Three-bed PVSA process for high-purity O₂ generation from ambient air

A three-bed PVSA (pressure vacuum swing adsorption) process, combining equilibrium separation with kinetic separation, was developed to overcome the 94% O₂ purity restriction inherent to air separation in the adsorption process. To produce 97+% and/or 99+% purity O₂ directly from air, the PVSA process with two zeolite 10X beds and one CMS bed was executed at 33.44-45.60 to 253.31 kPa. In addition, the effluent gas from the CMS bed to be used for O₂ purification was backfilled to the zeolite 10X bed to improve its purity, recovery, and productivity in bulk separation of the air. PVSA I, which made use of a single blowdown/backfill step, produced an O₂ product with a purity of 95.4-97.4% and a recovery of 43.4-84.8%, whereas PVSA II, which used two consecutive blowdown/backfill steps, produced O₂ with a purity of 98.2-99.2% and a recovery of 47.2-63.6%. Because the primary impurity in the O₂ product was Ar, the amounts of N ₂ contained in the product were in the range of 4000-5000 ppm at PVSA I and several tens of ppm at PVSA II. A nonisothermal dynamic model incorporating mass, energy, and momentum balances was applied to predict the process dynamics. Using the linear driving force (LDF) model with constant diffusivity for the equilibrium separation bed and a modified LDF model with concentration dependency of the diffusion rate for the kinetic separation bed, the dynamic model was able to accurately predict the results of the experiment.