References for the Bosen-Engels approach

Bosen, A.; Engels, H. Description of the phase equilibrium of sulfuric acid with the NRTL equation and a solvation model in a wide concentration and temperature range. Fluid Phase Equil. 1988, 43, 213–230.

Nilges, J.; Schrage, J. Vapor-liquid equilibrium of the system H2SO4-SO3. Fluid Phase Equil. 1991, 68, 247–261.