3 Oxidation of ρ-Methylbenzyl Radical and p-Xylylene L. A. ERREDE and W. D. ENGLISH
Downloaded by MICHIGAN STATE UNIV on February 18, 2015 | http://pubs.acs.org Publication Date: January 1, 1965 | doi: 10.1021/ba-1965-0051.ch003
Central Research Laboratories, 55119
Minnesota
Mining & Mfg. Co., St. Paul,
Minn.
The fractional conversion to p-methylbenzyl radicals by fast flow pyrolysis of p-xylene at low pressure is given explicitly in terms of the pyrolysis temperature and residence time. The fractional conversion of these monoradicals to p-xylylene is given in terms of the pressure and the surface to volume ratio in the post pyrolysis zone. These reactive species can be oxidized to p-toluic acid and/or terephthalic acid by in jecting oxidizing species at the appropriate point along the pyrolysis stream. The overall conversion of p-xylene to carboxylic acids per pass is equal to the thermal conversion of p -xylene to p-methylbenzyl radicals. This upper bound on yield per pass can be increased sig nificantly by induced thermal decomposition of the feed stock using thermally unstable addi tives.
past flow p y r o l y s i s of p - x y l e n e at l o w pressure p r o d u c e s a m i x t u r e of p r o d u c t s ( 1 ) that c a n b e t r a c e d to a c o m m o n i n t e r m e d i a t e , p - m e t h y l b e n z y l r a d i c a l ( 6 ) , as o u t l i n e d i n the r e a c t i o n scheme b e l o w . T h i s i n t e r m e d i a t e is f o r m e d b y t h e r m a l r u p t u r e of a C — H b o n d as t h e gas s t r e a m travels t h r o u g h t h e p y r o l y s i s z o n e of t h e flow system ( 1 2 ) . M o s t o f these r a d i c a l s are c o n v e r t e d to p - x y l y l e n e as t h e p y r o l y z a t e streams a w a y f r o m the f u r n a c e . S o m e u n d e r g o c o u p l i n g to g i v e 1,2-di-p-tolylethane a n d p - e t h y l t o l u e n e . I f these side reactions o c c u r i n t h e p y r o l y s i s z o n e , t h e p r o d u c t s c o n t i n u e to react to g i v e 4 , 4 ' - d i m e t h y l s t i l b e n e a n d p - m e t h y l styrene. I n a d d i t i o n , d i t o l y l e t h a n e c a n r e a r r a n g e t o o - m e t h y l d i p h e n y l methanes, w h i c h i n t u r n are c o n v e r t e d to t h e c o r r e s p o n d i n g anthracenes ( 1 ). p - X y l y l e n e t h a t is g e n e r a t e d i n t h e p y r o l y s i s z o n e c a n u n d e r g o r e a r r a n g e m e n t t o cyclo-octatetraene, w h i c h i n t u r n rearranges t h e r m a l l y to 2Φ In Selective Oxidation Processes; Fields, E.; Advances in Chemistry; American Chemical Society: Washington, DC, 1965.
3.
ERREDE AND
ENGLISH
p-Methylbenzyl
Radical
27
Downloaded by MICHIGAN STATE UNIV on February 18, 2015 | http://pubs.acs.org Publication Date: January 1, 1965 | doi: 10.1021/ba-1965-0051.ch003
styrene. D e m e t h y l a t i o n is a m a j o r c o m p e t i n g r e a c t i o n t h a t c o m p l i c a t e s the p y r o l y s i s .
T h e r a t i o of p r o d u c t s f o r m e d v i a side reactions, i n d i c a t e d b y l i g h t a r r o w s , to those p r o d u c e d v i a t h e m a i n reactions, i n d i c a t e d b y t h e h e a v y a r r o w s , increases w i t h i n c r e a s i n g severity of t h e p y r o l y s i s c o n d i t i o n s ( 6 ). A k i n e t i c s t u d y of this p y r o l y s i s ( 6 ) has s h o w n that t h e f r a c t i o n a l c o n v e r sion ( F ) of p-xylene to p - m e t h y l b e n z y l r a d i c a l s is g i v e n b y F = kite-ht
(1)
w h e r e t is the residence t i m e i n seconds, k is t h e rate constant f o r f o r m a t
t i o n of p - m e t h y l b e n z y l r a d i c a l s v i a t h e r m a l r u p t u r e of m e t h y l C — H b o n d , a n d k is t h e rate constant f o r t h e r m a l c r a c k i n g of t h e r a d i c a l i n t e r m e d i 2
ates.
B e l o w 1050° C , fci a n d k are g i v e n b y 2
h k
= 2
=
9.3 X 1 0
13
e-76/RT
2.4 X 10
