Adsorption volume

Thus, under the influence of the field, the adsorptivity of one of the surfaces should increase, while that of the other decreases (Sec. IV,B), though not by the same amount. (This fact can be demonstrated and is highly essential.) As a result, the adsorptivity of the sample as a whole should change. This effect might be detected by a change in pressure in the adsorption volume. At the same time, the catalytic activity of the sample should also change. One may expect a change in the reaction rate under the influence of the external field. 

Hence, the temperature coefficient of k1 having been measured, for an absolute calculation of k only kt) and bo must be known, and not the heat of adsorption, X. At the moment we are concerned with b0. A simple statistical estimate can be based on the assumption that in the absence of adsorption energy the adsorption space is filled at a proportion given by the ratio of the molecular adsorption volume (liquid volume Fm) to the molecular gas volume... 

According to the potential theory the volume V, defined by the adsorbent s surface and the equipotential plane , can contain adsorbate in three different conditions depending upon the temperature. Above the critical temperature the adsorbate can not be liquified and the gas in the adsorption volume V simply becomes more dense near the surface. At temperatures near, but less than the critical temperature, the adsorbate is viewed as a liquid near the surface and a vapor of decreasing density away from the surface. Substantially below the critical temperature... 

T 0.8 Tj.), the adsorption volume is considered to contain only liquid. Under the latter conditions one can write... 

According to the preceding equation, E is the isothermal work required to compress the vapor from its equilibrium pressure P to the saturated pressure Pq of the liquid in the adsorption volume. 

If two adsorbates fill the same adsorption volume as shown by the vertical dotted line in Fig. 9.2, their adsorption potentials E and Eq will differ only because of differences in their molecular properties. Consequently, the ratio of adsorption potentials is assumed by Dubinin to be constant and he calls E/Eq the affinity coefficient which, for an adsorbate pair, is a measure of their relative affinities for a surface or their... 

The similarity in the shapes of the characteristic curves, shown in Fig. 9.2, and the positive side of a Gaussian curve, led Dubinin and Radushkevich to postulate that the fraction of the adsorption volume V occupied by liquid adsorbate at various values of adsorption potentials E can be expressed as a Gaussian function. Thus,... 

A Correlation of the Calculated Intracrystalline Void Volumes and Limiting Adsorption Volumes in Zeolites... 

Figure 1. Relationship between the measured adsorption volumes, Fp (measd) and calculated void volume Vp of several zeolites. The dashed line corresponds to Vp (measd) = Vp (calcd). The symbols represent the zeolites as described in Tables I-VI A, X, L, Z (mordenite Zeolon), omega (to), and offretite-type 0. Vertical shaded areas containing plotted values of Vp (measd) correspond to calculated values of Vp for the main pore systems. The narrow area, 0, corresponds to the main c-axis void of zeolite 0. The value of Vp for Zt = Vp for zeolite 0. Symbols with the subscript t (At Xt) etc.) represent values of Vp for the total void volume shown by narrow shaded areas. The neopentane (NP) volumes lie consistently below the dashed line thus showing a paeking effect. In all of these zeolites of varying structure, the H20 and N2 volumes correspond with complete filling of the total voids even though this is not possible in the case of N2 in zeolites A, X, and L.

It is of interest to relate the void volume as calculated from water adsorption volume to the framework density of the zeolites—i.e., the density of the zeolite structure with no consideration of the nonframework atoms (cations and water). The framework density may be expressed in terms of grams per cubic centimeter or in terms of the number of tetrahedra per unit volume of 1000 A3. A plot of the framework density for zeolites of known structure vs. the void fraction, Vf, as determined from water... 

In Equation 6, do° is an experimentally determined adsorption value for a temperature To, and do the calculated limiting adsorption value for a pre-assigned temperature, T. In the case of zeolites, the limiting adsorption volumes. Wo, are perceptibly reduced with an increase in the size of the molecules adsorbed. Thus, Wo acquire the nature of effective values. 

It is agreed with literary data of absence of steric hindrance for adsorption of normal hydrocarbons on zeolites of a pentasile type [5-8]. Adsorption isotherms of 3-methylpentane lay below ones of n-hexane and starting US-69 sample at identical p/ps, the decrease of adsorption volume capacity made about 10%. In the investigated p/ps range adsorption isotherm of benzene on US-69 sample lays below, than for 2,3-dimethylbutane, and in initial area - even is lower than for cyclohexane contrary to a ratio of there kinetic diameters. At the same time, benzene isotherm increases faster, so that level of saturation for benzene can lay above, than for 2,3-dimethylbutane. Apparently, such character of benzene isotherm is connected to a feature of packing of molecules in pentasile channels, and also with stronger interaction adsorbate-adsorbate in comparison with interaction adsorbate-adsorbent. 

Comparing n-hexane adsorption on US-69 and modified zeolites is possible to mark, that internal adsorption volume of a sample prepared by impregnation by a solution of acids (BP-US-69 (2)) has decreased insignificantly, and its share has made 0.91-0.95 in relation to starting zeolite. On data of n-hexane adsorption available volume for molecules has made 0.8 from the value for US-69 for BP-US-69 (1) modified by reagent vapors. 

Polanyi [12] took a somewhat different approach to multilayer adsorption by assuming that dispersion forces play the determining role in adsorption, resulting in the existence of a potential field in the vicinity of the adsorbent surface. The adsorbed layer has the highest density at the solid surface and its density decreases as the distance from the surface increases. Thus, it is possible to draw equipotential surfaces as shown in Fig. 3.3. The space between each adjacent potential surface represents a defixute adsorption volume which is a function of the potential field. Mathematically, it can be represented as... 

More recently, Ustinov and coworkers [72, 73] developed a thermodynamic approach based on an equation of state to model the gas adsorption equilibrium over a wide range of pressure. Their model is based on the Bender equation of state, which is a virial-like equation with temperature dependent parameters based on the Benedict-Webb-Rubin equation of state [74]. They employed the model [75, 76] to describe supercritical gas adsorption on activated carbon (Norit Rl) at high temperature, and extended this treatment to subcritical fluid adsorption taking into account the phase transition in elements of the adsorption volume. They argued that parameters such as pore volume and skeleton density can be determined directly from adsorption measurements, while the conventional approach of He expansion at room temperature can lead to erroneous results due to the adsorption of He in narrow micropores of activated carbon. 

Figfure 25.6 Relationship between natural organic matter (NOM) adsorption capacity and available adsorption volume for different activated carbons at solution pH = 3. (Adapted from Ref. [61].)... 

Figure 10.3. The Langmuir adsorption isotherm plotted as volume of gas adsorbed (v) against the equilibrium partial pressure, P (nonlinear form), and as P/v against P (linear form). The isotherms are shown for fhree values of b, assuming an arbitrary maximum adsorption volume, Vm, of 5 units. 

ABSTRACT Experimental study was done on the effects of electromagnetic fields on gas adsorptive constant a/b of different coal rank. The research results show that the electromagnetic fields almost have no effects on gas adsorptive constant a, but can reduce adsorptive constant b obviously. Adsorptive constant b decreases with voltage and frequency of electromagnetic field exalting. The exerted electromagnetic fields can reduce the capability of coal adsorption to gas and gas adsorptive volume. 

BET testing was adopted in the experiment. Besides, Nj of high purity was taken as adsorbate and adsorption volume of Nj under different... 

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