Method for preparing caprolactam by using a microreactor under Lewis acid catalysis

Abstract

We establish the fact that in a continuous-flow scalable photoreactor system employed for the homogeneous photolysis of H2O2 into .OH radicals, the quantum yield of photolytic conversion in aqueous solution cannot be regarded as a linear function of H2O2 initial concentration. We were successful in repeatedly producing high concentrations of .OH radical (between 40 and 90 mM) from relatively low concentrations of hydrogen peroxide (between 0.1 M − 5 M) in aqueous solution in a scalable manner using our serially connected photoreactor system. Our investigation demonstrates that merely selecting a very high initial concentration of H2O2 will not necessarily result in the highest conversion into .OH radical. We also developed a simple and in-situ acid-base titrimetric method for quantitation of .OH radicals and demonstrated an accuracy of our method within ~±6.6% of a 31P NMR method. Hence, our proposed scalable .OH radical production method via continuous-flow photoreactors can be regarded as a safe, simple, accurate and cost-effective technique for various industrial processes, particularly in aquaculture and swimming pool disinfection, as a replacement of high concentrations of hazardous oxidisers.