Kinetics of reactions between magnetite and carbon monoxide between 723 and 823 K
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R. KNAPP,
KUN
LI, AND
WILLIAM
O. PHILBROOK
The k i n e t i c s of s o m e r e a c t i o n s between c a r b o n monoxide and m a g n e t i t e w e r e i n v e s t i g a t e d between 723 and 823 K. G a s - p h a s e m a s s - t r a n s f e r effects within and n e a r the porous s a m ples and s u r f a c e - r e a c t i o n k i n e t i c s w e r e c o n s i d e r e d . The e x p e r i m e n t s w e r e done on s i n t e r e d m a g n e t i t e disks whose void f r a c t i o n was 15 to 20 pct. A continuously w ei g h ed r o tating disk r e a c t o r p r o v i d e d uniform m a s s t r a n s f e r to the s a m p l e faces. The r e a c t e d disks w e r e a n a l y z e d by Mt~ssbauer s p e c t r o s c o p y and o t h er methods. The only p r o d u ct s p e c i e s found w e r e c e m e n t i t e and carbon, which s u g g e s t e d the e x i s t e n c e of two r e a c t i o n s : the f o r m a t i o n of c e m e n t i t e and carbon dioxide d i r e c t l y f r o m m a g n e t i t e and c a r b o n monox~ ide, and the d i s p r o p o r t i o n a t i o n of c a r b o n monoxide to carbon dioxide and f r e e carbon. T h es e r e a c t i o n s w e r e m o d e l e d m a t h e m a t i c a l I y . The s u r f a c e kinetic data for both r e a c tions w e r e found to be c o m p a t i b l e with r a t e e x p r e s s i o n s which w e r e d i r e c t l y p r o p o r t i o n a l to the s q u a r e of the p a r t i a l p r e s s u r e of c a r b o n monoxide and a p p r o x i m a t e l y i n v e r s e l y p r o p o r t i o n a l to the p a r t i a l p r e s s u r e of p r o d u ct c a r b o n dioxide.
FOR
a n u m b e r of y e a r s work has been in p r o g r e s s at C a r n e g i e - M e l l o n U n i v e r s i t y to b e t t e r understand v a r i ous d i r e c t r e d u c t i o n p r o c e s s e s . This work includes m o d e l i n g iron oxide r e d u c t i o n by hydrogen ~ and e x p e r i m e n t a l i n v e s t i g a t i o n s of i r o n oxide r e d u c t i o n by c a r bon monoxide. 2'3 A r e a c t i o n of g r e a t potential i m p o r tance to the l a t t e r s i t u a t i o n or to any " d i r e c t " r e d u c tion p r o c e s s i n v o l v i n g c a r b o n monoxide is the c a r b o n d e p o s i t i o n or Bell r e a c t i o n . 2 CO( g )
- -
CO2(G) + C(s)
[1]
This r e a c t i o n can o c c u r in a b l a s t f u r n a c e or shaft f u r nace and influence the t e m p e r a t u r e and c h e m i c a l c o m position p r o f i l e s in the shaft. The d e p o s i te d c a r b o n m a y r e s t r i c t gas flow or c a u s e p o r o u s o r e p e l l e t s or r e f r a c t o r y linings to d i s i n t e g r a t e . C l e a r l y t h e s e p h e n o m e n a a r e of c o n s i d e r a b l e i n t e r e s t . The m a g n i tu d e of t h e s e effects will depend on the r a t e at which c a r b o n d e p o s i t i o n o c c u r s . It is t h e r e f o r e i m p o r t a n t to d e s c r i b e the c a r b o n d e p o s i t i o n r e a c t i o n in o r d e r to c o r r e c t l y m o d e l all of the c a r b o n
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