The selectivity and conversion of the sulfuric acid-catalyzed Beckmann rearrangement of cyclohexanone oxime, dissolved in cyclooctane, to e-caprolactam are determined in a microreactor for conditions with a high concentration of e-caprolactam. The microreactor consists of a low-temperature mixing zone followed by a high-temperature reaction zone. The mixing is conducted in a splitand-recombine micromixer and a microchannel at 65°C, followed immediately by a second microchannel at 100-127°C to obtain complete conversion. Under these conditions a selectivity of 99 % is achieved. The residence time of the reactants in the microreactor setup is about 10 s. In literature, a selectivity of about 95 % for the same reaction in a similar setup is reported, but at a uniform temperature of 120-130°C for mixing and reaction. So, suppressing the reaction during mixing is a major tool to enhance the selectivity to e-caprolactam.

Beckmann rearrangement of cyclohexanone oxime dissolved in cyclooctane with oleum to ϵ‐caprolactam was demonstrated in a microreactor setup with internal recirculation operated in continuous mode. The core of the setup comprised a 316 stainless‐steel micromixer consisting of 17 split‐and‐recombine units connected to a delay loop, a 316 stainless‐steel microchannel reactor with an internal diameter of 0.250 mm and a length of 0.50 m. At 100 °C, the conversion of cyclohexanone oxime was complete and the selectivity towards ϵ‐caprolactam was approximately 99 %. The solvent cyclooctane reduces the observed purity of the produced oleum/ϵ‐caprolactam. This reduction in purity might be a severe hurdle for usage of a solvent on the industrial scale in the Beckmann rearrangement of cyclohexanone oxime in oleum to ϵ‐caprolactam.