Modeling syngas permeation through a poly dimethyl siloxane membrane by Flory–Rehner theory

Abstract

Poly dimethyl siloxane (PDMS) membranes show potential for the separation of carbon dioxide from hydrogen in syngas applications due to their strong affinity for CO2. The Flory–Rehner theory of mixing enables the sorption of gases within such a rubbery membrane to be modeled, as long as the Flory–Huggins interaction parameters are known. In this work, mixed gas permeation experiments are used to determine interaction parameters for a range of relevant gas pairs. For the N2–H2 system, the mixed gas performance is comparable to pure gas measurements and indicates that H2 does not interfere with the permeation of N2 through the membrane. In contrast, for the CO2–H2 system, the CO2 permeability falls with increasing H2 partial pressure, attributed to competitive sorption. The effect of a typical hydrocarbon impurity, toluene, upon CO2 and N2 permeability through PDMS was also measured. The addition of this aromatic hydrocarbon caused significant polymer swelling, which required solubility modeling with the Flory–Rehner model. A concentration dependent diffusivity was also required to fit the permeation data. The parameters determined from the laboratory experiments were used to model pilot plant results for a PDMS membrane separating CO2 from syngas, as part of the CO2CRC Mulgrave Project. It was found that the model could effectively predict experimental CO2, N2 and H2 permeabilities.