B-MCM-41 AS NANO-STRUCTURED CATALYST FOR THE IMPROVEMENT OF BECKMANN REACTION CONDITIONS
The Beckmann rearrangement of Cyclohexanone oxime at 300-380 °C and W/F = 20-60 gh/mol over a B-MCM-41 catalyst was studied at atmospheric pressure. The e-Caprolactam (precursor for nylon-6) was the major product on the whole temperature range studied and Cyclohexanone appeared as the main by-product and was generated probably due to the moderate acidity of these materials. The stability and the possibility of recycling of the catalyst were also analyzed. So, the catalyst could be used during 3600 min and then recovered and reused without significant changes in the active species. A reaction pathway was proposed in order to explain the results obtained. Finally, the better catalytic performance was observed at 320 °C and W/F = 40 gh/mol. Such conditions allowed us to achieve a Cyclohexanone oxime conversion of 54% with an e-Caprolactam selectivity of around 83%. Thus, under this soft reaction condition it could be achieved a high yield to e-Caprolactam with a low proportion of Cyclohexanone. This product mixture (e-Caprolactam and Cyclohexanone) may be separated by vacuum distillation; then the Cyclohexanone could be recycled by reaction with hydroxylamine to form again Cyclohexanone oxime (raw material for e-Caprolactam), marketed for the production of adipic acid, as adhesive in sealing PVC objects or as solvent in several industries.
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