Sabierova V. Transformation of coals into nanoporous materials under heat-shock alkali activation

Transformation of the coal structure during its conversion into activated carbons (AСs) under heat-shock alkaline (KOH) activation. Establishing patterns of molecular, supramolecular and porous structure reorganization during the coal transformation into nanoporous material. Elemental analysis, derivatography, X-ray diffraction, IR spectroscopy, low-temperature adsorption-desorption of nitrogen. Three main processes forming the AC structure with increasing temperature was identified as fragmentation of coal into potassium humates, formation of a secondary carbon framework from humates, and generation of micropores. The joint action of heat shock and KOH was found to increase the porosity of ACs only in the range of 400-850°C and mainly due to micropores; their dominant part is subnanopores one. Inserting a heat shock stage instead of programmed heating into alkali activation (800°C) of different rank coals leads to forming ACs with smaller yields (1.07-1.30 times), but increased specific surface area (≤2.5 times), total pore volume (≤2.2 times) and the volume of subnanopores (1.04-6.3 times). The oxygen of coal is proven to be responsible for the additional formation of pores and the efficiency of heat shock increases with the increase of oxygen content. Activation of anthracites revealed an additional mechanism of subnanopore formation not related to oxygen of coal. Scope - coal chemistry.