Heat of absorption of CO2 in aqueous ammonia, piperazine solutions and their mixtures

A reaction calorimeter CPA-122 was used to determine the heats of absorption of CO 2 in 5 wt% NH 3 (aq), 0.86 mol PZ and the blended solutions (1.5–3.1 mol) NH 3 /(0.43–0.86 mol) PZ at 40 °C, 60 °C and 80 °C. The heat of absorption of CO 2 in 5 wt% NH 3 (aq) at low CO 2 loadings ( 2 /mol-Am) was measured to be 74.8 kJ/mol CO 2 at 40 °C and 65.9 kJ/mol CO 2 at 80 °C, and found to decrease gradually in the high loading interval (>0.5 mol-CO 2 /mol-Am). The heat of absorption of CO 2 in 0.86 mol PZ solution was measured to be 73 kJ/mol CO 2 in the low CO 2 loading interval ( 2 /mol-Am), and found to decrease gradually in the high loading interval (>0.5 mol-CO 2 /mol-Am) at 40 °C and 60 °C. The heat of absorption of CO 2 in 3.1 mol NH 3 + 0.86 mol PZ solution demonstrated a high degree of consistency with that of CO 2 in 3.1 mol NH 3 (aq), which indicated that blending a small amount of PZ does not have a significant effect on the heat of absorption. The mechanism of the absorption process of CO 2 in the mixtures is also discussed in depth in this paper.