Studies on the CO2 adsorption onto coal fly ash zeolites at elevated pressures

Coal fly ash zeolites (CFAZs) of Na-X type were prepared by ultrasonic-assisted double stage fusion-hydrothermal synthesis from lignite coal fly ash at two different fusion temperatures 550 and 800 C. The detailed surface analyses were performed experimentally using N2 physisorption technique and by applying standardized mathematical models. CFAZs were studied for their carbon capture potential at 5.5 MPa regarding their application in a pressure-swing CO2 adsorption process. CO2 loaded CFAZs were investigated by weight analyses, Fourier-Transform Infrared (FTIR) and Thermal Gravimetric Analyses (TGA). FTIR reveals vibration modes typical for the zeolite Na-X framework, physically attached CO2 molecules and small amounts of carbonates. The adsorption capacity toward CO2 measured by weight analyses and TGA reaches 385 mgCO2/gCFAZ. Higher carbon capture ability was found at CFAZ prepared with a pre-fusion stage at 800 C, despite its the lowest specific surface area. A favourable effect of the increased content of mesopores in the CFAZ framework on the CO2 adsorption at elevated pressures has been established.