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Preparation and characterization of new Co-Fe and Fe-Mn nano catalysts using resol phenolic resin and response surface methodology study for Fischer-Tropsch synthesis

تعداد121صفحه در فایل word

Ph.D. Thesis

of the Thesis

Preparation and characterization of new Co-Fe and Fe-Mn nano catalysts using resol phenolic resin and response surface methodology study for Fischer-Tropsch synthesis

Abstract

We have prepared Co–Fe–resol/SiO₂ and Fe–Mn–resol/SiO₂ catalyst by a simple and cheap co-precipitation method with the addition of resol during the precipitation for the Fischer-Tropsch synthesis (FTS). Two catalysts fully characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature-programmed reduction (TPR), fourier transform infrared (FT-IR), energy dispersive X-ray (EDX) and N₂ adsorption-desorption. After the calcination of precursor, a porous catalyst containing metal oxide and metalic phases was obtained. In fact, the addition of resol significantly increased surface active sites and pore volume that were two important factors in determining the FTS activity and selectivity.

The FT–IR data shows that the catalysts calcined at 650 °C for 6 h is almost free of resol. The TPR spectrum of the catalysts shows the reduction temperatures particularly for catalysts are significantly fewer than previous reports on similar Co–Fe and Fe-Mn catalysts supporting higher activity of our catalysts.

A central composite design (CCD) and response surface methodology (RSM) involved a wide range of pressure, H₂/CO mole ratio, GHSV and temperature was designed for investigation of FTS. All responses including CO conversion, LHCs, HHCs and ROH fragments were optimized using quadratic model. The results of ANOVA were used for investigation of validity and predicability of the FT synthesis and an excellent confidense was observed between calculated and observed value for independent experiments.

دسته: زبان خارجه, زبان خارجه برچسب: Preparation and characterization of new Co-Fe and Fe-Mn nano catalysts using resol phenolic resin and response surface methodology study for Fischer-Tropsch synthesis

توضیحات

Table of Contents

Contents Page

Chapter 1: Introduction

1.1. Fischer–Tropsch technology: A general overview.. 2

1.2. FT synthesis. 5

1.2.1. FT reactions. 5

1.2.2. Reaction mechanisms. 6

1.2.2.1. Surface carbide mechanism.. 6

1.2.2.2. Surface enol mechanism.. 8

1.2.2.3. CO insertion mechanism.. 8

1.2.2.4. Alkenyl mechanism.. 9

1.2.3. Product selectivity. 10

1.3. FT catalysts. 12

1.3.1. Active metal catalysts. 12

1.3.1.1. Iron. 13

1.3.1.2. Cobalt 14

1.3.2. Bimetallic catalysts. 16

1.3.2.1. Preparation methods. 17

1.3.2.2. Co-Fe catalysts. 19

1.3.2.3. Fe-Mn catalysts. 21

1.3.3. Support effects on the catalytic performance of FT catalysts. 22

1.4. Process variables. 24

1.4.1. FT reactors. 24

1.4.2. Operating conditions. 28

1.4.2.1. Syngas composition. 28

1.4.2.2. Temperature. 29

1.4.2.3. Pressure. 29

1.4.2.4. Gas hourly space velocity (GHSV) 30

1.5. Design of Experiments (DOE) 30

1.5.1. Response Surface (method) objective. 32

1.5.2. Analysis of Variance (ANOVA) 35

1.6. Scope of the thesis. 37

Chapter 2: Experimental

2.1. Materials. 40

2.2. Apparatus. 40

2.2.1. Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) surface area measurement 40

