Thermal degradation of piperazine and diethanolamine blend for CO2 capture

• Thermal degradation of PZ/DEA is CO2 dependent.
• Presence of DEA catalyzed the thermal degradation of PZ.
• Major degradation product of PZ/DEA system is triethanolamine.
• Kinetic model shows good agreement with experimental results.

In amine-based post-combustion CO2 capture, solvent loss contribute to process operation problems like corrosion, fouling, foaming as well as is responsible for economic deficit. In this work, thermal degradation of blended 3.2 m DEA and 0.8 m was investigated at 135 °C, simulating the stripper temperature. CO2 loading of the system was varied from 0.0 to 0.4 mole CO2/mole alkalinity to explore its effect on degradation of the blended system. Experiments were conducted in 316 stainless steel cylinders, fitted with Swagelok® endcaps made of 316 stainless steel, which were kept in convection ovens. Degraded samples were analyzed by using gas chromatography (GC) for final concentration and identification of the degradation products. Thermal loss of PZ was high in the PZ/DEA blend than other investigated blends of PZ like PZ/MDEA, PZ/AMP, and PZ/MEA under similar experimental conditions. CO2 loading increased the rate of degradation of both PZ and DEA; however, rate of degradation of PZ was higher at high CO2 loading and increased abruptly than that of DEA. Concentration of PZ approached to zero within 300 h of experiment at high CO2 loading. Mechanism for the formation of major degradation products is proposed in the study. An empirical rate law is articulated to determine the loss of PZ. Results of model are in good agreement with experimental results.