In this work, carbon dioxide (CO 2 ) absorption experiments are performed in a custom designed vertical annular contactor (AC) at low rotational speeds. Methanol is used as solvent and Al 2 O 3 , SiO 2 and TiO 2 nanoparticles are combined with the methanol to produce nanofluids. The AC performance is compared to that of a modified version in which trays are added to enhance the CO 2 absorption rate (T-AC). Experiments in co-current and counter-current flows are carried out. In addition, two-phase flow patterns in the AC and in the modified version are analyzed by using a high speed visualization system. The results show no effect on the absorption rate for pure methanol at Re ω <17,000. In the counter-current flow, however, nanofluids show a better performance in the AC with maximum enhancements of 4.6% for TiO 2 , 1.2% for Al 2 O 3 and 1.1% for SiO 2 compared to pure methanol. The addition of trays enhances the CO 2 absorption rate up to 9%, 10%, 6% and 5% for pure methanol, Al 2 O 3 , SiO 2 , and TiO 2 , respectively for the counter-current flow. Likewise, the highest rotation effectiveness is found in the T-AC for Al 2 O 3 and TiO 2 with 24.2% and 14.4%, respectively.