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Preparation and Characterization of Amine-grafted Porous Silica Gel by One-pot Process for CO2 Adsorption

  • 이창훈 (Lee, Chang Hun, 대학원 화공생명공학과 화공생명공학전공)

초록/요약

Carbon dioxide is the main greenhouse gas that has greatly contributed to the global warming problem. The increase of CO2 concentration causes the trapping of heat from the Earth, and the rise in average temperature of the globe. The increase of average temperature has led to severe environmental problems such as climate changes, melting of the Antarctic glaciers, and rising of sea level. Main human source of CO2 is the fossil fuel based industries such as combustions and industrial process. In order to reduce the CO2 from these human activities, carbon capture and storage (CCS) is proposed, and numbers of researches have been performed to develop the technique for CCS. The types of carbon capture technique are absorption, adsorption, and membrane. The absorption process is the separation of CO2 from the flue gases by passing through column filled with liquid amine. However, there are certain limitations from liquid amine to be improved such as large energy input requirement, degradation and evaporation of solvent, toxicity, and corrosion of equipment. While the adsorption technique using solid adsorbents has emerged as a prospective alternative about problems from the liquid amine absorption, and development of solid adsorbents has been extensively studied. In adsorption technique, the CO2 adsorption is categorized into physical adsorption and chemical adsorption. The chemisorption of CO2 is the adsorption by the chemical reaction between CO2 and amine groups which are introduced to the solid adsorbent. The introduction of amine compounds is classified into physical impregnation and chemical grafting. The chemical grafting is the functionalization method using the reaction of amine compounds with the surface groups of solid adsorbents. Generally, the solid adsorbent for adsorption technique are the porous materials such as zeolite, activated carbon, MOF, and porous silica are used as solid adsorbents. Among these adsorbent, porous silica is a promising materials because of the high thermal stability, chemical manipulation of surface, and low cost of the source compounds. Although the porous silica with chemically grafted amine compounds has been investigated for CO2 adsorption based on these advantages, there have been few studies associated with the direct synthesis for amine-grafted silica gel. Thus the goal of this study was the investigation of one-pot process for the preparation of amine-grafted silica gels and the determination of optimum condition using sodium silicate as low-cost silica source by one-pot process. At first, the one-pot process for preparation of surface modified silica particles was investigated in this study. The surface modified silica particles were prepared by Stober method using TEOS as silica source and organosilanes with methyl, vinyl, aminopropyl, and mercaptopropyl groups were used as the surface modifier compounds. By the surface characterizations, it was concluded that the surface of silica particles could manipulated by the introduction of organo-chain and that the surface modified silica particles could be prepared by one-pot process. Secondly, the APS-grafted silica gels were prepared by one-pot process using sodium silicate as a low-cost silica source. It was confirmed that the silica gels were the agglomerates of silica particles by XRD and SEM analyses, and the introduction of aminopropyl groups on the surface of silica gels was confirmed by the FT IR analysis and CO2 uptake measurement. In addition, the effect of the surfactants on the pore properties and CO2 capacity of APS-silica gels. The addition of the surfactants improved the surface area and pore volume of APS-silica gel. As the improvement of pore properties, amine groups which were exposed on the outer surface and pore wall increased and the CO2 capacities were also improved. The pore properties of APS-silica gels were improved as increase in the amounts of surfactants. The P123 and F127 which had the longer hydrophobic chain than CTAB formed the larger pores, and therefore APS-silica gels with P123 and F127 exhibited the higher CO2 adsorption rates. From these analyses, it was concluded that APS-silica gel with 0.83 ratio of P123 was the optimum CO2 adsorbent and thus P123 was the adequate surfactant for APS-silica gel prepared by one-pot process using sodium silicate. Thirdly, the 3NAPS-grafted silica gels were prepared by one-pot process using sodium silicate. It was confirmed that the silica gels were the agglomerates of silica particles by XRD and SEM analyses, and the introduction of propyl diethylenetriamine on the surface of silica gels was confirmed by the FT IR analysis. In addition, PEG with different molecular weight was added in preparation process as the pore forming agents in order to improve the pore structure of 3NAPS-silica gels. The addition of PEG improved the pore properties and CO2 capacity. And it was confirmed that the higher molecular weight of PEG was more effective pore forming agent. But the effectiveness decreased as increasing the amounts of PEG, because the additional PEG resulted into the increase of PEG which remained inside pores. Thus, it was concluded that 0.83 ratio of PEG with 20k of molecular weight to 3NPAS was the adequate condition for 3NAPS-silica gels from one-pot process. Finally, the modifications of 3NAPS were performed by the introductions of AN by Michael adduct reaction and PO by amine curing reaction. The modification process was the transformation of primary amine into secondary amine which had the higher performance in desorption process and the resistance for the formation of urea. From FT IR analyses, the introductions of AN and PO were confirmed by the peaks related to nitrile groups and methyl groups, and primary amine was transformed into secondary amine. In addition, the differences in the ratio of secondary amine to primary amine were confirmed that PO was more reactive compound than AN for modification of 3NAPS. The increases in ratio of secondary amine to primary amine resulted into the decrease in the formation of isocyanate and urea in FT IR spectra, and therefore it was confirmed that the modification process improved the stability of 3NAPS. The improvement of stability and desorption performance from the introduction of AN and PO resulted into the more stable cyclic CO2 capacity. Especially, PO3NAPS silica gel which had the lower concentration of primary amine than AN3NAPS silica gel exhibited the more stable cyclic CO2 capacity. Thus, it was concluded that the PO was the adequate modifier compounds for the improvement of 3NAPS in the aspects of the resistance for the urea formation and the desorption performance.

