Hydrodeoxygenation of BHET/DMT on Bimetal catalysts as the Model Compounds of Polyester Waste and Fast Pyrolysis of Polyethylene Terephthalate

다국어 초록 (Multilingual Abstract)

The worldwide increase of plastic trash, especially polyethylene terephthalate (PET), has raised significant environmental and economic issues. Among emerging strategies, catalytic pyrolysis and hydrodeoxygenation has shown great promise for the direct conversion of PET into valuable aromatic hydrocarbons under thermal conditions. This study investigates the hydrodeoxygenation (HDO) of bis(2-hydroxyethyl) terephthalate (BHET), a model compound representing polyethylene terephthalate (PET) waste, using Ni–Fe bimetallic catalysts supported on γ-Al2O3 synthesized via spray pyrolysis. The objective was to enhance deoxygenation efficiency and aromatic hydrocarbon selectivity under atmospheric pressure conditions. Catalysts with different Ni/Fe ratios were analyzed using XRD, XPS, BET, TPR, and NH₃-TPD to investigate the structural, electrical, and acidic aspects affecting catalytic performance. Among all tested catalysts, Ni5-Fe15 exhibited the highest performance, achieving 99.79% BHET conversion and a 76.57% degree of deoxygenation at 500 °C. GC–MS analysis revealed dominant formation of benzene (37.21 area%), naphthalene (30.21 area%), and biphenyl (13.21 area%), confirming efficient C–O bond cleavage through synergistic Ni–Fe alloy interactions. Gas analysis indicated balanced H2 (47.49 mol%), CO (24.85 mol%), and CO2 (21.60 mol%) selectivity, suggesting concurrent decarbonylation and decarboxylation pathways. The spray pyrolysis synthesis provided uniform metal dispersion and enhanced acidity, resulting in superior catalytic stability and minimized coke formation. Overall, this work establishes Ni–Fe/γ-Al2O3 as a cost-effective and sustainable catalyst for converting PET-derived oxygenated intermediates into valuable aromatic hydrocarbons, contributing to the advancement of green catalysis and circular economy-based plastic recycling technologies. The selective HDO of BHET, a model compound had been tested using bimetallic Pt-Sn/γ- Al2O3 catalysts. The objective was to enhance deoxygenation efficiency and aromatic selectivity under mild, atmospheric conditions. Catalysts with different Pt/Sn ratios (Pt7Sn3, Pt7.5Sn2.5, Pt8Sn2, and Pt8.5Sn1.5) were synthesized using incipient wetness impregnation and studied using XRD, BET, H₂-TPR, NH₃-TPD, SEM-EDX, and XPS to clarify structure–function correlations. The Pt7.5Sn2.5 catalyst exhibited best performance, achieving 100% BHET conversion and a 94.24% degree of deoxygenation at 400 °C, with high selectivity toward benzene (45.42%), ethylbenzene (40.56%), and toluene (7.59%). This optimal behavior results from the synergistic electronic and structural interactions between Pt and Sn, which facilitate C–O bond cleavage while suppressing excessive hydrogenation and cracking. Reaction pathway analysis revealed that BHET transformation proceeds via benzoic acid and benzaldehyde intermediates, leading to fully deoxygenated aromatics. These findings highlight the potential of Pt–Sn/γ-Al₂O₃ catalysts for efficient, low-pressure chemical upcycling of PET-derived compounds. The proposed catalytic strategy provides a sustainable and scalable pathway for transforming polyester waste into valuable aromatic hydrocarbons, contributing to the advancement of circular economy and green chemical recycling technologies. The investigates the selective hydrodeoxygenation (HDO) of dimethyl terephthalate (DMT) a primary PET depolymerization intermediate into benzene, toluene, and xylene (BTX) over Co– Fe/SiO2 catalysts using tetralin as an in situ hydrogen donor. Bimetallic catalysts with varying Co/Fe ratios were synthesized via wet impregnation and characterized by BET, XRD, SEM-EDX, NH₃-TPD, H2-TPR, and XPS to correlate physicochemical properties with catalytic performance. The 5 wt% Co–15 wt% Fe/SiO2 catalyst exhibited the highest efficiency, achieving 99% DMT conversion, 28.9% benzene yield, and 95.1% deoxygenation degree at 450 °C after 1 h. The enhanced activity was attributed to strong Co–Fe alloy interactions that improved reducibility, dispersion, and acid–metal balance, facilitating selective C–O bond cleavage while preserving aromatic rings. Methyl benzoate was identified as a key intermediate, transforming via decarbonylation, decarboxylation, and methylation pathways. Reaction temperature and time significantly influenced selectivity, while tetralin effectively provided hydrogen without external supply. These findings highlight the potential of Co–Fe alloy catalysts and hydrogen-donor solvents to convert PET-derived intermediates into sustainable aromatic chemicals, offering a promising and scalable route for circular carbon utilization and reduced dependence on fossil-based aromatics. The study investigates of catalytic fast pyrolysis of waste polyethylene terephthalate (PET) conducted in a bubbling fluidized-bed reactor, emphasizing the effect of natural dolomite (CaMg(CO3)2) on product distribution and deoxygenation behavior. Calcined dolomite was characterized by XRD, BET, SEM-EDX, ICP-OES, and TGA, confirming its crystalline CaO–MgO phases, mesoporous texture (13.23 m²/g), and bifunctional basic–acidic surface active for C–O bond cleavage. Fast pyrolysis experiments were performed between 475–550 °C and at different fluidization velocities (2.0–3.0×Umf) to evaluate product yields of major products . At optimal conditions (500 °C, 2.5×Umf), catalytic pyrolysis produced a liquid yield of 35.66 wt%, biphenyl yield of 5.53 wt%, and decreased gas yield (37.87 wt%), outperforming non-catalytic reactions. The presence of dolomite increased the aromatic hydrocarbon peak area from 12.89% to 20.15%, enhanced H2 evolution (up to 9.65 mol%), and reduced CO2 selectivity from 51.94 mol% to 41.60 mol%, confirming its role in deoxygenation and CO2 sorption. Elemental analysis and FTIR/UV–Vis spectra of recovered terephthalic acid (rTPA) showed high structural similarity to pure TPA, indicating effective depolymerization and reformation. The study demonstrates that dolomite catalysis promotes deoxygenation and aromatic formation during PET pyrolysis, establishing a sustainable and cost-effective route for plastic waste valorization and green aromatic chemical production.

