A novel modification for silicalite-1 with high stability and selectivity in vapor phase Beckmann rearrangement of cyclohexanone oxime

Article abstract of DOI:10.1246/cl.2005.472

This paper presents a novel modification of highly siliceous MFI zeolites with hydrofluoric acid treatment: Silicalite-1 undergone such treatment exhibited remarkable improvements in stability and selectivity for Beckmann rearrangement of cyclohexanone oxime, which are even much better than those obtained by basic modification. Copyright

Full text of DOI:10.1246/cl.2005.472

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Chemistry Letters Vol.34, No.4 (2005)
A Novel Modification for Silicalite-1 with High Stability and Selectivity
in Vapor Phase Beckmann Rearrangement of Cyclohexanone Oxime
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ꢀyy
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Weichuan Tao,
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Dongsen Mao, Jianchao Xia, Qingling Chen, and Ying Hu
East China University of Science and Technology, Shanghai 200237, P. R. China
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Shanghai Research Institute of Petrochemical Technology, SINOPEC, Shanghai 201208, P. R. China
(Received December 28, 2004; CL-041620)
This paper presents a novel modification of highly siliceous
drofluoric acid exhibited remarkable improvements in stability
and selectivity for vapor phase Beckmann rearrangement of cy-
clohexanone oxime, which are even much better than those ob-
tained by basic treatment which has been considered to be the
most effective modification method up to date.
MFI zeolites with hydrofluoric acid treatment: Silicalite-1 un-
dergone such treatment exhibited remarkable improvements in
stability and selectivity for Beckmann rearrangement of cyclo-
hexanone oxime, which are even much better than those ob-
tained by basic modification.
Silicalite-1 was hydrothermally prepared by conventional
ꢁ
procedure from TEOS, TPAOH, and water at 120 C for 48 h.
ꢁ
White solid produced was washed, separated, dried at 100 C,
ꢁ
"
-Caprolactam, the raw material of nylon-6, is produced in-
and calcined at 600 C for 4 h in air. To this crystal was added
7.5 wt % ammonium nitrate solution to carry out ion exchange
dustrially by liquid phase Beckmann rearrangement of cyclohex-
anone oxime using concentrated sulfuric acid catalyst, which is a
source of pollution and equipment corrosion. Thus, many efforts
have been focused on the research of solid acid catalysts for their
ꢁ
treatment at 90 C for 1 h and repeated for 3 times and then
the crystal was washed and separated. Finally, the crystal was
ꢁ
ꢁ
dried at 100 C and calcined at 550 C for 4 h in air. The resulting
crystal was referred as catalyst S-1.
1
,2
environmental friendly manufacture. Among them, zeolites of
MFI-type, in particular those with a high silica/alumina ratio,
prove to be the most promising catalysts for the transformation
of oximes into amides.
Hydrofluoric acid treatment was carried out in an autoclave
under autogenous pressure. 0.04 wt % HF with the mass ratio of
HF to S-1 of 10:1 was added. The treatment was carried out at
ꢁ
It has been well illustrated in the literature that silanols on
zeolites surface are of great significance for Beckmann rear-
80–90 C for 1 h and was repeated for 3 times. The crystal ob-
tained was washed, separated, dried and named as FS-1. The ba-
sic treatment was performed in a similar way as hydrofluoric
acid treatment except that a mixture of ammonium nitrate
(7.5 wt %) and aqueous ammonia solution (28 wt %) with the
mass ratio of 3:1 was used and the resulting crystal was calcined
rangement reaction.3 For example, Sato et al. proposed that
–8
3
the terminal silanols on highly siliceous MFI zeolite are the ac-
4
tive sites. On the contrary, Kitamura et al. reported that the se-
lectivity to lactam was improved greatly when the terminal sila-
nol groups were eliminated, indicating that the terminal silanol
groups promoted the formation of by-products. On the other
ꢁ
at 550 C for 4 h in air. The catalyst with basic treatment was
named as NS-1.
5
,6
hand, H o¨ lderich and co-workers investigated the catalysis of
vapor phase Beckmann rearrangement over the parent and vari-
ous modified zeolites silicalite-1 and suggested that the silanol
nests were the most favorable active sites for Beckmann rear-
rangement due to the adjustment of acid strength caused by
the hydrogen bond, while terminal silanols were the least favor-
able. These results suggest that the catalytic performance of
highly siliceous MFI zeolite will be improved if the distribution
of various types of silanols can be adjusted by a suitable way.
Hence, many efforts have been concentrated on the adjustment
The Beckmann rearrangement reaction was carried out in a
ꢁ
fixed-bed reactor at 370 C under atmosphere pressure. The mix-
ture of cyclohexanone oxime (30 wt %) and ethanol was injected
to the reactor along with N2 as the carrier gas. The weight hour-
ꢂ1
ly-space-velocity (WHSV) of cyclohexanone oxime was 8 h
.
The effluent products were collected and analyzed by gas chro-
matograph (HP 4890, HP-1 capillary column, flame ionization
detector). The major by-products formed are cyclohexanone, cy-
anopentane, and cyanopentene, which is in accordance with the
9
literature.
5
,6,9–11
of silanols on zeolites surface.
siliceous MFI zeolites with nitrogen-containing basic solutions,
Until now, treating high
The changes of oxime conversion with time on stream over
the different catalysts are compared in Figure 1. It was found that
each catalyst exhibited a high initial oxime conversion about
99%, while their deactivation rate was quite different. The un-
treated catalyst S-1 underwent a quick activity loss and its con-
version dropped to 66.9% after 21 h reaction. The deactivation
rate of S-1 was greatly slow down after modification and catalyst
NS-1 gave a conversion of 88.3% after 29 h reaction. Particular-
ly, catalyst modified with hydrofluoric acid exhibited the lowest
deactivation rate. Its conversion remained nearly 96% after a rel-
atively long reaction time of 53 h (almost two times longer than
that for NS-1 catalyst). Unlike the conversion of oxime, no sig-
nificant change in the selectivity to caprolactam with time on
stream was observed over all three catalysts. The average selec-
1
0
which was developed by Sumitomo Company, has been con-
sidered to be the most effective modification method. However,
thus treated catalysts still deactivated at a relatively quick rate
with time on stream. Therefore, it is still interesting and of great
significance to explore other effective modification methods for
highly siliceous MFI zeolites applied in vapor phase Beckmann
rearrangement reaction.
Besides its widely use in surface etching, hydrofluoric acid
treatment is also an effective method of surface rehydroxylation
for silica.1 However, to the best of our knowledge, such treat-
ment for highly siliceous zeolites has not been reported so far. In
this paper, we report that zeolite silicalite-1 modified with hy-
2,13
Copyright Ó 2005 The Chemical Society of Japan

