (cm3g-l) Average pore diameter (nm) Pellet density (gcm-3)... 

KoTHmex activated carbon fiber fabrics AW-1101 (BET specific surface area of 880m /g, average pore diameter of 2nm) was provided by Taiwan Carbon Technology Co. Ltd. The support is pretreated in a boiling aqueous solution of 6.5wt.% HNO3 for 1 h. Then the support is rinsed with distilled water, air-dried for 12h at room temperature and for 5h at 393 K. BET specific surface area of the ACF is 950m /g. 

Type Composition Character Average Pore Diameter (nm) Specific Specific Solvent Surface Pore Uptake Area Volurc. (g/g) of ( /g) (Ml/g) resin ... 

In order to increase the flow rate without too much pressure, Experiment 4 was performed with a Fann filter press which has a wider cross sectional area. A constant air pressure of 100 psi was applied, the flow rate was 26 times that of Experiment 1 while the NaCl concentration was only slightly higher than that of Experiment 1. Although the flow rate was much increased in Experiment 4, the result was similar to Experiment 1. The water retained in the clay (Column 8) determined by drying was found to be close to the amount of anion-free water. The porosity of the sediment was 0.4 and the average pore diameter was 4466 X. It was concluded from this experiment, that the anion-free water was immobile even at 100 psi and 7.4 ft/day. The pore size distributionQof the sample showed 90% of the pores to have a diameter above 350 A and less than 3% of the pores to have a diameter below 100 X (Figure 4). 

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