Development of advanced zeolite catalysts for the vapor phase Beckmann rearrangement of cyclohexanone oxime

Development of advanced zeolite catalysts for the vapor phase Beckmann rearrangement of cyclohexanone oxime

ii~i~iiili~i~i;[email protected]~i~i~ii~i!i!i!i~i!~iii applied surface science ELSEVIER Applied Surface Science 121 / 122 (1997) 335-338 Development of advance...

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ii~i~iiili~i~i;[email protected]~i~i~ii~i!i!i!i~i!~iii applied

surface science ELSEVIER

Applied Surface Science 121 / 122 (1997) 335-338

Development of advanced zeolite catalysts for the vapor phase Beckmann rearrangement of cyclohexanone oxime Lian-Xin Dai 1, Yoshihide Iwaki, Katsuyuki Koyama, Takashi Tatsumi * Engineering Research Institute, School of Engineering, The Uni~,ersity o[ Tokyo, Yayoi, Tokyo 113, Japan Received 31 October 1996; accepted 12 February 1997

Abstract

The vapor phase Beckmann rearrangement of cyclohexanone oxime to e-caprolactam catalyzed by various zeolites was studied. The catalytic performance was greatly affected by both the zeolite structure and diluent solvent. When 1-hexanol was used in place of benzene, the catalytic performance of all catalysts except silicalite-I was greatly improved. In particular, the selectivity and stability of H-LTL and H-OFF-ERI zeolites remarkably increased; both catalysts exhibited ca. 100% oxime conversion and e-caprolactam selectivity of > 95% for 6 h. © 1997 Elsevier Science B.V. Keywords: Beckmann rearrangement; Zeolites; Diluent effect: Higher alcohols

1. Introduction

e-Caprolactam is an important intermediate in the manufacture of synthetic fibers. The current industrial route for the production of e-caprolactam is a liquid phase Beckmann rearrangement of cyclohexanone oxime using highly concentrated sulfuric acid as catalyst as well as diluent. However, this process has several disadvantages such as the by-production of a large amount of ammonium sulfate, and corrosion and environmental problems due to the use of fuming sulfuric acid. To overcome these inconveniences, strenuous efforts are being devoted to developing alternative heterogeneous catalysts, one of the most promising approaches being the use of the solid acid form of zeolites in place of sulfuric acid [1].

* Corresponding author. Tel.: +81-3-38122111; fax: +81-358006825; e-mail: [email protected] t E-mail: [email protected]

However, the zeolites such as Y [2-4] and mordenite [2] gave rise to relatively low selectivity for lactams and rapid decay of activity. Highly silicious ZSM-5 zeolites [5,6] have been reported to exhibit high activity and selectivity for e-caprolactam. Titanium silicalites, TS-1 and TS-2, have been found to be better catalysts for the transformation of cyclohexanone oxime than the other MFI and MEL zeolites, respectively [7,8]. Very recently, the use of ethanol/water mixture has been proved to be efl%ctive in retarding the deactivation of B-MFI zeolite [91. It is reported [4] that the Bronsted acidity of the zeolite catalyst is responsible for the activity in the conversion of oxime to caprolactam. However, Sato et al. pointed out that the weakly acidic or neutral silanol groups present on the external surface of the zeolites are the active sites of MFI zeolites for this rearrangement reaction [6]. The molecular size of e-caprolactam is supposedly larger than the diameter

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of the 10-membered ring channels of the zeolites. Yashima et al. [10] suggested that inside the channels the formation of by-products with smaller size could be accelerated at the expense of e-caprolactam and claimed the catalysts which have a smaller pore size than the molecular size of cyclohexanone oxime showed a high selectivity for e-caprolactam formation. However, the activity of the catalysts showing the high selectivity was relatively low. We have found that when 1-hexanol was used as diluent the H-BEA zeolite containing an interconnected threedimensional system of 12-ring channels exhibited excellent catalytic performance in contrast with other 12-membered ring zeolites such as Y [2-4], mordenite [2,10] and SAPO-5 [10], which give rise to relatively low selectivity for lactam and rapid decay of activity in the case of benzene diluent. Here we report that l-hexanol diluent is widely effective in improving the selectivity and stability of zeolite catalysts besides B E A zeolite in the vapor phase Beckmann rearrangement of cyclohexanone oxime.

