Mathematical modeling of CO2 facilitated transport across polyvinylamine membranes with direct operando observation of amine carrier saturation

In this work, we investigate the kinetics and mechanisms of CO2 facilitated transport across polyvinylamine (PVAm) membranes using mathematical modeling of experimentally measured CO2 fluxes across PVAm with operando surface-enhanced Raman spectroscopic (SERS) and Fourier-transform infrared (FTIR) spectroscopy characterization. The mathematical model was fit to experimentally measured CO2 fluxes as a function of CO2 partial pressure (2-99 kPa) and PVAm membrane thickness (1.7-4.1 mu m). Physically significant kinetic and thermodynamic parameters associated with CO2 transport were extracted from the model, such as the permeability of PVAm to CO2 via solution diffusion, the permeability of PVAm to carbamate (NHCOO-) via facilitated transport, and the carbamate formation/decomposition equilibrium constant. Our results show that the permeability of PVAm to carbamate via facilitated transport (2200 +/- 1200 Barrer) is about an order of magnitude greater than the permeability of PVAm to CO2 via solution-diffusion of CO2 (150 +/- 20 Barrer). Using operando SERS and FTIR, we directly observed saturation of the primary amine groups of PVAm with CO2 (carbamate) at a feed CO2 partial pressure of similar to 10 kPa, which was in good agreement with our model predictions. This work quantitatively describes CO2 facilitated transport across PVAm and provides direct evidence of the carrier saturation phenomenon-for the first time to our knowledge-from a molecular perspective through operando spectroscopic characterization.

Automated summary

In this work, the kinetics and mechanisms of CO2 facilitated transport across PVAm membranes were investigated using mathematical modeling and experimental characterization techniques. The study extracted important kinetic and thermodynamic parameters associated with CO2 transport, and found that the permeability of PVAm to carbamate via facilitated transport is about an order of magnitude greater than the permeability to CO2 via solution-diffusion. Direct evidence of carrier saturation phenomenon was observed and it was consistent with the model predictions.