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목차

Abstract i
Contents vii
List of Figures xi
List of Tables xv
Chapter 1. Introduction 1
1.1. Carbon Capture and Storage (CCS) 1
1.1.1. Requirements of CCS technique 1
1.1.2. Types of CCS technique 3
1.2. CO2 Adsorption Process 4
1.2.1. CO2 Adsorption of Porous Material 4
1.2.2. Amine Material 6
1.2.3. Preparation of Porous Silica Gel 9
1.2.4. Amine-functionalization of Porous Silica Gel 12
1.3. Objectives 14
Chapter 2. Preparation and Characterization of Surface Modified Silica Nanoparticle by One-pot Process 17
2.1. Introduction 17
2.2. Experimental 20
2.2.1 Materials 20
2.2.2 Preparation of Surface Modified Silica Nanoparticle 21
2.2.3 Characterization 23
2.3. Results and Discussion 24
2.3.1 Size and Morphology of Silica Nanoparticles 24
2.3.2 Characterization of Modified Silica Nanoparticles 27
2.3.3 Measurement of Surface Hydrophilicity 30
2.3.4 Analysis of Dispersion Property 34
2.4. Conclusion 36
Chapter 3. Preparation and Characterization of APS-grafted Silica Gel
using Surfactant-Type Pore Forming Agent 37
3.1. Introduction 37
3.2. Experimental 40
3.2.1 Preparation of APS-grafted Silica Gel 41
3.2.2 Characterization 42
3.3. Results and Discussion 43
3.3.1 Preparation of APS-grafted Silica Gel 43
3.3.2 Effect of Surfactant on APS-grafted Silica Gel 51
3.3.3 Effect of Surfactant Contents on APS-grafted Silica Gel 61
3.4. Conclusion 72
Chapter 4. Preparation and Characterization of 3NAPS-grafted Silica Gel using Polyethylene Glycol 74
4.1. Introduction 74
4.2. Experimental 77
4.2.1 Preparation of 3NAPS-grafted Silica Gel 78
4.2.2 Characterization 79
4.3. Results and Discussion 80
4.3.1 Preparation of 3NAPS-grafted Silica Gel 80
4.3.2 Effect of Molecular weight of PEG on 3NAPS-grafted Silica Gel 85
4.3.3 Effect of PEG Contents on 3NAPS-grafted Silica Gel 92
4.4. Conclusion 98
Chapter 5. Improvement on Stability of Amine-grafted Silica Gel by Amine Modification 100
5.1. Introduction 100
5.2. Experimental 103
5.2.1 Modification of 3NAPS and Preparation of Modified-Amine-Grafted Silica Gel 104
5.2.2 Characterization 105
5.3. Results and Discussion 106
5.3.1 Preparation of 3NAPS- and modified 3NAPS-grafted Silica Gels 106
5.3.2 Adsorption Behavior of 3NAPS- and modified 3NAPS-grafted Silica Gels 113
5.3.3 Cyclic Capacity of 3NAPS and Modified 3NAPS-Grafted Silica Gels 119
5.4. Conclusion 124
Chapter 6. Conclusions 126
References 131

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