Pore-volume Distribution

Fig. XVI-2. Comparison of the pore volume distribution curves obtained from porosimeter data assuming contact angles of 140° and 130° with the distribution curve obtained by the isotherm method for a charcoal. (From Ref. 38.)...

The result of this equation describes the quality of the separation on the basis of an ideal size exclusion mechanism with a given pore volume distribution. The quality of the packing is deliberately excluded from this consideration. This parameter should be measured separately and judged by the plate number. The ASTM standard method for HPSEC of polystyrene (4) contains the following equation for resolution (R,) ... 

Figure 10. Pore volume distribution of the support as assessed with ISEC (a) and the metal nanoclusters size distribution as assessed with TEM (b) for a Pd /CFP catalyst. (Reprinted from Ref. [68], 2004 with permission from Wiley.)...

Fig. 3.23 shows pore volume distributions of some commercially important porous materials. Note that zeolites and activated carbon consist predominantly of micropores, whereas alumina and silica have pores mainly in the me.sopore range. Zeolites and active carbons have a sharp peak in pore size distribution, but in the case of the activated carbon also larger pores are present. The wide-pore silica is prepared specially to facilitate internal mass-transfer. 

Figure 3.23. Pore volume distributions (Nt physi.sorption) of a. wide-pore silica, b. y-alumina, c. a-alumina, d. activated carbon, e. Raney Nickel and f. ZSM-5.

Pore. size and surface area distribution. Pore sizes and pore volume distributions may be calculated from the relative pressures at which pores are filled (in the adsorption mode) or emptied (in the desorption mode). Fig. 3.45 shows the pore size distribution of a commercial y-alumina. The distribution is very broad both meso- and macropores are present. In practice this is usually a desired situation a texture consisting of a network of large pores (main roads) and small pores (side roads) is ideal. 

Precursor Sbet m2/g Vtotal cm3/g Pore volume distribution, % V<2nm V2-3mn V 3-5mn V 5.50 nin Average pore size run... 

The first task was to produce carriers from different recipes and in different shapes as shown schematically in Fig. 8. The raw materials diatomaceous earth, water and various binders are mixed to a paste, which is subsequently extruded through a shaped nozzle and cut off to wet pellets. The wet pellets are finally dried and heated in a furnace in an oxidising atmosphere (calcination). The nozzle geometry determines the cross section of the pellet (cf. Fig. 3) and the pellet length is controlled by adjusting the cut-off device. Important parameters in the extrusion process are the dry matter content and the viscosity of the paste. The pore volume distribution of the carriers is measured by Hg porosimetry, in which the penetration of Hg into the pores of the carrier is measured as a function of applied pressure, and the surface area is measured by the BET method, which is based on adsorption of nitrogen on the carrier surface [1]. 

Figure 17.2. Typical pore volume distributions for three activated carbons used for liquid-phase processes(7)...

Another possible solution to the problem of analyzing multiple-layered membrane composites is a newly developed method using NMR spin-lattice relaxation measurements (Glaves 1989). In this method, which allows a wide range of pore sizes to be studied (from less than 1 nm to greater than 10 microns), the moisture content of the composite membrane is controlled so that the fine pores in the membrane film of a two-layered composite are saturated with water, but only a small quantity of adsorbed water is present in the large pores of the support. It has been found that the spin-lattice relaxation decay time of a fluid (such as water) in a pore is shorter than that for the same fluid in the bulk. From the relaxation data the pore volume distribution can be calculated. Thus, the NMR spin-lattice relaxation data of a properly prepared membrane composite sample can be used to derive the pore size distribution that conventional pore structure analysis techniques... 

We varied the gel-forming parameters, the content of Kaolin clay, the crystal size, and the thickness-to-diameter ratio in a series of experiments. A dual structure began to appear at about 35-40% Kaolin. If the clay content was increased to too high a level, the microspheres became too weak and began to have poor attrition resistance. The cost of the various grades also affected our choice. Figure 9 shows a comparison of pore volume distribution for a typical synthetic versus a clay modified catalyst. 

Kaolin had little or no cracking activity, and catalyst activity as tested in the laboratory was directly related to silica-alumina gel content. However, the catalyst performed much better in commercial tests than anticipated from laboratory testing. Undoubtedly, this open structure encountered much less severe conditions at the outer surface of the microsphere during regenerations and made internal catalytic surfaces more readily available. This first of the so-called "semisynthetics" was called Nalco 783, and the matrix is still used in many forms some 28 years later.(7,13) Today it is estimated that some 200,000 tons/yr. of kaolin clay is used for cracking catalyst manufacture as reported by Georgia Kaolin Corporation.(24) Figure 10 shows the pore volume distribution for Nalco 783 and two other commercial semisynthetics from that period. 

Santora BP, Gagne MR, Moloy KG, Radu NS. Porogen and cross-linking effects on the surface area, pore volume distribution, and morphology of macroporous polymers obtained by bulk polymerization. Macromolecules 2001 34 658-661. 

Fig. 5.23 Pore volume distribution of cement pastes from nitrogen adsorption. Curve 1 = cement with no admixture curve 2 = cement paste and 2% CaCl2 (Gouda).

Brunauer et alP have developed a means of determining the pore volume distribution wherein the pore shape has a negligible influence. 

Figure 11.11 (a) Pore volume distribution versus pressure plot, (b) Pore volume... 

Fleisch et al. (1984) measured the catalyst surface area and pore volume changes that occurred after severe deactivation of a 100- to 150-A pore catalyst. The results of these measurements are shown in Table XXVIII for various positions in the reactor bed. Catalyst surface area and pore volume are substantially reduced in the top of the bed due to the concentrated buildup of metals in this region. The pore volume distribution of Fig. 44 reveals the selective loss of the larger pores and an actual increase in smaller (<50-A) pores due to the buildup of deposits and constriction of the larger pores. Fleisch et al. (1984) also observed an increase in the hysteresis loop of the nitrogen adsorption-desorption isotherms between fresh and spent catalysts, which reflects the constrictions caused by pore... 

Fig. 44. Pore volume distribution of fresh and spent catalyst after processing residuum (Fleisch et al., 1984).

By determining the apparent density of coal in fluids of different but known dimensions, it is possible to calculate the pore size (pore volume) distribution. The open pore volume (V), the pore volume accessible to a particular fluid, can be calculated from the relationship... 

Graph 7 Accumulated pore volume distribution of concrete... 

Figure 2.2 Illustration of pore volume distribution curves for charcoal as obtained from a nitrogen adsorption isotherm (solid curve) and from a mercury porosimeter (broken curve). From data in Adamson [15].

Catalyst Characterization. Carbon contents were determined by the Carlo Erba method and sulfur content by high temperature combustion In O2 (ASTM-D1552-64). Surface area and pore volume distribution were measured via N2 adsorption desorption Isotherms (4). ESR measurements were carried out with a modified Varian Radical Assay Spectrometer at both 77 K and room temperature (3). 

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