Sorption experiment

If one is interested only in properties of the pore phase as a whole, such as the excess adsorption and the phase behavior, and not in properties that depend explicitly on local density, or on intermolecular correlations, then it may be sufficient to neglect entirely variations in the local density. It is in this spirit that we present a simple model for the adsorbed phase that yields closed expressions for the free energy and for the equation of state. Tlie model is a direct extension of van der Waals model for the bulk fluid. For simplicity we adopt the slit-pore geomet ry, although the significant conclusions of the study are not altered for pores of other shapes. As we shall demonstrate below, some features of the Thommes Findenegg experiment [31] can indeed be understood in terms of a simple van der Waals equation of state. 

Using a volumetric teclinique, Thommes and Findenegg [31] have measured the excess coverage F of SFe in controlled pore glasses (CPG, see Fig. 4.1) as a function of T along subcritical isochoric paths in bulk SFe. The experimental apparatus, fully described in Ref. 31, consists of a reference cell filled with pure SFe and a sorption cell containing the adsorbent in thermodynamic equilibrium with bulk SFg gas at a given initial temperature Tj of the fluid in both cells. The pressure P in the reference cell and the pressure difference AP between sorption and reference cell are measured. The density of (pure) SFe at Ti is calculated from P via an equation of state. 

At the beginning of an experimental scan, the reference-cell volume is adjusted such that AP(Ti) = 0 that is, the thermodynamic state of SFe is the same in both cells. The temperature is then lowered from 7 to a new temperature Ti+i = - AT. at which AP 0 becaiLse more SFg is 

In the meantime it has also become feasible to sjmthesize other meso-porous materials that differ from CPG in that ttiey consist of individual, disconnected cylindrical pores. These so-called SBA-15 or MCM-41 silica pores can be synthesized using a technical-grade triblock copolymer as the structure directing template in aequous H2SO4 solution and tetraethyl orthosilicate as the silica source [33, 34]. After calcination [35], one obtains a regular array of individual cylindrical pores as illustrated by the transmission electron micrographs (TEMs) shown in Fig. 4.2. 

A key result of the sorption experiments conducted 1 Thommes and Findenegg concerns the pore condensation line T p (pb) T b (Pb) at which pore condensation occurs along a subcritical isochoric path Pb/Pch 1 in the bulk (/ b and peb arc the density of tliis isochore and the bulk critical density, respectively). Experimentally, Txp (pb) is directly inferred from the temperature dependence of F (T), which changes discontinuously at n, (Pb) (see Ref. 31 for detaiLs). The pore condensation line ends at the pore critical temperature Tep (rigorously defined only in the ideal single slit-pore case) [31]. Because of confinement Tep is shifted to lower values with decreasing pore size. If, on the other hand, the pore becomes large, Tep — (the bulk 

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The exposure of heterogeneous materials to humid environments induces different morphological changes of the polymeric structure, depending on the affinity and mode of sorption of the water. Moy and Karasz 16) presented sorption experiments of... 

Another major drawback of polysaccharides is their hydrophilic nature leading to low degrees of adhesion between fiber and matrix [11]. Moisture absorption takes place by three types of mechanisms namely diffusion, capillarity, and transport via micro cracks [2]. Among the three, diffusion is considered to be the major mechanism. Water absorption largely depends on the water-soluble or hygroscopic components embedded in the matrix, which acts as a semipermeable membrane. While, fiber/matrix adhesion and fiber architecture also affect the moisture absorption. The results of the water sorption experiment showed an interesting trend. The extent of water uptake was not very significant and also did not increase linearly with amount of filler (Table-2). 

The fermentation wastes Corynebacterium glutamicum biomass) were obtained in a dried powder form from a lysine fermentation industry (BASF-Korea, Kunsan, Korea). The protonated biomass was prepared by treating the raw biomass with a 1 N HNO3 solution for 24 h, thereby replacing the natural mix of ionic species with protons. The resulting C glutamicum biomass was dried and stored in a desiccator and used as a biosorbent for the sorption experiments. 

A typical sorption experiment involves exposing a polymer sample, initially at an equilibrium penetrant concentration of c to a bathing penetrant concentration of Ci. The weight gain or loss is then measured as a function of time. The term sorption used in this context includes both absorption and desorption. The sorption is of the integral type if c° = 0 in the case of absorption or if cf = 0 in the case of desorption. Details of the experimental setup for the sorption measurement are discussed elsewhere [4],... 

