Ozone- and Plasma-assisted Catalytic Oxidation for the Destruction of Gaseous Naphthalene
Date Issued
2011
Date
2011
Author(s)
Yuan, Min-Hao
Abstract
This study investigated ozone- and plasma-assisted catalytic oxidation for the decomposition of gaseous organic compound in gas phase. Naphthalene (Nap), the most volatile, simple structured and abundant polycyclic aromatic hydrocarbons (PAHs) observed in the atmosphere, is taken as a target compound. The processes examined include the ozone catalytic oxidation (OZCO) and radio frequency-powered atmospheric-pressure plasma jet (APPJ) oxidation and APPJ with Pt/γ-Al2O3 catalysts, noted as catalytic APPJ (CAPPJ) oxidation.
The OZCO experiments were carried out at various constant reaction temperatures (T), space velocities (SV) and inlet concentrations of ozone (CO3,in) for the decomposition of Nap. The results indicate that the required T for the effective decomposition of Nap decreases with the increase in CO3,in at the same conversion level of Nap (XNap). Further, the values of XNap and mineralization extent of Nap (MNap) increase linearly with the increase of CO3,in. Regarding the T at XNap = 50% (T50), there is about 20 K reduction at SV = 100,000 1/h for the case of OZCO process with CO3,in of 1,750 ppmv (T50 = 460 K) compared to the process without ozone (T50 = 480 K). Further, the power law can be applied to describe the data of OZCO process by using the second order expression with respect to ozone and Nap concentration. The observed activation energy (E) and frequency factor (Af) are 68.3 kJ/mol and 5.36×1012 L2/(mol g-cat. s), respectively. For the sole catalytic oxidation process (CATO), the reaction is first order respect to Nap with E and Af of 150.0 kJ/mol and 3.26×1017 1/s. A significant reduction of E for the OZCO compared to CATO reflects the enhancement role of ozone in conjunction with catalyst.
The APPJ experiments were carried out at various input power (PWI), plasma energy density (Ē), initial concentration of pollutant (C0 or Cin), working gas (air and air/Ar) and SV of the catalyst for the decomposition of Nap/n-butanol (Nap/n-b), n-butanol and vinyl chloride (VC). The emission spectra of APPJ discharge show that the oxygen atom and metastable oxygen molecule (230-330 nm) are possibly the dominated active species in the jet effluent. The visible glow (600-800 nm) results from the interaction of discharged Ar molecule and Nap/n-b. It turns out that the value of plateau temperature (TP) of reactor in the presence of Ar is higher than that in air. Further TP increases with PWI because of more energy transfer from the heated electrons to gas molecules. However, TP decreases in the presence of the catalysts. It suggests that the role of the catalyst acts as a conducting medium with low electrical resistance and high surface area, absorbing charged as well as active species for the catalytic decomposition.
The effectiveness of plasma-assisted catalysis is evident as indicated by the increase of conversion and rate constant. At PWI = 250 W without catalyst, the values of XNap and Xn-b are 30% and 19%, respectively. In the presence of Pt/Al2O3 catalyst with SV = 17,400 1/h, XNap and Xn-b can reach as high as 99%. Note that the Xn-b in Nap/n-b is close to XN-b in n-butanol system. Therefore, the interaction of Nap and n-butanol is minor in APPJ and CAPPJ. The conversion decreases with increasing initial concentration. For example, at PWI = 250 W without catalyst, the values of XVC are 14% and 5.4% for CVC,in = 200 and 450 ppmv, respectively. At PWI = 250 W with SV = 17,400 1/h, XVC for CVC,in = 200 and 450 ppmv are 49% and 39%, respectively.
The kinetic models were proposed to describe the relationships of C/C0 (or =C/Cin) with the major parameters for the plasma and plasma-assisted catalytic decomposition of Nap, n-butanol and VC, showing good agreement with the experimental data. For the plasma system of APPJ the reaction order is –1.5 with respect to Cin, while –0.5 and 1 with respect to Cin and catalyst amount, respectively, for the plasma-catalysis system of CAPPJ.
The information obtained is useful for the rational design and operation for the destruction of gaseous pollutants via the OZCO, APPJ and CAPPJ processes.
Subjects
Polycyclic aromatic hydrocarbons (PAHs)
naphthalene
Pt/Al2O3
ozone-catalytic oxidation process
atmospheric-pressure plasma jet (APPJ)
SDGs
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-100-F92541110-1.pdf
Size
23.54 KB
Format
Adobe PDF
Checksum
(MD5):9b2602965742ce5e289844f06307c648