Masaru Kitamura

Some aspects of the vapor phase Beckmann rearrangement for the production of ε-caprolactam over high silica MFI zeolites

A high silica MFI zeolite catalyst has been developed for the vapor phase Beckmann rearrangement of cyclohexanone oxime to e-caprolactam. Methanol fed into the reactor with the oxime improves the yield of caprolactam. Methanol is not converted to dimethylether during the reaction. Moreover, when ammonia is fed to the catalyst with cyclohexanone oxime and methanol, the selectivity remains at a high level, without affecting the conversion. Hence, we conclude that the active sites of high silica MFI are extremely weak acid sites that cannot be detected by ammonia TPD measurement. A fluidized bed reaction system has been developed for the manufacturing process of caprolactam. High quality product is obtained with more than 95% yield.

A Vapor Phase Beckmann Rearrangement Over High-Silicious ZSM-5

A vapor phase Beckmann rearrangement of cyclohexanone oxime to τ-caprolactam over a high silicious ZSM-5 (Si/Al ≧ 1, 000) was studied in detail in relation to the hydrothermal synthesis of ZSM-5 and to its surface silanol groups. Two important factors were found to enhance the lactam selectivity; external surface area (ESA) and modification of the surface silanols with trimethylchlorosilane (TMCS). Thus the excellent results (oxime conversion=100%, lactam selectivity=95%) were obtained over the high silicious (Si/Al≧1,000) and high ESA (≧10m 2 /g) ZSM-5 which was further modified with TMCS (ref.1).

The Catalysis of Vapor-Phase Beckmann Rearrangement for the Production of ε-Caprolactam

Recently, Sumitomo Chemical Co., Ltd. developed the vapor-phase Beckmann rearrangement process for the production of ε-caprolactam. In the process, cyclohexanone oxime is rearranged into ε-caprolactam using a zeolite as a catalyst instead of sulfuric acid. EniChem in Italy developed the ammoximation process that involves the direct production of cyclohexanone oxime without producing any ammonium sulfate. Sumitomo Chemical Co., Ltd. has commercialized the combined process of vapor-phase Beckmann rearrangement and ammoximation in 2003.In this paper, the authors focus on some aspects of the vapor-phase Beckmann rearrangement catalysis. A solid catalyst that is mainly composed of a high-silica MFI zeolite (Silicalite-1) has been developed for the vapor-phase Beckmann rearrangement. This catalyst does not possess acidity that can be detected by ammonia TPD. Methanol fed into the reactor with cyclohexanone oxime improves the yield of caprolactam. Methanol reacts with terminal silanols on the zeolite surface and converts them to methoxyl groups. The modification of the catalyst by methanol has an important role for the Beckmann rearrangement reaction.Nest silanols located just inside the pore mouth of the MFI zeolite are supposed to be the active sites of the catalyst. We propose that the coordination between the NOH group of cyclohexanone oxime molecule and the nest silanols through hydrogen bonding is responsible for the reaction. The reaction mechanism of Beckmann rearrangement under vapor-phase conditions is the same as in the liquid phase, namely, the alkyl group in anti-position against the hydroxyl group of the oxime migrates to the nitrogen atoms position.

1.7 The Role of Alcohols on Lactam Selectivity in the Vapor-Phase Beckmann Rearrangement Reaction

Abstract For the vapor-phase Beckmann rearrangement reaction of cyclohexanone oxime over high-silicious pentasil zeolites, the selectivity to e-caprolactam increased when methanol was supplied with cyclohexanone oxime into the reaction system. FT-IR measurements showed that the neutral silanol groups of the zeolite were methylated by the alcohol. This indicates that the neutral silanol is not the active site for producing e-caprolactam.