Organic waste-derived carbonaceous electrodes for flow-electrode capacitive deionization of brackish water = 흐름 전극 축전식 탈염 공정의 기수 담수화 위한 유기성 폐기물 유래 탄소 전극

국문 초록 (Abstract)

본 학위논문에서는 유기성 폐기물 유래 탄소 전극을 활용한 흐름 전극 축전식 탈염 공정의 기수 담수화 기술로서 적용 가능성을 체계적으로 평가하였다. 본 학위논문의 주된 목적은 유기성 폐기물 유래 탄소 전극의 원료와 열분해 조건을 최적화함으로써 이의 유동 전극으로써 실현 가능성을 규명하고, 기수 담수화 성능과 연관된 유기성 폐기물 유래 탄소 전극의 주요한 속성(공극, 전기전도도, 젖음성 및 탭밀도)에 알칼리성 화학적 활성화 방법과 탄산칼슘 기반 템플레이팅 방법이 미치는 영향을 조사하며, 유기성 폐기물 유래 탄소 전극을 활용한 흐름 전극 축전식 탈염 공정의 경제성을 축전식 탈염공정과 비교하여 확인하는 것이다.
유기성 폐기물 유래 탄소 전극의 제조를 위한 최적의 원료 및 열분해 가스 분위기는 각각 쌀겨와 이산화탄소였다. 높은 열분해 온도는 쌀겨 유래 탄소 전극의 물리적 속성과 방향성을 향상시키는데 효과적이었으며, 이로 인해 흐름 축전식 탈염 공정의 전기화학적 속성 또한 향상하였다. 하지만, 800°C/이산화탄소 조건에서 제조된 쌀겨 유래 탄소 전극(RHCE800-C)을 활용한 흐름 전극 축전식 탈염 공정은 500°C, 650°C 와 800°C에서 제조된 쌀겨 유래 탄소 전극을 활용하였을 때보다 수율로 정규화된 기수 담수화 성능이 더 우수하였다. 따라서, 쌀겨 유래 탄소 전극의 열분해 온도는 800°C로 설정하였다.
탄산칼슘 기반 템플레이팅 방법은 알칼리성 화학적 활성화 방법보다 RHCE800-C의 공극, 전기전도도, 젖음성 및 탭밀도를 향상하는데 더 효과적이었다. 이로 인해, 탄산칼슘 기반 템플레이팅 방법(RHCE800-C와 탄산칼슘 템플레이트 혼합비 = 0.50)으로 개질된 RHCE800-C(RHCECC0.50-800-C)를 활용한 흐름 전극 축전식 탈염 공정이 RHCE800-C와 2.0 M 수산화나트륨 기반 화학적 활성화 방법으로 개질된 RHCE800-C(RHCESH2.0-800-C)보다 더 우수한 기수 담수화 성능을 나타냈다(기수 담수화 성능: RHCE800-C = 0.0488 mg/cm2‧min, RHCESH2.0-800-C = 0.0696 mg/cm2‧min 및 RHCECC0.50-800-C = 0.0804 mg/cm2‧min). RHCE800-C, RHCESH2.0-800-C 및 RHCECC0.50-800-C를 활용한 흐름 전극 축전식 탈염 공정의 담수화 기작은 전기 투석, 전기 흡착 및 유도전류 반응이었다.
