Light-enhanced Oxidative Adsorption Desulfurization Of Dibenzothiophene In Diesel Fuel Over TiO2-ZrO2 Mixed Oxides
Open Access
- Author:
- Thepwatee, Sukanya
- Graduate Program:
- Fuel Science
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 24, 2015
- Committee Members:
- Chunshan Song, Dissertation Advisor/Co-Advisor
Chunshan Song, Committee Chair/Co-Chair
Randy Lee Vander Wal, Committee Member
Xiaoxing Wang, Committee Member
Michael John Janik, Special Member - Keywords:
- Desulfurization
Diesel fuel
Photooxidation
Titanium dioxide
Zirconium dioxide
Adsorption
Dibenzothiophene - Abstract:
- This dissertation explores a novel approach for desulfurization of diesel fuel called light-enhanced oxidative adsorption desulfurization (LEOADS), which combines a photo-oxidation and an adsorption process that can take the advantages and avoid the disadvantages of the oxidative desulfurization and the adsorptive desulfurization. The key questions that are addressed in this dissertation are: 1) does the LEOADS process promote peroxide generation and DBTO2 generation? (2) What is the possible sulfur removal pathway over TiO2-ZrO2 under light irradiation? and (3) what is the role of TiO2-ZrO2 in the LEOADS process? The first part of this dissertation focuses on investigating the performance of the LEOADS process compared to the one-step adsorptive desulfurization and the multi-step photo-oxidative desulfurization. The LEOADS of DBT/diesel was carried out using a UV-Vis light together with air bubbling in the presence of TiO2-ZrO2 adsorbent. Under this process, the desulfurization performance increased to almost 9 fold greater than the conventional one-step adsorptive desulfurization, and increased by 1.4 fold compared to the two-step photo-oxidative desulfurization. Peroxide was found to be generated under light irradiation and play an important role in promoting the oxidation of DBT to DBTO2. Adding 20 mol% of Zr into TiO2 enhanced the LEAODS performance by 17 times larger than that using pure TiO2. In the second part, the oxidation pathway of DBT on the surface of the TiO2-ZrO2 is discussed in conjunction with the LEOADS process. The study of the oxidation pathway of DBT suggests that the improved desulfurization performance of the LEAODS process can be attributed to the enhanced oxidation reaction of DBT to DBTO2 due to the peroxide in situ generated under light irradiation and the photooxidation of DBT on the surface of the TiO2-ZrO2. The last part of this dissertation focuses on the characterization of the Ti1-xZrxO2 (x=0.0, 0.1, 0.2, 0.3 0.5, and 10.0) mixed oxides. The effects of Zr on the structure, band gap energies, and surface properties of the Ti1-xZrxO2 mixed oxides were determined by using XRD, NH3-TPD, UV-diffuse reflectance spectroscopy, XPS, SEM-EDX, and N2 adsorption desorption. The relationship between the characteristics of the Ti1-xZrxO2 and their desulfurization performance under the LEOADS and the two-step photo-oxidative desulfurization were examined. The results in this part revealed that the Ti0.9Zr0.1O2 provided the best performance per unit surface area under both the LEOADS and the two-step photo-oxidative desulfurization processes. The superior performance of the Ti0.9Zr0.1O2 was due to its high photocatalytic activity for DBT oxidation and the suitable adsorption sites for DBTO2. Based on the findings of this work, the following research is recommended for future study: 1) study the impact of the structure of alkyl aromatic on peroxide generation under light irradiation, 2) computational study of DBT oxidation on the surface of the TiO2-ZrO2 in the presence of peroxide and molecular oxygen, 3) study of the impact of light wavelength on peroxide generation and photooxidation of DBT using TiO2-ZrO2. These further studies can help designing a photocatalytic adsorbent and process that can drive the removal of refractory sulfur compounds in diesel fuel even faster.