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High-Purity Nitrogen By Pressure-Swing Adsorption Using Supported Cyanocobaltate Adsorbents

IP.com Disclosure Number: IPCOM000019363D
Publication Date: 2003-Sep-12
Document File: 6 page(s) / 411K

Publishing Venue

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Abstract

A family of cyanocobaltate complexes which demonstrate reversible pressure-swing oxygen sorption capacity have been developed. These materials possess a unique set of properties which make them attractive adsorbents for the production of nitrogen from air by Pressure Swing Adsorption (PSA), including (1) reasonably high equilibrium oxygen capacity, (2) high working capacity for oxygen over a standard PSA pressure envelope, (3) a Type I isotherm without hysteresis, (4) comparatively rapid adsorption and desorption kinetics, (5) infinite selectivity to oxygen, and (6) excellent chemical stability over a large number of adsorption/desorption cycles. While pellets of the neat complexes do show high equilibrium PSA capacity, their relatively slow sorption/desorption kinetics makes it advantageous to support these complexes on an inert support for use in a PSA system. A number of such supported materials have been prepared, using the complex Li3Co(CN)5 1.42DMF 0.48DMAc, 1, where DMF is N,N-Dimethylformamide and DMAc is N,N-Dimethylacetamide. Characterization of the resulting materials has shown that the support affects both the oxygen uptake kinetics and oxygen capacity. Three materials were evaluated: neat 1 extrudate, 1 supported on diatomaceous earth (Celite-631, average pore diameter of 6 microns), and 1 supported on silica (Philadelphia Quartz, average pore diameter of 300Å). These were first characterized by measuring their equilibrium oxygen uptakes and by fitting the transient uptake data to a distributed-resistance mass transfer model (DRM). The DRM assumes that the particles of 1 are present as small spheres and that both reaction on the surface of the sphere and oxygen diffusion through the bulk of the sphere contribute to the mass transfer resistance.

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High-Purity Nitrogen By Pressure-Swing Adsorption Using Supported Cyanocobaltate Adsorbents

         A family of cyanocobaltate complexes which demonstrate reversible pressure-swing oxygen sorption capacity have been developed.[1] These materials possess a unique set of properties which make them attractive adsorbents for the production of nitrogen from air by Pressure Swing Adsorption (PSA), including (1) reasonably high equilibrium oxygen capacity, (2) high working capacity for oxygen over a standard PSA pressure envelope, (3) a Type I isotherm without hysteresis, (4) comparatively rapid adsorption and desorption kinetics, (5) infinite selectivity to oxygen, and (6) excellent chemical stability over a large number of adsorption/desorption cycles. While pellets of the neat complexes do show high equilibrium PSA capacity, their relatively slow sorption/desorption kinetics makes it advantageous to support these complexes on an inert support for use in a PSA system. A number of such supported materials have been prepared, using the complex Li3Co(CN)5·1.42DMF·0.48DMAc, 1, where DMF is N,N-Dimethylformamide and DMAc is N,N-Dimethylacetamide. Characterization of the resulting materials has shown that the support affects both the oxygen uptake kinetics and oxygen capacity. Three materials were evaluated: neat 1 extrudate, 1 supported on diatomaceous earth (Celite-631, average pore diameter of 6 microns), and 1 supported on silica (Philadelphia Quartz, average pore diameter of 300Å). These were first characterized by measuring their equilibrium oxygen uptakes and by fitting the transient uptake data to a distributed-resistance mass transfer model (DRM). The DRM assumes that the particles of 1 are present as small spheres and that both reaction on the surface of the sphere and oxygen diffusion through the bulk of the sphere contribute to the mass transfer resistance.

where is the chemical potential driving force, c is the order of the surface reaction with respect to the driving force and B and k are the Toth isotherm parameters, obtained by fitting the equilibrium isotherm data to the form

The results of these experiments were as follows:

Table 1: Characterization of Adsorbents

Sample

Uptake @25°C

Ksurf@25°C

D/r2@25°C

Neat 1

1.15 mmol/g

0.0018 (mmol/g)1-c

0.04

1 on CeliteÒ

0.38 mmol/g

0.0067 (mmol/g)1-c

0.04

1 on Silica

0.20 mmol/g

0.039 (mmol/g)1-c

0.05

These materials are envisioned for use in Nitrogen PSA technology in two possible roles: (1) as a stand-alone “Deoxo” system operating on its own PSA cycle and located downstream of a conventional PSA or membrane or (2) in a layered bed arrangement where a layer of 1 is placed at the product end in a standard Nitrogen PSA bed. This second configuration has been described by Takahashi and Ochi[2], who disclosed a two-bed PSA process using a layered bed containing carbon molecular sieve and supported metal complexes. The metal complexes they proposed included iron porphyrin derivatives, cobalt amine...