Measurements of Diffusion Coefficients of CO$_{2}$ in 1-Butanol with a New Laminar Jet Apparatus and PFG-NMR, Pointing to Interfacial Mass Transfer Effects

Abstract: A novel laminar jet apparatus (LJA) was constructed for precise gas-liquid mass transfer measurements up to 12 bar, significantly extending the technique's operating window. It was applied to carbon dioxide + 1-butanol between 283 K and 333 K. Corresponding measurements were performed using pulsed field gradient NMR spectroscopy (PFG-NMR), which does not involve interfacial mass transfer. Fick diffusion coefficients from LJA and self-diffusion coefficients from PFG-NMR were compared in the limit of infinite dilution, where both must coincide. Both methods show consistent trends, but LJA data are systematically lower. Experimental errors cannot explain the deviations. We therefore hypothesize an additional gas-liquid interfacial mass transfer resistance. PCP-SAFT combined with density gradient theory predicts high CO$_{2}$ enrichment at the interface, and the deviations correlate with this enrichment. Whether such an interfacial resistance exists and is caused by enrichment remains to be established in future studies.