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Adsorbents fractional pore volumes

Zeolite A. The structure of zeolite A contains two types of voids (1) the a cage, 11.4 A in diameter, and (2) the P cage (or sodalite unit), 6.6 A in diameter (7). Table I compares experimentally determined pore volumes of zeolite A with the void volume as calculated from the structure (no influence of cations considered). Since the sodium zeolite A does not adsorb normal paraffins, data are included for the calcium-exchanged form. Also shown in column 5 is the void fraction, Vi, as calculated by... [Pg.320]

Prior to each TPD-TGA experiment, the samples were exposed to between 10 and 15 Torr of 2-propanol or 2-propanamine for approximately 5 min at 295K. This exposure was sufficient to fill a substantial fraction of the zeolite pore volume of each sample. Desorption measurements were performed following evacuation of the samples for 1 to 20 hrs to remove some of the weakly adsorbed species. While the evacuation time did affect the amount of weakly adsorbed species observed in TPD at lower temperatures, it had no affect on the well-defined, stoichiometric complexes observed in this study. Following an adsorption-desorption experiment, the sample... [Pg.90]

If, for example, the void shape is spherical, the fraction of the pore volume filled by adsorbate at a given value of rp on the adsorption branch of the isotherm is represented as... [Pg.21]

The A/m ratio may be estimated based on some inherent properties of the adsorbent its density p, porosity e, and the shape and size of the pores. The porosity is pores volume fraction of the total adsorbent particle volume, e = Vp/V. If the pores are assumed to be cylindrical, with diameter d and length L, then the pore surface area per unit pore volume is... [Pg.632]

Both measurement and modification of pore size distribution are rapidly growing fields. Pore size distributions are often reported in either differential or cumulative form. The former provides the percent or fraction of volume as a function of pore radius or diameter (i.e., dV/dr). That form makes it easy to discern the average pore diameter and skewness of the distribution. In contrast, the cumulative PSD clearly depicts total pore volume as a function of pore diameter and shows relative amounts of microporosity and macroporosity. Figures 14.5 and 14.6 show representative differential and cumulative PSDs, respectively, of some common adsorbents. [Pg.1127]

Adsorption measurements allow the determination of coke location. When the volume occupied by coke is much smaller than the volume inaccessible to adsorbates, it means that there is a pore blockage. However, in many cases the adsorption study is carried out at a different temperature than the reaction, and therefore diffusivity could be quite different. Another aspect that should be taken into account is that if the pretreatment for adsorption measurement requires temperatures higher than the reaction temperature, an important fraction of carbonaceous deposits could be stripped off the catalyst and, therefore, the pore volume measured in this way will be higher than the actual volume under reaction conditions. A modification in the coke structure might also occur under these circumstances ... [Pg.197]

Let us first consider a porous solid having a pore volume distribution f(r), that is f(r) dr is the pore volume of pores having radii ranging between r and r + dr. For a gas phase of pressure P, the threshold radius is calculated from either eq.(3.9-lla) for condensation mechanism or eq.(3.9-llb) for evaporation mechanism. Let this threshold radius be r, then the amount adsorbed at a pressure P is simply the fraction of pores having radii less than this threshold radius r, that is ... [Pg.120]

According to Hagymassy, Brunauer and Mikhail [36], the thickness of an adsorbed water layer at the saturation pressure of water vapor is about 6 monolayers. When the thickness of a water layer is 0.3 nm, the fraction of the pore volume of the support taken up by an adsorbed film of water can be calculated. Knijff [35] established that the fraction of the pore volume filled with 6 monolayers of water agrees well with the moisture content, at which the drying rate displays the first, slight drop below the level of the constant rate period. The rate of evaporation that is maintained during that period indicates that transport of the water film proceeds more slowly when the thickness of the water layer decreases below about 6 mono-layers. However, the drying experiments clearly indicate that liquid water can be transported not only by capillary pressure, but also as a film adsorbed on the surface of oxidic supports. A prerequisite for this mechanism of transport may be that the surface of the support is hydrophilic. [Pg.358]

VsA fraction of total pore volume occupied by adsorbate during adsorption... [Pg.710]

Other important stationary phases for liquid chromatography are ion-exchange resins (ion-ex-change chromatography, which uses anionic or cationic resins) and porous solids that do not adsorb the analytes but instead have pores so small that access to a fraction of the pore volume by some of the analyte molecules is more or less restricted depending on molecular size (size-exclusion chromatography). [Pg.177]

Fig. 2. Detection of delayed adsorption through Nj sorption, (a) Sorption isctham slxiwing a PASC. (b) PSD curves determined from the ABC and PASC isotherms depicted in (a). 6y is the adsorbed volume fraction (with respect to the total pore volume) and Dj represents the cavity (site) sizes. Fig. 2. Detection of delayed adsorption through Nj sorption, (a) Sorption isctham slxiwing a PASC. (b) PSD curves determined from the ABC and PASC isotherms depicted in (a). 6y is the adsorbed volume fraction (with respect to the total pore volume) and Dj represents the cavity (site) sizes.
Porosity can be defined as the fraction of the pore volume occupied by pore space or the volume of the pores divided by the volume of the material. Some porous polymer materials have been shown to be of practical use in the last decades. Porous polymer materials have recently become of immense interest to study arena in the development of new materials, because of their potential for appUcations in fuel cell membranes, chemical filtration, tissue engineering, adsorbents, catalysis, sensors, separations, electrochemical cells, storage and drug delivery, etc. [91-94]. [Pg.111]

Adsorption of supercritical gases takes place predominantly in pores which are less than four or five molecular diameters in width. As the pore width increases, the forces responsible for the adsorption process decrease rapidly such that the equilibrium adsorption diminishes to that of a plane surface. Thus, any pores with widths greater than 2 nm (meso- and macropores) are not useful for enhancement of methane storage, but may be necessary for transport into and out of the adsorbent micropores. To maximize adsorption storage of methane, it is necessary to maximize the fractional volume of the micropores (<2 nm pore wall separation) per unit volume of adsorbent. Macropore volume and void volume in a storage system (adsorbent packed storage vessel) should be minimized [18, 19]. [Pg.281]

From the above data, it would appear that methane densities in pores with carbon surfaces are higher than those of other materials. In the previous section it was pointed out that to maximize natural gas or methane storage, it is necessary to maximize micropore volume, not per unit mass of adsorbent, but per unit volume of storage vessel. Moreover, a porous carbon filled vessel will store and deliver more methane than a vessel filled wnth a siliea based or polymer adsorbent which has an equivalent micropore volume fraction of the storage vessel. [Pg.288]


See other pages where Adsorbents fractional pore volumes is mentioned: [Pg.79]    [Pg.36]    [Pg.68]    [Pg.328]    [Pg.183]    [Pg.23]    [Pg.112]    [Pg.298]    [Pg.354]    [Pg.1831]    [Pg.17]    [Pg.588]    [Pg.702]    [Pg.58]    [Pg.1823]    [Pg.360]    [Pg.14]    [Pg.500]    [Pg.57]    [Pg.475]    [Pg.616]    [Pg.736]    [Pg.135]    [Pg.488]    [Pg.144]    [Pg.443]    [Pg.233]    [Pg.18]    [Pg.10]    [Pg.578]    [Pg.170]    [Pg.1497]    [Pg.11]    [Pg.744]    [Pg.5]    [Pg.17]   
See also in sourсe #XX -- [ Pg.289 ]

See also in sourсe #XX -- [ Pg.289 ]

See also in sourсe #XX -- [ Pg.289 ]




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