AIChE - Proceedings - Non-Isobaric, Non-Isothermal, Non-Equilibrium Desorption of Nitrogen From a Packed Column of Small Adsorbent Particles by Oxygen Back Purge (2011 Annual Meeting)
2011 Annual Meeting
Non-Isobaric, Non-Isothermal, Non-Equilibrium Desorption of Nitrogen From a Packed Column of Small Adsorbent Particles by Oxygen Back Purge
Lehigh University
Lehigh University
Lehigh University
Efficient desorption of selectively adsorbed N2 from air in a packed column of LiX zeolite by rapidly purging the adsorbent with an O2 enriched gas is an important element of a rapid cyclic pressure swing adsorption (RPSA) process used in design of many medical oxygen concentrators (MOC). The amount of O2 purge gas used in the desorption process is a sensitive variable in determining the overall separation performance of a MOC unit. Various resistances like (a) adsorption kinetics, (b) column pressure drop, (c) non-isothermal column operation, (d) gas phase mass and thermal axial dispersions, and (e) gas-solid heat transfer kinetics determine the amount of purge gas required for efficient desorption of N2. The impacts of these variables on the purge efficiency were numerically simulated using a detailed mathematical model of non-isothermal, non-isobaric, and non-equilibrium desorption process in an adiabatic column.
The purge gas quantity required for a specific desorption duty (fraction of total N2 removed from a column) is minimum when the process is carried out under ideal, hypothetical conditions (isothermal, isobaric, and governed by local thermodynamic equilibrium). All above-listed non-idealities (a & e) can increase the purge gas quantity, thereby, lowering the efficiency of the desorption process compared to the ideal case. Items (a & c) are primarily responsible for inefficient desorption by purge, while gas phase mass and thermal axial dispersions do not affect the purge efficiency under the conditions of operation used in this study.
Smaller adsorbent particles can be used to reduce the negative effects of adsorption kinetics, especially for a fast desorption process, but increased column pressure drop adds to purge inefficiency. A particle size range of ~ 300 & 500 &m is found to require a minimum purge gas amount for a given desorption duty. The purge gas requirement can be further reduced by employing a pancake column design (length to diameter ratio, && 0.2) which lowers the column pressure drop, but hydrodynamic inefficiencies (gas mal-distribution, particle agglomeration) may be introduced. Lower &also leads to a smaller fraction of the column volume that is free of N2 at the purge inlet end which is required for maintaining product gas purity.
The simulated gas and solid temperature profiles inside the column at the end of the rapid desorption process show that a finite gas-solid heat transfer coefficient affects these profiles only in the purge gas entrance region of the column. The profiles in the balance of the column are nearly invariant to the values of that coefficient. Consequently, the gas-solid heat transfer resistance has a minimum influence on the overall integrated N2 desorption efficiency by O2 purge for the present application.
&Keywords: Desorption by purge, medical oxygen concentrator, model simulation, non-isothermal, non-isobaric, non-equilibrium
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Energy and Environmental Engineering Vol. 1(1), pp. 5 - 9 DOI: 10.13189/eee. (244Kb)
An Equilibrium Study on Trichloroethylene Adsorption and Desorption from ZSM-5 in Water
Harmonie A. Hawley1,2,*,
John Bergendahl2,
Robert Thompson31 The University of Texs at Tyler, Department of Civil Engineering, 3900 University Blvd, Tyler, TX 75799, USA2 Worcester Polytechnic Institute, Department of Civil & Environmental Engineering, 100 Institute Rd, Worcester, MA 01609, USA3 Worcester Polytechnic Institute, Department of Chemical Engineering, 100 Institute Rd, Worcester, MA 01609, USA
Zeolite ZSM-5 was found to effectively remove trichloroethylene (TCE) from water.This study measured the extent of uptake of TCE from water, determined adsorption isotherms, and evaluated desorption of TCE from ZSM-5.TCE was rapidly removed from water and followed linear and Freundlich adsorption isotherms.Desorption of TCE from ZSM-5 occurred, but the linear isotherm was still an acceptable model for the removal of TCE from water with ZSM-5.
Adsorption, Zeolites, Trichloroethylene Isotherms
Cite this paper
Harmonie A.
Bergendahl
An Equilibrium Study on Trichloroethylene Adsorption and Desorption from ZSM-5 in Water.
Energy and Environmental Engineering, 1 ,
doi: 10.13189/eee..}