Table of Contents ACKNOWLEDGEMENT 1 List of Tables 4 List of Figures 4 Abbreviations 6 INTRODUCTION 7 PART 1. OVERVIEW 9 1.1. Euro standards for sulfur content 9 1.2. Hydrodesulfurization 10 1.3 Oxidative desulfurization 11 1.4. Comparations of oxidative desulfuriation to hydrodesulfurization 12 1.5. Photocatalytic oxidation desulfurization 13 1.5.1. General 13 1.5.2. Fundamental of photocatalytic process 15 1.6. Advantage and Disadvantage of using TiO2 as Photocatalytic 17 1.6.1. Introduction of TiO2 17 1.6.2. Using TiO2 as photocatalyst 18 1.6.3. Application of TiO2Mont in environmental treatment 21 1.6.4. Some photocatalytic synthesis process for TiO2Mont 23 PART 2. EXPERIMENTAL 26 2.1. Chemicals 26 2.2. Experimental 26 2.2.1 Synthesis of TiO2 solgel 26 2.2.2 Synthesis of TiO2Montmorillonlite 27 2.2.3 Inspecting photoreactivity of catalysts in oxidative desulfurization 30 PART 3. CATALYST CHARACTERIZATION 32 3.1 XRay diffraction (XRD) spectroscopy 32 3.2 Energy dispersive Xray (EDX) spectroscopy 33 3.3 Ultra violetvisible spectroscopy (UVVIS) 34 3.4 High performance liquid chromatography (HPLC) 34 PART 4: RESULTS AND DISCUSSIONS 36 4.1 Xray diffraction results 36 4.2 Energy dispersive xray spectroscopy results 37 4.3 Ultra violetvisible spectroscopy results 38 4.4 High performance liquid chromatography results 40 CONCLUSION 44 REFERENCE 45
1 ACKNOWLEDGEMENT In order to complete this thesis, I have been trying a lot and the thesis would not have been possible without the time, support and dedication of many people At first, I would like to send my sincere thanks to Associated Professor Pham Xuan Nui PhD who is dedicated to guide me during the time, gave me a lot of knowledge about a new scope when I started to conduct this thesis During the implementation, my teacher always directed, instructed and made suggestion so that I can complete this thesis I sincerely thank Advanced Program, Departure of Oil Refining and Petrochemistry, Hanoi University of Mining and Geology for providing facilities to study, optimal laboratory conditions, which help me complete this thesis Finally, I would like to say thanks to my dear parents for supporting me spiritually throughout writing this thesis and my life in general Ha Noi, June 5th, 2017 Student Nguyen Huy Thanh Table of Contents List of Tables Table 1.1 European emission standards of sulfur contents Table 1.2 Results of desulfurizaion in diesel fuel 11 Table 4.1 The content of components in TiO2/Mont and CuO-TiO2/Mont 38 Table 4.2 Band gap energy of catalyst material TiO 2/Mont and CuOTiO2/Mont .39 Table 4.3 Thiophene conversion with different kinds of catalyst samples: TiO2/Mont and CuO-TiO2/Mont .43 List of Figures Figure 1.1 General mechanism of hecterogeneous photocatalysis .14 Figure 1.2 Operation of semiconducted particle being excited by light 16 Figure 1.3 Crystal structure of Titanium Dioxide 17 Figure 1.4 Energy diagram of Anatase and Rutile 20 Figure 1.5 Decomposition process of organic compound using TiO2 photocatalyst 22 Figure 1.6 Diagram for synthesis Ti(x)C16(y)-Mont .24 Figure 2.1 XRD diagram of Bentonite and Momorillonite (after purifying) 27 Figure 2.2 Preparation of Na-Montmorillonite .28 Figure 2.3 Experimental process for modifying montmorillonite 29 Figure 2.4 The Sol-gel was added to the mixture drop by drop 30 Figure 2.5 Inspecting photoreactivity of TiO2 and CuO-TiO2 Mont samples .30 Figure 4.1 XRD diagram of TiO2/Mont (a) and CuO-TiO2/Mont (b) 36 Figure 2.3: Modification process of Titanium dioxide on Monmorillonite Figure 4.2 The EDX spectroscopy of (a) TiO2/Mont and (b) CuO-TiO2/Mont sample .37 Figure 4.3 UV-Vis result of (a) TiO2-Mont, (b) CuO-TiO2/Mont 38 Figure 4.4 Standard curve result of Thiophene sample model with standard curve equation Spic = 66037,48 + 53521,98 x CThiophene 41 Figure 4.5 The conversion result of thiophene with TiO2/Mont catalyst sample after 180 minutes .41 Figure 4.6 The conversion result of thiophene with CuO-TiO 2/Mont catalyst sample after 180 minutes 42 Figure 4.7 Thiophene conversion with