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 N 2 unsteady-state permeation. MCM-48 membranes and powders were successfully modified with a polymer, polyethyleneimine (PEI) containing amino groups as confirmed by N 2 adsorption−desorption data, X-ray diffraction, Thermo gravimetric analysis (TGA), and N 2 unsteady-state permeation experiments. The PEI/MCM-48 membranes were permeable to N 2 after pore modification, suggesting incomplete filling of MCM-48 pores by PEI, which was confirmed by the N 2 adsorption−desorption experiments on the bulk PEI/MCM-48 powder. The PEI-modified MCM-48 membranes were highly selective to N 2 permeation from N 2 /CO 2 mixtures at room temperature in the presence of ∼2.6% water vapor. Binary-gas N 2 /CO 2 permeation data for the PEI-modified MCM-48 membranes showed much-higher N 2 permeance as compared to CO 2 permeance in the presence of water vapor. The selectivities increased with CO 2 concentration in the feed, and selectivities greater than 80 were observed. The N 2 /CO 2 selectivities diminished significantly at 363 K for the PEI/MCM-48 membranes.