Research on triazine-based nitrogen-doped porous carbon/Pebax mixed-matrix membranes for CO2 separation and its gas transport mechanism

Nitrogen-doped porous carbon (NPC) has a rich microporous structure and nitrogen-rich units, and its nitrogen-containing group can interact strongly with the PEO chain segment of Pebax, synergistically improving its CO2 adsorption ability and interface compatibility. This work prepared three types of triazine-based NPCs with mesoporous and high N-content and added NPCs to Pebax-2533 to prepare NPC/Pebax-2533 MMMs. The effects of N-type, N-content, and pore structure of NPCs on the gas separation performance of MMMs were studied. Constructing a continuous meso-microporous structure within the membrane and adding alkaline N-containing groups were beneficial for promoting rapid CO2 transport. Among the three NPCs, NPC-1/Pebax MMMs prepared using NPC-1 with the highest N-content (10.91%) and suitable pore structure exhibited the best gas separation performance. To investigate the gas transport mechanism of NPC in MMMs, NPC-1 was added to Pebax-2533 and Pebax-1657. The permeability of 3NPC-1/Pebax-2533 MMMs and 0.5NPC-1/Pebax-1657 MMMs reached 423 Barrer and 178 Barrer, with a CO2/N-2 selectivity of 61 and 75.8, respectively, both higher than the Pebax-2533 and Pebax-1657. Adding NPC-1 to Pebax-2533 and Pebax-1657 increased the solubility and diffusivity coefficient of MMMs by 40 similar to 80%, and the gas separation performance did not rapidly decrease after long-term stability of 120 h (15%CO2/N-2). Compared with NPC-1/Pebax-1657 MMMs, NPC-1/Pebax-2533 MMMs had higher CO2 permeability, mechanical properties, solubility, and diffusivity coefficient. The above results indicated that NPC was more suitable for Pebax-2533.