2.2.2. The X-ray diffraction (XRD) 41

2.2.3. Temperature-programmed reduction (TPR) 41

2.2.4. The scanning electron microscopy (SEM) 41

2.2.5. Laser particle size analyzer (LPSA) 41

2.2.6. Fourier transform infrared (FT-IR) spectroscopy. 42

2.3. Catalyst preparation. 42

2.3.1. Co-Fe-resol/SiO₂ catalyst 42

2.3.2. Fe-Mn-resol/SiO₂ catalyst 42

2.4. Catalyst testing. 43

2.5. DOE.. 46

Chapter 3: Results and discussion

3.1. Synthesis of Co-Fe and Fe-Mn catalysts. 48

3.2. Co-Fe catalyst 49

3.2.1. Catalyst characterization. 49

3.2.1.1. BET and BJH measurements. 49

3.2.1.2. XRD.. 50

3.2.1.3. TPR.. 51

3.2.1.4. FT-IR spectroscopy. 53

3.2.1.5. SEM… 54

3.2.1.6. EDX.. 55

3.2.1.7. Size distribution. 56

3.2.2. FT reaction over Co-Fe catalyst 56

3.2.2.1. Design evaluation. 59

3.2.2.2. Model analysis. 59

3.2.2.3. Model diagnostics. 62

3.2.2.4. Optimization. 67

3.3. Fe-Mn catalyst 72

3.3.1. Catalyst characterization. 72

3.3.1.1. BET and BJH measurements. 72

3.3.1.2. XRD.. 73

3.3.1.3. TPR.. 74

3.3.1.4. FT-IR spectroscopy. 76

3.3.1.5. SEM… 77

3.3.1.6. EDX.. 78

3.3.1.7. Size distribution. 79

3.3.2. FT reaction over Fe-Mn catalyst 79

3.3.2.1. Design evaluation. 81

3.3.2.2. Model analysis. 82

3.3.2.3. Model diagnostics. 84

3.3.2.4. Optimization. 89

3.4. Conclusions. 94

References. 97

List of Figures

Figures Page

Fig. 1.1. FT technology. 3

Fig. 1.2. Schematic representation of carbide mechanism. 7

Fig. 1.3. Schematic representation of enol mechanism. 8

Fig. 1.4. Schematic representation of CO insertion mechanism. 9

Fig. 1.5. Schematic representation of alkenyl mechanism. 10

Fig. 1.6. Product distribution in FT synthesis as a function of the chain growth probability (α). 11

Fig. 1.7. Types of FT reactors. 25

Fig. 1.8. (a) Linear Function; (b) Quadratic Function; (c) Cubic Function. 33

Fig. 1.9. (a) Three-dimensional illustration and (b) contour map of the information function for a rotatable quadratic design for two factors. 34

Fig. 2.1. Fixed bed reactor. 43

Fig. 2.2. Schematic representation of the catalyst test system and used reactor. 44

Fig. 2.3. Catalyst test system and reactor used in this project. 44

Fig. 2.4. Gas chromatograph. 45

Fig. 3.1. Preparation of resol phenolic resin. 48

Fig. 3.2. XRD patterns of precursor and Co-Fe-resol/SiO₂ catalyst (before and after the test). Co₃O₄ (Cubic); ○Fe₂O₃(rhombohedral); CoFe₂O₄ (cubic); Co₂SiO₄(orthorhombic); Fe₂SiO₄ (orthorhombic); Fe₃C (orthorhombic); Co₃C (orthorhombic); □Fe₃O₄ (cubic); CoO (cubic); Fe (Cubic). 50

Fig. 3.3. TPR profile of the Co-Fe-resol/SiO₂ catalyst before the test. 52

Fig. 3.4. Simplified representation of phase transformation during calcination and FT reaction over Co-Fe-resol/SiO₂catalyst. 53

Fig. 3.5. FT-IR spectra of: (a) Co-Fe-resol/SiO₂catalyst (precursor, before and after the test); (b) the catalyst was calcined at two different temperatures (550 °C and 650 °C). 54

Fig. 3.6. SEM images of Co-Fe-resol/SiO₂ catalyst in (a) precursor, (b) catalyst before and (c) after the test. 55

Fig. 3.7. The EDX spectrum of the Co-Fe-resol/SiO₂ catalyst before the test. 55

Fig. 3.8. The size distribution of the Co-Fe-resol/SiO₂ catalyst (a) before the test, (b) after the test. 56

Fig. 3.9. The predicted versus actual and Cook’s distance plots of all responses. 63

Fig. 3.10. CO conversion as a function of (a) GHSV and pressure (H₂/CO = 2.0, T= 350 °C); (b) H₂/CO and temperature (GHSV = 9 min^-1, P= 7 bar). 64

Fig. 3.11. Selectivities of LHCs, HHCs and ROH as a function of GHSV and pressure, Figs (a)-(c), respectively (H₂/CO = 2.0, T= 350 °C); and as a function of H₂/CO and temperature, Figs. (d)-(f), respectively (GHSV = 9 min^-1, P= 7 bar). 65

Fig. 3.12. Interaction plots for all studied responses as function of H₂/CO mol ratio and temperature (GHSV= 9 min^-1, P= 9 bar). 66

Fig. 3.13. Interaction plots for all studied responses as function of GHSV and H₂/CO mol ratio (P = 7 bar, T = 350 °C). 67

Fig. 3.14. Optimum conditions for obtaining the maximum amount of HHCs; a (P = 8.5 bar, GHSV = 6.00 min^-1), b (T= 370 °C, H₂/CO =2.2). 70

Fig. 3.15. Overlay plot for CO conversion 70%, LHCS 50%, HHCs 40% and ROH 5.5%. 70

