Characterization of the SO2−N-Formylmorpholine Complex: Application to a Regenerative Process for Waste Gas Scrubbing

This paper presents the results of fundamental investigations on physical and chemical interactions between sulfur dioxide and N -formylmorpholine (NFM), with a view to the development of a regenerative process for waste gas scrubbing. This solvent is a promising medium for such processes because of its high absorption capacity, its low-to-moderate vapor pressure for temperatures below 100 °C, and its reduced toxicity. The existence of a chemical interaction between SO 2 and NFM, with the formation of a 1:1 complex, was demonstrated by absorption tests, melting curve measurements, and the determination of vapor−liquid equilibrium from 25 to 80 °C. Further characterization was carried out by IR spectrometry. The formation of a solid complex with a melting point at 5.7 °C allows for the transport of absorbed sulfur dioxide under a convenient solid state; in addition, its stability was shown to decrease with temperature, which enables the solvent to be regenerated at high temperatures. The existence of a second complex with a 2:1 stoichiometry was suggested by modeling the gas−liquid equilibrium using the Harris and Prausnitz approach but could not be put into evidence by the other techniques. The parameters deduced by the above-mentioned model were successfully used for the prediction of the melting curve of an SO 2 −NFM system.