In distillation under reduced pressure, the direct contact gas-liquid contactors with bulk packing, make it possible to separate the constituents of corrosive mixtures and also to recover hazard products that could harm the environment like solvents . The first part of this work concerns distillation in the pressure range between 6 kPa and atmospheric pressure. The hydrodynamic study in a column packed with Raschig rings and Berl saddles - Pressure losses, retention, SDR, waterlogging flows - and the determination of HEPT separation parameters, separating power - Allow completing some results already published and lead to invstigating the gas-liquid interfacial area. The second part is thus devoted to the measurement of this area by implementing an absorption with chemical reaction under reduced pressure. (Na₂-SO₃-O₂-CO₂ + system). These measurements are preceded by a bibliography which takes up the main models of transfer of the matter, as well as the chemical methods and works devoted to the interfacial area in particular. The results show that this area increases with the liquid flow rate and confirm the differences observed in distillation under reduced pressure.