Adsorption apparatus

All equipment designed to measure surface area, adsorption-desorption isotherms or pore volume by adsorption actually determines the quantity of gas condensed on a solid surface at some equilibrium vapor pressure. The surface area or pore volumes and pore sizes are then calculated by means of an appropriate theory used to treat the adsorption and/or desorption data. Depending on the apparatus employed, the adsorbed quantity is measured as volume or weight. The accuracy of an adsorption apparatus is, therefore, dependent upon its ability to correctly measure either of these quantities. 

Many types of vacuum adsorption apparatus have been developed and no doubt every laboratory where serious adsorption measurements are made has equipment with certain unique features. The number of variations are limited only by the need and ingenuity of the users. However, all vacuum adsorption systems have certain essential features, including a vacuum pump, two gas supplies, a sample container, a calibrated volume, manometer and a coolant. 

Figure 14.1 shows a simplified vacuum adsorption apparatus which is suitable for nitrogen adsorption. 

Figure 14.1 Simplified vacuum adsorption apparatus. Shaded areas represent mercury heavy horizontal lines are fiducial marks.

Ideally, the sample should be placed in an open-ended glass cell and then closed with a torch to seal it into the adsorption apparatus. 

Logarithmic plots of the Freundlich equation, Q = kpn, where Q is the amount of methane adsorbed at a pressure p, and k and n are constants, for methane adsorption at 0°, 30° and 50°C. in Figures 6 and 7 indicate that the equation is valid up to at least 1000 torr. Equilibrium sorption points obtained on different samples in a manostatic adsorption apparatus are shown as solid points in Figures 6 and 7. The exponent n varied from 0.72 at 0° to 0.87 at 50°C. for the Pocahontas coal and from 0.78 at 0° to 0.94 at 50°C. for Pittsburgh coal (Table III). 

Nitrogen adsorption measurements were done using a Micromeritics model ASAP 2010 adsorption analyzer (Norcross, GA). Adsorption isotherms were measured at -196°C over the interval of relative pressures from 10 6 to 0.995 using nitrogen of 99.998% purity. Before each analysis the sample was degassed for 2 hours at 150°C under vacuum of about 10 Torr in the degas port of the adsorption apparatus. 

B. By applying the conservation equations (mass, energy) and the data from A, calculate the concentration as a function of time and position in the adsorption apparatus. 

The bulk crystal structure of the samples was determined by XRD (Rigaku D-max B) using a filtered Cu Ka radiation. Surface structure and composition were monitored by XPS (Perkin-Elmer PHI 5400). The N2 BET surface area and CO chemisorption were measured in a constant-volume adsorption apparatus. For the latter, two successive isotherms separated by evacuation were obtained at RT for a sample and the difference extrapolated to zero pressure was taken as chemisorbed CO. 

N diffuses into the structural pores of clinoptilolite 10 to 10 times faster than does CH4. Thus internal surfaces are kinetically selective for adsorption. Some clino samples are more effective at N2/CH4 separation than others and this property was correlated with the zeolite surface cation population. An incompletely exchanged clino containing doubly charged cations appears to be the most selective for N2. Using a computer-controlled pressure swing adsorption apparatus, several process variables were studied in multiple cycle experiments. These included feed composition and rates, and adsorber temperature, pressure and regeneration conditions. N2 diffusive flux reverses after about 60 seconds, but CH4 adsorption continues. This causes a decay in the observed N2/CH4 separation. Therefore, optimum process conditions include rapid adsorber pressurization and short adsorption/desorp-tion/regeneration cycles. 

Modification of silica gel with volatile or gaseous compounds is performed in the vapour phase. Industrial-scale reactors and laboratory scale gas adsorption apparatus have been used. In the industrial field, fluidized bed and fluid mill reactors are of main importance. In fluidized bed reactors,82 the particles undergo constant agitation due to a turbulent gas stream. Therefore, temperatures are uniform and easy to control. Reagents are introduced in the system as gases. Mass transport in the gas phase is much faster than in solution. Furthermore, gaseous phase separations require fewer procedural steps than solution phase procedures, and may also be more cost-effective, due to independence from the use and disposal of non-aqueous solvents. All these advantages make the fluidized bed reactors preferential for controlled-process industrial modifications. 

