Preparation of activated carbons from Spanish anthracite: II. Activation by NaOH

Abstract

This paper complements the previous one (activation with KOH) analysing the development of porosity of a Spanish anthracite by chemical activation with NaOH. The preparation method has been optimised through the analysis of diverse experimental variables. Among them, activating agent/coal ratio, drying process, method of mixing of the activating agent and coal, nitrogen flow during pyrolysis and mineral matter content of the coal, have been studied. The results obtained confirm the importance of the activating agent to coal ratio and the flow of gas during carbonisation on the development of porosity. In addition, it shows that chemical activation with NaOH can be successfully used to develop activated carbons with high surface area and micropore volumes (i.e., up to 2700 m 2/g and 1 cm 3/g). Comparing chemical activation using an impregnation method and physical mixing we conclude that physical mixing of NaOH and coal, which is a very easy preparation method, renders 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 high micropore volumes can be synthesised through a much simpler method. Physical mixing produces larger pore volumes by KOH activation than by NaOH activation.