The performance of a multistage agitated contactor (MAC) with cocurrent reactive gas liquid upflow was studied for the hydrogenation of nitrile butadiene rubber using a homogenous osmium complex catalyst. The hydrogenation performance was investigated under various catalyst concentrations, liquid flow rates, pressures, and polymer concentrations. The desirable hydrogenation conversion of over 95% was achieved under the industrially relevant operation conditions. A comprehensive reactor model consisting of stirred tanks in series with back flow (CTB) was applied to describe the liquid flow behaviour in the presence of the hydrogenation process. The established model satisfactorily predicted dynamic hydrogenation performance considering the gas liquid mass transfer effect and temperature profile in each stage. A modified CSTRs-in-series model accounting for mass transfer effect was proposed to predict the hydrogenation degree at steady state and a good agreement was demonstrated between the model prediction and the experimental data. (C) 2009 Elsevier Ltd. All rights reserved.