An easy way to predict and direct the porous structure of activated carbons derived from petroleum asphalt

Abstract

The carbonization temperature of carbon precursors before their activation is an important factor affecting the porous structure and properties of the resulting activated carbons. In this work сorrelation between the textural and adsorption properties of asphalt-based porous carbons and the carbonization temperature has been found. Additionally, the optimal carbonization temperature, and reasons why the carbonization temperature affects the main textural characteristics of the activated carbon were established. A series of porous carbons has been prepared from petroleum asphalt by a two-stage method, including carbonization of asphalt at different temperatures from 450 to 800 °C and KOH activation. To reveal the reasons of the correlation the carbonized samples were studied by TG-DTG, IR-Fourier, TEM methods. It is shown that the carbonization temperature effects on the structural defects, distance between the graphene layers, the reactivity and thermal stability of the carbonized asphalts. These specificities contribute to formation of porous structures of the activated carbons. The carbonization temperature 500–600 °С of the petroleum asphalt is found to be the optimal for further activation. The KOH activation of the petroleum asphalts carbonized at 500–600 °С provides microporous carbon with the high specific surface area (about 2000 m²g^-1) and the CO₂ uptake (3.3 mmolg^-1). Additionally, the specific surface area of the activated carbons is shown can be predicted from the temperature of 50% (T_50%) mass loss of the carbonized petroleum asphalt. The linear dependence of the T_50% on BET surface area can be fitted by T_50%=640–0.424S_BET with determination coefficient R² equal to 0.96.