The main focus of this project was the experimental investigation of hydrodynamics and mass transfer characteristics together with a chemical reaction in a bubble column at higher gas holdup. Experiments were performed for chemical absorption of CO₂ in alkaline solution of different pH, at homogenous bubbly flow conditions and up to 17% gas holdup. Ultrafast electron beam X-ray tomography (UFXCT) has been used to obtain local gas holdup data and bubble characteristics and a wire-mesh sensor was used to measure species concentration fields in the liquid bulk. In addition, experiments with the reaction of NO and Fe^II(edta) were carried out and a new fiber optical probe was employed for local measurement of product concentration in the bubble wake.