Silica MFI Zeolite Research Articles

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 ε-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.

The development of new heterogeneous catalytic processes for the production of ε-caprolactam

Two catalytic methods emerging newly for the production of ε-caprolactam are reviewed: the ammoximation, and the vapor phase Beckmann rearrangement. These processes do not produce any ammonium sulfate as a by-product. The key for the processes are the catalysts used. The TS-1 zeolite comprising Ti and Si oxides with the structure of MFI is applied as an effective catalyst in the ammoximation reaction. This work reviews its catalysis and the features of the reaction. Although many solid acid catalysts have been tested for the Beckmann rearrangement, recently high silica MFI zeolites without so-called acidic sites are developed for the reaction. A brief history of the catalyst development on the rearrangement is presented, and the catalysis of high silica MFI zeolite is reviewed.

Effects of metal impregnation on the activity, selectivity and deactivation of a high silica MFI zeolite when converting methanol to light alkenes

Catalytic conversion of methanol to light alkenes was investigated using a high silica zeolite of the pentasil type MFI structure. The reaction was carried out in a fixed bed reaction set-up at 400°C, WHSV=4 h −1, pressure of 1 atm, andMeOH/N 2 (wt) ratio of 2.78. The silicalite zeolite (UC-S-115) was modified by impregnation with metal nitrates of Ag, Ca, Cd, Cu, Ga, In, La and Sr to study their effects on the activity and selectivity of the catalyst to lower alkenes. Incorporation of La and Ag led to an improvement in light alkene selectivity of the silicalite by 18% and 14% respectively. This was attributed to enhanced shape selectivity of the silicalite resulting from reduction of the apparent pore size of zeolite channels. the active life-on-stream was slightly decreased due to coke deposition. A non-rigorous least square fit of the catalyst life exhibited an exponential decay as a function of coke deposition rate above 0.17 wt% h −1. Below 0.17 wt% h −1 however, the active life-on-stream becomes insensitive to the rate of coking and is probably determined largely by catalyst intrinsic properties.