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Adsorption: Journal of the International Adsorption Society (v.8, #2)
Highest Pressure Adsorption Equilibria Data: Measurement with Magnetic Suspension Balance and Analysis with a New Adsorbent/Adsorbate-Volume by F. Dreisbach; H.W. Lösch; P. Harting (pp. 95-109).
Adsorption data at high pressures provide information about properties of the adsorbent material and about the structure of the adsorbed phase. In order to obtain this information adsorption processes need to be measured in a wide pressure range and require careful experimental data handling. In this paper, an experimental installation with a magnetic suspension balance for the gravimetric measurement of adsorption equilibria data at pressures still inaccessible for this experimental technique will be presented. Using this instrument the adsorption data of He, CH4, N2 and Ar on a microporous activated carbon are measured at pressures up to 50 MPa at T = 298.15 K. The resulting data allow a critical discussion of the commonly used model for the volume of the adsorbent material (i.e. the Helium-volume). As a result of this, a new model for the volume of the adsorbed phase is proposed. This volume model allows to calculate a pressure dependent density of the adsorbed phase. The model and the resulting densities of the adsorbed phase are discussed concerning their physical sensitivity.
Keywords: gas adsorption equilibria; high pressure; buoyancy correction; density of adsorbed phase; compressibility of adsorbed phase
Thermodynamic Description of Excess Isotherms in High-Pressure Adsorption of Methane, Argon and Nitrogen by Alexander Herbst; Peter Harting (pp. 111-123).
In the present work the supercritical fluids argon, methane and nitrogen were picked out as examples, and the results of analysis concerning the adsorption of these fluids at activated carbon Norit R1 (Norit company, Germany) and SCS-3 (ISPE, Kiev) at different temperatures up to a pressure of 50 MPa are presented and discussed in this paper. The principle of working of the measuring device is described in this context as well.A three-parameter isothermal equation is used to represent the adsorption equilibrium. The isothermal equation is based on a physical model concept which has already been used for the modelling of adsorption processes with a pressure up to 15 MPa.
Keywords: excess adsorption; high pressure; gravimetric measurement; supercritical fluids; activated carbon
A Study on the Adsorption Isotherms in the Vicinity of the Critical Temperature by Li Zhou; Yaping Zhou; Shupei Bai; Bin Yang (pp. 125-132).
Adsorption data of nitrogen and methane on micro-porous activated carbon and on meso-porous silica gel were measured near the critical temperature. It was found that the values of the compressibility factor (z) exerted a significant effect on the behavior of isotherms. Selection of reliable z-values is very important for the analysis of experimental results obtained near the critical temperature. The isotherms on activated carbon always show type-I features at sub- and supercritical temperatures, but those on silica gel remarkably show a change from type-II at sub-critical temperatures to type-I at supercritical temperatures. The critical temperature appears to be shifted up in some case.
Keywords: equilibrium; experimental data; measurement techniques; gas phase; supercritical
Effects of the Operating Conditions on Coke Deactivation of 5A Molecular Sieve in N-Decane Adsorption/Desorption by M.A. Uguina; J.L. Sotelo; G. Calleja; J.A. Díaz; E. Castillo (pp. 133-140).
The influence of operating conditions (time-on-stream, temperature, pressure and paraffin feed concentration) on the deactivation of a 5A molecular sieve during the adsorption/desorption of n-decane has been studied using a cyclic operating procedure. After 10 adsorption/desorption cycles, the 5A molecular sieve used in this study showed the same deactivation level as an used industrial molecular sieve provided that the deactivation of the zeolite was due to coke deposition by site coverage and pore blockage. The temperature effect was studied in the range of 373–523 K, obtaining a minimum deactivation at 448 K. The pressure does not influence adsorption parameters in the range of 1–3 MPa, but it does affect the nature of the coke deposited on the zeolite. The influence of paraffin concentration can be considered negligible.
Keywords: 5A zeolite; coke deactivation; n-decane; liquid phase adsorption; adsorption/desorption cycles
Energy Transfer Between Aromatic Hydrocarbons Dissolved in a C18-Surfactant Layer Adsorbed on Laponite by Miguel G. Neumann; Hueder P.M. Oliveira; Ana Paola P. Cione (pp. 141-146).
The energy transfer between pyrene and perylene was studied in a system in which the hydrocarbons were dissolved in the surfactant layer adsorbed on the surface of an organoclay prepared by rapid mixing of Laponite clay and a C18 surfactant. The experimental quenching data gave critical energy transfer radii of 53.3 Å. A theoretical calculation of this radius using the Förster approximation indicated a value of 53 ± 7 Å for this interaction. All these values were in good agreement with similar experiments for the energy transfer between the hydrocarbons in organic solvents. Furthermore, the ratio I 1/I 3 of the intensities of the vibronic fine structure of the emission spectrum of pyrene in this system was found to be 1.25, similar to the value found for the same probe in several surfactants, indicating that pyrene is localized in the organic layer.
Keywords: clay-surfactant interactions; energy transfer; hydrocarbon adsorption
Air Separation by Carbon Molecular Sieves by A.I. Shirley; N.O. Lemcoff (pp. 147-155).
The separation of nitrogen from air on a carbon molecular sieve is achieved by a difference in the adsorption kinetics of oxygen and nitrogen. Assuming the oxygen is adsorbed under equilibrium conditions, a simplified analysis is developed for determining the process performance. As expected, a good agreement is observed between the simplified and full analysis for long cycle times, but for short cycle times, neglecting the oxygen adsorption kinetics leads to erroneous purity predictions. Also, the effect of the adsorption/desorption rate constants on the performance of the pressure swing adsorption process is analyzed, and it is found to be a function of the adsorption/desorption step length. Good agreement between the numerical simulation and experimental results is observed over a wide range of product purities.
Keywords: carbon molecular sieve; pressure swing adsorption; separation; nitrogen; air
Experimental Analysis on the Dynamic Characteristics of a Heat-Regenerative Adsorptive Air-Conditioning System by Y.B. Gui; R.Z. Wang; J.Y. Wu; Y.X. Xu; W. Wang (pp. 157-163).
Based upon a prototype heat powered heat-regenerative adsorptive air conditioning system, the effects of step times (heat recovery, mass recovery, and half-cycle) on the coefficient of performance (COP) and specific cooling power (SCP) are studied. The characteristics of real thermodynamic cycles and dynamic SCP are also analyzed. Strong dynamic behavior was found in that the COP and SCP varied with step times. It is found in experiment that a long heat-recovery time usually leads to a lower SCP. But both the COP and SCP can be increased 16% and 6%, respectively, if a very short time—0.5 min of mass recovery is initiated before heat-recovery. The appropriate half-cycle time for the prototype is about 20–25 minutes for which the SCP and COP are excellent.
Keywords: adsorption; heat-recovery; air-conditioning; prototype; dynamic characteristics; experiment