An industrial reactive separation process for NOx absorption into water and nitric acid in a world-kale mononitrobenzene (MNB) plant in Redcar, U.K., was investigated. Gas- and liquid-phase concentrations were measured in situ, while operating conditions such as temperature, pressure, and absorbent flow were varied. Furthermore, a comprehensive mass transfer/reaction model was developed in the process simulator Aspen Plus to simulate the absorption process, with the field process data used for validation. The model accurately predicted NOx removal from the gas (i.e., typically within 3.5% of the plant data). Other key findings are that the model successfully predicted changes in performance when key parameters such as temperature and pressure were varied. Furthermore, addition of a bleaching section was investigated, resulting in a significant improvement in NOx removal. Currently, the completed model is used to simulate existing and proposed NOx absorption systems and to develop new and innovative designs for NOx capture.