change of M-zeolite (M = Na or K) with NH4C1 aqueous solution followed by calcination at 773 K. Silicalite-I (JRC-Z5-1000H, S i / A I 2 = 1250) was used as received. The catalytic reaction of cyclohexanone oxime was conducted under atmospheric pressure using a continuous flow reactor made of stainless steel. The feed cyclohexanone oxime was dissolved in benzene or l-hexanol and injected with a syringe pump along with N 2 as a carrier gas. The reaction conditions were as follows: reaction temperature of 623 K, 0.1 MPa, o x i m e / d i l u e n t / N 2 molar ratio of 1 / 9 / 1 0 and W / F of 136 goat h mOloxlime. The collected reaction products were analyzed by a gas chromatograph equipped with a 4 m long packed column of silicone SE-52 (5%).

3. R e s u l t s

and discussion

Fig. 1 shows the conversion and selectivity change with time on stream when benzene was used as diluent. Although the initial conversions on H-LTL and H - O F F - E R I zeolites were considerably high, they gradually decreased with time on stream. Both the catalysts exhibited considerably high e-caprolactam selectivity. While the selectivity was relatively low, stable 100% conversion was attained for the H-BEA zeolite. Silicalite-1 with the MFI structure showed 100% conversion and stable activity. However, it showed lower selectivity than H-LTL and H - O F F - E R I zeolite.

2. E x p e r i m e n t a l

The following zeolites from Tosoh were used in this study: N a - B E A ( S i / A 1 2 = 25.6), K - L T L (Si/A12 = 6.2), Na-OFF-ER1 ( S i / A I 2 = 7.6), NaM O R ( S i / A I 2 = 19.1) and H-USY (Si/A12 = 6.3). The proton-form zeolites were obtained by ion ex-

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Fig. 1. Change in conversion and selectivity with time on stream in the vapor phase Beckmann rearrangement of cyclohexanone oxime. Reaction conditions: 623 K, 0.1 MPa, oxime/benzene/N2 = 1/9/10 (M), W / F = 136 g~at h molo~lime.(O) H-BEA; (~.) H-LTL; ( v ) H-OFF-ERI; ( [] ) silicalite-1.

L.-X. Dai et aL /Applied Surface Science 121 / 122 (1997) 335-338

Table 1 Vapor phase Beckmann rearrangement of cyclohexanone oxime over different zeolites a

When l-hexanol was fed with cyclohexanone oxime in place of benzene, the catalytic performance of H-LTL and H-OFF-ERI as well as H-BEA catalysts was greatly improved (Fig. 2). Especially, the selectivity and stability of H-LTL and H-OFF-ERI zeolites remarkably increased; both catalysts exhibited ca. 100% oxime conversion and e-caprolactam selectivity of > 95% for 6 h. The formation of 5-cyanopentane and 5-cyano-l-pentene and cyclohexanone over both zeolites were effectively retarded. It has been known that the activity and life as well as e-caprolactam selectivity on Y and mordenite zeolites were considerably low when benzene was used as diluent [2-4]. As can be seen in Fig. 2, however, in the case of l-hexanol, 100% conversion and stable activity was also obtained on H-USY zeolite. Although the activity of the H-MOR catalyst slightly decreased with time on stream, a considerably high conversion of ca. 90% was maintained after 6 h. The selectivities for ~-caprolactam on H-MOR and H-USY catalysts were as high as ca. 90% and 80%, respectively. In contrast, for silicalite1, using l-hexanol as diluent resulted in rapid catalyst deactivation although the selectivity was improved. This result is consistent with the observation by Kitamura and Ichihashi, who reported that over silicalite-1 the activity decay increased with increasing alcohol carbon number in the range C I - C 3 [11]. It is worth noting that in the case of 1-hexanol the

