Selective hydrogenation of alkynes for vitamin production in a three-phase structured reactor Sergio Vernuccio 1 *, Roman Goy 2 , Jonathan Medlock 2 , Philipp Rudolf von Rohr 3 1 Department of Chemical and Biological Engineering, Northwestern University, Evanston IL, USA 2 DSM Nutritional Products, Process R&D Basel, Switzerland 3 Institute of Process Engineering, ETH Zurich, Switzerland *Corresponding author: sergio.vernuccio@northwestern.edu Highlights  A structured reactor is presented to conduct three-phase hydrogenations of alkynes  A kinetic model is developed to describe the process over a wide range of conditions  An overall mass transfer coefficient is estimated from the results in continuous mode 1. Introduction The semi-hydrogenations of alkynes to alkenes are key transformations in the fine chemical industry to produce vitamins and aroma compounds. In industry, these three-phase reactions are usually carried out using palladium-based catalysts in slurry reactors. These catalysts, mostly in the form of fine powders to avoid mass transfer limitations, require filtration after the reaction [1]. Furthermore, these discontinuous processes involve a number of steps with the intermediate products being collected, stored and often transported to other facilities. To overcome these problems considerable efforts are directed to the conversion of traditional batch processes into discontinuous operations. This paper presents a novel combination of catalyst support and reactor design for the semi-hydrogenation of alkynes in prospect of process intensification. The solvent-free hydrogenation of 2-methyl-3-butyn-2-ol (MBY) to 2-methyl-3- buten-2-ol (MBE) was chosen as test reaction. MBE represents an important intermediate in the industrial synthesis of vitamin E. The selectivity of this process concerns the possibility of hydrogenating MBY to MBE while preventing its further hydrogenation to 2-methyl-2-butanol (MBA). The advantages of this structured reactor are high surface area, good mixing qualities and low pressure drops. Furthermore, it is characterized by a regular geometry easily reproducible and suitable for computational simulations. 2. Methods This paper is divided into three sections: i) Development of a kinetic model to describe the selective hydrogenation of MBY. ii) Application of the structured reactor in a semi-batch hydrogenation plant with identification of the kinetic regime. iii) Continuous operation of the structured reactor and estimation of the external mass transfer resistance. The kinetic model was developed using the experimental results collected in a stirred slurry reactor over a wide range of operating conditions. The structured reactor was manufactured with a regular structure by selective laser sintering [2]. The internal packing represents the negative pattern of tetrahedrally arranged overlapping spheres (Figure 1). The metal support was coated with an Al2O3/ZnO base layer, impregnated with palladium and characterized by SEM analysis. The reactor was implemented into a hydrogenation plant and operated in both semi- batch and continuous mode. Figure 1. Structured reactor used during the experimental activity. A part of the outer wall was removed for visualization purposes.