Gas adsorption system

In Chapter 2 we have introduced a number of thermodynamic surface excess quantities (Equations (2.11)—(2.14)) in the case of a simple gas adsorption system involving a single adsorptive. These quantities were expressed as a function of the surface excess amount, na. In the case of the process of immersion of a solid in a pure liquid, the same surface excess quantities can still be defined and it is useful to express them as a function of the surface area. Thus ... 

Move sewer and sewer gas adsorption system above-grade Segregate process water from rainwater Enclose or redesign API separator... 

Rudzinski W. and Panczyk T., Phenomenological Kinetics of Real Gas-Adsorption-Systems Isothermal Adsorption, Journal of Non-EqmHbrium Thermodynamics, 27 (2002)pp.l49-204. 

We csitu SAXS sample (liam-b(M 1G polyol liyleneterepht halat< -fiim ( Humilei loray ( o., I.td.) were used for the windows of in situ m< Lsuriiig chamber and sample holder, d he sample chamber is connected to the gas adsorption system. I lie adsorpt ion isotherm of watoi(Ui the samples can bo measured siinullnmxiusly by the volume-metric method under the same Cfuiditions as the SAXS measurement. 

The pore volume was determined by nitrogen sorption-desorption at -196°C with the gas adsorption system ASAP 2010 (Micromeritics). All the zeolite samples present a large micropore volume (0.25 to 0.32 cm g ). NaY, NaHFAU and especially HFAU (Table 1) have also mesopores. With this latter zeolite, it is due to dealumination during thermal treatment of NH4FAU, this treatment causing the formation of extraframework aluminium species (Table 1). 

The efficiency of activated carbon adsorption units is 90%-99%, depending on the specific solvent vapor used and the design of the carbon bed. If the gas adsorption system is equipped with an IR analyzer for monitoring the solvent vapor concentration, the discharge effluent can be... 

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]. 

The first term represents accumulation of energy in the solid, the second term is the heat transfer rate from the fluid to the solid, and the last term is the heat generated by adsorption. This last term can be quite large. Increases in gas temperature of over 100°C can occur in gas adsorption systems, and if oxygen is present activated carbon beds can catch on fire. 

Equations (33)-(35), on the other hand, show that a, can be calculated using the q-, values obtained by the shortcut method provided that and are estimated from some other data source. For pure gas adsorption, the denominator of Eq. (33) can be easily obtained by independently measuring the adsorption isotherm for the pure gas at the base temperature (T ) of the shortcut method. For a binary gas adsorption system, n Jp and n% can be estimated by independently measuring the total surface excess (/f" — n + ni) as functions of P at constant andy and as functions of y at constant P and [13] ... 

There are very few published experimental data on multicomponent gas isosteric heats of adsorption [21,29]. Even those are limited to the study of binary gas adsorption systems. Figures 8 and 9, respectively, show the isosteric heats of adsorption of CO2 and C2H4 from their binary mixture on NaX zeolite crystals measured as functions of CO2 loading (surface excess) at approximately constant... 

In Sect. 3 the measurement methods for gas adsorption equilibria which are presented in this book are outlined. Several other phenomena in gas adsorption systems like the kinetics of the mass exchange process, which could not be considered here are mentioned in brief in Section 4. There also some general information on gas adsorption systems will be given and references for the various fields mentioned will be provided. 

Gas adsorption equilibria can be measured by several basically different methods. In this section we are going to outline the classical ones, namely volumetry/manometry and gravimetry as well as some newer ones, oscillometry and impedance spectroscopy. Emphasis is given to the underlying physical principles. Complementary remarks deal with possibilities to measure binary coadsorption equilibria with and without gas phase analysis. Technical details of all the measurement methods are given in the subsequent chapters, Chaps. (2-6). Prior to considering the measurement methods some general remarks on experimental work with gas adsorption systems are in order. 

Adsorption isotherms, i. e. the thermal equations of state of the masses adsorbed are discussed in Chap. 7 for pure and mixture gas adsorption systems as well. This information should allow the reader to choose the isotherm for his data correlation problem properly and also to extend the range of adsorption data known of the system by cautious extrapolation. 

Additionally it should be mentioned that calorimetric measurements in gas adsorption systems can also be very well used to characterize the porosity of a sorbent material. As this field is well presented in the literature [1.3, 1.29, 1.61, 1.62] we do not go into details here but refer the reader to the (few) examples presented at the end of Chap. 2. 

Helium adsorption experiments at gas adsorption systems in equilibria states show that the volume (V ) of the combined sorbent/sorbate phase is not constant but depends, i. e. increases with the amount of gas adsorbed, cp. next Section 5 of this chapter and also Chaps. 2A. 

Gas adsorption systems normally do not only differ in their adsorption capacity, i. e. thermodynamic equilibria states, but also in their kinetic behavior, i. e. spontaneity of uptake or release of gas upon increase or decrease of sorptive gas pressure. Examples for this are given in Figures 1.18, 1.19, showing the uptake process of carbon dioxide (CO2 (4.5)) on dry Fig. (1.18), and prewetted. Fig. (1.19) zeolite molecular sieve MS Na 13X (Linde, UOP) at T = 323 K due to an increase of the sorptive gas pressure from 0.5 MPa to 6 MPa, [1.60]. 

Both concepts of masses of an adsorbate discussed so far - the Gibbs surface excess (m g) based on proposition (PI) and calculated by Eq. (1.27) and the absolute mass adsorbed (m ) based on proposition (P2) and calculated by either Eq. (1.34) or (1.35) - do have their physical limitations. Hence it is desirable to mention other possibilities to define and to measure masses of adsorbates in gas adsorption systems. 

Waiting times for thermodynamic equilibrium in the gas adsorption system are based on experimental experience which comes from gravimetric measurements, cp. Chap. 3. No general rules for these times are available today. 

Also the selectivities (Sik) of any two components i, k of the gas adsorption system can be calculated from eq. (2.33), Sect. 4.2 of Chap. 2 as adsorbate s Gibbs excess molar concentrations... 

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... 

Dielectric measurements of gas adsorption systems can be performed fairly quickly, typically within a few seconds [6.3]. Hence the kinetics of adsorption processes being slow on this time scale can be observed. Indeed these processes are sometimes invisible to purely manometric or even gravimetric measurements. As examples we mention internal diffusion, reorientation or catalytically induced chemical reaction processes of admolecules within a sorbent material. The mass of the adsorbed phase normally is constant during processes of this type, whereas the dipole moment of the admolecules and hence their polarization changes, cp. Sect. 3.2. 

We here restrict to consider only gas adsorption systems exposed to weak electric fields, these being considered as sensors for the system without changing its macroscopic properties. However, it should be mentioned that in principle the adsorption properties of a sorbent material are changed by the electric field. This so-called electro-adsorptive effect is important in microsystems as used, for example, in advanced gas sensing devices [6.4]. 

An instrument to measure the dielectric permittivity of a gas adsorption system basically consists of an electric capacitor (plates, cylinders, spheres) placed within an adsorption vessel. The vessel should be placed within a thermostat (water, oil etc.) and provided with tubes for gas supply and evacuation. Also manometers and thermometers are needed to measure the gas pressure (p) and temperature (T) inside the chamber. The capacitor is filled with sorbent material (powder, pellets, continuous matter etc.) which can be considered to be homogenous as long as its characteristic length - for example the diameter of cylindrical pellets - is small compared to a characteristic length of the capacitor. 

Figure 6.1. Installation for measurements of the static or frequency dependent dielectric permittivity of gas adsorption systems. IFT University of Siegen, 1988.

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