RHCE800-C, RHCESH2.0-800-C 및 RHCECC0.50-800-C의 제조 비용은 활성탄(MSP-20X)보다 매우 낮은 것을 확인하였다(제조비용: RHCE800-C = 33.93 $/kg, RHCESH2.0-800-C = 49.23 $/kg, RHCECC0.50-800-C = 37.50 $/kg 및 MSP-20X = 453.80 $/kg). RHCE800-C, RHCESH2.0-800-C 및 RHCECC0.50-800-C을 활용한 흐름 전극 축전식 탈염 공정의 비용으로 정규화된 기수 담수화 성능은 모두 활성탄 보다 높은 것으로 보아, RHCE800-C, RHCESH2.0-800-C 및 RHCECC0.50-800-C은 우수한 경제성을 갖는 것으로 사료된다. 특히, RHCECC0.50-800-C을 활용한 흐름 전극 축전식 탈염 공정의 비용으로 정규화된 기수 담수화 성능이 RHCE800-C와 RHCESH2.0-800-C 보다 상당히 우수하였다. 또한, RHCECC0.50-800-C을 활용한 흐름 전극 축전식 탈염 공정의 고유 소비 전력은 축전식 탈염 공정보다 낮기 때문에, RHCECC0.50-800-C을 활용한 흐름 전극 축전식 탈염 공정은 물 부족 현상을 해결하기 위한 담수를 생산하는 유망한 기술이라고 판단된다.

다국어 초록 (Multilingual Abstract)

Brackish water desalination via flow-electrode capacitive deionization (FCDI) utilizing organic waste-derived carbonaceous electrodes for producing fresh water was systematically evaluated. The main purposes of this dissertation were to (i) identify the effects of feedstock types and pyrolysis conditions (i.e., gas atmospheres and pyrolysis conditions) for fabricating organic waste-derived carbonaceous electrodes on brackish water desalination performance of the FCDI process, (ii) investigate the effects of the chemical activation using alkali agents and the calcium carbonate (CaCO3)-based templating method on the physicochemical properties of organic waste-derived carbonaceous electrodes related to brackish water desalination performance of the FCDI process, and (iii) demonstrate the feasibility of the FCDI process utilizing organic waste-derived carbonaceous electrodes for brackish water desalination.
The optimal feedstocks and gas atmospheres for the fabrication of organic waste-derived carbonaceous electrodes were rice husks and carbon dioxide, respectively. Higher pyrolysis temperatures were effective in improving the physical properties and bulk conductivity of rice husk-derived carbonaceous electrodes, resulting in excellent electrochemical performance of the FCDI stack. Nonetheless, the FCDI process utilizing rice husks-derived carbonaceous electrodes produced at 800 °C/carbon dioxide conditions (RHCE800-C) exhibited a higher average salt removal rate (ASRR) normalized with yields compared to those of 500 °C, 650 °C, and 950 °C. Hence, the pyrolysis temperatures of rice husk-derived carbonaceous electrodes were set to 800 °C.
To enhance the electrochemical performance of the FCDI stack, the CaCO3-based templating method was more beneficial in improving the physicochemical properties of RHCE800-C compared to the chemical activation using alkali agents (i.e., sodium hydroxide (NaOH)). As expected, the highest brackish water desalination performance was found for the FCDI process utilizing CaCO3-templated RHCE800-C at 0.50 of the mixing ratios of RHCE800-C and CaCO3-templates (RHCECC0.50-800-C; ASRR = 0.0804 mg/cm2‧min) than RHCE800-C (ASRR = 0.0488 mg/cm2‧min) and 2.0 M NaOH-activated RHCE800-C (RHCESH2.0-800-C; ASRR = 0.0696 mg/cm2‧min). Brackish water desalination via the FCDI process utilizing RHCE800-C, RHCESH2.0-800-C, and RHCECC0.50-800-C progressed through electrodialysis, electrosorption, and Faradaic reactions.
