Tri-functional carbon membrane for one-step uptake of low-concentration hydrogen to high purity

[Display omitted] •Carbon membrane integrates capture, pre-separation, and purification functions.•The mesoporous substrate utilizes Knudsen flow for H2 and transition flow for CH4.•The purity of H2 increases from 20 vol% to ∼ 99 vol% through a single-step process.•The selectivity of H2/CH4 is 359.1 and H2 permeance of 55.3 × 10-9 mol·m−2·s−1 Pa−1. The uptake of hydrogen (H2) from natural gas pipelines (CH4) through membrane separation technology is an efficient avenue of obtaining H2 resources. Carbon membranes have the potential to be an attractive option for energy-efficient gas separations in the next generation of membranes due to their precise molecular discrimination ability and easy scalability. Here, we report a carbon membrane composed of a mesoporous substrate, seed layer and sieving layer, achieving a one-step uptake with 55.3 × 10-9 mol·m−2·s−1 Pa−1 permeance and a separation factor for H2/CH4 of 359.1 by feeding hydrogen (20 vol%). As revealed by the kinetic diffusion experiment, H2 is transported in mesoporous substrate via Knudsen flow, differing from the transition flow taken by CH4, thus H2 diffusion rates exceed CH4 by an order of magnitude, which substantially increased H2 purity from 20 vol% to higher purity as gas mixtures passed through the substrate. Then, the H2 passed through the seed layer and sieving layer, resulting in a final H2 purity of ∼ 99 vol%, a sharp increase from the initial low concentration. This carbon membrane integrates three functions of capture, pre-separation and purification into one material and provides a new solution for the uptake of H2 from CH4.