목차 (Table of Contents)

• ABSTRACT i
• CONTENTS iv
• List of Figures ix
• List of Tables xii
• CHAPTER 1 Introduction 1
• 1.1. Background 1
• 1.2. Motivation of Research 2
• 1.3. Research objectives 3
• 1.4. Dissertation Overview 4
• 1.5. References 5
• CHAPTER 2 Literature Review 8
• 2.1. Concept of Polyester Waste 8
• 2.1.1. Global Production and Applications of Polyester 8
• 2.1.2. Sources and Characteristics of Polyester Waste 8
• 2.1.3. Environmental and Economic Impacts of Polyester Accumulation 9
• 2.1.4. Need for Sustainable Chemical Recycling Approaches 9
• 2.2. Fundamental Concepts of Polyester Decomposition 10
• 2.2.1. Chemical Structure and Properties of Polyester 10
• 2.2.2. Thermal Stability and Degradation Pathways of Polyester Polymers 12
• 2.2.3. Comparison of Mechanical, Chemical, and Energy Recycling Routes 12
• 2.3. Pyrolysis of Polyester Waste 14
• 2.3.1. Principles and Mechanisms of Polyester Pyrolysis. 14
• 2.3.2. Catalytic Versus Non-Catalytic Pyrolysis of Polyester Waste 14
• 2.3.3. Influence of Process Parameters (Temperature, Residence Time, Atmosphere) 14
• 2.3.4. Product Distribution: Gases, Pyrolysis Oil, and Solid Residues 15
• 2.3.5. Role of Catalysts in Enhancing Aromatic Yields 15
• 2.4. Hydrodeoxygenation (HDO) as PET Upgrading Strategy 15
• 2.4.1. Principles of HDO: C–O bond cleavage, deoxygenation pathways 16
• 2.4.2. Limitations of direct PET HDO (high MW, insolubility, morphology) 16
• 2.4.3. Use of PET-derived intermediates (BHET, DMT) for mechanistic insights. 17
• 2.5. Catalysts for HDO of PET-Derived Compounds 17
• 2.5.1. Noble Metals and Non-Noble Metals: Activity and Selectivity 17
• 2.5.2. Bimetallic Catalysts: Pt–Sn Alloy 18
• 2.5.3. Bimetallic Catalysts: Ni–Fe Alloy 18
• 2.5.4. Bimetallic Catalysts: Co–Fe 18
• 2.5.5. Structure–Activity Relationships 19
• 2.6. Role of Solvents and Hydrogen Donors 19
• 2.6.1. Solubility challenges of BHET and DMT 19
• 2.6.2. 2-ethylphenol for BHET: high solubility, dual role as solvent and H-donor 20
• 2.6.3. Tetralin as solvent and H2 donor for HDO of DMT 20
• 2.7. References 20
• CHAPTER 3 Hydrodeoxygenation of bis(2-hydroxyethyl) terephthalate as a model compound of polyethylene terephthalate waste using spray pyrolysis synthesis of γ-Al2O3 supported Ni-Fe catalyst 26
• 3.1. Introduction 26
• 3.2. Experimental section 31
• 3.2.1. Materials 31
• 3.2.2. Catalyst preparation 31
• 3.2.3. Catalyst characterization 32
• 3.2.4. Experimental setup and analytical method of products 33
• 3.2.5. Kinetics of BHET deoxygenation over Ni5–Fe15 catalyst 34
• 3.3. Results and discussion 35
• 3.3.1. Catalyst characterization 35
• 3.3.2. Thermal characteristic of BHET and 2-ethylphenol as solvent 49
• 3.3.3. Catalytic activity of HDO for BHET in monometallic and NiFe Catalyst 55
• 3.3.4. Catalytic activity of HDO for BHET in Ni5-Fe15 effect of temperature reaction 59
• 3.3.5. Reaction pathways of BHET over Ni5-Fe15 65
• 3.3.6. Catalyst deactivation of Ni5-Fe15 73
• 3.3.7. Kinetics of HDO BHET over Ni5-Fe15 at 475 ℃ 74
• 3.3.8. Calculation deoxygenation degree for optimum condition 76
• 3.4. Conclusions 77
• 3.5. References 77
• CHAPTER 4 Selective Hydrodeoxygenation of BHET Using Bimetallic Pt–Sn/γ-Al2O3 Catalysts: Catalyst Design, Reaction Pathway, and Performance Evaluation 86
