High temperature chlorination of titanium bearing minerals: part III
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E . DUNN,
Jr.
F l u i d i z e d bed c h l o r i n a t i o n of t i t a n i u m m i n e r a l s has b e c o m e the e s t a b l i s h e d t e c h n i q u e f o r t i t a n i u m t e t r a c h l o r i d e p r o d u c t i o n . Although v a s t a m o u n t s of t i t a n i u m t e t r a c h l o r i d e have b e e n m a d e in t h e s e r e a c t o r s , the m e c h a n i s m of the r e a c t i o n s taking p l a c e is s t i l l not understood. Every year several papers appear discussing the c a r b o n / c h l o r i n e a t t a c k on the t i t a n i u m oxide l a t t i c e in t e r m s of a v o l a t i l e c a r b o n s p e c i e s , f o l l o w i n g the i d e a s of B e r g h o l m 1 published s o m e 15 y e a r s ago. Even atomic or molecular radicals are s o m e t i m e s c o n s i d e r e d to be i n v o lv e d . A t t e m p t s to make c h l o r i n a t e d c a r b o n c o m p o u n d s by d i r e c t c h l o r i n a t i o n of carbon have y i e l d e d v e r y low r a t e s ; r a t e s s e v e r a l o r d e r s of m a g n i t u d e below c h l o r i n a t i o n r a t e s of f l u i d i z e d r e a c t o r s c h l o r i n a t i n g t i t a n i a in any of i t s f o r m s . S i m i l a r l y , the c h l o r i n a t i o n r a t e s o b s e r v e d with c a r b o n monoxide as a r e d u c i n g ag en t f o r the c h l o r i n a t i o n a r e too low to a c c o u n t f o r the r e a c t i o n and f u r t h e r m o r e the f o r m a t i o n of c a r b o n m o n o x i d e in the bed f r o m c a r b o n d io x i d e r e d u c t i o n by the i n e r t c ok es u s e d is f ar too slow to a c c o u n t f o r the t i t a n i u m c h l o r i n a t i o n r a t e s o b s e r v e d . T h e r e d u c t i o n of c a r b o n di ox i d e on the c a r b o n s u r f a c e is s e r i o u s l y , if not t o t a l l y , inhibited by the p r e s e n c e of c h l o r i n e . T h e d i r e c t c h l o r i n a t i o n of t i t a n i a is a p o s s i b l e r e a c t i o n , but b e i n g s e v e r e l y l i m i t e d by the t h e r m o d y n a m i c s i n v o l v e d can only o p e r a t e when the T i C h p a r t i a l p r e s s u r e is v e r y low. T h e d i r e c t c h l o r i n a t i o n r e a c t i o n cannot ex p la in an i n c r e a s e in c h l o r i n a t i o n r a t e as the t i t a n i u m t e t r a c h l o r i d e p a r t i a l p r e s s u r e b u i l d s up. A p a p e r on high t e m p e r a t u r e c h l o r i n a t i o n of t i t a n i a by c a r b o n and c h l o r i n e was p r e s e n t e d by this a u t h o r at the May 1962 m e e t i n g of the E l e c t r o c h e m i c a l S o c i e t y with an a b s t r a c t p u b l i s h e d 2 d e s c r i b i n g the p e c u l i a r a u t o c a t a l y t i c r e a c t i o n which t a k e s p l a c e and d o m i n a t e s the c a r b o n / c h l o r i n e a t t a c k on the t i t a n i u m l a t t i c e . T h e v o l a t i l e t i t a n i u m b e a r i n g s p e c i e s was e x p e c t e d to be an o x y c h l o r i d e (probably TiOCI2). T h e r e d u c e d o x y c h l o r ide T
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