Pore Size Control of Microporous Carbon Membranes and Application to H₂ Separation

Abstract

Three methods of efficient pore size control for microporous carbon membranes were developed, (1) vaporphase synthesis of furfuryl alcohol (FFA) carbon membranes, (2) pore size control by post-activation and (3) quaternary ammonium salt-mediated method for the direct synthesis of microporous carbon membranes with large pores. (1) At first, a H2-permselective FFA carbon membrane with pore size of 0.30 nm was prepared through optimization of the conditions of FFA deposition and carbonization process. (2) Next, the FFA carbon membranes were activated using various gases and vapors such as H2, CO2, O2 and steam (H2O). Different pore sizes and morphological changes were observed by changing the activation agent and temperature. After activation using H2 at 700 , the pore size of the microporous carbon membrane was increased from 0.30 to 0.45 nm. (3) Quaternary ammonium salt-mediated synthesis was developed for the direct synthesis of microporous carbon membranes with pore size larger than 0.40 nm. Using two types of cationic tertiary amines with different chain lengths, microporous carbon membranes with uniform pores of 0.4 nm and 0.5 nm were successfully synthesized. Using these methods, microporous carbon membranes with uniform pore sizes from 0.30 to 0.50 nm were successfully prepared, and were used in various H2 separation processes. These microporous carbon membranes showed superior H2-permselectivity in various H2 separation processes such as H2/CO, H2/CO2 and dehydrogenation of organic hydrides in a membrane reactor. The present techniques are expected to achieve precise pore size control of microporous carbon membranes.

Nanoporous Carbons with Tuned Porosity

“…Research development after that initial work has shown that the choice of the polymeric precursor is important because pyrolysis of different precursors may yield different kinds of carbon membranes having completely different porous textures from microporous to macroporous, and adsorption/separation behaviors [168]. Mainly microporous carbon membranes have been synthesized from several precursors, including polyimides [169,170], coal tar pitch [171], furfuryl alcohol [172], PVDC copolymer [173], or phenolic resin [174]. The pyrolysis of polyimides is one of the most investigated methods, as it allows to prepare either amorphous or graphitic carbons, and nanoporous or dense (non-porous) materials, by simply selecting the molecular structure of the precursor and the pyrolysis conditions.…”