To evaluate the concentration dependence of D, a series of sorption experiments are performed at successive concentration intervals. A numerical differentiation is then performed on the plot of Da(c ) versus r to obtain a first approximation for the relationship between Da and cx. Similarly, the cx dependence of Dd, where d denotes desorption, can be determined from desorption data. This estimation method works quite satisfactorily for cases where D has a mild dependence on Ci and both Da(cx) and Dd(cx) give good estimates of D(cx). It is to be... 

For a classical diffusion process, Fickian is often the term used to describe the kinetics of transport. In polymer-penetrant systems where the diffusion is concentration-dependent, the term Fickian warrants clarification. The result of a sorption experiment is usually presented on a normalized time scale, i.e., by plotting M,/M versus tll2/L. This is called the reduced sorption curve. The features of the Fickian sorption process, based on Crank s extensive mathematical analysis of Eq. (3) with various functional dependencies of D(c0, are discussed in detail by Crank [5], The major characteristics are... 

Low temperature CO sorption experiments monitored with the IR spectroscopy were used to determine the nature of active (acid) sites present in the Fe-TON zeolites. It is well known that CO is a useful probe molecule for Lewis acid sites. Narrow and well resolved bands appear in the region 2135 - 2150 cm"1. The IR spectra of CO sorbed in amount sufficient to cover all Lewis sites in the Fe-TON of different Si/Fe ratios are presented in Figure 2A. The samples of a high iron content (Si/Fe=27, 36) showed a significantly lower thermal stability. The activation of the NFL form of these Fe-TON... 

The information addressed here emphasized that the HOC sorption capacity in context relates to the chemical structures of SOM. Aromatic structures of SOM were reported to be the domains primarily responsible for HOC sorption, supported by positive correlations between aromaticity and Koc. Recently, aliphatic components, particularly paraffinic carbons, of SOM are reported to sorb significant amounts of HOCs, similarly supported by positive correlations between aliphaticity and Koc values. From a series of sorption experiments and literature review, we concluded... 

Abstract Batch and column sorption experiments have been performed to study a... 

Thus, either type I or type IV isotherms are obtained in sorption experiments on microporous or mesoporous materials. Of course, a material may contain both types of pores. In this case, a convolution of a type I and type IV isotherm is observed. From the amount of gas that is adsorbed in the micropores of a material, the micropore volume is directly accessible (e.g., from t plot of as plot [1]). The low-pressure part of the isotherm also contains information on the pore size distribution of a given material. Several methods have been proposed for this purpose (e.g., Horvath-Kawazoe method) but most of them give only rough estimates of the real pore sizes. Recently, nonlocal density functional theory (NLDFT) was employed to calculate model isotherms for specific materials with defined pore geometries. From such model isotherms, the calculation of more realistic pore size distributions seems to be feasible provided that appropriate model isotherms are available. The mesopore volume of a mesoporous material is also rather easy accessible. Barrett, Joyner, and Halenda (BJH) developed a method based on the Kelvin equation which allows the calculation of the mesopore size distribution and respective pore volume. Unfortunately, the BJH algorithm underestimates pore diameters, especially at... 

Laboratory sorption experiments are used to determine the distribution of a compound between the solid and liquid phases in the absence of other processes involved (e.g. biodegradation, precipitation) under controlled conditions. Sorption experiments are usually performed by adding particulate matter, free of surfactants, to solutions with different known surfactant concentrations at constant temperature (sorption isotherms). The experiments performed at high concentrations of... 

Equilibrium times of sorption experiments for different surfactants in different environmental matrices... 

Recently, new sorption experiments have been conducted with marine sediments [30] and microalgae [31]. Specifically these experiments have... 

Frequently it is convenient, when conducting sorption experiments, to use a cosolvent such as methanol to facilitate transfer of a volatile or insoluble solute. Equation 31 may be used to estimate the effect of the cosolvent on measured sorption coefficient. If fc equals 10- and a is conservatively chosen as unity, the methanol is predicted to decrease the sorption of anthracene (ac = 9.76 log Kow = 4.54 50) by 1% relative to the case of no cosolvent. The effect of the cosolvent should be smaller for solutes with smaller HSA (or KQW), which is consistent with the observed negligible impact of methanol at f. < 10 3.6 52). ... 

