The LLE in aqueous solutions of N- methylpiperidine (NMPD, tertiary amine) and 2- methylpiperidine (2MPD, secondary amine) were investigated as function of CO2 dissolution. New experimental techniques were developed in order to determine the temperatures of phase separation in aqueous solutions loaded with controlled quantities of gas. The experimental investigation with NMPD and 2MPD solutions shows opposite effects on phase separation temperatures with CO2 dissolution. The influence of CO2 on LLE was discussed in terms of chemical reactions occurring in aqueous solutions of secondary and tertiary amines.