Chemistry Letters Vol.34, No.4 (2005)
473
1
00
arrangement to "-caprolactam from cyclohexanone oxime can
be catalyzed by silanols around 100 C, while the desorption
ꢁ
9
9
8
8
7
7
6
5
0
5
0
5
0
5
FS-1
of the originally produced "-caprolactam from catalyst surface
NS-1
ꢁ
3,14
occurs at a considerably higher temperature (>350 C).
If
the produced "-caprolactam can not desorb from catalysts sur-
face smoothly, it may transfer to coke or other by-products,
which lowers the selectivity to lactam and shortens catalyst
3,15
12
13
life. On the other hand, Barrett et al. and Kohler et al. veri-
fied experimentally that the terminal silanols possess a higher
adsorptivity for basic compounds than the associated silanols.
It is proposed that most of the hydrogens may be involved in
H-bonding in associated silanols; as a result there is little reac-
S-1
5
10 15 20 25 30 35 40 45 50 55
Time on stream / h
Figure 1. Variation of oxime conversion with reaction time
over different silicalite-1 catalysts. Reaction conditions: T ¼
1
6
tive hydrogen to react with basic compounds. The above re-
sults implied that the desorption rate of the produced caprolac-
tam from silicalite-1 catalyst surface depends greatly on the ratio
of the associated silanols to the isolated silanols. The higher the
ratio the easier the desorption of the produced caprolactam from
catalyst surface, which results in higher stability and selectivity
for caprolactam synthesis.
ꢁ
ꢂ1
3
70 C, P ¼ 0:1 MPa, WHSV ¼ 8 h , solvent: ethanol, carrier
ꢂ1
gas: N2, flow rate of N2 ¼ 60 mL min
.
3
720
3
685
3500
In conclusion, compared with untreated samples, silicalite-1
with hydrofluoric acid treatment exhibited a much lower deacti-
vation rate and higher selectivity to lactam in Beckmann rear-
rangement of cyclohexanone oxime. The stability and selectivity
of zeolite silicalite-1 for the vapor phase Beckmann rearrange-
ment of cyclohexanone oxime was closely dependent on the ra-
tio of the associated silanols to the isolated silanols, which ac-
counts for the excellent catalytic performance of HF modified
silicalite-1.
S-1
NS-1
FS1
4000
3800
3600
Wavenumbers / cm
3400-
3200
3000
1
Figure 2. FT-IR spectra of different silicalite-1 catalysts.
The authors thank National Basic Research Program of
China (No. 2003CB615801) for financial support. Mrs. Yang
Yiqing and Mr. Lu Liyuan in SRIPT are thanked for their helps
in the FT-IR measurements.
tivity to lactam of S-1, NS-1, and FS-1 was 93.6, 93.2 and
96.1%, respectively, the highest value being observed on FS-1.
The above results show that hydrofluoric acid modification for
silicalite-1 significantly improves its catalytic performance for
the Beckmann rearrangement of cyclohexanone oxime; and that
the improvements are even much better than those obtained by
basic treatment which has been considered to be the most effec-
tive modification method up to date.
References
1
2
H. Ichihashi and H. Sato, Appl. Catal., A, 221, 359 (2001).
