Binary separations by pressure swing adsorption processes

(1992) Binary separations by pressure swing adsorption processes. PhD thesis, King Fahd University of Petroleum and Minerals.


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Theoreical and experimental investigations are reported for the sorption, diffusion and separation of pure and binary mixtures of gses in microporous adsorbents - 4A zeolite and carbon molecular sieve (CMS). A mathematical model is developed for the sorption and diffusion of binary mixtures of N₂ and O₂ in 4A zeolite and CMS accounting for variable intracrystalline diffusivity, non-linear isotherm, non isothermal adsorption and film resistance to heat and mass transfer. The model results are expressed as a normalized uptake ratio versus dimensionless time (t): the uptake ratio moves from a diffusion to an equilibrium control regime as t moves from O to₀₀. In the diffusion control regime the uptake ratio was found to decrease with Biot number independent of pressure for the constant diffusivity case, but is highly dependent on both pressure and composition for the variable diffusivity case. Theoretical adsorption and desorption curves are modelled for axial dispersion and cell model adsorbers, for equilibrium and non-equilibrium systems having non linear Langmuir type of isotherms. As representative systems ethylene-helium and methane-helium on 5A zeolite are selected for the equilibrium systems and ethylene-helium on 4A zeolite and oxygen-helium on CMS for the non-equilibrium systems. The time to change the dimensionless exit concentration level between 0.99 and 0.01 (t₀.₉₉₋₀.₀₁) is chosen as the criterion to find a correspondence between the Peclet number in the axial dispersion model and N, the number of cells in the cell model. Computations were performed to estimate t₀.₉₉₋₀.₀₁ for all the systems by both models for various values of the non-linearity parameter. For both the equilibrium and the non-equilibrium processes the ratio of Peclet number changes from a value of 2 at low to unity when is high (= 0.85) during adsorption. However, this ratio can ben taken as 2 during desorption. The studies involving the CMS indicate that a totally different rate factor and trend is observed in LDF approximation. This difference is a reflection of the barrier resistance mechanism.

Item Type: Thesis (PhD)
Subjects: Chemical Engineering
Department: College of Chemicals and Materials > Chemical Engineering
Committee Advisor: Loughlin, Kevin F.
Committee Members: Shaikh, A. K. and Oweimreen, G. A. and Hassan, M. M.
Depositing User: Mr. Admin Admin
Date Deposited: 22 Jun 2008 13:51
Last Modified: 01 Nov 2019 13:52