Preparation of active carbon from brown coal and weathered coal with alkali

Active carbons were prepared from such low-rank coals as brown coal (Yallou rn, Australia; C 64%, Ash 1.4%) and weathered coal (Inner-Mongolia, China; C 54%, Ash 19%) with a relatively large quantities of NaOH or KOH (alkali r atio to coal 2-2.5) under a lower temperature (773-973 K) than the conventi onal steam activation (1173-1273 K). For instance, active carbons with spec ific surface area of more than 1000 m(2)/g were obtained with high yields ( 33-36%), when weathered coal was activated by NaOH (ratio 2.5-3.0) at 973 K . The effect of alkali could be improved significantly by pre-heating (773 K) of coals, affording the active carbons with higher values specific surface area (1300 m(2)/g) at 823 K. This would be due to that the pre-heating of the coals decreased with the degree of consumption of alkali with carbon di oxide generated by the decarboxylation during the activation process. The removal of ash, especially silica in the weathered coal, was performed easily by this method by washing the final product. The ash content of the active carbon from weathered coal was at least 4 %, while it was almost nil for the product from brown coal.