Preparation of supported asymmetric carbon molecular sieve membranes

Abstract

Asymmetric carbon membranes were made by casting a solution of 13 wt% polyamic acid in N-methylpyrrolydone (NMP) upon a macroporous carbon support. The polymeric solution was coagulated in a bath of isopropyl alcohol and dried at room temperature and at 150°C in air. The resulting polymer was heat treated under vacuum involving two steps: (i) imidization at 380°C during 1 h (heating rate: 1°C/min) and (ii) carbonization at 550°C for 1 h (heating rate: 0.5°C/min). The carbon membrane obtained in only one casting step shows an asymmetric structure formed by a dense skin layer with a thickness of around 1 μm and a porous substrate (≈6 μm thickness) of the same material. The gas permeation results indicate that the gas transport through the membrane occurs according to an activated mechanism (molecular sieving). The selectivity and permeation rate measured at 25°C for the O 2/N 2, He/N 2, and CO 2/CH 4 systems were respectively: α(O 2/N 2)=5.3, P(O 2)=1.14×10 −9 mol/m 2 s Pa; α(He/N 2)=26.5, P(He)=5.7×10 −9 mol/m 2 s Pa; α(CO 2/CH 4)=37.3, P(CO 2)=4.0×10 −9 mol/m 2 s Pa.