The classical Beckmann rearrangement is an important step in the production of ϵ-caprolactam, the monomer for nylon-6. Nowadays, nearly 90% of caprolactam is produced by the conventional cyclohexanone process in large-scale industrial production.

G. S. Luo and colleagues from Tsinghua University, Beijing, China, designed a new microstructured chemical system, including micromixer, delay loop and microhydrolyzer, to carry out the Beckmann rearrangement of cyclohexanone oxime. The cyclohexanone oxime was dissolved in n-octane as the continuous phase, and oleum was dispersed in the octane solutions as microdroplets in the micromixer.

The rearrangement reaction proceeded in the delay loop connecting directly to the micromixer. The conversion of cyclohexanone oxime and selectivity of caprolactam were investigated under various conditions. 100 % conversion of cyclohexanone oxime and > 99 % selectivity of caprolactam were gained in this microsystem with reaction time less than 40 s. Molar ratios of oleum to less than 40 s. Molar ratios of oleum to cyclohexanone oxime can be controlled as low as 0.8, which is much lower than the industrial value of 1.2–1.7.

• Beckmann rearrangement in a microstructured chemical system for the preparation of ε-caprolactam,
  J. S. Zhang, K. Wang, Y. C. Lu, G. S. Luo
  AIChE J. 2012, 58 (3), 925–931.
  DOI: 10.1002/aic.12612