During amine scrubbing of CO 2 from flue gas, carbamate and bicarbonate species are formed, the amount of which is directly related to the process performance. In this study we present a fast calibration-free spectroscopic technique for determining the speciation of CO 2 −H 2 O−alkanolamine systems and in turn the amine protonation and carbamate thermodynamic equilibrium constants. The method is based on in situ infrared monitoring of the liquid phase during CO 2 absorption by an aqueous amine solution in a stirred vessel, combined with mathematical hard modeling of the reaction mechanism. The species concentrations are calculated by fitting of a thermodynamic model to multivariate spectroscopic measurements using nonlinear regression. Successful applications include the determination of the amine protonation and carbamate equilibrium constants of one primary (MEA), one secondary (DEA), and one sterically hindered primary (AMP) amine at 40 °C.
The three-phase hydrogenation of nitrobenzene catalysed by nanosized gold over titania was investigated in a slurry. Simultaneous in situ ATR-FTIR monitoring of the liquid phase and at the solid/liquid catalyst interface identified the species adsorbed on the catalyst and those in the liquid phase during the reaction. Nitrosobenzene was not detected analytically while the spectroscopic measurements strongly indicated phenylhydroxylamine as an intermediate reacting before desorbing from the catalyst surface. Under the same reaction conditions, azobenzene and hydrazobenzene were identified as intermediates during the hydrogenation of azoxybenzene to aniline. When nitrosobenzene or phenylhydroxylamine was alternately fed as reactant, azoxybenzene was produced via a disproportionation route. With the former, azoxybenzene was not further reduced by hydrogen because nitrosobenzene deactivated the catalyst. Combined with H(2) uptake, the spectroscopic measurements provided new insights into the reaction mechanism of the gold catalysed hydrogenation of nitrobenzene and an update of the corresponding kinetics.
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