Preparation of activated carbons from Spanish anthracite II. Activation byNaOH

This paper complements the previous one (activation with KOH) analysing the development of porosity of a Spanish anthracite by chemical activation wit h NaOH. The preparation method has been optimised through the analysis of d iverse experimental variables Among them, activating agent/coal ratio, dryi ng process, method of mixing of the activating agent and coal, nitrogen flo w during pyrolysis and mineral matter content of the coal, have been studie d. The results obtained confirm the importance of the activating agent to c oal ratio and the flow of gas during carbonisation on the development of po rosity. In addition, it shows that chemical activation with NaOH can be suc cessfully used to develop activated carbons with high surface area and micr opore volumes (i.e., up to 2700 m(2)/g and 1 cm(3)/g). Comparing chemical a ctivation using an impregnation method and physical mixing we conclude that physical mixing of NaOH and coal, which is a very easy preparation method, landers the best results. Therefore physical mixing has been also applied in this work to KOH with rather interesting results. Although impregnation produces a higher development of porosity for KOH, activated carbons with h igh micropore volumes can be synthesised through a much simpler method. Phy sical mixing produces larger pore volumes by KOH activation than by NaOH ac tivation. (C) 2001 Elsevier Science Ltd. All rights reserved.