Abstract

Process Intensification of Hydrogenation Reactions in Catalyst-coated Tube Reactors

Nikolay Cherkasov, Research Fellow, University of Warwick

The fine chemicals industry heavily relies on batch reactors which are very inefficient in terms of space-time yield and safety. Flow chemistry solves these problems and provide a possibility for process intensification and production with lower capital requirements. Unfortunately, heterogeneously-catalysed gas-liquid reactions attract little attention even despite their sizable share of 10% of all industrial processes. We studied the application of millimetre tube reactors wall-coated with noble metal catalysts for hydrogenations such as nitrobenzene, alkynes to alkenes (2-methyl-3-butyn-2-ol) and conjugated unsaturated aldehydes (cinnamaldehyde) over Pd and Pt-based catalysts. Compared to the batch reactor with the same catalyst, the selectivity to unsaturated alcohol in cinnamaldehyde hydrogenation was 6 times as high in the tube reactor, about 90% vs 15%. The decreased selectivity in batch was caused by protection (acetalization) of aldehydes in the presence of acid sites on the silica support, while these sites were quickly deactivated in the tube reactor. The long term stability study in selective hydrogenation of 2-methyl-3-butyn-2-ol showed a turnover number of above 105, 100 times higher than in the batch. An increased temperature from 70 to 160 oC allowed for 8 times higher reaction rates compared to batch with the same 1% substrate decomposition.