Polyethyleneimine-Modified MCM-48 Membranes: Effect of Water Vapor and Feed Concentration on N₂/CO₂ Selectivity

Abstract

Ordered mesoporous MCM-48 membranes with cubic pore structure were prepared by the solution growth method on symmetric α-alumina supports using cetyltrimethylammonium bromide as a surfactant. The surfactant was removed by Soxhlet extraction using an ethanol/HCl mixture to synthesize defect-free MCM-48 membranes as confirmed by N2 unsteady-state permeation. MCM-48 membranes and powders were successfully modified with a polymer, polyethyleneimine (PEI) containing amino groups as confirmed by N2 adsorption−desorption data, X-ray diffraction, Thermo gravimetric analysis (TGA), and N2 unsteady-state permeation experiments. The PEI/MCM-48 membranes were permeable to N2 after pore modification, suggesting incomplete filling of MCM-48 pores by PEI, which was confirmed by the N2 adsorption−desorption experiments on the bulk PEI/MCM-48 powder. The PEI-modified MCM-48 membranes were highly selective to N2 permeation from N2/CO2 mixtures at room temperature in the presence of ∼2.6% water vapor. Binary-gas N2/CO2 permeation data for the PEI-modified MCM-48 membranes showed much-higher N2 permeance as compared to CO2 permeance in the presence of water vapor. The selectivities increased with CO2 concentration in the feed, and selectivities greater than 80 were observed. The N2/CO2 selectivities diminished significantly at 363 K for the PEI/MCM-48 membranes.