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Polyether Block Amide Membranes for CO2 Separation: Nanostructuring and Interfacial Engineering

  • 성문숙 (Mun Suk Seong, 서강대학교 일반대학원)

초록 (요약문)

Chemical separation processes account for approximately 10–15% of global energy consumption due to their reliance on energy-intensive thermally driven techniques. In light of the escalating energy crisis and accelerating climate change, there is an urgent demand for more energy-efficient alternatives. Membrane-based gas separation offers a compact, scalable, and low-energy solution compared to conventional technologies. Among various membrane materials, polymers are widely utilized due to their low cost and excellent processability. Notably, poly(ether-block-amide) (Pebax), composed of rigid polyamide (PA) and soft polyether (PE) segments, has emerged as a promising candidate for CO₂ separation owing to its mechanical robustness and high CO2 affinity. However, the gas separation performance of Pebax is hindered by the semi-crystalline nature of the PE segments, which limits CO2 diffusivity. Furthermore, the fabrication of thin-film composite membranes is challenged by high solution viscosity, poor substrate wettability, and microphase separation between the PA and PE blocks. To overcome these limitations, this thesis presents a material innovation and scalable fabrication strategy. A high-flux Pebax membrane was developed via in situ radical polymerization of poly(ethylene glycol) methyl ether acrylate (PEGMEA) within the Pebax matrix. This reaction induces the formation of micellar poly(poly(ether glycol) methyl ether acrylate) (PPEGMEA) domains, enhancing the fractional free volume and PEG content. The resulting Pebax/PPEGMEA membranes exhibited a 1054% increase in CO2 permeability, reaching 1388.3 Barrer, with CO2/O2 and CO2/N2 selectivities of 17.1 and 46.7, respectively. For thin-film composite membrane fabrication, a dual strategy was employed: (1) hydrophilic modification of a PDMS gutter layer via hydrosilylation to form PDMS-PEG, and (2) solvent vapor-induced swelling using hexane and ethanol. This synergistically enhanced interfacial compatibility and coating uniformity while suppressing defect formation. The resulting flat-sheet membranes achieved a CO2 permeance of 271 GPU with CO2/O2 and CO2/N2 selectivities of 14.0 and 32.0, respectively. To enable scalable membrane fabrication, a distinct strategy was developed for hollow fiber membranes using sequential inner-surface coating. A PDMS–PEG gutter layer was first applied and dried via solvent vapor exposure, followed by roller-assisted coating and drying of a Pebax–PPEGMEA selective layer. This approach improved interfacial compatibility and film uniformity. The resulting membranes exhibited excellent single-gas CO2 separation performance, achieving a permeance of 128.5 GPU with CO2/N2 and CO2/O2 selectivities of 29.1 and 15.9, respectively. Under simulated LNG flue gas conditions (CO2/O2/N2 = 5/15/80 mol%), the membranes maintained a high CO2/N2 separation factor of 16.1. Overall, this study demonstrates a universal and scalable approach for enhancing the performance of Pebax-based membranes through material design and process engineering, offering a promising platform for advanced CO2 separation technologies.

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목차

Abstract 8
List of Figures 10
List of Tables 16
CHAPTER 1 17
1.1 Carbon Dioxide Capture Processing 18
1.2 Membrane Materials for Carbon Dioxide Separations 21
1.2.1 Polymeric Membranes 22
1.2.2 Inorganic Membranes 26
1.2.3 Mixed Matrix Membranes 27
1.3 Research Objectives 27
1.4 Dissertation Overview 29
CHAPTER 2 34
2.1 Gas Transport Mechanism 35
2.1.1 Solution-Diffusion Model 35
2.1.2 Permeation 38
2.1.3 Sorption 38
2.1.4 Diffusion 42
2.2 Challenges of Polymeric Membranes 44
2.2.1 Plasticization 44
2.2.2 Physical aging 45
2.3 PEO-based Polymeric Membranes 46
CHAPTER 3 52
3.1 Introduction 53
3.2 Experimental 54
3.2.1 Materials 54
3.2.2 Preparation of Pebax/PPEGMEA membranes 54
3.2.3 Gas transport characterizations 55
3.2.4 Supplementary Characterizations 56
3.3 Results and discussion 56
3.3.1 Structure characterizations of Pebax/PPEGMEA membranes 56
3.3.2 Morphologies of Pebax/PPEGMEA membranes 66
3.3.3 Gas transport properties of Pebax/PPEGMEA membranes 68
3.4 Conclusion 76
CHAPTER 4 82
4.1 Introduction 83
4.2 Experimental 85
4.2.1 Materials 85
4.2.2 Synthesis of PDMS-PEG 85
4.2.3 Fabrication of dense membranes 87
4.2.4 Swelling of dense membranes 87
4.2.5 Fabrication of composite thin film membranes 87
4.2.6 Gas transport characterization 88
4.2.7 Supplementary characterizations 88
4.3 Results and discussion 89
4.3.1 Hydrophilic modification of PDMS gutter layer 89
4.3.2 Solvent vapor-induced swelling effect 95
4.3.3 Pebax-PPEGMEA TFC membranes 100
4.3.4 Gas separation performance of TFC membranes 105
4.4 Conclusions 112
CHAPTER 5 119
5.1 Introduction 120
5.2 Experimental 121
5.2.1 Materials 121
5.2.2 Fabrication of hollow fiber membranes 122
5.2.3 Gas transport characterization 123
5.2.4 Supplementary characterizations 123
5.3 Results and discussion 124
5.3.1 Composite hollow fiber membranes 124
5.3.2 Gas separation properties of HFMs 135
5.4 Conclusion 138
CHAPTER 6 143
6.1 Summary and Conclusions 144
6.1.1 Summary 144
6.1.2 Conclusions 145
6.1.3 Recommendations for Future Work 146
APPENDIX A 148
APPENDIX B 150
APPENDIX C 151

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