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 degreesC, and its reduced toxicity. The existence of a chemical interaction between SO2 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 degreesC. Further characterization was carried out by IR spectrometry. The formation of a solid complex with a melting point at 5.7 degreesC 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 SO2-NFM system.