Carbon monoxide isotope enrichment and separation by pressure swing adsorption
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Carbon monoxide isotope enrichment and separation by pressure swing adsorption Shubhra J. Bhadra · Armin D. Ebner · James A. Ritter
Received: 26 March 2012 / Accepted: 20 August 2012 / Published online: 5 September 2012 © Springer Science+Business Media, LLC 2012
Abstract Simulations of three different 3-bed 3-step pressure swing adsorption (PSA) cycles were carried out to study the enrichment and recovery of 14 CO from an isotopic mixture of 14 CO, 13 CO and 12 CO using NaX zeolite. Each PSA cycle included feed pressurization/feed (FP/P), heavy reflux (HR) and countercurrent depressurization (CnD) steps; they differed only in the way the CnD step was carried out: PSA Cycle I was carried out under total reflux (i.e., with no 14 CO heavy product production); PSA Cycle II was carried out with discontinuous 14 CO heavy product production; and PSA Cycle III was carried out with continuous 14 CO heavy product production. The effects of the CnD step valve coefficient (cv ), heavy reflux ratio (RR ), and cycle time (tcyc ) on the PSA process performance were determined in terms of the 14 CO enrichment, 14 CO recovery and CO feed throughput. The results showed that there was essentially no limit to the extent of the 14 CO enrichment, despite the inherently low 14 CO/12 CO (1.05) and 14 CO/13 CO (1.12) separation factors for these isotopes on NaX zeolite. Under total reflux an optimum cv was found for the CnD step and 14 CO enrichments as high as 152 were obtained. Using the optimum cv under finite reflux, a 14 CO enrichment approaching 20 and a 14 CO recovery approaching 100 % were easily achieved with discontinuous (PSA Cycle II) or continuous (PSA Cycle III) 14 CO heavy product production. There was essentially no difference in the performance of PSA Cycles II and III, a counterintuitive result. The 14 CO enrichment and the 14 CO recovery both increased with decreasing CO feed throughputs and higher RR , which were always very close to unity. S.J. Bhadra · A.D. Ebner · J.A. Ritter () Department of Chemical Engineering, University of South Carolina, Columbia, SC 29208, USA e-mail: [email protected]
Keywords Isotope separation · PSA · Pressure swing adsorption · Carbon isotope separation · Nuclear waste Nomenclature parameter in Eq. (8), K Bi Toth isotherm parameter in Eq. (7), kPa−1 bi bi0 parameter in Eq. (8), kPa−1 Cp,a,i heat capacity of component i in the adsorbed phase, kJ/mol/K Cp,g,i heat capacity of component i in the gas phase, kJ/mol/K Cp,p heat capacity of the particle, kJ/mol/K valve coefficient, dimensionless in unit specific cv Eq. (14) F flow rate, SLPM overall heat transfer coefficient, kW/m2 /K hw Hi isosteric heat of adsorption of component i, kJ/mol LDF mass transfer coefficient of component i, s−1 ki L length of the column, m average molecular weight of the gas phase, mol/kg Mg Toth isotherm parameter in Eq. (7) nj parameter in Eq. (9) nt,i parameter in Eq. (9) no,i N number of components P pressure, kPa high pressure, kPa PH low pressure, kPa PL pressure downstream of the valve, kPa Po amount adsor
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