抄録
Brown coals have a considerable amount of acidic functional groups of which the main component is carboxyl groups, and the acidity has a wide distribution, which can be changed by heat-treatment. The acidity distribution and its change by heat-treatment were analyzed by deconvolution of the acid-dissociation curve obtained by aqueous titration into several Gaussian type components. For Loy Yang brown coal from Australia dried at 50℃ under vacuum (LY50), the acid dissociation constant, K_a, was distributed over a wide pK_a range between 2 and 9. Then, the acidity distribution curve was divided into four component groups which were characterized by average pK_a values: average pK_a value of 3.8 (Group A), 5.2 (Group B), 6.8 (Group C), and 8.3 (Group D). Among them, Groups A, B, and C were assigned to carboxyl groups. From the changes of the amount of carboxyl groups when brown coal was heat-treated up to 400℃, it was found that the way of decrease was different among these acidic groups. The decrease of the amount of carboxyl groups was significant in Group C, and at 325℃ most of them disappeared. On the other hand, the carboxyl groups in Group A remained even at high temperature of 400℃.
