Carbon aerogels from gallic acid–resorcinol mixtures as adsorbents of benzene, toluene and xylenes from dry and wet air under dynamic conditions

Abstract

Carbon aerogels were prepared by carbonization of organic aerogels synthesized by the polycondensation reaction of gallic acid–resorcinol mixtures with formaldehyde. One carbon aerogel was further CO 2-activated. They were characterized by gas adsorption, mercury porosimetry, immersion calorimetry, and temperature programmed desorption. Pore texture of carbon aerogels was constituted by a well-developed, monomodal mesoporous network superimposed over a microporous network with different mean micropore widths according to the degree of activation. In some cases, the BET surface area was lower than that determined by immersion enthalpy into benzene. Dynamic adsorption of benzene, toluene, and xylenes, in dry or wet air flow, was carried out on carbon columns to obtain the breakthrough curves. Adsorption from dry air was governed by the total microporosity of the adsorbent. Amounts adsorbed at the breakthrough point were close to or higher than W 0(CO 2) and lower than W 0(N 2) and increased in the order benzene < toluene < xylenes, in agreement with the variation in relative pressure of the hydrocarbons. Results obtained with wet air were qualitatively similar to those obtained with dry air. However, slightly lower amounts were adsorbed at the breakthrough from the wet versus dry air because of competition between water and hydrocarbon molecules.