Mixed-matrix membranes consisting of Pebax and novel nitrogen-doped porous carbons for CO2 separation

Fabricating high-performance mixed matrix membranes (MMMs) for CO2 separation is of great importance for industrial application, but the poor compatibility between polymer and filler hinders their further development. Herein, novel nitrogen-doped porous carbons (NPC) were gained by a facile hydrothermal reaction between glucose and melamine, subsequently KOH activation. Highly micropore NPC with the BET surface area of 1229.36 m(2) g(-1) and Langmuir surface area of 1868.46 m(2) g(-1) accompanied with the BJH pore volume of 0.68 cm(3) g(-1) was achieved by scanning electron microscopy (SEM) and N-2 adsorption. After blending with polyetherblock-amide (Pebax), the as-obtained MMMs showed excellent mechanical properties probably due to the homogeneous dispersion of NPC in the Pebax as shown in SEM results. The nitrogen in MMMs was expected to be significantly increased upon incorporation with NPC, as verified by attenuated total reflectance Fourier transform infrared spectroscopy, thus increased the CO2 transport. MMM with 5 wt% NPC exhibited a CO2 permeability of 553 Barrer. This value is much higher than that of the pristine Pebax membrane. Surprisingly, a significantly improved CO2 /N-2 selectivity of as high as 56.4 was observed for MMMs. Thus, MMM having a 5 wt % NPC had an excellent gas separation, approaching Robeson's upper bound revised in 2019, which was superior to the one incorporated with other activated carbons prepared from similar reactants. The enhanced separation performance is mainly ascribed to the presence of nitrogen-containing groups for high CO2 affinity and also the micropore structure to promote CO2 diffusion in NPC. These results indicated that the improvement in gas permeability and ideal selectivity simultaneously could be achieved by MMMs using the microporous and functional nanofillers.

Automated summary

Fabricating high-performance mixed matrix membranes (MMMs) for CO2 separation is important for industrial applications, but the poor compatibility between the polymer and filler hinders their development. In this study, nitrogen-doped porous carbons (NPC) were synthesized and blended with polyetherblock-amide (Pebax) to create MMMs with improved mechanical and CO2 separation properties. The incorporation of NPC increased the nitrogen content and enhanced the CO2 permeability and selectivity of the MMMs. The MMMs with 5 wt% NPC showed excellent gas separation performance, approaching the upper limit set by Robeson in 2019.