For laboratory-scale modification, distinction has to be made between static and dynamic adsorption procedures. In a static procedure, the substrate is contacted with a known volume of gas at a well-defined pressure. The modifying gas may be stationary or circulating in a closed loop. Modification in a static gas adsorption apparatus allows the careful control of all reaction parameters. Temperature and pressure can be controlled and easily measured. Adsorption kinetics may be determined by following the pressure as a function of the reaction time. Figure 8.13 displays a volumetric adsorption apparatus, in which mercury is used, as a means to change the internal volume and for pressure measurement. 

Figure 8.13 Dynamic volumetric gas adsorption apparatus, (A) sample compartment, (B) calibrated volume bowls, (C) cryogenic trap, (D) manometer, (E) evacuation line, (F) circulation pump.

Some examples where the authors apply the GCMC method for determining the PSD on different carbon materials can be found in the literature [67-75], However, the DFT method is more used than the GCMC one, because the DFT method is included in the software of commercial adsorption apparatuses. 

A typical commercial volumetric adsorption apparatus is shown in Figure 6.8 [20], The volumetric sorption equipment is equipped with pressure transducers in the dosing volume compartment of the apparatus and high-precision pressure transducers dedicated to measure the pressure in the sample cell [21,22], Hence, the sample cell is isolated throughout equilibration, which assures a very small void volume, and as a result a highly accurate determination of the adsorbed amount [21],... 

FIGURE 6.8 Representation of a standard volumetric adsorption apparatus. (Taken from Thommes, M., in Nanoporous Materials Science and Engineering, Lu, G.Q. and Zhao, X.S. (eds.), Imperial College Press, London, UK, 2004, 317. With permission.)... 

Chromatographic Adsorption Apparatus Electrical Connections of Le Boulenge Chronograph Schematic Diagram of Aberdeen Chronograph Camera Chronograph... 

The BET surface area of the catalysts was determined using an automated nitrogen adsorption apparatus Micromeritics ASAP 2000. 

A classical volumetric adsorption apparatus equipped with absolute capacitance pressures transducers can be used for the estimation of adsorption isotherms in the pressure range 10-3 mbaradsorption measurements the carbon black samples are extracted with toluene and water/methanol (1 1) and after drying degassed overnight at 200 °C at a pressure below 10 4 mbar. The time allowed for equilibrium of each point of the isotherm is 5-90 min depending on the sample and the adsorbed amount. 

The adsorption isotherms for water with five of the samples were obtained at 25° C. by using a volumetric adsorption apparatus described previously (13). Prior to adsorption measurements these samples were also outgassed at 160° and 10-6 mm. Hg. Each adsorption isotherm consisted of 20 to 40 experimental points covering the relative pressure range 0.01 to 0.95. 

Pore Size Distribution of Porous Systems as Determined with an Automatic Adsorption Apparatus and Digital Computer... 

Figure 1. Gas-handling system of automated adsorption apparatus...

A further step in the application of automatic adsorption apparatus is to run a sequence of samples without operator attention. This has been accomplished for adsorption data alone, and, in principle, is possible with complete adsorption-desorption data. 

The organic adsorption apparatus, based on a glass Bourdon gage and Teflon stopcocks, has been described (14). After each activation, the first propanol isotherm, measured at 25°, gave the total amount adsorbed. The B point was employed as a measure of the monolayer capacity, but there was a general agreement with the V /s estimated from BET plots. 

A new experimental sorption apparatus, based on previous experiences [3,9], was designed for this study. This apparatus is described and the first results of the study are presented. The adsorption apparatus was tested by determining the adsorption of salicylic acid on activated carbon from supercritical CO2 as reported elsewhere [11],... 

Pure silica MCM-41 materials were supplied by Chonnam National University, Korea. The preparation of the MCM-41 samples and adsorption experimental operation procedures are described in detail in Ref. 3. An outline is as follows MCM-41 samples were compacted into 10-12 mesh pellets with a hand-operated press with a relatively small external pressure of 2 MPa for 3 s before it could be used in adsorption apparatus, and then were calcined at 500 C for 12 h, 200 C for 4 h and 120 C for 2 h, in sequence, prior to use. This was done to minimise the pressure drop in the sample cell Nitrogen adsorption and XRD measurements were carried out to ensure that the MCM-41 structure was maintained. 

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