SYNTHESIS OF HYDROTALCITE WITH HIGH LAYER CHARGE FOR CO2 ADSORBENT

Hydrotalcite-like compounds (HT) with 24% to 48% Al3+-substitution have been synthesized in the Mg2+-Al3+-Fe(CN)(6)(4-) system. Conditioning of the synthesized and air-dried compound with K4Fe(CN)(6)(4-) solution at 80 degrees C was essential to obtain the 80-90% pure ionic Fe(CN)(6)(4-) form on an equivalent basis. A linear decrease in a(o) with an increase in the mole ratio of R=Al3+/(Mg2+Al3+) was extended to R=0.48. The CO2 adsorption profiles were dependent upon both the interlayer distance and the Al3+-substitution. The expanded space with the large anion Fe(CN)(6)(4-) can accommodate more effectively CO2 gas in comparison with the NO3- and mixed ionic forms. The optimum space and charge density in the interlayer as a CO2 adsorption field could be found on the hydrotalcite with the Al3+-substitution of 37 %. The isosteric heat of CO2 adsorption was 43.3 kJ mol-1 in the range of adsorption of 20 to 40 cm(3) g(-1) at 298 K and 0.1 MPa.