The manufacturing costs of RHCE800-C (33.93 $/kg), RHCESH2.0-800-C (49.23 $/kg), and RHCECC0.50-800-C (37.50 $/kg) were considerably lower than activated carbons (MSP-20X; 453.80 $/kg). The higher cost-normalized ASRR values of the FCDI process utilizing RHCE800-C, RHCESH2.0-800-C, and RHCECC0.50-800-C (0.226–0.343 mg/cm2·min·$) compared to MSP-20X (0.028 mg/cm2·min·$) suggest that RHCE800-C, RHCESH2.0-800-C, and RHCECC0.50-800-C have excellent economic feasibility. Among them, the FCDI process utilizing RHCECC0.50-800-C exhibited the highest cost-normalized ASRR values (0.343 mg/cm2·min·$). Moreover, the FCDI process utilizing RHCECC0.50-800-C exhibited a lower specific energy consumption (0.63–1.32 kWh/m3) than membrane capacitive deionization (specific energy consumption = 0.70–1.80 kWh/m3). Hence, the FCDI process utilizing RHCECC0.50-800-C should be a promising option to secure alternative water resources for solving the water shortage through brackish water desalination.

목차 (Table of Contents)

• ABSTRACT i
• CONTENTS iii
• LIST OF TABLES ix
• LIST OF FIGURES xi
• CHAPTER 1 INTRODUCTION 1
• 1.1 Motivation of research 1
• 1.2 Structure of research 4
• CHAPTER 2 RESEARCH HYPOTHESES AND OBJECTIVES 6
• 2.1 Hypotheses 6
• 2.1.1 Effects of feedstock types and pyrolysis conditions for fabricating organic waste-derived carbonaceous electrodes on flow-electrode capacitive deionization of brackish water 6
• 2.1.2 Chemical activation of rice husks-derived carbonaceous electrodes for enhancing brackish water desalination by flow-electrode capacitive deionization 6
• 2.1.3 Calcium carbonate-based templating as a novel approach to form well-developed pore structures of rice husks-derived carbonaceous electrodes for enhancing brackish water desalination via flow-electrode capacitive deionization 7
• 2.1.4 Cost-benefit estimation of flow-electrode capacitive deionization utilizing rice husks-derived carbonaceous electrodes for brackish water desalination 7
• 2.2 Objectives 8
• CHAPTER 3 BACKGROUND AND LITERATURE REVIEW 9
• 3.1 Membrane-based desalination technologies 9
• 3.1.1 Pressure-driven membrane processes 11
• 3.1.2 Osmotically driven membrane processes 14
• 3.1.3 Thermally driven membrane processes 16
• 3.1.4 Electrochemical membrane processes 18
• 3.1.5 Current disadvantages of membrane-based desalination technologies 22
• 3.2 Flow-electrode capacitive deionization 23
• 3.2.1 Overview of flow-electrode capacitive deionization 23
• 3.2.2 Desalination mechanisms 25
• 3.2.3 Components of flow-electrode capacitive deionization process 30
• 3.3 Organic waste-derived carbonaceous electrodes 35
• 3.3.1 Carbonaceous materials 35
• 3.3.2 Organic waste-derived carbonaceous electrodes 36
• 3.3.3 Modification strategies 37
• CHAPTER 4 ANALYTICAL METHODOLOGIES AND EXPERIMENTAL SET-UP 41
• 4.1 Analytical methods for characterization of organic waste-derived carbonaceous electrodes 41
• 4.1.1 Field emission-scanning electron microscopy 41
• 4.1.2 Energy dispersive X-ray spectroscopy 42
• 4.1.3 Brunauer-Emmett-Teller theory and Barrett-Joyner-Halenda method 43
• 4.1.4 X-ray diffraction 47
• 4.1.5 Raman spectroscopy 48
• 4.1.6 Fourier transform infrared spectroscopy 49
