Beckmann Rearrangement of Cyclohexanone Oxime to ϵ‐Caprolactam in a Microreactor

The selectivity and conversion of the sulfuric acid‐catalyzed Beckmann rearrangement of cyclohexanone oxime, dissolved in cyclooctane, to ϵ‐caprolactam are determined in a microreactor for conditions with a high concentration of ϵ‐caprolactam. The microreactor consists of a low‐temperature mixing zone followed by a high‐temperature reaction zone. The mixing is conducted in a split‐and‐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 ϵ‐caprolactam.