A new zeolitic hydroxymethylimidazolate material and its use in mixed matrix membranes based on 6FDA-DAM for gas separation

Abstract

The new ZIF named UZAR-S13 is formed by Zn2+ and 4(5)-(hydroxymethyl)imidazolate. UZAR-S13 has two distinct phases according to SEM and XRD: amorphous spheres and sheet crystals. UZAR-S13 and byproducts, with no N2 adsorption, rendered a notable CO2 uptake (up to 3.8 mmol g−1 at 30 bar and 0 °C), approaching values of known ZIFs. The most promising materials were included as fillers in mixed matrix membranes based on copolyimide 6FDA-DAM to study the separation of CO2/CH4, CO2/N2, H2/CO2 and H2/CH4 mixtures. The pore blocking hindered the gas flow of bulky molecules (CH4, N2 and CO2). The high CO2 adsorption on sheet crystals also contributed to the decrease in the permeability of CH4, N2 and CO2, giving poor selectivities. In contrast, the MMMs improved both the H2/CH4 selectivity (8.9–12.7 vs. 7.2) and permeability of H2 (544–597 vs. 505 Barrer) of the bare 6FDA-DAM membrane. This emphasizes the potential application of the fillers in the separation by molecular sieving of gas mixtures without CO2.