Masatake Yamamoto

Pore size control of carbonized BPDA-pp′ ODA polyimide membrane by chemical vapor deposition of carbon

Abstract A BPDA-pp′ ODA polyimide film was formed on the outer surface of a porous alumina support tube (outside diameter = 2.4 mm), and it was carbonized at an optimized temperature, 700°C. The membrane obtained showed a permeance of 3 × 10−9 mol · m−2 · s−1 · Pa−1 for O2 and 2 × 10−8 mol · m−2 · s−1 · Pa−1 for CO2 and a permselectivity of 10 for O 2 N 2 and 47 for CO 2 N 2 at 35°C. The membrane was then modified with carbon deposits formed by pyrolysis of propylene at 650°C. The permselectivities for O 2 N 2 and CO 2 N 2 at 35°C were increased to 14 and 73, respectively. Coexisting water vapor decreased permeances of O2 and N2 but did not change the O 2 N 2 permselectivity.

Gas permeation and micropore structure of carbon molecular sieving membranes modified by oxidation

Abstract A BPDA-pp′ODA polyimide film was formed on the surface of a porous alumina support tube, which was then carbonized at an optimized temperature of 700°C. The membrane was further oxidized with either an O 2 –N 2 mixture or pure O 2 at 100–300°C. Oxidation at 300°C increased permeances, without damaging permselectivities, of the membrane. No difference in permeances between single and binary CO 2 –N 2 systems was observed. The carbon membranes possessed slit-shaped molecular sieving pores, in which molecules could pass one another by moving to the wider side of the slit. Permselectivity of the permeating molecules was determined by the narrow width of the slit-shaped micropores.

Carbon molecular sieve membrane formed by oxidative carbonization of a copolyimide film coated on a porous support tube

Abstract A copolyamic acid was synthesized from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) as the dianhydride and 4,4′-oxydianiline (4,4′-ODA) and 2,4-diaminotoluene (2,4-DAT) as the diamine and was coated on the outer surface of a porous alumina support tube. The film was imidized and then carbonized by varying reaction period, temperature and atmosphere. Permeances of the BPDA-ODA/DAT carbon membrane were much lower than those of BPDA-ODA carbon membranes. However, the performance of the BPDA-ODA/DAT copolyimide-based membrane was greatly improved by treating in air at temperatures up to 500°C for 1 h, followed by carbonizing in nitrogen at temperatures up to 700°C. Permeance to CO 2 for the BPDA-ODA/DAT carbon membrane prepared under optimum conditions was 3 × 10 −8 mol m −2 s −1 Pa −1 , and the separation coefficient of CO 2 to CH 4 was 60 at a permeation temperature of 35°C. These were comparable to the results of carbon membranes prepared from BPDA-ODA polyimide. The micropore structure of the BPDA-ODA/DAT carbon membrane was thus successfully controlled by an optimized combination of oxidation and carbonization after imidization.