Prussian Blue Analogues for CO2 and SO2 Capture and Separation Applications

Adsorption isotherms of pure gases present in flue gas including CO2, N-2, SO2, NO, H2S, and water were studied using prussian blues of chemical formula M-3[Co(CN)(6)](2)center dot nH(2)O (M = Co, Zn) using an HPVA-100 volumetric gas analyzer and other spectroscopic methods. All the samples were characterized, and the microporous nature of the samples was studied using the BET isotherm. These materials adsorbed 8-10 wt % of CO2 at room temperature and 1 bar of pressure with heats of adsorption ranging from 200 to 300 Btu/lb of CO2, which is lower than monoethanolamine (750 Btu/lb of CO2) at the same mass loading. At high pressures (30 bar and 298 K), these materials adsorbed approximately 20-30 wt % of CO2, which corresponds to 3 to 5 molecules of CO2 per formula unit. Similar gas adsorption isotherms for SO2, H2S, and NO were collected using a specially constructed volumetric gas analyzer. At close to 1 bar of equilibrium pressure, these materials sorb around 2.5, 2.7, and 1.2 mmol/g of SO2, H2S, and NO. In particular, the uptake of SO2 and H2S in Co-3[Co(CN)(6)](2) is quite significant since it sorbs around 10 and 4.5 wt % at 0.1 bar of pressure. The stability of prussian blues before and after trace gases was studied using a powder X-ray diffraction instrument, which confirms these materials do not decompose after exposure to trace gases.