Abstract
Simulations of three different 3-bed 3-step pressure swing adsorption (PSA) cycles were carried out to study the enrichment and recovery of 14CO from an isotopic mixture of 14CO, 13CO and 12CO 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 14CO heavy product production); PSA Cycle II was carried out with discontinuous 14CO heavy product production; and PSA Cycle III was carried out with continuous 14CO heavy product production. The effects of the CnD step valve coefficient (c v ), heavy reflux ratio (R R ), and cycle time (t cyc ) on the PSA process performance were determined in terms of the 14CO enrichment, 14CO recovery and CO feed throughput. The results showed that there was essentially no limit to the extent of the 14CO enrichment, despite the inherently low 14CO/12CO (1.05) and 14CO/13CO (1.12) separation factors for these isotopes on NaX zeolite. Under total reflux an optimum c v was found for the CnD step and 14CO enrichments as high as 152 were obtained. Using the optimum c v under finite reflux, a 14CO enrichment approaching 20 and a 14CO recovery approaching 100 % were easily achieved with discontinuous (PSA Cycle II) or continuous (PSA Cycle III) 14CO heavy product production. There was essentially no difference in the performance of PSA Cycles II and III, a counterintuitive result. The 14CO enrichment and the 14CO recovery both increased with decreasing CO feed throughputs and higher R R , which were always very close to unity.
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Abbreviations
- B i :
-
parameter in Eq. (8), K
- b i :
-
Toth isotherm parameter in Eq. (7), kPa−1
- \(b_{i}^{0}\) :
-
parameter in Eq. (8), kPa−1
- C p,a,i :
-
heat capacity of component i in the adsorbed phase, kJ/mol/K
- C p,g,i :
-
heat capacity of component i in the gas phase, kJ/mol/K
- C p,p :
-
heat capacity of the particle, kJ/mol/K
- c v :
-
valve coefficient, dimensionless in unit specific Eq. (14)
- F :
-
flow rate, SLPM
- h w :
-
overall heat transfer coefficient, kW/m2/K
- ΔH i :
-
isosteric heat of adsorption of component i, kJ/mol
- k i :
-
LDF mass transfer coefficient of component i, s−1
- L :
-
length of the column, m
- M g :
-
average molecular weight of the gas phase, mol/kg
- n j :
-
Toth isotherm parameter in Eq. (7)
- n t,i :
-
parameter in Eq. (9)
- n o,i :
-
parameter in Eq. (9)
- N :
-
number of components
- P :
-
pressure, kPa
- P H :
-
high pressure, kPa
- P L :
-
low pressure, kPa
- P o :
-
pressure downstream of the valve, kPa
- q i :
-
amount adsorbed of component i, mol/kg
- \(q_{i}^{s}\) :
-
Toth isotherm parameter in Eq. (7), mol/kg
- \(q_{i}^{*}\) :
-
equilibrium amount adsorbed of component i, mol/kg
- \(q_{o,i}^{s}\) :
-
parameter in Eq. (10), mol/kg
- \(q_{t,i}^{s}\) :
-
parameter in Eq. (10), mol/kg/K
- R :
-
universal gas constant, kPa m3/mol/K
- r b :
-
radius of the column, m
- r p :
-
radius of the particle, m
- R R :
-
reflux ratio
- S g :
-
specific gravity
- t :
-
time, s
- t cyc :
-
cycle time, s
- T :
-
temperature, K
- T F :
-
feed temperature, K
- T o :
-
ambient temperature, K
- v :
-
interstitial velocity, m/s
- y i :
-
mole fraction of component i
- z :
-
axial coordinate in the bed, m
- ε b :
-
bed porosity
- ε p :
-
particle porosity
- μ g :
-
viscosity of the gas phase, kg/m/s
- ρ p :
-
particle density, kg/m3
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Bhadra, S.J., Ebner, A.D. & Ritter, J.A. Carbon monoxide isotope enrichment and separation by pressure swing adsorption. Adsorption 19, 11–23 (2013). https://doi.org/10.1007/s10450-012-9406-2
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DOI: https://doi.org/10.1007/s10450-012-9406-2