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activity and life on silicalite-I was even lower than that on H-MOR zeolite. The difference in diluent effect among zeolite structures may be ascribed to the difference in the pore structure, acidity and h y d r o p h i l i c ity/hydrophobicity. Although no improving effect of 1-hexanol on the activity was observed for silicalite-1 with the MFI structure, the diluent of 1-hexanol was effective for the zeolites with 12-membered ring channels, even for LTL and OFF-ERI with unidimensional channel structure. It is conceivable that the active sites for the formation of by-products were effectively covered with 1-hexanol, resulting in the

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Reaction conditions: 623 K, 0.1 MPa, o x i m e / l - h e x a n o l / N 2 = 1 / 9 / 1 0 (M), W / F = 136 goat h moloxlime and time on stream = 6 h. b Mostly higher polymers.

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Fig. 2. Change in conversion and selectivity with time on stream in the vapor phase Beckmann rearrangement of cyclohexanone oxime. Reaction conditions: 623 K, 0.1 MPa, o x i m e / 1 - h e x a n o l / N 2 = 1 / 9 / 1 0 (M), W / F = 136 gcat h molo×lime. (Q)) H-BEA; ( A ) H-LTL; (x7) H-OFF-ERI; (rq) silicalite-l; (©) H-USY; ( × ) H-MOR.

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increase in the activity and selectivity for e-caprolactam formation. Research is in progress on the interaction of the acid sites with alcohols. The decreasing effectiveness of alcohols with their increasing carbon number for silicalite-1 may be related to its hydrophobicity because of virtual absence of A1. As shown in Table 1, BEA, LTL and OFF-ERI zeolites gave significantly high selectivities for ecaprolactam formation, which may be due to their relatively weak acidity. In contrast, probably because of their stronger acidity, H-USY and H-MOR catalysts exhibited higher selectivities of 5-cyanopentane, 5-cyano-l-pentene and cyclohexanone than the other zeolites. The highest selectivity for some unidentified by-products (mostly higher polymers) over the H-USY zeolite may result from the presence of supercages. H-USY has another disadvantage: the conversion of 1-hexanol on H-USY was > 30% after 1 h to ca. 10% after 6 h of time on stream. For the other zeolites, however, 1-hexanol conversion was about 5% after 1 h and gradually decreased to lower than 1% after 6 h. The present study has revealed that 1-hexanol diluent is widely effective in improving the activity,

selectivity and catalyst life of zeolites with 12-membered ring structure and relatively weak acidity in the vapor phase Beckmann rearrangement of cyclohexanone oxime.tes.

References [l] W. Hoelderich, M. Hesse, F. Naumann,Angew. Chem. Int. Ed. Engl. 27 (1988) 226. [2] P.S. Landis, P.B. Venuto,J. Catal. 6 (1966) 245. [3] P.B. Venuto, P.S. Landis, Adv. Catal. 18 (1968) 259. [4] A. Aucejo, M.C. Burguet, A. Corma, V. Fornes, Appl. Catal. 22 (1986) 187, and references cited therein. [5] H. Sato, N. Ishii, K. Hirose, S. Nakamura, Stud. Surf. Sci. Catal. 28 (1986) 755. [6] H. Sato, K. Hirose, M. Kitamura, Y. Nakamura, Stud. Surf. Sci. Catal. 49 (1989) 1213. [7] A. Thangaraj, S. Sivasanker, P. Ratnasamy, J. Catal. 137 (1992) 252. [8] J.S. Reddy, R. Ravishankar, S. Sivasanker, P. Ratnasamy, Catal. Lett. 17 (1993) 139. [9] J. Roeseler, G. Heitmann,W.F. Hoelderich, Appl. Catal. A 144 (1996) 319. [10] T. Yashima, K. Miura. T. Komatsu, Stud. Surf. Sci. Catal. 84 (1994) 1897. [11] M. Kitamura, H. Ichihashi, Stud. Surf. Sci. Catal. 90 (1994) 67.