Development mechanism of pore structures based on burn-off properties of carbon structures during activation process

By picking Taixi anthracite and Datong bituminous coal as the feedstocks, the activated carbons with 10%-75% burn-offs were prepared at different activation temperatures. The burn-off properties of amorphous carbon and crystalline structure were investigated, and the external carbon loss of the particle was also considered. Combined with the textural characteristics of activated carbons in different activation stages, the formation and development mechanism of micropore and mesopore were explained. The results indicated the amorphous carbon got burnt when the burn-off was lower than 30%. The micropores which pore size was smaller than 1.35 nm were formed in TX-activated carbons. By comparison, the micropore and mesopore could be formed simultaneously in DT-activated carbons, and the mesopore size could reach to 50 nm. As the burn-off increasing, the crystallite reaction began to take place. When the burn-off was higher than 50%, the crystallites reduced not only in thickness, but also in layer sizes. In this stage, the mesopore of 2-4 nm could be developed continuously between the crystalline structures by etching action, and the ultramicropores could be formed in the inner part of the crystallites as the increase of lamellar spacing. As a rapid shrinking of crystallites in DT-activated carbons, the pore structure could collapse and shrink leading to the reduction of original pore volume.