Crosslinked Facilitated Transport Membranes Based on Carboxymethylated NFC and Amine-Based Fixed Carriers for Carbon Capture, Utilization, and Storage Applications

Engineering CO2-Ultraselective Membranes: Molecularly Tailored Low-Crystallinity Polyvinylamine-PEGDGE Networks

Facilitated transport membranes (FTMs) with an ultraselective layer prepared from amine-rich polyvinylamine (PVAm)/2-(1-piperazinyl)ethylamine salt of sarcosine (PZEA-Sar) (denoted by PM) and an amorphous dendritic cross-linked network of PVAm-functionalized poly(ethylene glycol)diglycidyl ether (PEGDGE) (named PP) were designed for CO2 separations. The developed membranes expedited CO2 transport over N2 through the synergistic effect from the induced CO2-philic ethylene oxide groups and highly hydrophilic and polar hydroxyl groups together with the low-crystallinity PP networks, which offer a high diffusion rate for CO2-amine complexes through the membrane and stabilize small molecular mobile carriers via hydrogen bonding. The best (PM/PP-10)/polysulfone (PSf) composite membranes achieved a superior CO2/N2 selectivity of 230 (4.6 times higher compared to that of the pristine PVAm/PSf membranes) paired with a CO2 permeance of 100 GPU, exceeding the 2019 Robeson upper bound. Molecular dynamics (MD) simulations for the PVAm and PVAm/PP-10 membranes suggested that the PVAm matrix was swelled by the introduced PP-10 network with increased fractional free volume (FFV). The engineering of the molecular structure and the manipulation of FFV strongly push the limits of selectivity for PVAm-based FTMs, which may open doors to provide a facile and scalable approach to developing CO2-ultraselective membranes for carbon capture from flue gases.

Effect of Mobile Carrier on the Performance of PVAm-Nanocellulose Facilitated Transport Membranes for CO2 Capture

Facilitated transport membranes obtained by coupling polyvinylamine with highly charged carboxymethylated nanocellulose fibers were studied considering both water sorption and gas permeation experiments. In particular, the effect of the L-arginine as a mobile carrier was investigated to understand possible improvements in CO₂ transport across the membranes. The results show that L-arginine addition decreases the water uptake of the membrane, due to the lower polyvinylamine content, but was able to improve the CO₂ transport. Tests carried on at 35 °C and high relative humidity indeed showed an increase of both CO₂ permeability and selectivity with respect to nitrogen and methane. In particular, the CO₂ permeability increased from 160 to about 340 Barrer when arginine loading was increased from 0 to 45 wt%. In the same conditions, selectivity with respect to nitrogen was more than doubled, increasing from 20 to 45. Minor improvements were instead obtained with respect to methane; CO₂/CH₄ selectivity, indeed, even in presence of the mobile carrier, was limited to about 20.

Analysis of CO2 Facilitation Transport Effect through a Hybrid Poly(Allyl Amine) Membrane: Pathways for Further Improvement

Numerous studies have been reported on CO₂ facilitated transport membrane synthesis, but few works have dealt with the interaction between material synthesis and transport modelling aspects for optimization purposes. In this work, a hybrid fixed-site carrier membrane was prepared using polyallylamine with 10 wt% polyvinyl alcohol and 0.2 wt% graphene oxide. The membrane was tested using the feed gases with different relative humidity and at different CO₂ partial pressures. Selected facilitated transport models reported in the literature were used to fit the experimental data with good agreement. The key dimensionless facilitated transport parameters were obtained from the modelling and data fitting. Based on the values of these parameters, it was shown that the diffusion of the amine-CO₂ reaction product was the rate-controlling step of the overall CO₂ transport through the membrane. It was shown theoretically that by decreasing the membrane selective layer thickness below the actual value of 1 µm to a value of 0.1 µm, a CO₂ permeance as high as 2500 GPU can be attained while maintaining the selectivity at a value of about 19. Furthermore, improving the carrier concentration by a factor of two might shift the performances above the Robeson upper bound. These potential paths for membrane performance improvement have to be confirmed by targeted experimental work.