different kinds of catalyst samples: TiO2/Mont and CuO-TiO2/Mont .42 Abbreviations ULDS : Ulltra-low-sulfur-diesel VB : Valance Band CB : Conduction Band BG : Band Gap SC : Semiconductor Surface Mont : Montmorillonite CTABr : Cetyltrimethylammonium bromides INTRODUCTION Nowadays, environmental pollution is becoming an urgent issue European Standards for fuels now are more and more restrictive Sulfur-containing organic compounds are potential pollutants present mainly in fuel oils which are difficult to be removed Traditional methods used for desulfurization such as hydrodesulfurization (HDS) shows out ineffectively in deep desulfurization (for sulfur-containing heterocyclic compounds) and costly One of the new materials that is catching the attention of scientists is TiO photocatalyst With the presence of TiO2 and ultraviolet irradiation, researchers found that organic compounds, pollutants are easily disintegrated [1] This special ability of TiO2 has been applied in water purification, air and disinfection technologies Many toxic and hazardous compounds are efficiently degraded by heterogeneous photocatalyst The use of titanium dioxide as photocatalyst for air and water treatment is well documented as well as the fundamental mechanisms of the process [2] The main primary step is the adsorption of the substrate on the support Thus, efforts have been carried out on the synthesis of new materials having high specific surface area, low particles size with the highest expected photoreactivity Supported TiO2 on different minerals or TiO2 thin films appeared as solutions to overcome the recovery problem and also to enlarge the application fields [3] Mesoporous materials which can be easily separated from the treated effluent, have been synthesized, and demonstrated their feasibility for photocatalytic treatment of fuel They are mainly based on clay minerals, zeolites, silica or activated carbons Among them, pillared clays (PILCs), constitute a group of mesoporous materials Pillared interlayered clays (PILCs) form a well-known family of microporous and mesoporous materials [4] They are prepared by multi-step molecular engineering processes The insertion of pillaring agents (organic, organometallic, or inorganic complexes) expands the interlayer spacing leading to a two-dimensional channel system with porous structures comparable to those of zeolites [5] After the calcination process, the inserted cationic polymers yield rigid and are thermally stable leading to oxide species in form of pillars, which hold (separated) the clay layers separated and prevent their collapse at high temperatures Thus, PILCs may be viewed as clay layers separated by metallic oxide based pillars (alumina, titania, zirconia, iron oxide, etc.), or alternatively, as dispersed nanometric oxide particles which aggregation is hindered by the presence of the clay layers [4] The main objective in the formation of PILCs is to achieve as basal spacing as large as possible contributing to the development of higher surface area and porous volume The addition of TiO to the PILCs has been previously studied For this reason, the main objectives of this thesis are the analysis of the influence of TiO2 content in the structure of the PILCs This thesis describes synthesis and characterization of montmorillonite based porous clay heterostructure with modified titanium dioxide in their pillars Likewise this thesis discusses the role of CuO located in the pillars and its effect in oxidative desulfurizaion leading to an advantageous way to design functional materials with photocatalytic and adsorbent applications for deep desulfurizaion in fuel Thesis objects: • Modification of bentonite by titanium dioxide • Doping copper oxide on titanium dioxide • Investigating photocatalytic activity of synthesised samples PART OVERVIEW 1.1 Euro standards for sulfur content Emissions of SOx, NOx, from the combustion of organic compounds which contain heteroatoms as sulfur, nitrogen in fuel has become an environmental issue over the world Because these