This study investigated the absorption performance of CO, into a diethylenetriamine (DETA)-based solution containing piperazine (PZ) or 1-(2-aminoethyl)piperazine (AEPZ) as an activator in a packed column with Dixon rings. The effects of various operation conditions such as the activator concentration, gas flow rate, liquid flow rate, CO2 partial pressure, and solution temperature on overall gas-phase volumetric mass-transfer coefficient (K(G)a(v)) were explored. Results indicate that the presence of PZ in DETA solution yields a better enhancement effect on K(G)a(v) than AEPZ, and, thus, a combination of 5%PZ+25%DETA solution is expected to be a promising absorbent for CO2 absorption. The results further show that K(G)a(v) increases with an increase in the liquid flow rate and a decrease in CO2 partial pressure and first increases and then decreases with an increase in solution temperature. On the other hand, the gas flow rate has an insignificant effect on K(G)a(v). A simplified empirical correlation for K(G)a(v) as a function of the operation parameters has been proposed, and most of the calculated values are in agreement with the experimental data with a deviation within +/- 15%.