Nadine Kaltenborn

The permeation and separation performance of an ultramicroporous carbon membrane for separation of CO2/N2 mixtures were investigated. The experiments were conducted using the steady‐state measurement method with pure gases (dead‐end mode) and a CO2/N2 gas mixture (20/80 mol.‐%) (cross‐flow mode) in the temperature range from 293 K to 363 K and at feed pressures of up to 1.4 MPa and atmospheric pressure on the permeate side. The membrane exhibited a selectivity of about 25 and permeability of about 500 Barrer for CO2 in the mixture with N2. The single‐gas measurements do not reflect the membrane performance correctly. An adsorption‐selective effect is assumed to be the main separation mechanism. Moreover, membrane‐aging effects causing blocking due to pore constrictions through adsorption were observed. These pore constrictions lower the permeability, but they raise the selectivity. Operation at high temperatures leads to a reduction of aging effects.

Carbon membranes have great potential for highly selective and cost‐efficient gas separation. Carbon is chemically stable and it is relative cheap. The controlled carbonization of a polymer coating on a porous ceramic support provides a 3D carbon material with molecular sieving permeation performance. The carbonization of the polymer blend gives turbostratic carbon domains of randomly stacked together sp2 hybridized carbon sheets as well as sp3 hybridized amorphous carbon. In the evaluation of the carbon molecular sieve membrane, hydrogen could be separated from propane with a selectivity of 10 000 with a hydrogen permeance of 5 m3(STP)/(m2hbar). Furthermore, by a post‐synthesis oxidative treatment, the permeation fluxes are increased by widening the pores, and the molecular sieve carbon membrane is transformed from a molecular sieve carbon into a selective surface flow carbon membrane with adsorption controlled performance and becomes selective for carbon dioxide.