Screening Metal–Organic Frameworks for Dynamic CO/N₂ Separation Using Complementary Adsorption Measurement Techniques

Abstract

Carbon monoxide (CO)/nitrogen (N 2 ) separation is a particularly challenging separation, yet it is the one with great industrial relevance for its use in petrochemical synthesis. Although an expensive cryogenic step can be used to perform such separation, it remains ineffective in purifying CO from syngas streams with a significant N 2 content. Taking advantage of the lower energy requirement of adsorption processes, we have explored the use of metal−organic frameworks (MOFs) as adsorbents for this difficult separation. We have screened a range of MOF candidates for CO/N 2 separation covering a range of chemical and textural features, using the flux response technology to evaluate their dynamic performance for throughput testing alongside equilibrium uptake measurements. We have identified Ni-MOF-74 and Co-MOF-74 as the most promising candidates because of their high metal density and strong metal−CO interactions. We have investigated further the effect of N 2 impurity concentrations upon CO/N 2 separation using breakthrough adsorption testing and cyclic testing (up to 20 cycles). Overall, using multiple adsorption measurement techniques, this study demonstrates the CO/N 2 dynamic separation performance of M-MOF-74 and its ability to be applied for an industrially relevant separation.

Optimisation of Cu+ impregnation of MOF-74 to improve CO/N2 and CO/CO2 separations

“…In an industrial setting, an adsorbent must maintain high adsorption capacity and selectivity over multiple cycles and require minimal energy for regeneration. Previous studies have tested the cyclability of Ni-MOF-74 ( ref. 6 ) and Cu impregnated MOFs for CO purification, 22,23,25 with He purging 22 and vacuum swing 25 regeneration techniques favoured to minimise any potential overreduction which would be associated with thermal regeneration.…”

“…Yet, vacuum swing and He purging would not regenerate the Ni 2+ sites of the MOF. A high regeneration temperature is required due to the high CO isosteric heat of adsorption value of Ni-MOF-74 ( ref. 6 ) (−54.4 kJ mol −1 at low loading) potentially leading to undesired chemisorbing Cu 0 sites.…”

“…cryogenic distillation. 2 MOFs have shown the most promising performance to date, 6 recording the highest CO adsorption uptakes and theoretical CO/X selectivities (where X = H 2 , N 2 and CH 4 ). 5,7 …”

High-throughput screening of metal – Organic frameworks for CO2 and CH4 separation in the presence of water

“…Experimental screenings of MOFs were also performed, although on a much smaller scale. Evans et al [65] performed binary gas breakthrough measurements of dynamic capacity of CO and N 2 adsorption in 10 MOFs, to verify their performance in CO/N 2 separation, and applicability in petrochemical industry. Han et al [66] investigated CO 2 and N 2 adsorption and diffusion in 8 selected MOFs, in dry and humid conditions.…”

The development of a comprehensive toolbox based on multi-level, high-throughput screening of MOFs for CO/N2separations

“…Distillation, which operates based on exploiting differences in the volatility of the components to be separated is not very effective for separating CO/N 2 mixtures , as they have similar physical properties, with boiling points of 82 K (CO) and 77 K (N 2 ), respectively, and hence their separation requires high energy input. Despite the importance of CO/N 2 separations, and to the best of our knowledge, there are not any robust technologies, currently proven and operating, that can perform the purification process at relatively high N 2 content at a commercial scale [18][19][20].…”