Thermal Decomposition Patterns in Methylammonium Cation

patterns of the 4 forms are generally comparable. ... Thermal Decomposition Patterns ..... A similar attack by methanol on TTMA cation generates dimet...
5 downloads 0 Views 1MB Size
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)—