The performance of a multistage horizontal rotating foam stirrer reactor in semi-continuous operation was studied for the selective hydrogenation of functionalized alkynes to alkenes, an important process in the fine chemicals industry. This new type of multiphase reactor consists of a horizontal vessel compartmentalized by vertical baffles and equipped with an impeller in each compartment. The impeller is a donut-shaped foam block, which is also used as catalyst support. The advantage of this reactor configuration compared to batch slurry reactors is the better catalyst handling, since the catalyst is fixed on the stirrer. In addition, a higher selectivity towards the desired product is achieved as a result of a narrower residence time distribution. A reactor model consisting of stirred tanks in series with backflow and dead volume was used to describe the liquid flow behaviour. The effects of liquid flow rate, backmixing and number of stages for the hydrogenation reaction are discussed, and optimal operation conditions are suggested. (C) 2014 Elsevier Ltd. All rights reserved.