emission gases are one of the main reason of acid rain, Global warming-up and atmospheric pollution [1] To minimize the amount of SOx emissions, many countries in the world have put strict requirements on the sulfur content in fuel.The amount of sulfur contained in the material Example, sulfur content in diesel must be reduced from 500ppmw to less than 15ppmw for diesel and from 300ppmw to less than 30 ppmw for gasoline Therefore, Deepdesulfurizaion method are increasingly interested in, recently Table1.1 European emission standards of sulfur contents [6] Name n/a EU Directive - CEN Standard Implementation Date Sulfur Limit (ppm) EN (d) EN (g) October, 1994 2000 Euro 93/12/EEC Euro 93/12/EEC Euro 98/70/EC Euro 2003/17/E C EN (d) EN (g) EN (d) EN (g) 590:1993 228:1993 October, 1996 590:1999 228:1999 500 (diesel) January, 2000 350 (diesel) 150 (gasoline) January, 2005 50* January, 2009 10, 10** 590:2004 228:2004 EN 590:2009 Note: * 10ppm fuel must be available ** nonroad fuels limit 1.2 Hydrodesulfurization Currently, in our Country, the method is mainly used to remove sulfur out of liquid fuel is hydrodesulphurization process (HDS) using metal - sulfide catalyst carried on Al2O3-support Chemical theory [3] of Sulfur elimination reactions: Mercaptan, sulfur and di-sulfur compounds gently react to form aromatic and saturated compound corresponding Sulfur element which is linked in aromatic ring, such as thiophene is so much harder to eliminate All of these reactions are exothermic reactions, they create hydro sulfur and consume hydrogen Example: - Mercaptan compound R - SH + H2 → R - H + H2S - Sulfur-containing heterocyclic compounds R – S – R’ + H2 → R – H +R’ – H + H2S + H2 → C4H10 + H2S S Thiolane + H2 → C4 H10 + H2S S Thiophene + H2S → S + H2S Benzylcyclohexane Dibenzothiophene After HDS process, sulfur is separated from sulfur-containing compounds, reducing the amount of sulfur in diesel fuel down to allowed level about 500 ppm Therefore, HDS process is applied to desulfurization of compounds such as mercaptan, thiophene, disulfur, benzothiophene which are contained in crude oil and its product Catalysts which are used for this process are normally metals such as Co, Mo, Ni-Mo supported on solid acid Nowadays, for deep desulfurization in compounds which have high molecular weight and aromatic compounds, high active catalysts are used such as: CoMo/Al 2O3, CoMoP/Al2O3, GaCr/HZSM-5 or a mixture of CoMoP/Al2O3 + GaCr/HZSM-5 10 Diesel fuel contains a lot of hardly reduced sulfur-containing compounds because they are in heavy fractions and have high boiling temperature Normally, the amount of sulfur-containing compounds in fuel is from 9,000 to 2,000 ppm including compounds contain sulfur which are easy and difficult to eliminate The productivity of desulfurization in diesel fuel using CoMoP/Al 2O3 catalyst is given in Table 1.2 Table 1.2 Results of desulfurizaion in diesel fuel Temperature (K) Sulfur content in products Desulphurization (ppm) (%) 590 610 630 640 1190 680 170 50 efficiency 87 92 98 99 * Disadvantages: HDS must be implemented at high temperature and pressure condition requiring long catalyst ‘s life cycle and high activity for deep sulfurizaiotn Especially, this process consume a lot of energy considerably but still not desulfur deeply for some common compounds such as dibenzothiophene (DBT), especially for dimetyldibenzothiophen (4.6-DMDBT) so that the sulfur content in fuel remains high at about 500 ppm The above conditions are also leading to high cost of the products Therefore, deep desulfurization without using hydrogen and harsh conditions have been developed to overcome the disadvantages of HDS process Due to that, sulfur content in fuel can reduced below 10 ppm 1.3 Oxidative desulfurization Oxidative desulfurization is not a new concept and has been discussed for several years in previous publications.The advantage that oxidative desulfurization has over conventional to HDS is that the difficult-to-desulfurize, sufur-containing heterocyclic compounds such as dibenzothiophenes (DBT) are easily oxidized at low temperature and pressure conditions to form the corresponding sulfones This overall process is demonstrated as below The oxidant can be supplied by either hydrogen peroxide/peracid sor organic peroxide [4] Note that there is no hydrogen consumed in this reaction The sulfones are highly polar compounds and are easily 34 3.3 Ultra violet-visible spectroscopy (UV-VIS) Ultraviolet–visible spectroscopy refers to absorption spectroscopy or reflectance spectroscopy in the ultraviolet-visible spectral region This means it uses light in the visible and adjacent ranges The absorption or reflectance in the visible range directly affects the perceived color of the chemicals involved In this region of the electromagnetic spectrum, atoms and molecules undergo electronic transitions Absorption spectroscopy is complementary to fluorescence spectroscopy, in that fluorescence deals with transitions from the excited state to the ground state, while absorption measures transitions from the ground state to the excited state Molecules containing π-electrons or non-bonding electrons (nelectrons) can absorb the energy in the form of ultraviolet or visible light to excite these electrons to higher anti-bonding molecular orbitals [2] The more easily excited the electrons (i.e lower energy gap between the HOMO and the LUMO), the longer the wavelength of light it can absorb Based on the fact of four type of transition- ππ*, n-π*, σ-σ*, and n-σ* The energy required for various transitions obey the following order σ-σ*>n-σ*>π-π*>n-π* 3.4 High performance liquid chromatography (HPLC) Chromatography is a technique to separate mixtures of substances into their components on the basis of their molecular structure and molecular composition This involves a stationary phase (a solid, or a liquid supported on a solid) and a mobile phase (a liquid or a gas) The mobile phase flows through the stationary phase and carries the components of the mixture with it Sample components that display stronger interactions with the stationary phase will move more slowly through the column than components with weaker interactions This difference in rates cause the separation of variuos components Chromatographic separations can be carried out using a variety of stationary phases, including immobilized silica on glass plates (thin-layer chromatography), volatile gases (gas chromatography), paper (paper chromatography) and liquids (liquid chromatography) High performance liquid chromatography (HPLC) is basically a highly improved form of column liquid chromatography Instead of a solvent being allowed to drip through a column under gravity, it is forced through under high pressures of up to 400 atmospheres That makes it much faster All chromatographic separations, including HPLC operate under the same basic principle; separation of a 35 sample into its constituent parts because of the difference in the relative affinities of different molecules for the mobile phase and the stationary phase used in the separation 36 PART 4: RESULTS AND DISCUSSIONS 4.1 X-ray diffraction results The XRD diagram of those samples: TiO2/Mont and CuO-TiO2/Mont after calcining at 500oC in hours were shown in Figure 4.1 Figure 4.1: XRD diagram of TiO2/Mont (a) and CuO-TiO2/Mont (b) The d001 distance of these samples TiO2/Mont and CuO-TiO2/Mont after calcining are 10.002 A and 14.053, respectively Comparing to the d 001 distance of the initial mont sample in figure we can see that, there is a light decrease in distance of TiO2/Mont sample after calcining This can be explained due to losing water and CTABr in the structure of material, resulting in decreasing distance of peak The light decrease in distance of CuO-TiO 2/Mont sample can be explained due to dispersing of TiO2 among Na-Mont layers After calcining at 500oC, CTABr was gone, TiO2 pillars are fixed in spaces of Mont layers Otherwise, from the figure, we can see that there is transference of peak d 001 into the higher 2-thetal angle between TiO2/Mont (2θ = 9.16) and CuO-TiO2/Mont (2θ = 4.18) samples shows out that the degree of order of TiO 2/Mont sample is lower than CuO-TiO2/Mont sample 37 Otherwise, the peaks centered at 2θ = 25.5 o in the XRD differaction diagram shows out the formations of anatase TiO2 after calcining at 500oC These are activated phase of photocatalyst on Mont support The temperature of calcining is also effected in forming activated phase of the new photocatalyst materials due to transfering of anatase TiO phase to rutile TiO2 phase at high temperature (about 600oC) According to the information which was shown in chapter 1, anatase phase of TiO2 have the highest oxidative activation comparing to Rutile and Brookkite For TiO2 crystall, Anatase will start transfering to Rutile at 500oC, however, for TiO2 modified on Montmorillonite support, the anatase form of TiO2 is still stable at 500oC without appearence of Rutile phase This can be explained due to dispersing of TiO Montmorillonite support and forming pillars in the support which is resulting in changing phase-transfering temperature of TiO2 [33] Nevertheless, the higher the temperatures ( more than 500oC), the larger size of TiO2 particles [33] Therefore, The calcination temperature at 500oC is the most suitable one 4.2 Energy dispersive x-ray spectroscopy results The EDX spectroscopy result of TiO 2/Mont sample and CuO-TiO2/Mont sample are shown in Figure 4.2 and Table 4.1 Figure 4.2 The EDX spectroscopy of (a) TiO2/Mont and (b) CuO-TiO2/Mont sample 38 Table 4.1 The content of components in TiO2/Mont and CuO-TiO2/Mont TiO2/Mont CuTiO2/Mont Element Weight% Element Weight% Si 11.00 Si 10.92 Al 4.89 Al 4.68 Ti 28.48 Ti 29.38 O 48.16 O 49.64 Cu Cu 1.12 The results show that, titanium and oxygen elements are presented in both catalyst samples with high intensities Table 4.1 indicates that, the element ratios of titanium and oxygen is 1:2 repectively, in Ti/Mont sample which is corresponding to the molecular formular of TiO2 Otherwise, Cu elements are also presented in Cu-TiO 2/Mont sample, which means copper (II) acetate monohydrate Cu(CH 3COO)2.H2O completely played its roll as the precursor to form CuO in the sol-gel 4.3 Ultra violet-visible spectroscopy results The UV-Vis diagram of those samples TiO2/Mont and CuO-TiO2/Mont after calcining at 500oC in hrs are shown in Figure 4.3: (a) (b) Figure 4.3 UV-Vis result of (a) TiO2-Mont, (b) CuO-TiO2/Mont 39 From the UV-vis spectroscopy result, apply Kubelka-Munk equation to determine the maximum wavelength K −M = (1 − R )2 α = 2R s where: • α is adsrobent coefficient factor • s is independent coefficient factor From the tangents, we can determind the band gap energies (E g) by the following equation [35]: Eg = 1240/λambient absrobent The obtained results are shown in Table 4.2 Table 4.2: Band gap energy of catalyst material TiO2/Mont and CuO-TiO2/Mont Samples Eg (eV) TiO2/Mont 3.24 CuO-TiO2/Mont 2.95 From the Table 4.2, we can see that, the band gap energies of TiO 2/Mont and CuO-TiO2/Mont are 3.24 eV and 2.95 eV, respectively Once again, this result confirms that, TiO2 completely exists on the catalyst samples and shows out photocatalytic activity to oxidative desulfurization processes in fuel Otherwise, from Table 4.2, we also see that, the band gap energy of CuOTiO2/Mont sample (2.95eV) is lower than TiO2/Mont sample (3.24eV), resulting in being more effective photocatalysis for CuO-TiO2/Mont sample using as catalyst which is one of our goals This result can be explained due to successful doping of CuO into TiO2 pillars, which is leading to be decrease in band gap energy TiO2/Mont has a strong absorption between 200nm and 380nm which is attributed to 3.24 eV photon energy which is nearly the same as typical of TiO [39] With the copper doping, there is enhancement in the optical absorption, thus a significant right shift in the absorption spectra towards longer wavelengths that is shift to the 40 visible range of 400-800 nm, because of the coverage of CuO spectra in UV and visible regions Also, the copper doped TiO2 sample exhibits enhanced