Liquid phase hydrogenation in a structured multichannel reactor

A compact, structured, multichannel reactor was tested for two exemplary reactions: the selective hydrogenation of aromatic aldehyde and the tandem C–C coupling–hydrogenation. In the case of hydrogenation reaction up to 50% yield with ca. 96% selectivity was attained in a single pass (single channel of 10 cm length of catalytic bed) at a liquid phase residence time of ca. 10 s, proving the effectiveness of the designed reactor. By controlling the point of injection of hydrogen into the reactor an increase in the yield of hydrogenation up to 73% was achieved using two channels in a consecutive mode. The designed compact reactor was also proven to be an excellent tool for kinetic studies: the kinetics of the three-phase hydrogenation was evaluated showing: (i) reaction limitation for applied reaction conditions, (ii) Langmuir–Hinshelwood mechanism of hydrogenation, and finally (iii) the dominating role of adsorption of reactant and absorption of hydrogen in the mechanism of hydrogenation at higher temperatures. Furthermore, the compact reactor was also successfully used for conducting sequential coupling Heck reaction with consecutive hydrogenation of double C–C bond. A stepwise conversion of the substrates to the final product was achieved with ca. 6 min residence time at relatively low temperature and pressure. In conclusion, the developed structured compact reactor was demonstrated as a promising alternative to replace conventional batch reactors and establish continuous synthesis of pharmaceutical intermediates and specialty chemicals.