Comparison and evaluation of agglomerated MOFs in biohydrogen purification by means of pressure swing adsorption (PSA)

- HKUST-1 and ZIF-8 extrudates with negligible loss of surface area were prepared.
- Adsorption isotherms of carbon dioxide and hydrogen in the extrudates were measured.
- Diffusion parameters of carbon dioxide in the extrudates have been measured.
- UTSA-16 outperforms HKUST-1 and ZIF-8 in simulated PSA for 60/40 CO2/H2 separation.

In this work, the agglomeration of HKUST-1 and ZIF-8 with polyvinylalcohol (PVA) has been studied. Extrudates with very low reduction of surface area with respect to powder (less than 3% for a PVA content of 2.9%) have been obtained. The adsorption isotherms of carbon dioxide and hydrogen on HKUST-1 and ZIF-8 extrudates for pressures up to 30-50 bar, and temperatures between 298 and 338 K, have been measured. Diffusion parameters of carbon dioxide on these adsorbents have been measured taking into account the effect of dispersion and macropore diffusion on the experimental signal used, resulting in reciprocal diffusion time constants in the crystals of 0.034 s−1 in HKUST-1, and 0.14 s−1 in ZIF-8 at 298 K. The performance of HKUST-1, ZIF-8 and UTSA-16 extrudates in the separation of carbon dioxide from a mixture with hydrogen by PSA has been compared by simulation. UTSA-16 presents the best performance for biohydrogen purification for a feed mixture containing 40% hydrogen and 60% carbon dioxide. This is attributed to its high selectivity towards carbon dioxide, and to its high volumetric heat capacity.