Role of carbon treating in piperazine oxidation

Bench-scale experiments were performed to test the effects of carbon treating (8 x 30 mesh, lignite-based granular activated carbon from Nowata Filtration) on the oxidation of aqueous piperazine (PZ) at conditions of CO2 capture. The combined mitigation with carbon treating and N2 sparging was also tested. When carbon treating is applied, the UV-Vis absorbance at 320 nm, the NH3 production rate, and the accumulation rate of dissolved Fe concentration and total formate concentration decrease. The effects of carbon treating last even when the carbon is bypassed, which is possibly due to the removal of catalytic degradation products. Therefore, it is better to apply carbon treating in the early stages of oxidation. Combining carbon treating and nitrogen sparging is more effective in oxidation mitigation than applying the methods separately. The amount of Fe removed by the carbon bed is greater than the result calculated from the solvent inventory and concentration difference of Fe in solvent, indicating that Fe colloids or other "soluble" Fe will dissolve into the solvent and replace the dissolved Fe that is adsorbed and removed. The carbon removes the degradation products that can complex with Fe3+, even if they are not complexed. Since the source of Fe includes fly ash and corrosion, removing the complexing agents instead of all the available Fe is a more feasible target.