39 Thermal Decomposition Patterns in Methylammonium Cation-Exchanged Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 1, 2015 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1971-0101.ch039
Y-Type Faujasites E. L. WU, G. H. KÜHL, T. E. WHYTE, JR., and P. B. VENUTO Mobil Research and Development Corp., Paulsboro, N. J. 08066
The mono-, di-, tri-, and tetramethylammonium exchanged forms of a Y-type faujasite have been prepared. The cationic size determined the extent of exchange; hydronium ion incorporation was indicated. Thermal decomposition patterns of the 4 forms are generally comparable. Detailed transformations were analyzed for the tetramethylammonium (TTMA) form by in situ infrared observations and identification of decomposition products. These cations decomposed by a combination of reactions involving low-temperature decomposition in the presence of the intrazeolitic pool of hydroxylic sorbate, "methyl disporoportionation between methyl-containing species and possible surface methoxy intermediates, and high-temperature ylide or carbene mechanisms. The protonic sites generated and associated zeolitic changes were compared with those of NH faujasite. 4
• " p h e t h e r m o c h e m i s t r y of N H
4
c a t i o n - e x c h a n g e d zeolites has b e e n t h e
subject of n u m e r o u s studies (4, 22, 24, 27, 28).
T h e transformations
i n v o l v e d are r e l a t i v e l y s i m p l e : d e a m m o n i a t i o n to give t h e h y d r o g e n f o r m a n d d e h y d r o x y l a t i o n b y e l i m i n a t i o n of w a t e r at h i g h e r temperatures. O t h e r s t r u c t u r a l changes m a y o c c u r , d e p e n d i n g o n p r o c e s s i n g c o n d i t i o n s ( J O ) . I o n exchange of a l k y l - s u b s t i t u t e d a m m o n i u m cations i n t o zeolites (2, 26) has b e e n r e p o r t e d ; t h e r m a l transformations i n s u c h systems are e x p e c t e d to b e c o n s i d e r a b l y m o r e c o m p l e x a n d interesting. T h e i m p o r t a n c e of t h e a n i o n i n d e t e r m i n i n g t h e d e c o m p o s i t i o n p a t h w a y of q u a t e r n a r y a m m o n i u m salts w a s r e c o g n i z e d b y I n g o l d i n 1927 (7). A t 1 3 5 ° - 1 4 0 ° C , tetramethylammonium ( T T M A ) hydroxide decomposes 490 In Molecular Sieve Zeolites-I; Flanigen, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
39.
wu ET AL.
Thermal
Decomposition
491
Patterns
to g i v e t r i m e t h y l a m i n e , d i m e t h y l e t h e r , or m e t h a n o l , d e p e n d i n g o n e x p e r i m e n t a l c o n d i t i o n s (8, 15).
W i t h t h e w e a k e r base, c h l o r i d e ,
t i o n occurs at a h i g h e r t e m p e r a t u r e Salts w i t h other o r g a n i c
(16).
decomposi
( 3 6 0 ° C ) to f o r m m e t h y l c h l o r i d e
anions d e c o m p o s e b e t w e e n
100°
and
2 5 0 ° C , also via s i m p l e d i s p l a c e m e n t of t r i m e t h y l a m i n e (16,
32).
More
complex
have
been
pathways i n v o l v i n g y l i d e or carbene
mechanisms
p o s t u l a t e d i n other T T M A - c a t i o n systems (6, 9, 15, 31, 33, 34,
35).
