Steam Activation of Anthracite Intercalated with Nitric Acid

Аннотация

The steam activation of anthracite (C^daf = 95.1%), which was preliminarily intercalated with nitric acid (140°C) and converted into anthracite nitrate (AN)—a material with intercalated nitrate anions that hypothetically formed intraskeleton ion pairs with the radical-cation polyarene fragments of coal, was studied. Activated carbons (ACs) were formed in the course of the gasification of AN with water vapor (850°C); their yield decreased with time in accordance with a first-order rate equation: the rate constant of AN gasification (0.015 min^–1) was higher by a factor of 3 than that in the case of the initial anthracite. The specific surface area (S_BET) of AC from AN was higher by a factor of 1.5 (940 vs. 600 m²/g), and it developed more rapidly by a factor of 4.5–10.0; that is, the intercalation promoted the formation of a porous structure. For AN, the dependence of SBET on the degree of combustion loss (φ) was extremal with a maximum at φ = 67%, and the values of S_BET = 800–1000 m²/g acceptable for carbon adsorbents were reached in a narrow range of φ = 60–70%. At φ > 70%, differences in the characteristics of ACs from AN and anthracite were leveled. In general, the influence of intercalation on the steam activation of anthracite was manifested in an increase in the rate of gasification (by a factor of 3), a larger specific surface area (by a factor of 1.5), and a considerable increase (by a factor of 4.5–10) in the rate of its formation.