9 Pyrolysis of 2, 2-Dimethylpropane in a Continuous Flow Stirred Tank Reactor J. A. RONDEAU and G. M. C Ô M E ENSIC, Institut National Polytechnique de Lorraine, Laboratoire de Cinétique Appliquée, 1, rue Grandville, F-54042 NANCY Cedex, France J. F. L A R G E
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Université de Technologie, Départment de Génie Chemique, B.P. 233, F-60206 COMPIEGNE, France F u n d a m e n t a l w o r k o n t h e k i n e t i c s of h y d r o c a r b o n c r a c k i n g i s f u l l y j u s t i f i e d b y s t r o n g i n d u s t r i a l i n t e r e s t (1 t o 5). U p t o n o w k i n e t i c s t u d i e s of c o m p l e x r a d i c a l r e a c t i o n s in the g a s e o u s p h a s e h a v e b e e n c o n d u c t e d m a i n l y i n b a t c h r e a c t o r s . N e v e r t h e l e s s , the u s e of a c o n t i n u o u s f l o w s t i r r e d t a n k r e a c t o r ( C F S T R ) s e e m s v e r y p r o m i s i n g b e c a u s e i t g i v e s a d i r e c t m e a s u r e m e n t of r e a c t i o n r a t e s (6) a n d a l s o i t i s w e l l a d a p t e d t o t h e s t u d y o f f a s t r e a c t i o n s . The p e r f o r m a n c e of an a c t u a l continuous r e a c t o r w i t h c o m p l e x r e a c t i o n s depends on the f o l l o w i n g f a c t o r s : - the k i n e t i c l a w s - the r e s i d e n c e t i m e d i s t r i b u t i o n c h a r a c t e r i z i n g the " m a c r o m i x i n g " (7) - the s e g r e g a t i o n c h a r a c t e r i z i n g the d e g r e e of m i x e d n e s s (8). In v i e w of the i n t e r a c t i o n b e t w e e n t h e s e k i n e t i c a n d h y d r o d y n a m i c p h e n o m e n a , the r e s i d e n c e t i m e d i s t r i b u t i o n ( R T D ) n e v e r gi.ves s u f f i c i e n t i n f o r m a t i o n f o r t h e c a l c u l a t i o n of t h e r e a c t o r y i e l d e x c e p t i n t h e c a s e o f f i r s t o r d e r r e a c t i o n s J(9, t o 1 1 ) , I n s p i t e of s u c h d i f f i c u l t i e s , t h e h y p o t h e s i s of m a x i m u m m i x e d n e s s m i g h t be v a l u a b l e f o r g a s e o u s s y s t e m s , w h e n the r e a c t o r i s s u f f i c i e n t l y s t i r r e d , a n d m i g h t a l l o w a c c u r a t e d e t e r m i n a t i o n of r e a c t i o n r a t e s . W e h a v e s t u d i e d the p y r o l y s i s of 2 - 2 d i m e t h y l - p r o p a n e (neopentane) i n the g a s e o u s p h a s e at about 5 0 0 ° C and at s m a l l e x t e n t s of r e a c t i o n . T h e k i n e t i c p a r a m e t e r s o b t a i n e d f r o m t h e s e investigations in a continuous s t i r r e d reactor have been compared to the v a l u e s p r e v i o u s l y d e t e r m i n e d f r o m b a t c h e x p e r i m e n t s (12 t o 19). E x p e r i m e n t a l D e s i g n and
Procedure
It i s d i f f i c u l t to d e s i g n a g o o d C F S T R f o r two m a i n r e a s o n s : - the a c t u a l r e a c t o r m u s t h a v e a R T D v e r y c l o s e to the
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Albright and Crynes; Industrial and Laboratory Pyrolyses ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
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INDUSTRIAL AND LABORATORY PYROLYSES
Time
Figure 1.
(min)
Residence time distribution. Downstream signal as a response to an upstream step input signal of methane: C = C [1-U (t)] with U(t) = 0ift
