MEASUREMENT OF HYDROXYL-GROUPS IN COALS OF DIFFERENT RANK BY ACETYLATION WITH KETENE AND OTHER REAGENTS

Acetylation of a rank series of coals with ketene indicated that, in general agreement with the earlier conclusions of Horton, the percentage of the oxygen in coals present as hydroxyl (OH), i.e. acetylated by ketene, was much greater than was indicated by acetylation with 'conventional' reagents. The percentage reached a maximum value of 90% for Cresswell coal (84.5% C); for the present coal series the maximum was lower and occurred at a lower rank than reported by Horton. Acetylation of the coals with several liquid reagents, with the aid of microwave heating, gave a similar pattern of results, but with OH values generally higher than those reported earlier from 'conventional' acetylation, and one higher than the corresponding 'ketene' value. In all cases the extent of acetylation was determined by alkaline hydrolysis of the acetylated coal sample, followed by acidification, distillation and titration of the liberated acetic acid. It is concluded that acetylation of coals by 'conventional' methods may well be incomplete, leading to low values for OH groups and consequent uncertainty about the levels of other oxygen groups, particularly ethers, which have to be obtained by difference.