The effects of modes of hydrogen input and reactor configuration on reaction rate and H₂ efficiency in the catalytic hydrogenation of alkynol to alkenol

Abstract

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 has been used. This paper investigates the effect of such modes of operation on reaction rate using a selective hydrogenation of 3‐butyn‐2‐ol over Pd/Al2O3 to obtain 3‐buten‐2‐ol as the model reaction. The two modes of operation were first tested in a commercial PARR stirred tank reactor and then repeated in an oscillatory baffled reactor (OBR) in order to validate the experimental results. Our investigation demonstrates that an enhanced reaction performance and 10 times better H2 efficiency were obtained when the pressure was maintained constant during the reaction by feeding gas as required, ie hydrogen‐on‐demand mode. The method of a continuous flow of hydrogen in hydrogenation means that excess hydrogen is vented out when operating at ambient pressures or builds up at elevated pressures. Our work also enables a comparison of reactor designs on reactor performance, and three times higher H2 efficiency and 2.3 times shorter residence time were achieved when using the OBR instead of the PARR due to its enhanced and uniform mixing, regardless of the mode of operation.

Design, performance characterization and applications of continuous oscillatory baffled reactors

“…The use of a pulsed baffled tube photochemical reactor has been demonstrated for three-phase heterogeneous catalysed photo-reactions and has shown good performance due to the effective solid handling capacity of this reactor type Skelton, 2000, 1999). Navarro-Fuentes et al (2019b carried out catalytic hydrogenation of alkynol to alkenol in an OBR and found that due to the enhanced multiphase mixing and mass transfer, the OBR consumes five times less power, provides more than two times higher 𝐻𝐻 2 efficiency and 50% lower residence time to achieve the same reaction performance obtained in a commercial STR.…”

Gas-Phase Catalytic Hydrogenation/Isomerization in the Transformation of 3-Butyn-2-ol over Pd-Ni/Al2O3

“…The existing literature on alkynol hydrogenation has focused on tertiary alkynols, notably 2-methyl-3-butyn-2-ol . The only reported transformation of secondary alkynols involved liquid-phase conversion of 3-butyn-2-ol using Pd/Al 2 O 3 in pressurized (oscillatory baffled vs stirred tank) reactors. , We have recently reported the formation of 2-butanol and 2-butanone as by-products in the continuous hydrogenation of 3-butyn-2-ol over a commercial Pd/Al 2 O 3 catalyst . Four possible reaction pathways are associated with the hydrogenation of 3-butyn-2-ol, as shown in Figure .…”

Highly selective catalysts for the hydrogenation of alkynols: A review

“…Pd NPs supported by oxides with hierarchical porosities and special functional groups have also been widely applied in the semi-hydrogenation of alkynols to enols [38][39][40][41][42][43][44][45][46][47][48][49][50]. The formation of interfaces between Pd NPs and oxide supports and the introduction of organic groups allow one to tune the adsorption of substrates and intermediates on the catalyst surface and thus realize chemoselective hydrogenation.…”