Volumetric adsorption analyzers

Nitrogen adsorption - desorption isotherms were obtained from a volumetric adsorption analyzer ASAP 2010 manufactured by Micromeritics. The samples were first degassed for several hours at 350°C. The measurements were then carried out at -196°C over a wide relative pressure range from 0.01 to 0.995. The average pore diameter and the pore size distribution were determined by the B JH method from the adsorption branch of isotherm [18],... 

FIGURE 4.11 Cumulative pore volume corresponding to the three samples presented in Figure 4.4. These cumulative pore volumes have been obtained by applying the DFT methods to each N2 adsorption isotherms using the software provided by two different commercial volumetric adsorption analyzers. 

The currently available volumetric adsorption analyzers are fully automated. The measurement of each isotherm is done automatically according to the created program, in which adsorbate dose, pressure table and other parameters are specified. Prior adsorption measurements samples are outgassed under vacuum at a given temperature. Normally, outgassing is performed for a few hours at 473 K to achieve vacuum below 1.3 10 Pa,... 

The nitrogen adsorption/desorption isotherms were measured at 77 K using the ASAP 2010 volumetric adsorption analyzer (Micromeritics Inc., Norcross, GA). The specific surface areas of the investigated samples were determined using the standard BET method at the relative pressure p/po in the range 0.04 to 0.25. The total pore volume was estimated fium single point adsorption at the relative pressure of about 0.99. 

The pore volumes and the micropore distribution parameters of the carbon samples were analyzed in an automatic volumetric sorption analyzer (model ASAP 2000, Micromeritics Instrument Co. Norcross, GA, USA) using N2 and CO2 adsorption at 77 and 273 K, respectively. Five different experiments were carried out to determine the experimental error with sample CA-3 finding a value around 3%. 

BET surface area and microporous volume determination. Surface area measurements were performed by nitrogen physisorption at 77 K using the static volumetric apparatus (Micromeritics ASAP 2000 adsorption analyzer) with application of the BET method. All measurements were performed after treatment of solids under vacuum at 110 °C. 

Nitrogen adsorption measurements were performed at 77 K using a static volumetric apparatus (Micromeritics ASAP 2010 adsorption analyzer). The samples were degassed at 473 K for 24 hours and 10 Pa before analyses. 

Hydrogen uptake of reduced catalysts (X) was measured by volumetric method with an AUTOSORB-l-C analyzer (Quantachrome Instruments). Hydrogen adsorption was carried out at 373 K after in situ H2 reduction at 773 K for 6 h in the adsorption cell. The dispersion and particle size of metallic Co were calculated by the following equations, assuming that the stoichiometry for hydrogen adsorption on the metallic site is unity ... 

Figure 4.6b), and NLDFT method (Figure 4.6c). All these PSDs were obtained using the software provided by the manufacturer of the commercial volumetric analyzer, where the N2 adsorption isotherms were measured. Note that CMS1, for the reason commented before (lack of N2 adsorption at 77 K due to diffusional problems), cannot be analyzed. The three methods qualitatively show the same evolution of the PSD, that is, the expected one deduced from the N2 adsorption isotherm analysis. The micropore size and the width of the distribution increase in the order ACF1 < AC2 < AC1. 

Adsorption isotherms were determined in an automated volumetric gas adsorption apparatus (Autosorb 1, Quantachrome Co.). Adsorption of nitrogen was performed at 77 K. Before measurements, samples were outgassed at 672 K for at least 8 hr in vacuum. Where some bumoff of the char was desired, the reactions were performed in an Online Instruments TG-plus thermogravi metric analyzer. The reactions were performed in a mixture of helium and oxygen, flowing at a rate of about 220 cc/min. Samples of 30-50 mg were dispersed on a circular platinum pan with a large flat surface and raised sides, resulting in a particle beds of about 1 mm thickness. Temperatures between 573-748 K... 

Adsorption-desorption isotherms for nitrogen at 77 K were determined in a volumetric device (Micromeritics Asap 2000). Data were analyzed using t- and BJH methods. 

The optimal calcination method for zeolite beta was established by thermogravimetric analysis using a PL-Thermal Sciences STA 1500 apparatus. Chemical compositions of the zeolites were determined by atomic absorption spectroscopy on a Varian AAIO spectrometer after dissolution of the samples in hydrofluoric acid. The structure was confirmed by x-ray diffraction on a Siemens D-5000 diffractometer and with infrared spectroscopy on a Mattson Instruments Galaxy 2000 spectrometer. Total surface area, micropore area and micropore volume of the samples were determined by argon adsorption on a Micromeritics ASAP 200M volumetric analyzer using standard techniques. Crystal diameters were determined by scanning electron microscopy. 

Bakaev et al. [77] employed a similar approach to study CO2 adsorption on glass surfaces. Their results confirm that CO2 molecule is sensitive to the structure of the surface while Ar does not show this characteristic. In another paper Bakeva et al. [78] studied CO2 adsorption on glass fibers in a wide temperature range. Employing the classical volumetric technique they have determined the adsorption isotherms and also calculated the isosteric heats of adsorption. They have also analyzed their data in terms of the independent adsorption sites model [74,79,80]. The most important equation of this model is... 

In the presented paper we will be started from the imagination about the volumetric form of the polymeric chains adsorption assuming that the anchor fit of the polymeric chain on the surface of adsorbent is realized via little number of z (z < N, where TV is a general number of links of the polymeric chain) of the end links forming the Langmuir connection with the active centers of adsorbent. In spite of fact, that the presented model, as it was mentioned earlier, in detail was analyzed with the use of the methods of self-consistent field and scaling, but it was not obtained its thermodynamical evolution. 

The standard method to measure pure gas adsorption equilibria most often used today is the volumetric or manometric method. Chap. 2. Basically it is the mass balance of a certain amount of gas partly adsorbed on the sorbent material. This method can be realized in either open or closed systems, the former ones often using a carrier gas, the adsorption of which normally being neglected. Complemented by a gas analyzer (chromatograph, mass spectrometer) this method also can be used to measure multicomponent or coadsorption equilibria. 

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... 

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