W e n o w r e p o r t results of a s t u d y of the t h e r m a l d e c o m p o s i t i o n terns i n t h e 4 m e t h y l - s u b s t i t u t e d a m m o n i u m
(MA)
exchanged
pat
Y-type
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 1, 2015 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1971-0101.ch039
faujasites, d e t a i l e d t r a n s f o r m a t i o n of the T T M A f o r m , a n d the r e s u l t i n g g e n e r a t i o n of p r o t o n i c a c i d i t y . Experimental Materials. T h e m e t h y l a m m o n i u m Y - z e o l i t e s ( T a b l e I ) w e r e p r e p a r e d b y i o n - e x c h a n g i n g N a Y ( 5 g r a m s ) w i t h 4 1 0 0 - m l p o r t i o n s of 1 Ν a l k y l a m m o n i u m salt s o l u t i o n at 80 ° C . M o n o m e t h y l a m m o n i u m ( M M A ) chloride, dimethylammonium ( D M A ) chloride, and tetramethylammonium ( T T M A ) bromide (Matheson, C o l e m a n , a n d B e l l ) a n d the trimethylammonium ( T M A ) chloride (Eastman Organic Chemicals) were used as r e c e i v e d . Table I. U n i t Cell Composition of Mono-, D i - , T r i - , and Tetramethylammonium Y and Parent N a Y Faujasites Sample
Na
Ν
Na Y MMA Y DMA Y TMA Y TTMA Y
52.2 9.3 11.8 20.8 28.4
36.5 34.0 25.5 17.7
a
A10
Si0
2
2
52 52 52 52 52
6.2 6.2 5.7 6.0
Calculated by difference, assuming N a + Ν + Η =
140 140 140 140 140
A10 . 2
T h e ammonia ( Matheson anhydrous ) was purified b y fractional con d e n s a t i o n a n d d i s t i l l a t i o n i n v a c u u m . R e s e a r c h grade h e l i u m ( M a t h e s o n ) w a s d r i e d o v e r 5 A m o l e c u l a r sieve p r i o r to use. Apparatus and Procedures. T h e r m a l analyses w e r e p e r f o r m e d u s i n g D u P o n t 900 d i f f e r e n t i a l t h e r m a l ( D T A ) a n d 950 t h e n n o g r a v i m e t r i c ( T G A ) analyzers. B a s i c d e c o m p o s i t i o n p r o d u c t s i n t h e T G A effluent w e r e t i t r a t e d w i t h s u l f a m i c a c i d at r e g u l a r t e m p e r a t u r e i n t e r v a l s (11). T T M A - Y w a s e x a m i n e d in situ u s i n g a h i g h - t e m p e r a t u r e i n f r a r e d c e l l (36) i n w h i c h simultaneous zeolite t r e a t m e n t a n d s p e c t r a l o b s e r v a t i o n c o u l d be effected. T h e c e l l w a s c o n n e c t e d to a c o n v e n t i o n a l v a c u u m a n d g a s - h a n d l i n g system ( u l t i m a t e v a c u u m , 10" t o r r ) . S p e c t r a w e r e r e c o r d e d o n a P e r k i n - E l m e r 421 g r a t i n g spectrophotometer, m o d i fied b y the a d d i t i o n of a p r e s a m p l e c h o p p e r to e l i m i n a t e the effect of spurious r a d i a t i o n o r i g i n a t i n g f r o m the h o t s a m p l e a n d c e l l . S p e c t r a l r e s o l u t i o n w a s 4 c m " at 3600 c m a n d 2 c m " at 1600 c m " . 6
1
- 1
1
1
In Molecular Sieve Zeolites-I; Flanigen, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
492
MOLECULAR SIEVE ZEOLITES
1
S a m p l e s ( 2 - g r a m ) of T T M A - Y w e r e c a l c i n e d i n a t u b u l a r r e a c t o r u n d e r v a c u u m a n d the d e c o m p o s i t i o n p r o d u c t s ( T a b l e I I ) over 2 m a j o r t e m p e r a t u r e ranges w e r e c o l l e c t e d . A f t e r gas f r a c t i o n a t i o n w h e r e n e c essary, c o m p o n e n t s i n the v a r i o u s fractions w e r e a n a l y z e d b y i n f r a r e d a n d mass s p e c t r o s c o p y ( C E C M o d e l 21-104, i o n i z a t i o n v o l t a g e 10 e v ) .
Table II. Analysis of Organic Decomposition Products from Thermal Decomposition of T T M A Y in V a c u u m " Temp. Range, Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 1, 2015 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1971-0101.ch039
Product,
Estimated
Mole
%
b
150°-275°
c
(CH.) N CH NH C H (CH ) 0 CO CH OH H C H C H 3
2
4
3
2
9
2
6
4
8
Total
ά
5 24 23 14 —
6 4 Tr 4
3
3
275°-450°
50 11 — Tr 10
8
4
°C
9 23 21 13 1 1 1 14 8 5
— — 15 9 5
° 10" Torr, held at 275° for 3 hr and 450° for hr. Noncondensables were allowed to expand into an evacuated bulb and condensables collected in liquid nitrogen traps. Estimated, based on relative pressure of the fractions and mass spectral analysis. Trace (Tr)—
