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Use of Titanium Dioxide (Tio2)

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Use of Titanium Dioxide (Tio2) ABSTRACT GAS PHASE OXIDATION OF DIMETHYL SULFIDE BY TITANIUM DIOXIDE BASED CATALYSTS by Sachin Kumar In this study, a low temperature catalytic oxidation process was investigated for the oxidation of dimethyl sulfide using titania-based catalysts. TiO2 catalysts doped with vanadia were made using a wet incipient method and a flame synthesis method. The catalysts were characterized using XRD, Raman spectroscopy and BET surface area analysis to study the TiO2 phase transition as functions of calcination temperature and V/Ti mass ratio. A flow reactor was used to investigate the performance of the catalysts, and the exit gases were analyzed using gas chromatography. It was found that low concentrations of vanadia (V/Ti mass ratio ≤ 2%) inhibited phase transformation and sintering, which resulted in more activity per unit mass of the catalysts, and the catalysts having a V/Ti mass ratio of 2% were able to degrade dimethyl sulfide most efficiently. GAS PHASE OXIDATION OF DIMETHYL SULFIDE BY TITANIUM DIOXIDE BASED CATALYSTS A Thesis Submitted to the Faculty of Miami University In partial fulfillment of the requirements for the degree of Master of Science Department of Paper Science and Engineering by Sachin Kumar Miami University Oxford, OHIO 2004 Advisor: Dr. Catherine Almquist Reader: Prof. Michael H. Waller Reader Dr. Martin D. Sikora TABLE OF CONTENTS Page 1.0 Introduction 1 1.1 Thermal Catalysis 3 2.0 Research Goals and Objectives 5 2.1 Experimental Design 5 3.0 Experimental Methods 7 3.1 Catalyst Preparation 7 3.1.1 V2O5/TiO2 Catalysts 7 3.1.1.1 Wet Incipient method 7 3.1.1.2 Flame Synthesis Method 9 3.2 Catalyst Characterization 11 3.2.1 X-ray Diffraction Analysis 11 3.2.2 Raman Spectroscopy 15 3.2.3 BET Surface Area 15 3.3 Catalyst Performance 18 3.3.1 Thermal Catalysis 18 4.0 Results and Discussion 22 4.1 Thermal Catalysis with V2O5/TiO2 Catalysts 22 4.1.1 Catalysts Characterization 22 4.1.2 Catalyst Performance 29 4.1.3 Catalyst Performance of Flame Synthesis Catalysts 38 5.0 Summary and Recommendations for Future Work 40 ii 6.0 References 42 Appendices Appendix A Article Published in Catalysis Today Journal Other Appendices Available upon request iii LIST OF TABLES Page Table 1. Experimental Design 6 Table 2. Catalysts selected for performance testing 29 iv LIST OF FIGURES Page Figure 1. Catalysts prepared using Wet Incipient Method 8 Figure 2. Flame-Synthesis Method 9 Figure 3. Bragg’s Law [6] 12 Figure 4. The THETA:THETA Goniometer [4] 13 Figure 5. Diffraction Pattern plot obtained at the different 2θ angles 14 Figure 6. SA 3100 COULTER Surface Area Analyzer [10] 17 Figure 7. Scheme of the Thermocatalytic Experimental Design 18 Figure 8. Lindberg/Blue Tube Furnace 19 Figure 9. HP 6890 Gas-Chromatograph 19 Figure 10. Diffusion of DMS in Air 20 Figure 11. Variation in Peak Area with DMS concentration 21 Figure 12. XRD spectra for pure Degussa P25 TiO2 as received 25 0 and after calcinations at 400, 500, 600 C in air Figure 13. Fraction anatase TiO2 in V2O5/TiO2 catalysts as functions of 26 V/Ti mass ratio and calcination temperatures Figure 14. Particle size for the anatase fraction at different calcination temperatures 27 Figure 15. BET surface area reduction as functions of calcinations temperature 28 and V/Ti mass ratio Figure 16. Raman spectra for catalysts calcined in air at 400 0C for 24 h 30 at varying V/Ti mass ratios v Figure 17. Effect of V/Ti Ratio on DMS Degradation for Catalysts Calcined at 4000C 32 Figure 18. Effect of V/Ti Ratio on DMS Degradation for Catalysts Calcined at 5000C 32 Figure 19. Effect of V/Ti Ratio on DMS Degradation for Catalysts Calcined at 5500C 33 Figure 20. Effect of V/Ti Ratio on DMS Degradation for Catalysts Calcined at 6000C 33 Figure 21. Effect of Calcination Temperature on DMS Degradation at V/Ti=0% 36 Figure 22. Effect of Calcination Temperature on DMS Degradation at V/Ti=1% 36 Figure 23. Effect of Calcination Temperature on DMS Degradation at V/Ti=2% 37 Figure 24. Effect of Calcination Temperature on DMS Degradation at V/Ti=5% 37 Figure 25. Formation of V2O5 crystallites on the surface of the catalysts 38 Figure 26. DMS destruction for catalysts with different V/Ti ratios prepared 40 using Flame synthesis method vi NOMENCLATURE λ - Wavelength θ - Angle B - Anatase peak width at half height height D - Crystal Diameter eV - Electron Volt f - Fraction of TiO2 IA - Intensity of anatase reflection IR - Intensity of rutile reflection kV - Kilo Volt ms - milli Second NH4VO3 - Ammonium Metavanadate TCD - Thermal Conductivity Detector Detector TiO2 - Titanium Dioxide TRS - Total Reduced Sulfur VOC - Volatile Organic Compounds V/Ti - Vanadia to Titania ratio UV - Ultra Violet XRD - X-Ray Diffraction vii ACKNOWLEDGEMENT I acknowledge the following people for their help and support. Dr. Catherine Almquist Prof. Michael H Waller Dr. Martin D Sikora Rodney J Kolb Students, Faculty and Staff of Paper Science XRD Spectral Analysis John P Morton (Geology) Dr. John Rakovan (Geology) RAMAN Analysis Dr. Andre J Sommer (Chemistry & Biochemistry) BET Surface Area Analysis Dr. James Allan Cox (Chemistry & Biochemistry) Ms. Diep Vu Ca (Chemistry & Biochemistry) Collaborative Work Dr. John L. Graham (UDRI, Dayton) Dr. Sukh Sidhu (UDRI, Dayton) viii 1.0 INTRODUCTION Volatile organic compounds (VOC’s) along with nitrogen oxides and sulfur oxides are the most important polluting gases emitted by manufacturing industries. The predominant VOC’s emitted by the paper industry are methanol, total reduced sulfur (TRS) gases and chlorinated gases. VOC’s are compounds that contain hydrogen and some may contain oxygen, nitrogen and other elements, but specifically exclude methane, carbon monoxide, carbon dioxide, carbonic acid, and metallic carbides and carbonate salts. VOC’s are responsible for urban smog and the reduction of air quality. Therefore the United States Environmental Protection Agency (US EPA) has imposed regulations for these emissions. Because of the current and future regulations concerning gaseous emissions, there is an increasing interest in cost effective VOC abatement technologies. A key challenge to destroy VOC’s is that they are often produced in small concentrations in large volumes of air, and this makes the available control technologies expensive on the basis of cost per mass of pollutant destroyed [1]. The VOC’s are commonly degraded in vent streams using controlled high- temperature incineration, fume incineration and regenerative or recuperative thermal oxidation. These processes, while effective, require very high temperatures, usually on the order of 800ºC to 1,000ºC. Maintaining the necessary harsh conditions requires the consumption of large amounts of fossil fuels (eg. methane) and leads to the formation of undesirable end products such as carbon dioxide, oxides of nitrogen (NOX) and even hazardous organic compounds. Carbon dioxide is a green house gas, and the increase in carbon dioxide levels in the atmostphere over the past 100 years is regarded as a cause for the increase in the temperature of the earth’s atmosphere. In addition, when the 1 concentration of the compounds to be removed is very low (traces), incineration is not economically efficient. Thus for many applications, development of new oxidation technologies would lead to energy savings and reduced air emissions. An alternative approach to incineration is to utilize catalytic oxidation. Through the proper selection of the catalyst media, high efficiency can be obtained at much lower temperatures; conditions in the range of 200ºC -300ºC are typical. At these relatively mild conditions equipment is easier to design and maintain, and capacity is higher. Furthermore, catalysts can offer high selectivity for desirable end products and will not produce NOX under typical operating conditions. A significant challenge of utilizing catalysts for environmental compliance is the high cost of the precious metal catalysts used and their susceptibility to physical and chemical damage. Consequently, there is interest in developing alternative catalysts that are less expensive and more robust than the materials presently in wide use. One strategy to improve the activity of alternative catalysts is to manufacture them as nanostructured materials either in the form of nanoparticles or with nanoscale crystallites. This thesis outlines a study where a low-temperature method of VOC abatement was investigated: thermal catalysis. 2 1.1 THERMAL CATALYSIS Thermal catalysis is an alternative process to incineration for degrading VOC’s at lower temperatures. Oxidation catalysts consisting of V2O5 deposited on TiO2 have drawn considerable attention due to their successful application in the selective catalytic reduction of NOX reactions. They have also been demonstrated as effective catalysts for partial oxidation of organic compounds. The goal of this work is to assess whether this catalyst system could be used to destroy dimethyl sulfide (DMS), one of the key odor- causing pollutants by the pulp and paper industry. From a scientific viewpoint, this catalytic system is an interesting example of the strong interaction between the support (TiO2) and the active phase (V2O5). In particular, the spreading of vanadium (V), over the TiO2 support leads to a modification of the chemical-physical peculiarities of TiO2 and to an enhancement of its catalytic properties [2]. V/TiO2 (anatase) catalysts are generally obtained by depositing V species on commercial anatase by impregnation techniques. The overall V content that can be introduced is largely dependent on the surface area of the anatase. Segregated vanadia (V2O5) crystallites are evidenced, once a nominal vanadia monolayer covering the anatase surface is exceeded. Other methods, including sol-gel chemistry, co-precipitation, and laser induced pyrolysis methods, have opened the possibility of generating small anatase particles containing highly accessible V species, resulting in apparently high reaction rates per gram of catalyst [2].
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