Insight into controllability and predictability of pore structures in pitch-based activated carbons

Abstract

Tailoring porosity of pitch-based activated carbons (PACs) on a large scale is of high importance and usually achieved by introducing additives or templates and adjusting activation conditions. Since pitch is a kind of extraordinarily complex mixtures, it is highly necessary to investigate the effect of pitch composition on pore structure of PACs. Herein, a coal-tar pitch was subdivided by solvent fractionation into toluene-soluble (TS), pyridine-soluble (PS), quinoline-soluble (QS), and quinoline-insoluble (QI) fractions followed by activation using KOH or steam, respectively, to obtain PACs. It is found that the formation of pores in PACs is significantly dependent on pitch composition and activation methods. The light fractions (TS and PS) are more favorable for pore development in the KOH-activated carbons, whereas pores in the H2O-activated carbons are easily achieved by using the heavy fractions (QS and QI). The possible pore-formation mechanisms were also proposed, which indicates that the big differences intrinsically originate from the chemical properties (such as molecular size, structures, reactivity with activation agents and rheological behaviors of the molecular aggregations) of pitch compositions. When commercial pitches are employed for the precursors, a synergistic effect on pore development occurs both in KOH- and H2O-activated PACs seriously depending on their mass percentages of light or heavy fractions. It suggests that the mass percentage can be an index to foresee the porous properties of PACs. These findings open up a significantly important and more practical approach applicable to tailor the pores in PACs on an industrial scale just through adjusting pitch compositions.