Adsorption pore volume distribution

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. 

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]. 

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).

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... 

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). 

Pore radii and pore volume distributions can be calculated on the basis of the classical Kelvin equation which can be adapted to various pore shapes. For t materials the corrected Kelvin equation according to Broekhoff and de Boer leads to better quantitative results. The Broekhoff-de Boer theory also explains why stable adsorption on the inner walls of pores is possible up to a certain critical thickness of the adsorbed layer, without giving rise to immediate capillary condensation of the gas. 

Using equations 2 to 9 and the excess adsorption data we have determined the unknown parameters of our model that is to say a ii and bmoi for each compounds and the parameters of the pore volume distribution frmction Vipons, Zpores, mw, nt2H, (Zih and 05//. This optimisation procedure is done using the whole set of data V/ppres, V2pores, mm, m2H, ctjh and 05// are characteristics of the adsorbent and should not be determined separately for each adsorbate. Tables I to III show these values of the parameters and the average deviation between the recalculated excess results and the experimental excess data for each adsorbate. 

Newcombe et al. 536] also concluded that the adsorption of four NOM ultrafiltration fractions on to activated carbon was consistent with the pore volume distributions of the carbons and the hydrodynamic diameters of the fractions. ... 

X-ray powder diffraction patterns were obtained on oriented film specimens [7] (2 to 45° 2 , Philips PW 1120, monochromatized CuKa radiation, continuous peak registration). BET surface area and the pore volume distribution were determined from Nj adsorption-desorption isotherms at 77 K (degassing at 393 K, lO" mbar, 5h Sorptomatic 1900, Carlo Erba Instruments). The IR-spectra were recorded on KBr wafers [4] with a Specord 80M spectrometer. The XPS (X-ray photoelectron spectroscopy) spectra were obtained with VG ESCALAB 200 MKII spectrometer equipped with a twin anode AIKa source (1486 eV). The thermogravimetric (TGA) analyses were carried out with a Setaram TG 85 thermobalance at a heating rate of 6 K min in a helium flow of 30 ml min . The chromium content of the samples was determined by EPMA (JEOL 840 scanning electron microscope) with energy dispersive spectrometer (EDS, Tracer Northern) and by AAS (atomic absorption spectroscopy, Perkin Elmer 3030) analyses. 

Therefore, these results indicate that Cr-K10 has, at least in part, a pillared structure. The results for Cr-PB indicate (Fig. 1 and Table 1) that this material has a micro-porous structure with some contribution of mesopores (shape of Nj adsorption-desorption isotherm) and a narrow pore volume distribution with a maximum at a pore radius of 2.1 nm. All Cr-PILC studied exhibit hysteresis loop of type H4 [11] which can be attributed to solids with a slit-shaped porous structure. Heat treatment results only in a small decrease of the BET surface area for both Cr-KIO and Cr-PB (Table 1). Sulfidation does not influence significantly the porous texture of both Cr-PILC as well [12]. 

Nitrogen adsorption experiments were performed using a Micromeritics ASAP 2000 sorption apparatus. Surface areas and pore volume distributions were ealculated using the BET [21] and the BJH [22] methods, respectively. Prior to analysis, the samples were outgassed at 400 °C for 12 hours. Results of the niU"ogen adsorption study show that dealumination by both hydrothermal and AHFS treatment results in materials which differ in textural properties when compared with each other and with the parent material. Figure 1 shows the nitrogen... 

Specific surface area and pore volume distribution were measured by nitrogen adsorption in an Accusorb 2100E Micromeritics adsorption analyzer. The data were interpreted using the BET equation, assuming a cross-sectional area of 16.2 for Nj. 

Bjelopavic, M., Newcombe, G., and Hayes, R. (1999). Adsorption of NOM onto activated carbon effect of surface charge, ionic strength, and pore volume distribution. J. Colloid Interface Sci., 210, 271—80. 

Newcombe, G., Drikas, M., and Hayes, R. (1997). Influence of characterized natural organic material on activated carbon adsorption II. Effect on pore volume distribution and adsorption of 2-methyhsobomeol. Water Res., 31, 1065—73. 

The BET surface area and pore volume distribution were measurement by nitrogen adsorption in an Accusorb 2100E Micromeritics analyzer. 

The integral Eq. (73) is analogous to Eq. (60). Both integral equations represent the overall adsorption isotherm, which is measured experimentally. According to Eq. (73) the overall isotherm is expressed in terms of the pore volume distribution and the kernel function depending on the pore widlh. 

Since the relationships between A and x are known for difierent pore ranges and different pore geometries [13, 143, 153-157], they can be utilized to convert the adsorption potential distribution to the pore volume distribution via the following equation ... 

The HK micropore volume distribution for a slit-like microporous structure can be obtained by multiplying the adsorption potential distribution [see Eq. (24) and Fig. 10] by Eq. (77). For cylindrical and spherical micropore geometries another expressions for the derivative dAldx should be used [160]. An illustration of the HK pore volume distributions is shown in Fig. 12 for the WV-A900, BAX 1500 and NP5 active carbons. Similarly, the mesopore volume distribution can be calculated from the multilayer and capillary condensation range of the adsorption isotherm. In this case, the corrected Kelvin equation should be used to calculate the derivative dAldx. 

While the adsorption potential distribution is a model-independent thermod3noamic function, the pore volume distributions are obtained by assuming the relationship between the adsorption potential and the pore width. Thus, the adsorption potential distribution can be considered an imique and primary characteristics of a given adsorption system, whereas the... 

Another important conclusion concerns the geometrical heterogeneity of nanoporous carbons, which is characterized by the micropore and mesopore volume distributions. The current work demonstrates that in terms of the condensation approximation both these dishibutions are directly related to the adsorption potential distribution. As shown the pore volume distribution can be obtained by multiplication of the adsorption potential distribution... 

A brief review of methods based on the integral adsorption Eq, (73) showed that they are attractive to evaluate the pore volume distribution. The analytical solution of this integral for sub-integral functions represented by the Dubinin-Astakhov equation and gamma-type... 

It is evident that the most valuable information eoneeming the adsorption capacity of a given aetivated earbon is its adsorption isotherm for the solvent being adsorbed and its pore volume distribution eurve. Figure 22.1.10 presents idealized toluene adsorption isotherms for three earbon types ... 

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