Effects of O2 and SO2 on the Capture Capacity of a Primary-Amine Based Polymeric CO2 Sorbent

Abstract

Postcombustion CO2 capture is most commonly carried out using an amine solution that results in a high parasitic energy cost in the stripper unit due to the need to heat the water, which comprises a majority of the amine solution. It is also well-known that amine solvents suffer from stability issues due to amine leaching and poisoning by flue gas impurities. Solid sorbents provide an alternative to solvent systems that would potentially reduce the energy penalty of carbon capture. However, the cost of using a particular sorbent is greatly affected by the usable lifetime of the sorbent. This work investigated the stability of a primary amine-functionalized ion-exchange resin in the presence of O2 and SO2, both of which are constituents of flue gas that have been shown to cause degradation of various amines in solvent processes. The CO2 capture capacity was measured over multiple capture cycles under continuous exposure to two simulated flue gas streams, one containing 12 vol % CO2, 4% O2, 84% N2, and the other containing 12.5 vol % CO2, 4% O2, 431 ppm SO2, balance N2 using a custom-built packed bed reactor. The resin maintained its CO2 capture capacity of 1.31 mol/kg over 17 capture cycles in the presence of O2 without SO2. However, the CO2 capture capacity of the resin decreased rapidly under exposure to SO2 by an amount of 1.3 mol/kg over 9 capture cycles. Elemental analysis revealed the resin adsorbed 1.0 mol/kg of SO2. Thermal regeneration was determined to not be possible. The poisoned resin was however, partially regenerated with exposure to 1.5 M NaOH for 3 days resulting in a 43% removal of sulfur, determined through elemental analysis, and a 35% recovery of CO2 capture capacity. Evidence was also found for amine loss upon prolonged (7 days) continuous exposure to high temperatures (120 °C) in air. It is concluded that desulfurization of the flue gas stream prior to CO2 capture will greatly improve the economic viability of using this solid sorbent in a postcombustion CO2 capture process.