Total Pore Surface Research Articles

The influence of pyrolysis conditions on the reactivity of CHAR in H 2O

A German gas flame coal was used in a study of the effects of pyrolysis conditions on the reactivity of the subsequent chars (0.1 – 0.3 mm particle size) in steam. Most of the chars were prepared in inert gas atmospheres i.e. helium or argon under a variety of conditions of heating rate (3 K/min to 4000 K/s), temperature (500 to 900 °C), soak time (0.2 s to 4 h), and pressure (1 – 66 bar). Reactive gas atmospheres, steam and hydrogen were used as pyrolysis gases only for selected experiments. Proximate and ultimate analysis of the chars, total pore volumes and surface areas and the concentration of active sites of selected samples were determined. Pyrolysis conditions applied were found to have a marked influence on the char reactivity, thus a correlation between the treatment conditions and rates of reaction was sought.

Chromatographic Characteristics of polymer-based high-performance liquid chromatography packings

Rigid macroporous polystyrene-based and polyacrylamide-based packings have been developed for reversed-phase high-performance liquid chromatography. Data on pore size distribution, total pore volume and surface area have been obtained for comparison with silica-based packings. Columns containing these polymer-based packings have good permeability with maximum working pressures of 5000 p.s.i. and 3500 p.s.i. for polystyrene-based packing differs from that for the polyacrylamide-based packing. The dependence of column efficiency on teh flow velocity of the mobile phase as a function of solute type and temperature has been studied. Plate height is reduced as a function of solute type and temperature has been studied. Plate height is reduced considerably at higher temperature. This is tentatively interpreted in terms of a reduction in solute dispersion due to improved mass transfer in the stationary phase.

Some physical properties of Canadian coals and their effects on coal reactivity

The pore volume, surface area and compressibility of eleven Canadian coals, varying in rank from lignite to semianthracite, have been determined by mercury porosimetry, gas adsorption method and relations derived from helium and mercury densities. The total pore volume was measured in the diameter range of 0.2 nm–2.98 μm, which was subdivided into two groups, namely the micropore region (< 0.0036 μm) and the combined meso- and macropore region (0.0036–2.98 μm). It has been determined that the porosity of the eleven coals studied varies from 2 to 39%. It has been found that the total pore volume, micropore volume, surface area and the apparent compressibility of these coals decrease with increase in the carbon content, or the rank of the coals. The effect of the total pore volume, micropore volume and surface area on chemical reactivity of the coal is discussed separately. A good correlation was obtained between the carbon content and helium density of the coal after correction is made for the mineral content.

A model to study the dynamics of glomerular ultrafiltration and glomerular capillary permselectivity characteristics

A model, based on recent developments of the pore theory of transport across membranes, is developed to describe solute and fluid transport across the glomerular capillary wall. The model allows the prediction of the glomerular capillary permselectivity parameters r o (pore radius), A p l (total capillary pore surface area/capillary thickness), and K f (the hydraulic permeability), as well as the average transmembrane hydrostatic pressure drop ( ΔP ) and the efferent arteriolar colloid osmotic pressure ( π E). The input data required are the glomerular filtration rate, initial glomerular plasma flow, systemic protein concentration, and sieving ratios for a few test solutes of known hydrodynamic radius. The model is then applied to results obtained previously on four groups of Wistar rats with accessible surface glomeruli where direct measurement of ΔP and π E and independent estimates of K f were made by micropuncture techniques. The model predictions are shown to correspond quite closely to direct measurements and previous findings on these rats and would be a useful tool in analyzing the dynamics of glomerular ultrafiltration as well as glomerular permselectivity where direct measurements are difficult or impossible.

Permselectivity of of the glomerular capillary wall. Studies of experimental glomerulonephritis in the rat using neutral dextran.

Polydisperse [3h] dextran was infused into eight Munich-Wistar rats in the early autologous phase of nephrotoxic serum nephritis (NSN), thereby permitting direct measurements of pressures and flows in surface glomeruli and fractional clearances for dextrans [(U/P) dextran/(U/P) inulin] ranging in radius from 18 to 42 A. Despite glomerular injury, evidenced morphologically and by a marked reduction in the glomerular capillary ultrafiltration coefficient, the glomerular filtration rate remained normal because of a compensating increase in the mean net ultrafiltration pressure. In NSN rats, as in normal controls, inulin was found to permeate the glomerular capillary wall without measurable restriction, and dextrans were shown to be neither secreted nor reabsorbed. For dextran radii of 18, 22, 26, 30, 34, 38, and 42 A, (U/P) dextran/(U/P) inulin in NSN and control rats, respectively, averaged 0.90 vs. 0.99, 0.81 vs. 0.97, 0.63 vs. 0.83, 0.38 vs 0.55, 0.20 vs. 0.30, 0.08 vs. 0.11, and 0.02 vs. 0.03. Using a theory based on macromolecular transport through pores, the results indicate that in NSN rats, effective pore radius is the same as in controls, approximately 50 A. In NSN, however, the ratio of total pore surface area to pore length, a measure of the number of pores, is reduced to approximately 1/3 that of control, probably due to a reduction in capillary surface area. These results suggest that proteinuria in glomerular disease is not due simply to increases in effective pore radius or number of pores, as previously believed. Using a second theoretical approach, based on the Kedem-Katchalsky flux equations, dextran permeability across glomerular capillaries was found to be slightly lower, and reflection coefficient slightly higher in NSN than in control rats.

