Conversion of Alexandriya Brown Coal Into Microporous Carbons Under Alkali Activation

We studied the pore structure of activated carbons (ACs) formed during the thermolysis of Aleksandriya brown coal (Ukraine), which was preliminary impregnated with alkali metal hydroxides, МОН with M being Li, Na, or K. We explored how pore structure parameters such as surface area, a total pore volume, meso- and micropore volume are modified with changing processing parameters such as temperature, an alkali/coal ratio (up to 2 g/g) and the nature of alkali cation. We also determined pore size distribution for meso- and micropores and compared all the three hydroxides as to their effect on porosity development. The formation of microporous structure is evidenced on heating a KOH-impregnated coal (1 g/g) from 400 to 800 0 С: a surface area rises from 13 to 1005 m 2 /g, while a micropore volume fraction increases from 1 to 68 % of the total pore volume. Microporous carbon is formed at 800 0 C over 1 h in a yield of 30 % with SBET=1005 m 2 /g, a total pore volume of 0.55 cc/g and a micropore volume of 0.38 cc/g. The total pore volume grows monotonously in the range LiОНPotassium hydroxide is found to promote microporosity development, whereas both LiOH and NaOH (at 18 mmol/g) act as inhibitors for micropore growth.