Cryogenic air separation at low pressure using MFI membranes

Abstract

Ultra-thin MFI membranes were for the first time evaluated for air separation at low feed pressures ranging from 100 to 1000mbar at cryogenic temperature. The membrane separation performance at optimum temperature at all investigated feed pressures was well above the Robeson upper bound for polymeric membranes at near room temperature. The O2/N2 separation factor at optimum temperature increased as the feed pressure was decreased and reached 5.0 at 100mbar feed pressure and a membrane temperature of 67K. The corresponding membrane selectivity was 6.3, and the O2 permeance was as high as 8.6×10−7molm−2s−1Pa−1. This permeance was about 100 times higher than that reported for promising polymeric membranes. The membrane selectivity and high O2 permeance was most likely a result of O2/N2 adsorption selectivity. The increase in O2/N2 separation factor with decreasing pressure and temperature was probably due to increased adsorption selectivity at reduced temperature. This work has demonstrated the potential of MFI zeolite membranes for O2/N2 separations at cryogenic temperature.