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 CO₂ in 5 wt% NH₃ (aq), 0.86 mol PZ and the blended solutions (1.5–3.1 mol) NH₃/(0.43–0.86 mol) PZ at 40 °C, 60 °C and 80 °C. The heat of absorption of CO₂ in 5 wt% NH₃ (aq) at low CO₂ loadings (<0.5 mol-CO2/mol-Am) was measured to be 74.8 kJ/mol CO2 at 40 °C and 65.9 kJ/mol CO2 at 80 °C, and found to decrease gradually in the high loading interval (>0.5 mol-CO₂/mol-Am). The heat of absorption of CO₂ in 0.86 mol PZ solution was measured to be 73 kJ/mol CO₂ in the low CO₂ loading interval (<0.5 mol-CO2/mol-Am), and found to decrease gradually in the high loading interval (>0.5 mol-CO₂/mol-Am) at 40 °C and 60 °C. The heat of absorption of CO₂ in 3.1 mol NH₃ + 0.86 mol PZ solution demonstrated a high degree of consistency with that of CO₂ in 3.1 mol NH₃ (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 CO₂ in the mixtures is also discussed in depth in this paper.