G. Dahlhoff, J. P. M. Niederer, and W. F. H o¨ lderich, Catal.
Rev.—Sci. Eng., 43, 381 (2001).
To clarify the effect of HF modification on catalytic behav-
ior of silicalite-1 for Beckmann arrangement reaction, the FT-IR
spectra of FS-1 and S-1 together with NS-1 were measured. As
shown in Figure 2, three peaks were detected and assigned to ter-
3
4
5
H. Sato, K. Hirose, and Y. Nakamura, Chem. Lett., 1993, 1987.
M. Kitamura and H. Ichihashi, Stud. Surf. Sci. Catal., 90, 67 (1994).
G. P. Heitmann, G. Dahlhoff, and W. F. H o¨ lderich, J. Catal., 186, 12
(1999).
ꢂ1
ꢂ1
6
7
G. P. Heitmann, G. Dahlhoff, J. P. M. Niederer, and W. F.
H o¨ lderich, J. Catal., 194, 122 (2000).
S. Bordiga, I. Roggro, P. Ugliengo, A. Zecchina, V. Bolis, G.
Artioli, R. Buzzoni, G. Marra, F. Rivetti, G. Spano, and C. Lamberti,
J. Chem. Soc., Dalton Trans., 2000, 3921.
minal silanols (ꢃ3720 cm ), vicinal silanols (ꢃ3685 cm ) and
ꢂ1
silanol nests (ꢃ3500 cm ), respectively. The first one belongs
to isolated silanols while the latter two to silanols associated
by hydrogen bonding. By comparing the intensities of different
silanols, we obtained that the ratio of the associated silanols to
the isolated silanols decreased in the order: FS-1 > NS-1 ꢄ
S-1. This order agrees well with that of catalytic performance.
The good relationship between the catalytic behavior and the ra-
tio of the associated silanols to the isolated silanols can be ex-
plained as follows: (1) It has been reported that the associated si-
lanols are favorable than the isolated counterparts for the selec-
8
9
1
1
C. Flego and L. Dalloro, Microporous Mesoporous Mater., 60, 263
(2003).
H. Sato, K. Hirose, M. Kitamura, and Y. Nakamura, Stud. Surf.
Sci. Catal., 49, 1213 (1989).
0 M. Kitamura, H. Ichihashi, and H. Tojima, U.S. Patent, 5 403 801
(1995).
1 L. Forni, G. Fornasari, G. Giordano, C. Lucarelli, A. Katovic, F.
Trifiro, C. Perri, and J. B. Nagy, Phys. Chem. Chem. Phys., 6,
1842 (2004).
3
,4
tive formation of lactam. On the other hand, it was also report-
ed that the isolated terminal silanols promote the non-selective
12 D. A. Barrett, V. A. Brown, R. C. Watson, M. C. Davies, P. N. Shaw,
H. J. Ritchie, and P. Ross, J. Chromatogr., A, 905, 69 (2001).
1
1
4
,9
conversion of cyclohexanone oxime, which makes the lactam
selectivity decrease and the catalyst deactivate quickly. Accord-
ingly, higher ratio of the associated silanols to the isolated sila-
nols means higher selectivity for caprolactam formation and less
coke precursor production, which in consequence delay the de-
3 J. K o¨ hler and J. J. Kirkland, J. Chromatogr., 385, 125 (1987).
4 Y. Ko, M. H. Kim, S. J. Kim, G. Seo, M. Y. Kim, and Y. S. Uh,
Chem. Commun., 2000, 829.
1
5 T. Takahashi, T. Kai, and E. Nakao, Appl. Catal., A, 262, 137
(2004).
16 J. Nawrocki, J. Chromatogr., A, 779, 29 (1997).
1
1
activation of catalyst. (2) It has been demonstrated that the re-
Published on the web (Advance View) February 26, 2005; DOI 10.1246/cl.2005.472