Cation exchange capability and reactivity of low-rank coal and chars

Abstract

AbstractIn this work the C.E.C. and its effect on the reactivity of low rank coal and chars were investigated. The C.E.C. was measured by potentiometric titration and was correlated with the solution pH, the carbonization extent and the oxygen content. Coal and chars presented permanent C.E.C. primarily derived from inorganic sites and was independent of solution pH, and variable C.E.C. derived from organic matter and was increased continuously, and reversibly, as the solution pH increased. The latter is due to the complete dissociation of the carboxylic groups of the organic matter of the coal and, thus, the C.E.C. is directly related with the oxygen content. The C.E.C. of chars decreased with the carbonization extents and its variation was described by a modified cumulative distribution function of the Weibull probability density function. A linear correlation was identified between the C.E.C. and the elemental oxygen conversion, justifying further the direct relation between the C.E.C. and the oxygen functional groups. Following the decrease of the C.E.C., the potassium chemisorption capacity of the chars also decreased. Chars of decreased C.E.C. were less reactive during CO2 gasification and reduced maximum weight loss and CO formation rates were obtained, also shifted at higher temperatures.