Abstract
The combination of pressure swing adsorption (PSA) with a downstream redox chemical looping cycle to remove trace oxygen is proposed for the production of high-purity nitrogen from atmospheric air. The non-stoichiometric perovskite SrFeO 3 − δ is selected for the redox chemical looping cycle because of its favourable thermodynamics, rapid oxidation kinetics and intermediate reduction temperatures. Long term stability of the material was demonstrated over 250 redox cycles via thermogravimetry. Oxidation kinetics were measured and incorporated in a 1D convection–diffusion model of a packed bed reactor configuration. The model indicates that, for a targeted oxygen impurity level of x O 2 < 3 × 1 0 − 6 , a chemical looping unit added to a PSA system could approximately triple the capacity and reduce the energy demand to 14 kJmol − 1 of N 2 . • Analysis of SrFeO 3 chemical looping oxygen separation for residual oxygen removal. • Analysis shows a competitive energy balance for high purity nitrogen production. • Chemical stability of SrFeO 3 shown over 250 cycles. • Validated model shows promising packed bed reactor performance.
Highlights
Nitrogen makes up 78% of the earth’s atmosphere
The combination of pressure swing adsorption (PSA) with a downstream redox chemical looping cycle to remove trace oxygen is proposed for the production of high-purity nitrogen from atmospheric air
The nonstoichiometric perovskite SrFeO3−δ is selected for the redox chemical looping cycle because of its favourable thermodynamics, rapid oxidation kinetics and intermediate reduction temperatures
Summary
Nitrogen makes up 78% of the earth’s atmosphere. Its triple bond N≡N is extremely stable, making the gas inert under most circumstances. Each of these technologies use mechanical compression as the source of work that powers the separation of nitrogen from air, but the processes after compression are quite different [2]. The capacity of a PSA unit decreases significantly with increasing purity (see Fig. 1), while the installation cost and power demand remain approximately the same This is because the PSA packed beds need to be regenerated much more frequently to maintain the high purity. A scaled up system for the production of 1000 N m−3 h−1 of nitrogen with an oxygen impurity xO2 < 3e−6 is modelled
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