Volumetric adsorption system

Nitrogen adsorption and desorption isotherms were performed at 77 K on a Micromeritics ASAP 2400 volumetric adsorption system. The pore size distribution and surface area were deduced from the adsorption isotherms using the BJH method and the BET equation. 

The specific surface area of the fibers was determined using inert gas adsorption in a commercial volumetric adsorption system (Micromeritics Instrument Corp.). Krypton gas was used because of its sensitivity to the small specific surface areas of the glass fibers ( 0.2 mz/g). The fibers were degassed at 100°C to a pressure of 80mTorr before introducing the adsorbate gas into the sample chamber. Several samples were also outgassed at 80 and 200°C (to 80 mTorr) to confirm that outgassing was sufficiently complete under the standard test conditions. A standard five-point surface area determination was made for each inert gas adsorption experiment. 

Nitrogen adsorption-desorption isotherms were measured at 77 3 K using a commercial volumetric adsorption system Autosorb-1 or NOVA-1200 (both from Quantachrome Corp ). The samples were outgassed at 10" Torr and 573 K for 3 h prior to the analysis X-ray powder diffraction (XRD) patterns were obtained on PW 1840 diffractometer (Phillips), with Co Ka radiation, 40 KV, 25 mA. 

Porosity and pore-size distributions were determined by gas adsorption and immersion calorimetry, with the measurement of helium and bulk densities. Volumes of micropores were calculated using the Dubinin-Radushkevich (DR) equation (Section 4.2.3) to interpret the adsorption isotherms of N2 (77 K), CO2 (273 K) and n-C4H o (273 K). Volumes of mesopores were evaluated by subtracting the total volume of micropores from the amount of nitrogen adsorbed at p/p° = 0.95. The two density values for each carbon were used to calculate the volume of the carbon skeleton and the total volume of pores (including the inter-particle space in monolithic disks). Immersion calorimetry of the carbon into liquids with different molecular dimensions (dichloromethane 0.33 run benzene 0.37 nm and 2,2-dimethylbutane 0.56 nm) permits the calculation of the surface area accessible to such liquids and subsequent micropore size distributions. The adsorption of methane has been carried out at 298 K in a VTI high-pressure volumetric adsorption system. Additional techniques such as mercury porosimetry and scanning electron microscopy (SEM) have also been used for the characterization of the carbons. 

Volumetric Flow Rate The equipment size is normally dictated by its capacity and is therefore directly related to investment costs. Incineration systems are capable of handling large amounts of waste gases and are often the most cost-effective method when handling large flows. Adsorption systems can handle large volumes of gases, provided that the gas stream is fairly dilute. Absorption will... 

The many different procedures which have been devised for the determination of the amount of gas adsorbed may be divided into two groups (a) those which depend on the measurement of the amount of gas removed from the gas phase (i.e. gas volumetric methods) and (b) those which involve the measurement of the uptake of the gas by the adsorbent (e.g. direct determination of increase in mass by gravimetric methods). Many other properties of the adsorption system may be related to the amount adsorbed, but since they require calibration they will not be discussed here. In practice, static or dynamic techniques may be used to determine the amount of gas adsorbed. 

Praliaud and Martin (77) proposed the formation of Ni-Si and Ni-Cr alloys on silica and chromia supports, respectively, under H2 at sufficiently high temperatures. They suggested that hydrogen spilt over from Ni to the Cr203 carrier and partially reduced it to Cr°, which was then alloyed with Ni as indicated by magnetic measurements. The same technique in conjunction with IR spectroscopy and volumetric adsorption of H2 was applied to partially reduced Ni-on-alumina and Ni-on-zeolite catalysts by Dalmon et al. (78). These supported Ni systems contained Ni° and Ni+. H2 was found to be activated only when the couple Ni°/Ni+ was present according to... 

As far as the adsorption and skeletal isomerization of cyclopropane and the product propene are concerned, results mainly obtained by infrared spectroscopy, volumetric adsorption experiments and kinetic studies [1-4], revealed that (i) both cyclopropane and propene are adsorbed in front of the exchangeable cations of the zeolite (ii) adsorption of propene proved to be reversible accompanied by cation-dependent red shift of the C=C stretching frequency (iii) a "face-on" sorption complex between the cyclopropane and the cation is formed (iv) the rate of cyclopropane isomerization is affected by the cation type (v) a reactant shape selectivity is observed for the cyclopropane/NaA system (vi) a peculiar catalytic behaviour is found for LiA (vii) only Co ions located in the large cavity act as active sites in cyclopropane isomerization. On the other hand, only few theoretical investigations dealing with the quantitative description of adsorption process have been carried out. 