Fig. 3.16. XRD patterns of the Fe-Mn-resol/SiO₂ catalyst (before and after the test). ●Fe₂O₃ (rhombohedral); ▲Mn₂O₃ (cubic); ■Fe₃O₄ (orthorhombic); ○Fe₂C (orthorhombic); ΔFeO (cubic); □MnO (cubic). 73

Fig. 3.17. TPR profile of the Fe-Mn-resol/SiO₂ catalyst before the test. 75

Fig. 3.18. Simplified representation of phase transformation during calcination and FT reaction over Fe-Mn-resol/SiO₂catalyst. 76

Fig. 3.19. FT-IR spectra of precursor and Fe-Mn-resol/SiO₂catalyst before and after the test. 77

Fig. 3.20. SEM images of Fe-Mn-resol/SiO₂ catalyst in (a) precursor, (b) catalyst before and (c) after the test. 78

Fig. 3.21. The EDX spectrum of the Fe-Mn-resol/SiO₂ catalyst before the test. 78

Fig. 3.22. The size distribution of the Fe-Mn-resol/SiO₂ catalyst (a) before and (b) after the test. 79

Fig. 3.23. The predicted versus actual and Cook’s distance plots of all responses. 85

Fig. 3.24. CO conversion as a function of (a) GHSV and pressure (H₂/CO = 2.0, T= 350 °C), (b) H₂/CO and temperature (GHSV = 9 min^-1, P= 7 bar). 86

Fig. 3.25. 3D representations of the effect of GHSV and pressure on studied responses (H₂/CO = 2.0, T= 350 °C) (left series, a, c, e ); the effect of H₂/CO and temperature on studied responses (GHSV = 9 min^-1, P = 7 bar) (right series, b, d, f). 87

Fig. 3.26. Interaction plots for all studied responses as function of H₂/CO molar ratio and temperature (GHSV= 9 min^-1, P= 9 bar). 88

Fig. 3.27. Interaction plots for all studied responses as function of GHSV and H₂/CO molar ratio (P = 7 bar, T = 350 °C). 89

Fig. 3.28. Optimum conditions for obtaining the maximum amount of HHCs; a (P = 9.5 bar, GHSV = 6.00 min^-1), b (T= 362 °C, H₂/CO =2.15). 91

Fig. 3.29. Overlay plot for CO conversion 70%, LHCS 50%, HHCs 40% and ROH 6.5%. 92

List of Tables

Tables Page

Table 1.1. Usage ratio of H₂/CO in various FT reactions. 28

Table 1.2.0020 Typical product selectivities for LTFT and HTFT processes. 29

Table 1.3. Determining α for rotatability. 35

Table 2.1. The chemicals used in this thesis. 40

Table 3.1. Textural properties of the Co-Fe-resol/SiO₂ catalyst for precursor and catalyst before and after the test. 49

Table 3.2. Phases and JCPDS of the Co-Fe-resol/SiO₂ catalyst before the test. 51

Table 3.3. Phases and JCPDS of the Co-Fe-resol/SiO₂ catalyst after the test. 51

Table 3.4. Catalytic performance of the Co-Fe-resol/SiO₂ catalyst under different operational conditions during FT reaction. 57

Table 3.5. Response surface quadratic evaluation of data. 60

Table 3.6. Statistical evaluation parameters and the optimized coded equations of all responses. 61

Table 3.7. Optimized conditions for obtaining the maximum LHCs selectivity. 68

Table 3.8. Optimized conditions for obtaining the maximum HHCs selectivity. 68

Table 3.9. Optimized conditions for obtaining the maximum ROH selectivity. 69

Table 3.10. The predictability of the optimized model using five independent experimental runs. 71

Table 3.11. Textural properties of the precursor and Fe-Mn-resol/SiO₂ catalyst before and after the test. 72

Table 3.12. Phases and JCPDS of the Fe-Mn-resol/SiO₂ catalyst before the test. 74

Table 3.13. Phases and JCPDS of the Fe-Mn-resol/SiO₂ catalyst after the test. 74

Table 3.14. Catalytic performance of the Fe-Mn-resol/SiO₂ catalyst under different operational conditions during FT reaction. 80

Table 3.15. Response surface quadratic evaluation of data. 82

Table 3.16. Statistical evaluation parameters and the optimized coded equations of all responses. 83

Table 3.17. Optimized conditions for obtaining the maximum LHCs selectivity. 90

Table 3.18. Optimized conditions for obtaining the maximum HHCs selectivity. 91

Table 3.19. The predictability of the optimized model using six independent experimental runs. 93

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