Efficiency of Thermal Shock in the Thermal Alkaline Conversion of Fossil Coals into Nanoporous Materials

The efficiency of thermal shock (TS), which was introduced instead of temperature-programmed heating (4 K/min) in the alkaline activation (KOH, 800°C) of fossil coals of the entire metamorphic series (С daf = 70.4–95.6%), was evaluated by comparing the porous structure characteristics of activated carbons (ACs). ACs with increased specific surface areas (by a factor of ≤2.5) and pore volumes (by a factor of ≤2.2) but with lower (by a factor of 1.07–1.30) yields were formed upon TS. The effect of TS expressed by an increase in the specific surface area ∆ S was maximal on the conversion of brown coal (∆ S = 870 m 2 /g), and it decreased to a minimum in coals with С daf = 90 ± 1% (∆ S = 109 m 2 /g) or increased on the activation of anthracites (∆ S = 496 m 2 /g). It was shown that the efficiency of TS increased with O daf , which is responsible for the formation of subnanopores, for lignites and coals. On the activation of anthracites, an additional pore formation mechanism not associated with oxygen groups was activated.