Application of a structured multifunctional reactor for the oxidation of a liquid organic feedstock

Abstract

Experiments are performed in a structured packed bed reactor that has been developed for the selective oxidation of organic liquids to produce pharmaceutical products. Molecular oxygen is used as the oxidant, providing a “cleaner processing route”, than in established methods. The structured assembly consists of an integrated heat exchange system, a gas/liquid mixing zone, and provision for reactant injection. To illustrate the application, the selective oxidation of benzyl alcohol to benzaldehyde was studied. The reactor consisted of parallel reaction channels (10 cm long and square shaped) that were packed with Ru/Al 2O 3 (0.9 wt% Ru) catalyst particles. From experiments in three different sizes of channel: 2 mm × 2 mm, 3 mm × 3 mm, and 5 mm × 5 mm (at P = 8 bar, T = 388 K, with liquid and gas flows L = 3.2 kg m −2 s −1, G = 1.35 × 10 −2 kg m −2 s −1), it was shown that in a short 10 cm length of channel, a product yield up to ca. 29% (with minimum 99.5% selectivity) could be obtained. Conversions were highest in the 3 mm × 3 mm channel. From the experiments with the reactor mounted both in horizontal and vertical planes, it was shown that gravitational influences are minor. The choice of solvent was shown to affect the yield of benzaldehyde. The highest yield was with toluene; the application of dioxane/water mixture (70/30 by vol.) and N-methyl pyrrolidone (NMP) not only decreased the yield by factor 2, but NMP also caused deactivation of the catalyst. Preliminary results are presented of work with Pt/C (Pt 3 wt%) catalyst.