Oxidation of Coal: a Mechanistic Puzzle

A l l coa ls , o t h e r than a n t h r a c i t e s , tend t o be ve ry s e n s i t i v e t o o x i d a t i o n . Even exposure t o a i r a t ambient temperature causes d e t e r i o r a t i o n t o the e x t e n t t h a t p r o p e r t i e s such as s o l u b i l i t y , cak ing, f l u i d i t y , t a r y i e l d , e t c . , a re adverse ly a f f e c t e d . A l though the loss o f h e a t i n g va lue and decrease i n t a r y i e l d due t o o x i d a t i o n can be e x p l a i n e d i n terms o f loss i n hydrogen contents , d e t a i l s o f the chemical changes and the mechanism o f o x i d a t i o n a r e u n c e r t a i n . There i s agreement among coal chemists t h a t the i n i t i a l s tages o f a i r o x i d a t i o n i n v o l v e chemiso rp t i on o f oxygen a t r e a d i l y access ib le su r face s i t e s , b u t f u r t h e r d e f i n i t i o n o f the mecha n i s t i c pa th a t t h e molecular l e v e l i s s t i l l c o n t r o v e r s i a l .