Oxysulfonation of coke coal by nitrosylsulfuric acid

Abstract

The interaction of coke coal with nitrosylsulfuric acid NOHSO₄ in acetonitrile at 20–25°C, times to 24 h, and the NOHSO₄/coal ratio R ≤ 50 mmol/g was studied. The process leads to the formation of oxysulfonated coal accompanied by an increase in the weight (to 46%), a decrease (by a factor of 3.8–7.3) in the concentration of radicals, and the formation of the following O-, S-, and N-containing groups in the coal structure: carboxyl, phenol, sulfo groups (≤1.9 mmol/g), and nitroso groups (≤0.9 mmol/g). Changes in the characteristics of oxysulfonated coal under varying R and upon hydrolysis were established by IR and EPR spectroscopy and elemental analysis. The results were interpreted within the framework of a mechanism that included the formation of coal radical cations as a result of electron transfer from coal to the nitronium cation, the intercalation of the bisulfate anion into the coal structure, and the nitrosation and sulfonation of coal arenes. Side oxidation reactions occurred simultaneously with the formation of carboxyl, phenol, and quinoid groups.