Porosity of cellulose fibers chars activated by CO₂

Abstract

Porosity variation of activated carbons, prepared under different activation times and CO₂ flows, is provided. Cellulose fibers of Eucalyptus saligna (Myrtaceae) wood were first pyrolysed in N₂ with a heating rate of 5ºC min^-1 , up to 800ºC. Samples were then activated at 850ºC, in CO₂ flows of 15 to 120 mL min^-1, during 1, 2 and 3 hours. Porosity of carbons was characterized by determining the burn-off grades of activated cellulose fibers, the specific surface areas S_BET of the pores, the average radius of gyration of micropores R_g and the meso/macropores K/Q₀ Porod relations. Concomitant increase of CO₂ flow and activation time induced burn-off increase and micropores Rg reduction. However, improvement of S_BET areas allows the authors to conclude that smaller size micropores were created in larger amounts. Under the same conditions, increases of K/Q₀ indicated a sensitive creation of macropores and/or the mesopores coalescence