Oxygen-Selective Adsorption in RPM3-Zn Metal Organic Framework


Development of an oxygen selective adsorbent is anticipated to reduce the material and energy requirements for adsorptive separations of air by a factor of four, due to the relative concentrations of N2 and O2 in air, thereby decreasing the parasitic energy losses, carbon dioxide emissions, and cost of oxygen purification via pressure-swing adsorption. Here, we report that RPM3-Zn (a.k.a. Zn2(bpdc)<2(bpee); bpdc = 4,4'-biphenyldicarboxylate; bpee = 1,2-bipyridylethene) is oxygen selective over nitrogen at temperatures from 77 K to 273 K, although the oxygen capacity of the sorbent decreased markedly at increasing temperatures. Due to an oxygen diffusivity that is ∼1000-fold greater than nitrogen, the effective oxygen selectivity increases to near infinity at low temperature at equal contact times due to N2 mass transfer limitations for gate-opening. The kinetic limitation for N2 to open the structure has a sharp temperature dependence, suggesting this effective kinetic selectivity may be "tuned in" for other flexible metal-organic-frameworks. Although the low temperature oxygen selectivity is not practical to displace cryogenic distillation, the results suggest a new mechanism for tailoring materials for kinetic selectivity, namely, capitalizing upon the delayed opening process for a particular gas relative to another.


Chemical and Biochemical Engineering

Keywords and Phrases

Air cleaners; Air purification; Carbon; Carbon dioxide; Crystalline materials; Distillation; Energy dissipation; Global warming; Kinetics; Mass transfer; Nitrogen; Organic polymers; Organometallics; Oxygen; Temperature; Temperature distribution; Zinc; Air separation; Carbon dioxide emissions; Cryogenic distillations; Gate openings; Kinetic selectivity; Mass transfer limitation; Metal organic framework; Pressure swing adsorption; Gas adsorption; Air separation; Kinetic selectivity; RPM3-Zn

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Article - Journal

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© 2017 Elsevier, All rights reserved.

Publication Date

01 Jun 2017