Effect of water vapour on the porous structure of activated carbon from lignite

A Bulgarian lignite from the Chukurovo deposit was used to produce an activated carbon by one-step steam pyrolysis at 650 °C. The effects of the presence of water vapour on the yield and composition of the solid, liquid and gas products were investigated. The water vapour present during pyrolysis-activation contributes to distillation of low molecular weight products and reacts with the coal and the volatile products obtained during pyrolysis. These processes lead to an increase in the yield of liquid and gas products and a decrease in the solid yield. The resulting carbon is characterized by a more developed porous structure, a higher N₂ BET surface area and higher adsorption capacity for iodine and methylene blue compared to the solid product obtained after pyrolysis in an argon atmosphere. The concentration of the activated carbon surface functional groups is considerably higher than that of the char obtained by pyrolysis in an argon atmosphere under the same heating conditions.