absorbance in the visible light region compared to un-doped TiO sample, thus enhanced light harvesting in both UV and visible light regions Therefore doping with copper can enhance effective response in the visible region of TiO2 4.4 High performance liquid chromatography results From the above UV-vis result, a servey was conducted by reactions on thiophene sample (600 ppm) to prove the photoreactivity of those samples again and find out exactly how efficient the ODS conversions are The mechanism of oxidative desulfurization can be described as following - When TiO2 is illuminated by ultraviolet light, it will form free radicals as: O2•, •OH - After that, the Thiophene which are adsorbed on TiO will be oxidized by positive vacancies to form free cation radical in form of sulfone C4H4S + hVB + → C4H4S•+ C4H4S•+ O2-• → C6H4SO2 (Sulfone) 0.2 g of each catalysts was diluted in 20 mL of the fuel sample model which contain Thiophene ( 600 ppm of concentration in acetonnitrile solvent ) stirring constantly, providing heat for about 30 minutes in darkness to reach thermodynamic equilibrium conditions before conducting reactions After the system reaches the equilibrium condition ( at 70oC for the best productivity), taking ml of H2O2 slowly to the system, turning on the UV lights and timing for the time after 15 minutes, 30 minutes, 60 minutes, 120 minutes ( add ml H 2O2 more) and finally 180 minutes These reactions are conducted at 70 oC The higher the the temperature, the higher the conversions are This can be explained as: Increasing temperature is leading to increase in breaking up of H 2O2 moleculars, is resulting in creating more free radical such as O2•, •OH But, the solvent was used here is Acetone nitrile, which has boiling point at 82 oC, therefore 70 oC is the most suitable choice HPLC standard curve result is shown in Figure 4.4 41 Figure 4.4 Standard curve result of thiophene sample model with standard curve equation Spic = 66037,48 + 53521,98 x CThiophene The final conversion result (after 180 minutes) of thiophene with TiO 2/Mont and CuO-TiO2/Mont catalyst samples are shown in Figure 4.5 and Figure 4.6, respectively Figure 4.5: The conversion result of thiophene with TiO2/Mont catalyst sample after 180 minutes 42 Figure 4.6: The conversion result of thiophene with CuO-TiO2/Mont catalyst sample after 180 minutes Figure 4.7 and Table 4.3 are used to compare the difference in Thiophene conversion with different kinds of catalyst samples: TiO2/Mont and CuOTiO2/Mont Figure 4.7: Thiophene conversion with different kinds of catalyst samples: TiO2/Mont and CuO-TiO2/Mont 43 Table 4.3: Thiophene conversion with different kinds of catalyst samples: TiO2/Mont and CuO-TiO2/Mont Catalyst samples TiO2/Mont Conversion (%) 15 minutes 30 minutes 33.4 36.7 60 minutes 46.8 120 minutes 180 minutes 54.4 71.9 CuOTiO2/Mont 32.5 56.7 71.4 37.6 88.8 From the result, we can see that, using those catalyst material did get quite high conversion for the oxidative desulfurization of Thiophene The longer the time of reaction, the higher the conversions are This is obviously true, because, TiO2 on Montmorillonite need some interval times to be illuminated by UV light and form •O2, •OH-, after that, adsorbed Thiophene on TiO surface can be oxidized by positive vacancies The conversion of Thiophene with CuO-TiO2/Mont sample (88.8%) are higher than with Ti/Mont (71.9%) This can be explained due to the effect of doped CuO on TiO2/Mont, which is resulting in decreasing band gap energy of TiO ( this is suitable to the UV-Vis result) 44 CONCLUSION After a period of time conduct the research, my thesis has obtained some of the following results: *Conducted refining bentonite Di Linh to purity Montmorillonite , with completed lossing of Quart, the result are determined by XRD spectroscopy *Modified TiO2 on Montmorillonote support by CTABr The obtained results show out that: Montmorillite has been modified by TiO2 - XRD spectroscoppy expressed the formation of TiO2 between 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