It has been found that sulfur dioxide solubility in organic solvents can be well-correlated by Lewis basicity numbers. Mixtures of sulfur dioxide and solvent (N-methylpyrrolidone (NMP), N,N′-(dimethylpropylene)urea (DMPU) and methyldiethanolamine (MDEA)) have been prepared in a 1:1 mole ratio at low temperatures. The melting points of the mixtures are measured, and the mixtures have been analyzed by infrared, ultraviolet-visible, and nuclear magnetic resonance spectroscopy. The solubility of sulfur dioxide has been measured in NMP and DMPU at 25 °C. At sulfur dioxide concentrations of 0.2-0.6 kPa, the solubility is determined using a continuous stirred tank reactor. The absorption of sulfur dioxide proved to be completely reversible. A model where physical and chemical interactions are incorporated showed good correlation with the experimental results.

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 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 °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 SO2−NFM system.