Preparation of porous carbons from phenol-formaldehyde resins with chemical and physical activation

Porous carbons with high porosities were prepared from phenol-formaldehyde resins using chemical and physical activation methods. The resin precursor employed was synthesized with an initial formaldehyde-to-phenol ratio of 1. 33 by mole. The chemical activation process consisted of KOH impregnation f ollowed by carbonization in nitrogen at 500-900 degrees C for 0-3 h, wherea s the physical activation was performed by carbonizing the resins at 900 de grees C followed by gasifying the char in CO2 to different degrees of burn- off. Both activation methods can produce carbons with surface areas and por e volumes greater than 2000 m(2)/g and 1.0 cm(3)/g, respectively. The influ ence of different parameters during chemical activation. such as carbonizat ion temperature and time. KOH/resin ratio and heating rate, on the carbon y ield and the surface characteristics was explored. and the optimum preparat ion conditions were determined. With physical activation the resulting carb ons are mainly microporous and their porosity is an increasing function of the degree of burn-off. At similar porosity levels the carbon yield during physical activation was found to be lower than that with chemical activatio n. An SEM study showed that carbons produced from CO2 activation have a mor e compact surface than those produced from KOH activation. (C) 2000 Elsevie r Science Ltd. All rights reserved.