Carbon dioxide separation from hydrogen and nitrogen by fixed facilitated transport in swollen chitosan membranes

The separation of carbon dioxide from hydrogen and nitrogen at high temperatures would be valuable to fuel cell, flue gas purification, and ammonia processes. A feed gas mixture of carbon dioxide, hydrogen and nitrogen (10% CO2, 10% H2, and 80% N2) was used to evaluate water-swollen chitosan as a facilitated transport membrane for these applications. The amino group of the chitosan repeating unit could be the fixed carrier that facilitates carbon dioxide transport in the presence of water. Carbon dioxide transport properties of a water-swollen chitosan membrane were measured over temperature and pressure ranges of 20–150 °C and 1.5–5 atm, respectively. The average levels of water (total, free and bound) in the membranes were measured and correlated with carbon dioxide transport properties. At a feedstream pressure of 1.5 atm, all free water was lost from the membrane at temperatures above 110 °C and only bound water could contribute to facilitated transport. This mechanism change resulted in maxima in the CO2 permeability (482 barrers), the CO2/H2 selectivity (43.4), and the CO2/N2 selectivity (250) at T = 110 °C. Each type of water appeared to have a different efficiency in contributing to the facilitated transport of carbon dioxide through chitosan membranes.