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The effects of modes of hydrogen input and reactor configuration on reaction rate and H
 2
 efficiency in the catalytic hydrogenation of alkynol to alkenol

Hydrogenation often involves three phases where hydrogen-on-demand is the typical mode of operation in industrial scale reactors. In research labs and publications, however, continuous hydrogen flow was used. This paper investigates the effect of such modes of operation on reaction rate using the selective hydrogenation of 3-butyn-2-ol over Pd/Al2O3 to obtain 3buten-2-ol as the model reaction. The two modes of operation were firstly tested in a commercial PARR stirred tank reactor, then repeated in an oscillatory baffled reactor (OBR) in order to validate the experimental results. Our investigation demonstrates that enhanced reaction performance was obtained when the pressure is kept constant during the reaction by feeding gas as required, i.e. hydrogen-on-demand mode, with up to 10 times better H2 efficiency. The method of continuous flow of hydrogen in hydrogenation means that excess hydrogen is vented out when operating at ambient or build up at elevated pressures. Our work also enables the comparison of reactor designs on reactor performance, H2 efficiency was three times higher and the residence time 2.3 times shorter when using the OBR instead of the PARR due to its enhanced and uniform mixing, regardless of the mode of operation.