• 4.6. Introduction 86
• 4.7. Experimental section 90
• 4.7.1. Materials 90
• 4.7.2. Catalyst preparation 90
• 4.7.3. Catalyst characterization 90
• 4.7.4. Catalytic Reaction and analytical methods of products 91
• 4.7.5. Kinetics of BHET deoxygenation over Pt-Sn catalysts 93
• 4.8. Results and discussion 94
• 4.8.1. Catalyst characterization 94
• 4.8.2. Catalytic activity of HDO for BHET: Effect of Pt/Sn ratio at 475 ℃ 108
• 4.8.3. Catalytic activity of HDO for BHET: Effect of reaction temperature on Pt7.5Sn2.5 112
• 4.8.4. Performance of HDO of BHET over different reaction time and catalyst deactivation catalyst of Pt7.5Sn2.5 at 400 ℃ 115
• 4.8.5. Stability of 2-ethylphenol as solvent 119
• 4.8.6. Reaction Pathways HDO of BHET over Pt-Sn Catalyst 124
• 4.8.7. Kinetics of HDO BHET over Pt7.5Sn2.5 128
• 4.9. Conclusion 130
• 4.10. References 131
• CHAPTER 5 Selective hydrodeoxygenation of Dimethyl Terephthalate (DMT) to aromatics over Co–Fe/SiO2 with in situ H2 from tetralin 137
• 5.11. Introduction 137
• 5.12. Experimental section 140
• 5.12.1. Materials. 140
• 5.12.2. Catalyst preparation 140
• 5.12.3. Catalyst characterization 141
• 5.12.4. Experimental setup and analytical method of products 142
• 5.13. Results and discussion 143
• 5.13.1. Catalyst characterization 143
• 5.13.2. Catalytic Activity of HDO for DMT in Monometallic and Co-Fe Catalysts 162
• 5.13.3. HDO of DMT in 5 wt% Co–15 wt% Fe/SiO2: Effect of Reaction Temperature 166
• 5.13.4. HDO of DMT in 5 wt% Co-15 wt% Fe/SiO2: Effect of Reaction Time 169
• 5.13.5. Reaction pathways of DMT over 5 wt% Co–15 wt% Fe/SiO2 172
• 5.13.6. Catalyst Deactivation 174
• 5.13.7. Dehydrogenation of tetralin over 5 wt% Co15 wt% Fe/SiO2 176
• 5.14. Conclusions 180
• 5.15. References 180
• CHAPTER 6 PET waste to terephthalic acid, biphenyl, and benzoic acid via dolomite catalytic fast pyrolysis in fluidized-bed reactor: experimental and techno-economic analysis 186
• 6.16. Introduction 186
• 6.17. Material and methods 188
• 6.17.1. Materials. 188
• 6.17.2. Preparation of PET waste and catalysts 188
• 6.17.3. Characterization of PET waste and catalysts 191
• 6.17.4. Experimental Setup and product analysis 191
• 6.17.5. Characterization char, rPTA and liquid product 196
• 6.17.6. Process simulation description 196
• 6.17.7. Techno-economic analysis 200
• 6.18. Results and discussion 205
• 6.18.1. Catalysts characterization 205
• 6.18.2. Characteristics of PET waste, char and rPTA 213
• 6.18.3. Effect of Temperature on Non-Catalytic Pyrolysis 217
• 6.18.4. Effect of Fluidization Velocity on Non-Catalytic Pyrolysis 220
• 6.18.5. Effect of dolomite catalyst under varying temperatures 223
• 6.18.6. Effect of dolomite catalyst under varying fluidization velocity 227
• 6.18.7. Reaction pathways of dolomite catalytic pyrolysis of PET waste 230
• 6.19. Economic assessment 233
• 6.20. Operational cost 237
• 6.21. Profitability analysis 237
• 6.22. Sensitivity analysis 238
• 6.23. Conclusion 242
• 6.24. References 242
• CHAPTER 7 Conclusions and Further Research 251
• 7.1. Conclusions 251
• 7.2. Further research 254
• APPENDIX 255
• A1. Additional data for Chapter 3 255
• A2. Additional data for Chapter 4 256
• A3. Additional data for Chapter 6 258
• Acknowledgements. 267