In the sorption experiments of Icopini et al. (2004), the measured isotopic contrast between Fe(II)aq and the goethite starting material was -0.8%o after Fe(II) had sorbed to the surface over 24 hours in this case, the isotopic fractionation between sorbed Fe(II) and Fe(II)aq is not the 0.8%o measured difference, but is approximately +2.1%o based on an inferred 8 Fe value for the sorbed component as calculated from Fe mass balance (Fig. 4), as was noted in that study. Measured differences in Fe isotope compositions between ferric oxide/hydroxide and Fe(II)aq during dissimilatory Fe(III) reduction and photosynthetic Fe(II) oxidation have been proposed to reflect fractionation between soluble Fe(II) and Fe(III) species, where the soluble Fe(III) component is postulated to be bound to the cell and is not directly measured (Beard et al. 2003a Croal et al. 2004). In the case of dissimilatory Fe(III) reduction, assuming a static model simply for purposes of illustration, if 50% of the Fe in a pool that is open to... 

The isotopic effects of sorption remain relatively unknown, with disparate interpretations of its significance during DIR. An important avenue of future research will be to quantify the rates of isotopic exchange between sorbed Fe(II) and Fe(II)3q, and to investigate a range of ferric oxide/hydroxide substrates. Because traditional sorption experiments generally... 

Fig. 1.18A shows the pore size distribution for nonporous methacrylate based polymer beads with a mean particle size of about 250 pm [100]. The black hne indicates the vast range of mercury intrusion, starting at 40 pm because interparticle spaces are filled, and down to 0.003 pm at highest pressure. Apparent porosity is revealed below a pore size of 0.1 pm, although the dashed hne derived from nitrogen adsorption shows no porosity at aU. The presence or absence of meso- and micropores is definitely being indicated in the nitrogen sorption experiment. 

SORPTION EXPERIMENTS. Sorption experiments were carried out using a Cahn 1000 recording balance, with an accuracy of 0.03 mg. The balance and its accessories are shown in Figure 1. The instrument is equipped with an MKS Baratron pressure transducer (0-100 torr, 0.15% accuracy) with a digital readout for pressure measurements. 

Prior to conducting the sorption experiment, the coal extract (200 mg) was first placed in a Wig-L-Bug capsule and ground for 1 minute under nitrogen. This grinding effectively reduces the extract to a fine powder, which is then used for the sorption experiment. Approximately 50-70 mg of the extract was then placed on the sample pan and the hangdown tube was replaced. The sample was maintained at 30.00 0.02 C by means of a constant temperature bath which surrounded the hangdown tube. 

SORPTION EXPERIMENTS. The extracts were exposed to benzene vapor at several relative vapor pressures (p/p )- Two types of sorption experiments were conducted. Experiments in which the benzene vapor pressure is raised from zero to a higher value are termed integral sorptions. Sorption experiments starting with the extract and vapor in equilibrium at a finite, nonzero pressure, and proceeding to a higher pressure, are termed incremental sorptions. 

As discussed above, we believe adsorption becomes less important and absorption (swelling) becomes more important as the size of the added alkyl group increases. Since the x parameter describes the "goodness" of the solvent-polymer solution, and has nothing to do with surface interactions, the more reliable x parameter will be obtained for the O-octylated extract-benzene system. Even so, the ground O-octylated extract possesses considerable surface area and any adsorption of benzene onto surfaces will lead to errors in x-Sorption experiments were therefore conducted on the unground extract, which possessed only 11 w /g surface area, x was determined to be 0.65, which was independent of pressure. 

The presence of solutes other than ethanol might be expected to reduce the mole fractions of ethanol and water and influence the nonideality of the ethanol-water system. However, both Williams (1983), who modelled a batch wine fermentation, and Rottenbacher (1985), in ethanol sorption experiments with yeast pellets in a fluidized bed, established that the ethanol-water-yeast system behaves as if the water and ethanol content of the pellets were a simple ethanol-water solution supported by a solid matrix which influences neither mole fractions nor activity coefficients. 

In a zeolite catalyst sample, which was coked via dealkylation of ethylbenzene at reaction temperatures somewhat higher than those of the sorption experiments, the diffusion coefficient of ethylbenzene remained essentially unchanged even though the sorption capacity significantly decreased due to deposition of carbonaceous material. 

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