Influence of Pyrocarbon Deposition in the Porous Structure of Activated Carbons

Deposition of pyrolytic carbon from the vapor phase onto the surface of various activated carbons, i.e., industrial (SKT and AG-3) and specially prepared via addition of KOH to a composition of carbon black with petroleum pitch followed by carbonization and washing, was studied. The deposition was carried out by passing benzene vapor in a stream of N₂ through heated activated carbon. The obtained modified samples were studied using molecular probes by measuring adsorption isotherms of benzene and CCl₄ at 20°C on the same samples. The results showed that the weight gain increased from 3% to 15% depending on the sample and the volume of micropores of width 0.4-0.6 nm increased to 0.07-0.15 cm³/g as the deposition time increased from 60 to 450 min. The modified activated carbons obtained in this manner could be used further to obtain carbon molecular sieves with pore sizes from 0.3 to 0.4 nm.