Vapour-phase Beckmann rearrangement using B-MFI zeolites

The vapour-phase Beckmann rearrangement has been studied using a boron-MFI zeolite. The multitude of papers concerning this reaction state the maximum yield of epsilon-caprolactam at a temperature of 350 degrees C and ambient pressure. Investigation of different process parameters showed that decreasing the pressure in addition to reducing the temperature to 300 degrees C leads to an improvement in caprolactam selectivity. This resulted in a drop in catalyst lifetime. In order to reduce deactivation, the addition of water to the reaction is useful. Contrary to former papers, it was shown that the deactivation rate decreased with a raising amount of added water up to 6 mol water per mol cyclohexanone oxime. The conversion was slightly increased with no considerable effect on the selectivity. Due to the short catalyst service time, a regeneration of deactivated catalysts is inevitable. Using air or oxygen as a regenerating agent, it is possible to regain complete activity and selectivity. Nitrogen can also be used as a regeneration gas, although a slight drop in activity must be accepted. For industrial application, a continuous reaction-regeneration system should be employed when using fluidized bed reactors. Therefore, the reaction was studied in a fluidized bed reactor of laboratory scale. The yields achieved in this apparatus were in good agreement with the results obtained in a fixed bed reactor.