CO2 Absorption Rate and Capacity of Semi-Aqueous Piperazine for CO2 Capture

Abstract

Abstract Aqueous piperazine (PZ) is a representative second-generation solvent for flue gas amine scrubbing; however, the solid precipitation of aqueous PZ at lean loading needs to be addressed. Semi-aqueous piperazine composed of PZ, water, and a physical solvent (sulfolane or imidazole) has been characterized in a wetted wall column. No precipitation was observed in 5 m PZ in SUF/water or IMI/water in the loading range of 0.15–0.45 mol CO2/mole alkalinity at 20–60 °C. The average viscosity at 40 °C in this range is about 25 cP in 5 m PZ in 1SUF/1water, 9.5 cP in 5 m PZ in 1SUF/3water, and 15 cP in 5 m PZ in 1IMI/1water, greater than 4 cp in 5 m aqueous PZ. Adding SUF or IMI into aqueous PZ increases absorption rate (kg’) at lean and median loading but decreases kg’ at rich loading. kg’ in semi-aqueous PZ increases as temperature decreases from 60 to 20 °C. At 40 °C, kg’avg in 5 m semi-aqueous PZ is 15–35% greater for the operating range of 0.1–5 kPa P*CO2, and 20–50% greater for 0.1–1.5 kPa P*CO2 (natural gas conditions). CO2 cyclic capacity slightly increased after adding SUF or IMI.