Pre-combustion gas separation by ZIF-8-polybenzimidazole mixed matrix membranes in the form of hollow fibres—long-term experimental study

Abstract

Polybenzimidazole (PBI) is a promising and suitable membrane polymer for the separation of the H 2 /CO 2 pre-combustion gas mixture due to its high performance in terms of chemical and thermal stability and intrinsic H 2 /CO 2 selectivity. However, there is a lack of long-term separation studies with this polymer, particularly when it is conformed as hollow fibre membrane. This work reports the continuous measurement of the H 2 /CO 2 separation properties of PBI hollow fibres, prepared as mixed matrix membranes with metal-organic framework (MOF) ZIF-8 as filler. To enhance the scope of the experimental approach, ZIF-8 was synthesized from the transformation of ZIF-L upon up-scaling the MOF synthesis into a 1 kg batch. The effects of membrane healing with poly(dimethylsiloxane), to avoid cracks and non-selective gaps, and operation conditions (use of sweep gas or not) were also examined at 200°C during approximately 51 days. In these conditions, for all the membrane samples studied, the H 2 permeance was in the 22–47 GPU range corresponding to 22–32 H 2 /CO 2 selectivity values. Finally, this work continues our previous report on this type of application (Etxeberria-Benavides et al . 2020 Sep. Purif. Technol. 237 , 116347 ( doi:10.1016/j.seppur.2019.116347 )) with important novelties dealing with the use of ZIF-8 for the mixed matrix membrane coming from a green methodology, the long-term gas separation testing for more than 50 days and the study on the membrane operation under more realistic conditions (e.g. without the use of sweep gas).

Recent Progress and Challenges in the Field of Metal–Organic Framework-Based Membranes for Gas Separation

“…One strategy to improve the stability is to functionalize MOF-based membranes to change their resistance for potentially damaging contaminants. Although significant studies have been reported that subjected ZIF-8/polybenzimidazole MMMs to long-term gas separation testing for more than 50 days under more realistic conditions (e.g., in the absence of sweep gas) [205], there have been limited studies investigating the stability of MOF-based membranes.…”