1.Abstract Brazilian Pre-Salt oil reserves present associated natural gas (NG) exhibiting high concentrations of CO2 which requires gas purification processes for compliance with specifications imposed by the local Regulatory Agency. Due to its recognized small footprint as compared to amine based absorption route, membrane equipment show considerable potential for offshore applications. Of particular interest is the use of contactors, which combines membrane permeation with facilitated transport via liquid absorption. Process design and optimization of such innovative alternative demand flexible models to predict equipment performance at a variety of process conditions. This work presents a mathematical tool for analyzing CO2 separation with hollow-fiber membrane contactors, using aqueous solutions of ethanolamines. The model is applied to assess the technical feasibility of offshore CO2 separation with membrane contactors. The developed simulator is based on rigorous principles of thermodynamics, fluid mechanics, heat transfer and mass transport. Chemical absorption modeling is approached as a typical application of the well known Chemical Theory, which aims to model chemically and/or physically complex equilibrium systems via a set of chemical equilibrium processes involving real and fictitious species. Vapor–liquid Equilibria of real species are superimposed on the multi-reaction chemical equilibria for formation of fictitious species - non-ionic and non-volatile complexes. A process flowsheet is simulated to assert technical feasibility of this technology to offshore installations.