APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session D04: Transport Phenomena in Membranes for Separations II
3:00 PM–6:00 PM,
Monday, March 6, 2023
Room: Room 127
Sponsoring
Unit:
DPOLY
Chair: Vera Bocharova, Oak Ridge National Lab
Abstract: D04.00006 : Chain End Functionalization of Polyoxymethylene Polymer Membrane for Better CO2 Separation
4:00 PM–4:12 PM
Abstract
Presenter:
Yasemin Basdogan
(California Institute of Technology)
Authors:
Yasemin Basdogan
(California Institute of Technology)
Zhen-Gang Wang
(Caltech)
(PEO)-based polymers have been leading membrane materials for CO2/N2 separation. The ether oxygen moiety is a unique functional group that exhibits affinity towards CO2 but not N2, which leads to high CO2 solubility and CO2/N2 solubility selectivity. In this study we systematically study the effect of increasing the ether-oxygen content on a polymer's performance for the separation of CO2 from N2 and O2 gas. We study pure gas solubility and diffusivity as well as solubility and diffusivity selectivity. We use the oxygen to carbon ratio as the indicator for the ether-oxygen content in the polymer membrane. We select five polymers that have oxygen to carbon ratio from 0 to 1. We use equation of state calculations to calculate the gas solubility, and molecular dynamics simulations to calculate gas diffusivity in the polymer melt. We show that we can significantly control the CO2/N2 solubility selectivity of a memebrane material by increasing the oxygen ether content in the polymer without affecting the CO2/N2 diffusivity selectivity. We note that the highest diffusivity selectivity for both CO2/N2 and CO2/O2 gas pairs were found in the POM membrane; thus we suggest POM polymer membrane as a promising polymer for the CO2 separation from N2 and O2 gas. To increase the CO2/N2 diffusivity selectivity, we further investigate the role of the chain ending with POM polymer membrane by altering it from hydrogen to an azo (CN=CN) and triazine (nitrogen containing heterocycle) functional groups. We conclude adding nitrogen containing functional groups to the chain ends of the polymer significantly slows down the gas diffusion thus makes these polymer membranes not optimal candidates for neither CO2/N2 nor CO2/O2 separation. We also convert the terminal groups of POM polymers to acrylate, acetyl, and ethoxy groups and compare their CO2 separation performance. The terminal hydroxyl groups forms hydrogen bonding and reduce the chain flexibility, leading to lower gas diffusivity and permeability. Converting the terminal hydroxyl groups to acrylate, acetyl, and ethoxy groups eliminates the effect of hydrogen bonding and increases the gas diffusivity as well as the diffusivity selectivity.