Development of hydrogen-selective CAU-1 MOF membranes for hydrogen purification by ‘dual-metal-source’ approach

Abstract

Hydrogen provides reliable, sustainable, environmental and climatic friendly energy to meet world's energy requirement and it also has high energy density. Hydrogen is relevant to all of the energy sectors-transportation, buildings, utilities and industry. In all of these sectors, hydrogen-rich gas streams are needed. Thus, hydrogen-selective membrane technology with superior performances is highly demanded for separation and purification of hydrogen gas mixtures. In this study, novel [Al4(OH)2(OCH3)4(H2N-BDC)3] xH2O (CAU-1) MOF membranes with accessible pore size of 0.38 nm are evaluated for this goal of hydrogen purification. High-quality CAU-1 membranes have been successfully synthesized on a-Al2O3 hollow ceramic fibers (HCFs) by secondary growth assisted with the homogenously deposited CAU-1 nanocrystals with a size of 500 nm as seeds. The energy-dispersive X-ray spectroscopy study shows that the HCFs substrates play dual roles in the membrane preparation, namely aluminum source and as a support. The crystals in the membrane are intergrown together to form a continuous and crack-free layer with a thickness of 4 mm. The gas sorption ability of CAU-1 MOF materials is examined by gas adsorption measurement. The isosteric heats of adsorption with average values of 4.52 kJ/mol, 12.90 kJ/mol, 12.82 kJ/mol and 27.99 kJ/mol are observed for H2, N2, CH4, and CO2 respectively, indicating different interactions between CAU-1 framework and these gases. As-prepared HCF supported CAU-1 membranes are tested by single and binary gas permeation of H2/CO2, H2/N2 and H2/CH4 at different temperatures, feed pressures and testing time. The permeation results show preferential permeance of H2 over CO2, N2, and CH4 with high separation factors of 12.34, 10.33, and 10.42 for H2/CO2, H2/N2, H2/CH4, respectively. The temperature, pressure and test time dependent studies reveal that HCFs supported CAU-1 membranes possess high stability, resistance to cracking, temperature cycling, high reproducibility, these of which combined with high separation efficiency make this type of MOF membranes are promising for hydrogen recycling from industrial exhausts.