On the Transport of CO2, N2, and H2O in Poly(N-vinylformamide-co-vinylamine) Copolymers with Different Amine-to-Amide Ratios
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Date
2021-12
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The Ohio State University
Abstract
Coal-fired power plants are responsible for nearly half of the world's total electricity production but are environmentally concerning due to their emissions of CO2, a greenhouse gas. One method to reduce the environmental impact of burning coal while preserving the technology and infrastructure of current facilities is through sequestering CO2 from flue gas. A promising technology to capture CO2 at the source is via facilitated transport membranes (FTMs), which are gas-permeable membranes that use reversible chemical reactions to selectively transport CO2 across them at higher rates than other inert molecules (e.g., N2). The copolymer poly(N-vinylformamide-co-vinylamine) (PNVF-co-PVAm) has shown promise as a FTM material due to its high reactivity with CO2 in the presence of moisture. This polymer contains both amide and amino groups, and the ratio of these functional groups is determined by the degree of hydrolysis (DoH). A membrane with a higher DoH contains more amino groups that react with CO2 but fewer amide groups that form hydrogen bonds with water molecules, which swell the membrane to allow for faster diffusion of guest molecules.
Gas permeation and gravimetric analyses were carried out to quantify the relationship between DoH and important membrane properties like permeance, diffusivity, and solubility of CO2 in PNVF-co-PVAm membranes with different DoH. The CO2 permeance was found to be approximately 250 Gas Permeation Unit (GPU, 1 GPU = 1 x 10^-6 cm^3 (STP) / cm^2 / s / cmHg) in a membrane with 0% DoH and increased sharply with increasing DoH before plateauing around 500 GPU for a DoH above 60%. The solubility of CO2 in the membrane also increased with increasing DoH, from 10 cm^3 (STP) / cm^3 / atm at 0% DoH to 120 cm^3 (STP) / cm^3 / atm at 100% DoH. However, the CO2 diffusivity was halved by increasing the DoH from 0% to 100%. This showed that, although a higher DoH increased the chemisorption of CO2, it resulted in a reduced fractional free volume that limited the diffusion of guest molecules.
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Keywords
Gas-Permeable Membrane, Carbon Capture, Facilitated Transport, Gas Separation