Pore Structure of Solids

Abstract A small grain of iron catalyst, used in the synthesis of ammonia, has an external surface of about 1 cm2/g, but it has an internal surface of 100,000 cm2/g. Since catalysis takes place on the surface, obviously the surface in the pores is of vital importance. But not all pores are of equal importance; in very narrow pores the diffusion is slow; in large pores the surface is small. The sizes of pores have just as important roles in adsorbents, like silica gel and active carbon, and in other solids, like concrete. The determination of the distribution of the total pore surface and the total pore volume in pores of different widths is called pore structure analysis. The first methods for pore structure analysis were proposed in 1945; Ritter and Drake used the mercury porosimeter, and Wheeler used nitrogen adsorption isotherms. Subsequently others improved Wheeler's method. Recently we proposed two new approaches for pore structure analysis, both based on adsorption isotherms: one for the analysis of very narrow pores, the micropores, and one for the analysis of the wider pores. The first is the only method proposed for micropore analysis, the second is an improvement on the previous methods for the analysis of wider pores.

Adsorption of gas on ion exchangers. III. The pore structure of m‐aminophenol–formaldehyde condensation resins

Abstractm‐Aminophenol was condensed with formaldehyde in an acid medium in the presence of a water‐soluble inorganic salt (NaCl, CaCl2 etc) and/or poly(ethylene glycol). The pore structure characteristics of the condensation products were investigated by measurements of average pore size, pore size distribution of channels, total pore volume, surface area, and electron microscopic observation. The type and concentration of inorganic salts appeared to be a significant variable for the resulting pore structure, while poly(ethylene glycol) had a little effect. The nongel interstices of products were channels between many agglomerates of minute spherical gel particles with narrow pore size distribution. The diameters of these spherical gel particles were 3–10 × 10−1µ from the scanning electron microscopic observation. Apparent dissociation constants of functional groups of resin, pKa and pKb, estimated by using the Henderson‐Hasselbach equation, were 10.94 and 10.99, respectively. The resin had an ion‐exchange capacity of 1.0 meq/g for base and 4.8 meq/g for acid.

Gaseous reduction of iron oxides: Part III. Reduction-oxidation of porous and dense iron oxides and iron

The internal reduction of high-grade granular hematite ore in hydrogen and carbon monoxide, and also the internal oxidation of porous iron granules in CO2-CO mixtures have been investigated. To assist the interpretation of the rate data for porous iron and iron oxides, rate measurements have been made also with dense wustite, previously grown on iron by oxidation. The iron formed by reduction of dense wustite is porous, similar to that observed when porous hematite is reduced. It is found that the rate of dissociation or formation of water vapor or carbon dioxide on the iron surface is about an order of magnitude greater than that on the surface of wustite. The results of the previous investigations using dense iron and wustite are in general accord with the present findings. The rate of reduction of hematite increases with increasing pore surface area of the reduced oxide. The results indicate that the rate of reduction of granules is controlled primarily by the formation of H2O or CO2 on the pore walls of wustite. The specific rate constants evaluated from internal reduction, using the total pore surface area, are about 1/50 to 1/100 of those for dense wustite. These findings indicate that with porous wustite or iron, the effective pore surface area utilized is about 1 to 2 pct of the total pore surface area. The rate of reduction in H2-CO mixtures is in accord with that derived from the rate constants for reduction in H2 and CO.

Surface area and volume of pores as characteristics of silica supports for gel permeation chromatography

A comparison of porous silica gels of different origin was made. It was shown that there is no simple correlation between the mercury porosimetry curve and the corresponding chromatographic data. The pore surface area was found to be an important parameter reflecting both the size and the shape of the pores. A linear dependence was established between log M infl and log V/ SA, where M infl is the molecular weight at the inflection point of the chromatographic calibration curve, V is the total pore volume and SA the total pore surface area.