• 4.1.7 X-ray photoelectron spectroscopy 50
• 4.1.8 Elemental analysis 51
• 4.1.9 Electrophoretic light scattering method 52
• 4.1.10 Electrochemical impedance spectroscopy 53
• 4.2 Description of flow-electrode capacitive deionization unit stack 55
• 4.3 Operational modes of flow-electrode capacitive deionization 59
• 4.4 Performance indicators of flow-electrode capacitive deionization 61
• 4.4.1 Average salt removal rate 61
• 4.4.2 Charge efficiency 62
• 4.4.3 Molar energy consumption 63
• CHAPTER 5 EFFECTS OF FEEDSTOCK TYPES AND PYROLYSIS CONDITIONS FOR FABRICATING ORGANIC WASTE-DERIVED CARBONACEOUS ELECTRODES ON FLOW-ELECTRODE CAPACITIVE DEIONIZATION OF BRACKISH WATER 64
• 5.1 Abstract 64
• 5.2. Introduction 65
• 5.3 Materials and Methods 68
• 5.3.1 Resources and chemicals 68
• 5.3.2 Preparation procedures of organic waste-derived carbonaceous electrodes 69
• 5.3.3 Characterization of organic waste-derived carbonaceous electrodes 70
• 5.3.4 Experimental procedures for estimating the electrochemical performance of the FCDI stack and the brackish water desalination performance of the FCDI process 71
• 5.4 Results and Discussion 74
• 5.4.1 Effects of feedstock types and gas atmospheres for fabricating organic waste-derived carbonaceous electrodes on brackish water desalination performance of the FCDI process 74
• 5.4.1.1 Feedstock types 74
• 5.4.1.2 Gas atmospheres 76
• 5.4.2 Characteristics of RHCE500-C, RHCE650-C, RHCE800-C, and RHCE950-C 78
• 5.4.2.1 Surface morphologies 78
• 5.4.2.2 Crystalline structures, bulk elemental compositions, bulk conductivity, and wettability 81
• 5.4.2.3 Physical properties 84
• 5.4.2.4 Surface functionalities 87
• 5.4.2.5 Rheological properties 92
• 5.4.3 Effects of pyrolysis temperatures of RHCE on the electrochemical performance of the FCDI stack and the brackish water desalination performance of the FCDI process 95
• 5.4.4 Effects of operational parameters on brackish water desalination performance of the FCDI process utilizing RHCE800-C 100
• 5.4.4.1 Flow rate of feed water 100
• 5.4.4.2 Applied voltage 102
• 5.4.4.3 Dosage of RHCE800-C 104
• 5.4.4.4 Initial NaCl concentrations 106
• 5.4.5 Brackish water desalination mechanisms 109
• 5.5 Conclusions 111
• CHAPTER 6 CHEMICAL ACTIVATION OF RICE HUSKS-DERIVED CARBONACEOUS ELECTRODES FOR ENHANCING BRACKISH WATER DESALINATION BY FLOW-ELECTRODE CAPACITIVE DEIONIZATION 112
• 6.1 Abstract 112
• 6.2 Introduction 113
• 6.3 Materials and Methods 116
• 6.3.1 Materials and reagents 116
• 6.3.2 Preparation procedures of RHCEs 117
• 6.3.3 Characterization of RHCEs 118
• 6.3.4 Procedures for evaluating the electrochemical performance of the FCDI stack and the brackish water desalination performance of the FCDI process 119
• 6.4 Results and Discussion 122
• 6.4.1 Comparison of brackish water desalination performance by the FCDI process employing RHCE800-C, RHCESH2.0-800-C, RHCESB2.0-800-C, and RHCESC2.0-800-C 122
• 6.4.2 Characteristics of RHCE800-C, RHCESH0.0-800-C, RHCESH0.5-800-C, RHCESH1.0-800-C, RHCESH2.0-800-C, and RHCESH4.0-800-C 124
• 6.4.2.1 FE-SEM-EDX analyses 124
• 6.4.2.2 XRD, EA, bulk conductivity, and contact angle analyses 127
• 6.4.2.3 BET analysis 130
• 6.4.2.4 Raman, FTIR, and XPS analyses 133
