Raman Spectroscopic Investigations into Links between Intrinsic Reactivity and Char Chemical Structure

Many factors affect the gasification reactivity of chars. These include physical structure (e.g., surface area and pore structure), catalytically active inorganic species, and chemical structure (the extent of ring condensation of the carbonaceous matrix and the nature of the functional groups that comprise the char structure). This work uses Raman spectroscopy to investigate the relationships between the char chemical structure and intrinsic reactivity. Chars made from an Australian bituminous coal and a Chinese lignite at temperatures of 900 and 1100 degrees C were characterized in terms of their intrinsic reactivities with CO2 and H2O (separately). Unreacted and partially reacted chars were characterized using Raman spectroscopy and gas adsorption to determine chemical structure indicators and surface area, respectively. The ratio of small to large aromatic rings decreased with increasing carbon conversion for all chars in all reactants, and for the bituminous coal char, this was related to the reactivity behavior as a function of conversion. While reaction seemed to affect the structure of the lignite chars in a similar manner, this did not influence the intrinsic reactivity of the lignite chars to the same extents, perhaps because of the significant influence of catalytic activity of inorganic species.