(377g) Amine-Containing Membranes with Functionalized Multi-Walled Carbon Nanotubes for CO2/H2 Separation

Facilitated transport membranes (FTMs) is a great candidate for CO₂/H₂ separation, due to both high CO₂ permeability and high CO₂/H₂ selectivity. However, it is still a challenge to meet the industrial demands at a high pressure of 1.5 MPa or greater and a temperature of 100 °C or higher. In this work, amino-functionalized multi-walled carbon nanotubes (AF-MWNTs) were chosen primarily as the mechanical reinforcing filler to enhance the membrane stability against compaction. The acid treatment and amino-functionalization of MWNT could improve its compatibility with an amine/PVA membrane matrix and thus enhance the membrane stability and transport performance. The effects of AF-MWNT loading on the stability and transport performance of the amine-containing membrane were investigated to attain the optimal membrane composition.

At 107 °C and 0.2-MPa feed pressure, the membrane incorporated with 10 wt.% AF-MWNTs showed a CO₂ permeability of 3196 Barrer and a CO₂/H₂ selectivity of 205, which were slightly lower than those of the membrane without the nanofiller due to the reduced amine concentration of the AF-MWNTs. At 1.5-MPa feed pressure, the same membrane exhibited the best transport performance, showing a CO₂ permeability of 776 Barrer and a CO₂/H₂ selectivity of 31, owing to the reinforcement effect of the AF-MWNTs against membrane compaction under the high pressure. However, both the CO₂ permeability and CO₂/H₂ selectivity were lower, which was due to the carrier saturation phenomenon. Furthermore, the incorporation of 10 wt.% AF-MWNTs led to a significant improvement on membrane stability. The transport performance and selective layer thickness of this membrane maintained for 100 h, which suggested that the incorporation of AF-MWNTs improved the resistance to membrane compaction upon a high feed pressure. In addition, the representative transport performances of all membranes under 0.2-MPa and 1.5-MPa feed pressures well surpassed the theoretical upper bound. Therefore, this work is considered as one of the crucial steps to enable the application of facilitated transport membranes to high-pressure gas processing such as syngas purification.