• 6.4.2.5 Electrophoretic light scattering and viscosity analyses 137
• 6.4.3 Effects of the NaOH concentrations for chemical activation of RHCE800-C on the electrochemical performance of the FCDI stack and the brackish water desalination performance of the FCDI process 140
• 6.4.4 Effects of operational factors on brackish water desalination performance of the FCDI process employing RHCESH2.0-800-C 145
• 6.4.4.1 Flow rate of feed water 145
• 6.4.4.2 Applied voltage 147
• 6.4.4.3 Dosage of RHCESH2.0-800-C 149
• 6.4.4.4 Initial NaCl concentrations 151
• 6.4.5 Brackish water desalination mechanisms by FCDI process employing RHCESH2.0-800-C 154
• 6.5 Conclusions 156
• CHAPTER 7 CALCIUM CARBONATE-BASED TEMPLATING AS A NOVEL APPROACH TO FORM WELL-DEVELOPED PORE STRUCTURES OF RICE HUSKS-DERIVED CARBONACEOUS ELECTRODES FOR ENHANCING BRACKISH WATER DESALINATION VIA FLOW-ELECTRODE CAPACITIVE DEIONIZATION 157
• 7.1 Abstract 157
• 7.2 Introduction 158
• 7.3 Materials and Methods 161
• 7.3.1 Materials and reagents 161
• 7.3.2 Preparation procedures of RHCEs 162
• 7.3.3 Characterization of RHCEs 163
• 7.3.4 Experimental conditions for evaluating the electrochemical performance of the FCDI stack and the brackish water desalination performance of the FCDI process 164
• 7.4 Results and Discussion 167
• 7.4.1 Characteristics of RHCE800-C, RHCECC0.00-800-C, RHCECC0.05-800-C, RHCECC0.25-800-C, RHCECC0.50-800-C, and RHCECC1.00-800-C 167
• 7.4.1.1 FE-SEM-EDX analyses 167
• 7.4.1.2 XRD, EA, bulk conductivity, and contact angle analyses 170
• 7.4.1.3 BET analyses 173
• 7.4.1.4 Raman, FTIR, and XPS analyses 176
• 7.4.1.5 Electrophoretic light scattering and viscosity analyses 180
• 7.4.2 Effects of the mixing ratios of RHCE800-C and CaCO3 on the electrochemical performance of the FCDI stack and the brackish water desalination performance of the FCDI process 183
• 7.4.3 Effects of operating factors on brackish water desalination performance of the FCDI process applying RHCECC0.50-800-C 188
• 7.4.3.1 Flow rate of feed water 188
• 7.4.3.2 Applied voltage 190
• 7.4.3.3 Dosage of RHCECC0.50-800-C 192
• 7.4.3.4 Initial NaCl concentrations 194
• 7.4.4 Brackish water desalination mechanisms by FCDI process applying RHCECC0.50-800-C 197
• 7.5 Conclusions 199
• CHAPTER 8 COST-BENEFIT ESTIMATION OF FLOW-ELECTRODE CAPACITIVE DEIONIZATION UTILIZING RICE HUSKS-DERIVED CARBONACEOUS ELECTRODES FOR BRACKISH WATER DESALINATION 200
• 8.1 Abstract 200
• 8.2 Introduction 201
• 8.3 Materials and Methods 203
• 8.3.1 Resources, chemicals, and materials 203
• 8.3.2 Manufacturing cost estimation of RHCE800-C, RHCESH2.0-800-C, and RHCECC0.50-800-C 204
• 8.3.3 Experimental procedures 205
• 8.4 Results and Discussion 207
• 8.4.1 Comparison of unit price of RHCE800-C, RHCESH2.0-800-C, RHCECC0.50-800-C, and MSP-20X with brackish water desalination performance of the FCDI process 207
• 8.4.2 Comparison of specific energy consumption of the FCDI process utilizing RHCECC0.50-800-C and the mCDI process 210
• 8.5 Conclusions 213
• CHAPTER 9 SUMMARY AND RECOMMENDATIONS FOR FUTURE RESEARCH 214
• 9.1. Summary 214
• 9.2 Recommendations for Future Research 218
• REFERENCES 219
• ACKNOWLEDGEMENTS 234
• CURRICULUM VITAE 235
• 초록 249