Cyclohexanone Oxime Conversion Research Articles

Vapor Phase Beckmann Rearrangement of Cyclohexanone Oxime over Different Ferrierite Zeolite Catalysts

Ferrierite zeolite catalysts prepared using different procedures have been tested for their activity for vapor phase Beckmann rearrangement of cyclohexanone oxime to e-caprolactam. We report here the results of a study seeking the influence of temperature, nitrogen feed rate, oxime concentration and solvents on the catalyst performance. At low concentration of oxime (2.5 wt%), using acetonitrile as solvent the maximum in the conversion of oxime and selectivity to e-caprolactam has been obtained. The presence of weak, medium and strong acid sites as indicated by temperature-programmed desorption of NH3 corroborates well with the catalytic activities of various ferrierites shown here. Solvent polarity is found to significantly affect the conversion of cyclohexanone oxime.

Synthesis of ϵ‐Caprolactam from Cyclohexanone Oxime Using Zeolites Hβ, HZSM‐5, and Alumina Pillared Montmorillonite

AbstractThe Beckmann rearrangement of cyclohexanone oxime (CHO) to ϵ‐caprolactam (ϵ‐C) was studied in a plug flow reactor at 300–400°C under atmospheric pressure by using Hβ, ZSM‐5, and alumina pillared montmorillonite. With Hβ(X) Y zeolites, raising the SiO2/Al2O3 molar ratio (X) results in the enhancement of catalyst acid strength with concomitant decrease of the total acid amount. In creasing the calcination temperature (Y) causes remarkable diminution of catalyst surface area, acid strength, and acid amount. A similar trend was found for AlPMY catalysts. In there action of CHO, the initial catalytic activity correlates well with the total acid amount of various catalysts except for Hβ(10) Y (Y > 600°C). The reaction proceeds on both Brönsted and Lewis acid sites and the catalyst deactivation most likely occurs at the strong Brönsted acid sites. The effect of solvents in the feed on the catalytic results was also investigated; it was found that polar solvents such as ethanol or n‐butanol give high ϵ‐C yield and longer catalyst life time. In the reaction of CHO/C2H5OH over Hβ(10)800 at 400°C and W/F 74.6 gh/mol, the CHO conversion and ϵ‐C yield remain 100% and 92%, respectively, for at least 20 h time‐on‐stream. The reaction paths and the mechanism for ϵ‐C formation are proposed.

The Role of Acid Site Strength in the Beckmann Rearrangement

A range of catalysts including β-zeolite, mordenite, ZSM-5, Y-zeolite, mesoporous alumino silicate, and amorphous silica−alumina with varying Si:Al ratios have been tested in the range 250−350 °C for the Beckmann rearrangement of cyclohexanone oxime into caprolactam. All catalysts studied exhibited some level of deactivation which was characterized by a loss in conversion of cyclohexanone oxime with time on stream. There were considerable differences in resistances to deactivation through coke formation. Thus, mesoporous alumino silicate showed little decay in conversion with up to 16 wt % coke, whereas 6% coke on ZSM-5 caused a loss of 78% of the initial conversion. In general, the best catalysts were those which operated well in the presence of coke. Selectivity to caprolactam was in the range of 30−75% but did not change in a systematic fashion with time on stream. The number and strength of Bronsted and Lewis acid sites on each catalyst were determined from FTIR analysis of pyridine adsorption. These ...

Mesoporous molecular sieve Al-MCM-41 as a novel catalyst for vapor-phase Beckmann rearrangement of cyclohexanone oxime

Vapor-phase Beckmann rearrangement of cyclohexanone oxime to e-caprolactam has been studied at 1 atm and 300–400 °C using mesoporous molecular sieve Al-MCM-41. Benzene and ethanol are utilized as solvents for cyclohexanone oxime. Increasing the reaction temperature enhances the catalyst activity and stability whereas e-caprolactam selectivity varies only slightly. Ethanol exhibits much better catalytic results than benzene. Excellent catalyst performance is attained at 1 atm, 400 °C and W/FC 149.2 g h/mol by using ethanol in the feed; the cyclohexanone oxime conversion and the e-caprolactam selectivity remain higher than 99 and 90%, respectively, during at least 1200 h process time. The highly efficient catalysis on Al-MCM-41 is attributed to its large surface area, uniform mesopores as well as the weak and medium acidity.

Catalyst deactivation of high-silica HZSM-5 in the Beckmann rearrangement reaction of cyclohexanone oxime

The Beckmann rearrangement of cyclohexanone oxime was carried out over high-silica HZSM-5 zeolites and boron-modified HZSM-5 to elucidate the effects of silica alumina ratio and boron modification on the catalyst deactivation rate. The relationship between cyclohexanone oxime conversion and time on stream could be represented by the equation x( t) = x(0)·exp(− b· t) where x( t) and x(0) are conversions at a time on stream t and at the initial stage t = 0, respectively, and b is the deactivation coefficient. The deactivation coefficient increased with increasing concentration of strong acid sites. When the deactivated zeolites were evacuated under a pressure of 1 Torr at 573 K for 5 h, the catalytic activity was recovered up to 50% of the initial activity. The deactivation of the ZSM-5-type zeolite was mainly due to the adsorption of volatile material on the acid sites.

The relationship between acidity of aluminas and their selectivity in the conversion of cyclohexanone oxime into caprolactam

A range of aluminas modified by addition of sodium, phosphate, sulphate, chloride and boria have been tested for the Beckmann rearrangement of cyclohexanone oxime to caprolactam in the temperature range 300–350 °C. A relationship was observed between the selectivity to caprolactam and the surface concentration of acidic sites of intermediate strength.

Vapour phase beckmann rearrangement of cyclohexanone oxime over MEL type zeolites

The vapour phase Beckmann rearrangement of cyclohexanone oxime to e-caprolactam is reported over different MEL zeolites viz., silicalite-2, titanium silicate-2 (TS-2), ZSM-11 and alumino-titanium-silicate (Al-TS-2) and fumed silica. TS-2 exhibits 100% conversions with lactam selectivities close to 90%. The titanium containing analogs are also more resistant to deactivation than the parent zeolites. The conversion of cyclohexanone oxime and selectivity for e-caprolactam increase with temperature. The selectivity for e-caprolactam increases with the duration of run at all the temperatures.

Influence of boria loading on the acidity of B2O3/Al2O3 catalysts for the conversion of cyclohexanone oxime to caprolactam

Abstract Boron oxide catalysts supported on alumina have been prepared with boria loadings in the range 0–20 wt.-%. These materials were characterized by B.E.T. surface area measurements, X-ray diffraction and temperature-programmed desorption of ammonia and were used as catalysts for the Beckmann rearrangement of cyclohexanone oxime to caprolactam by passing the oxime vapour through a reactor containing the catalysts at 300°C. The surface areas of the samples decreased as the boria loading was increased, and all catalysts tested for the rearrangement reaction diminished in activity with time-onstream. There was a direct relationship between the amount of coke which formed on the surface and the loss in catalytic activity. This loss was least for the highest boron oxide loading tested, and this catalyst also featured the least amount of coke formation. Selectivity to caprolactam was associated with the presence of surface acidic sites of intermediate strength. A correlation was observed between the concentration of these surface sites and the selectivity to caprolactam.