Piperazine/4-hydroxy-1-methylpiperidine for CO₂ capture

Aqueous piperazine (PZ)/4-hydroxy-1-methylpiperidine (HMPD) was rigorously evaluated for CO₂ capture from flue gas. CO₂ cyclic capacity, CO₂ absorption rate, solvent viscosity, solvent volatility, and solid solubility were investigated as a function of the solvent composition. 2 m PZ/3 m HMPD is the composition that offers the best overall performance with more than twice the CO₂ cyclic capacity and absorption rate of 7 m MEA. This blend also shows much greater resistance to oxidative degradation than MEA at the same conditions, as well as lower amine volatility. When compared to 5 m PZ, 2 m PZ/3 m HMPD has 40% greater CO₂ cyclic capacity, 10% slower absorption rate and 10% greater viscosity. 2 m PZ/3 m HMPD also has much better solid solubility than 5 m PZ, with no precipitation down to −10 °C in the normal range of CO₂ loading. The cost of large-scale production of HMPD was also investigated based on current synthesis routes. The capital and energy cost for flue gas CO₂ capture using 2 m PZ/3 m HMPD is expected to be much lower than 7 m MEA, and comparable to 5 m PZ.