A new model has been developed to describe the curve of three-phase mass trasfer with non-linear equilibrium between a continuous and dispersed phases. An improved homogeneous model was applied, which takes into account the diffusion and chemical reaction in the dispersed phase. The non-linear isotherm was correlated by two or three linear segments. The absorption rate can be calculated for all mass-trasfer and reaction kinetic parameters in the case of first- and zero-order reactions. The film-penetration theory was used involving, as limiting cases, the absorption rates for film and surface renewal theories. The model introduced here involves, as limiting cases, previous models known from the literature.