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Influence of the type of CaO on carbon capture

https://doi.org/10.1590/0104-6632.20160332s20140245

“The reaction of calcium oxide with carbon dioxide is one of the most important methods for the capture and concentration of greenhouse gas from the flue gases of industrial plants. In this work, the carbonation reaction of CaO obtained from various sources with CO2 was investigated by a thermogravimetric method. These sources include commercial lime or CaO, CaCO3, Ca(OH)2, CaC2O4.H2O, a synthesized nanoporous sorbent, limestone and acetic acid washed limestone. The effect of structural parameters of the sorbents on the reactivity and CO2 capture capacity were studied using pore size distribution data.”

“The various types of lime used in this work as starting materials for investigating the carbonation reaction behavior were as follows:

  1. Commercial lime (CaO, Merck Art. No.102109).
  2. CaO from calcination of calcium carbonate (CaCO3, Merck Art. No.102059).
  3. CaO from calcination of natural limestone. The natural limestone used in this work was from Abyek mine. The XRF analysis of this sorbent is shown in Table 1.
  4. CaO from calcination of limestone washed with acetic acid solution. For this sample, 105 g limestone was added to 500 mL of 3M acetic acid. The reaction time was about 3 h. Then it was filtered and dried at 120 ºC for 4 h.
  5. CaO from decomposition of commercial calcium hydroxide (Ca(OH)2, Merck Art No. 102047).
  6. CaO from decomposition of commercial calcium oxalate (CaC2O4.H2O, Aldrich).
  7. CaO from calcination of a synthesized nano calcium carbonate. This sample was prepared by reaction of calcium nitrate with sodium bicarbonate solutions under ultrasonic treatment (Nouri, Ale Ebrahim and Naser Nejad, 2014).”

“The carbonation reactions were carried out in the TGA at 650 ºC. The conversion-time profiles of different sorbents are shown in Figure 2. It is clear that the reactivity and CO2 capture capacity of the different sorbents are not similar.”

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Figure 2 Conversion-time profiles for different sorbents reacting with 10% CO2 at 650 ºC”

“The overall reaction rate is a function of surface reaction kinetics, diffusion through the CaCO3 product layer surrounding the CaO grains, diffusion through the macropores of the pellet, and the gas film around the pellet. In the fast kinetic control stage, the thickness of the CaCO3 product layer is thin. Thus, the sorbent with higher surface area and pore volume shows higher reactivity because there is more space for the surface reaction. The sudden change in the reaction rate can be explained by the change in the morphology of the sorbent during the reaction.”

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