The BET surface areas and the hydrogen and carbon monoxide adsorption isotherms were determined by volumetric adsorption performed with a Texas Instrument quartz spiral BOURDON gauge in a system already described elsewhere (ref. 3). 

The preparation of zeolite-binder agglomerates as spheres or cylindrical pellets which have high mechanical attrition resistauce is not difficult. However, lo use (he zeolite in a process of adsorption or catalysis, the diffesion characteristics must not be unduly affected. Consequently. the binder system must permit a macroporosity ihet does not increase unduly the tliffesion resistance. Therefore, the problem, Is to optimize tha zeolite-binder combination to achieve a perticle of maximum density (to produce a high volumetric adsorption capacity) with maximum mechanical attrition resistance and minimum diffusion resistance,... 

Hydrogen volumetric adsorption measurements were carried out in a conventional high vacuum system equipped with a capacitance gauge, MKS Baratron, model 220 BHS. The time spent between succesive isotherm points was routinely 20 minutes. The final hydrogen pressure was 300 Torr. 

In the direct calorimetric determination (-id/f rta)r), the amount adsorbed (%) is calculated either from the variations of the gas pressure in a known volume (volumetric determination) or from variations of the mass of the catalyst sample in a static or continuous-flow apparatus (gravimetric determination). In a static adsorption system, the gas is brought into contact with the catalyst sample in successive doses, whereas in a dynamic apparatus the catalyst is swept by a continuous flow. Comparative calorimetric studies of the acidity of zeolites by measuring ammonia adsorption and desorption using static (calorimetry linked to volumetry) and temperature-programmed (DSC linked to TG) methods can be found in the literature [17],... 

When one wishes to measure the adsorption of binary or more complicated mixtures of adsorbates foen the above simple volumetric/gravimetric systems are not suitable and one has to resort to more complicated systems. Such a system has been developed at Imperial College and elsewhere and is referred to as the isosteric method [1,2]. 

The most commonly used methods for gas adsorption systems are manometric or volumetric, gravimetric, and different chromatographic methods. Combinations of two methods can be used for measuring adsorption of gas mixtures [8]. 

Volumetric / manometric measurements, Chap. 2, and gravimetric measurements, Chap. 3, can be performed simultaneously on the same gas adsorption system in a single instrument. For pure gas adsorption this will not lead to basically new information on the system as both methods lead to the same result, i. e. the reduced mass of the adsorbate phase, cp. Eqs. (2.4) and (3.5). However, for binary gas mixture adsorptives these measurements allow one to determine the masses of both components of the adsorbate without analyzing the (remnant) adsorptive gas mixture, i. e. without needing a gas chromatograph or a mass spectrometer. Measurements of this type seem to have been performed first in the authors group in 1989 and published in 1990, cp. [4.1-4.3], [2.20], [3.20, 3.22] for CH4 / N2 and CH4 / CO gas mixtures at ambient temperature up to pressures of 12 MPa. In fact this method can be used for any binary gas adsorptive with non-isomeric components, i. e. components with different molecular masses. Meanwhile this method has been commercialized by BEL - Japan, Osaka, with this company offering a fully... 

The breakthrough curve in an adsorption system depends on several parameters. On the one hand, it depends on the space velocity of the stream (the ratio between the volumetric flow and the volume of the bed) it is clear that the adsorbent bed can be used for a larger period of time with low space velocities. But, the breakthrough curve also depends on the characteristics of the stream to be treated (composition, concentration of impurities, temperature, pH) and on the adsorbent (surface characteristics, particle size). As an example, the adsorption kinetics is highly favored by decreasing the particle size of the carbon. It results in a shorter MTZ, and thus, the carbon adsorbent is better exploited. 

Despite this limitation, a number of relevant conclusions may be drawn. Thus, in Collins et al hydrogen adsorption by a 3% Au/Ceo.eaZro.sgOg (Au/CZ) catalyst, with a BET surface area, 62.8 m .g" was investigated at room temperature using volumetric adsorption and FTIR techniques. This approach has an unusual, and certainly very fruitful, combination of techniques. As discussed below, it has rendered interesting data on the amount and nature of the hydrogen chemisorbed on Au/CZ and closely related catalysts. Likewise, these techniques have also provided useful information about the influence of different catalyst pre-treatments and of CO co-adsorption, on the chemistry of the Hj-(Au/CZ) system. 

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