Design of a green one-step catalytic production of ε-caprolactam (precursor of nylon-6)

摘要

The ever-increasing industrial demand for nylon-6 (polycaprolactam) necessitates the development of environmentally benign methods of producing its precursor, ε-caprolactam, from cyclohexanone. It is currently manufactured in two popular double-step processes, each of which uses highly aggressive reagents, and each generates substantial quantities of largely unwanted ammonium sulfate as by-product. Here we describe a viable laboratory-scale, single-step, solvent-free process of producing ε-caprolactam using a family of designed bifunctional, heterogeneous, nanoporous catalysts containing isolated acidic and redox sites, which smoothly convert cyclohexanone to ε-caprolactam with selectivities in the range 65–78% in air and ammonia at 80°C. The catalysts are microporous (pore diameter 7.3 Å) aluminophosphates in which small fractions of the and tetrahedra constituting the 4-connected open framework are replaced by and tetrahedra, which become the loci of the redox and acidic centers, respectively. The catalysts may be further optimized, and already may be so designed as to generate selectivities of ≈80% for the intermediate oxime, formed from NH2OH, which is produced in situ within the pore system. The advantages of such designed heterogeneous catalysts, and their application to a range of other chemical conversions, are also adumbrated.