Abstract:

Catalytic ozonation of propanal at ambient temperatures (23–25 °C) was investigated by varying propanal and ozone concentrations and catalyst type. The catalysts tested included wood fly ash (WFA), magnetically separated ash, synthetic hematite and magnetite, and metal oxide nanoparticle impregnated activated carbon and peanut hull char. A power law model independent of ozone concentration for WFA (r_w, moles g⁻¹ s⁻¹) and magnetite (r_m) were, respectively, r_w = k′_w C_R^0.89 and r_m = k′_mC_R^1.55, where k′_w, and k′_m were 2.36 × 10⁻⁶ g⁻¹ s⁻¹ (moles)^−0.11 (m³)^0.89 and 6.5 × 10⁻⁴ g⁻¹ s⁻¹ (moles)^−0.55 (m³)^1.55, respectively (5–15 ppmv). Magnetite and hematite present in the WFA were theorized to be the primary active sites, since magnetically separated WFA had a significantly higher reaction rate (~12×, mol m⁻² s⁻¹) than that of WFA. X-ray diffraction analysis demonstrated a qualitative increase in magnetite and hematite in the magnetically separated ash, and synthetic magnetite and hematite had reaction rates >80× and 200× that of WFA or activated carbon (surface area basis). Supercritical deposition of hematite on/in peanut hull char successfully generated a porous, pelleted catalyst from an agricultural residue capable of oxidizing propanal at rates 12× activated carbon and similar to commercially available catalysts (per mass basis). Water vapor significantly increased the propanal reaction rate when using wood fly ash and activated carbon.