- 學位論文
添加導電性物質(碳黑、奈米碳管、石墨烯)於活性碳流動電極電容去離子(FCDI)系統之脫鹽效能研究
Effects of addition of conductive materials (carbon blacks, carbon nanotubes or graphene) to activated carbons in flow-electrode capacitive deionization (FCDI) system on desalination performance
摘要
世界各國的水資源需求量增加，但淡水卻無法隨需求量增加，因此如何獲得潔淨淡水是人類極需解決的問題。現今的脫鹽技術以逆透法或熱處理法為主，但成本昂貴且能耗高。流動電極電容去離子(Flow-electrode Capacitive Deionization, FCDI)是電容去離子(Capacitive Deionization, CDI)系統的新型態系統，具有諸多優勢，包括：去除效率高、可處理高濃度溶液，並可實現連續脫鹽，是具有發展潛力的脫鹽技術。 本研究以活性碳為流動電極材料，應用於流動電極電容去離子系統，除探討處理不同鹽類濃度之效能外，亦探討添加不同比例的導電性物質(包括：碳黑、奈米碳管或石墨烯(rGO) )是否可有效促進 FCDI之效能。 FCDI 系統於 3 種不同氯化鈉濃度 (1, 10, 30 g/L)之脫鹽表現 ，以短流封閉系統(Short-Circuit Closed, SCC)操作 3 小時，流動電極材料為 5 wt%活性碳。FCDI系統處理 1 g/L 的 NaCl 時，NaCl 去除效率高達 99%，但因為在 3 小時內，大部分離子已被去除，因此，ASRR只有 6.4·10-3 μmol/cm2 /min ，且系統的充電效率偏低(23.59%)，能源消耗較高8.4·10-2 kWh/mmol。處理10 g/L 的NaCl時，NaCl去除效率降為47%，擁有好的ASRR 2.31*10-2 μmol/cm2 /min，但充電效率可提高至72.1%。當NaCl 濃度提高至30 g/L 時，由於處理溶液濃度高，NaCl 去除效率與充電效率(55.2%)表現略微下降，但 ASRR 可提升至 2.38·10-2 μmol/cm2 /min，表示 FCDI 系統處理高濃度 NaCl時，擁有良好的脫鹽效能。 於 5 wt%活性碳流動電極中添加不同比例(0.5, 1, 1.5, 2 wt%)的碳黑，測試添加碳黑後，FCDI系統處理 10 g/L NaCl 之效能影響。活性碳流動式電極中加入碳黑，能有效提高 NaCl 去除效率。當碳黑添加比例為 2 wt%，NaCl 處理效率從 47%提高至 82% ，ASRR從原本的2.3·10-2 μmol/cm2 /min 上升至 4.2·10-2 μmol/cm2 /min。但添加碳黑於5 wt%活性碳流動電極中，並無法有效促進充電效率，充電效率落在 63~72%範圍，能源消耗則因添加碳黑而從2.7·10-2 kWh/mol略微提升到2.8·10-2 kWh/mol 。 於 5 wt%活性碳流動電極中添加不同比例(0.2, 0.5 wt%)的奈米碳管，測試添加奈米碳管後，FCDI系統處理 10 g/L NaCl 之效能。在添加0.2 wt%奈米碳管去除率的表現只從原本的47%提升到49.69%，並無太大的上升趨勢，但充電效率卻有顯著的提升，從72%上升至91.55%，能源消耗也隨之減少，原為2.7·10-2 kWh/mol下降至 2.1·10-2 kWh/mol。當添加0.5 wt%奈米碳管時，NaCl去除率只有47.61%，並沒有明顯提高NaCl去除率，但充電效率獲得改善(87.85%)，能源消耗也有降低 2.2·10-2 kWh/mol，結果顯示添加0.2 wt%的奈米碳管於5 wt%活性碳流動電極，是表現最好的添加奈米碳管比例。 於 5 wt%活性碳流動電極中加入不同比例(0.2, 0.5 wt%)的石墨烯，測試添加石墨烯後，FCDI系統處理 10 g/L NaCl 之效能。活性碳流動式電極中加入石墨烯，NaCl去除率隨著添加比例提高也有所上升，添加0.5 wt%石墨烯時，NaCl去除率從47%上升至55.6%，添加石墨烯也可以有效提高 NaCl 充電效率，隨著加入的石墨烯比例提高，充電效率也隨之提高，從72.1%上升至90%。能源消耗也從2.7·10-2 kWh/mol下降至2.17·10-2 kWh/mol。 添加碳黑於活性碳流動式電極可以有效地增加NaCl去除效率，卻對充電效率和能源消耗並無太大的改善，而添加奈米碳管於活性碳流動式電極，雖可在充電效率和能源消耗得到很好的優化，但在NaCl去除率上並無顯著改變，當添加石墨烯於活性碳流動式電極，在NaCl去除率、充電效率、能源消耗，都可獲得提升，顯示添加石墨烯於活性碳流動式電極應用於FCDI系統擁有發展潛力。
並列摘要
Water resource is highly needed worldwide, yet the supply of fresh water cannot keep up with the demand. Thus, there is an urgent need for people to find a solution to access clean fresh water. The common desalination technologies used today are mainly based on thermal treatments or reverse osmosis, but they are costly and energy-intensive technologies. A novel kind of capacitive deionization (CDI) system called flow-electrode capacitive deionization (FCDI) is emerging. FCDI system has advantages of high removal efficiency, the ability to handle solutions with high saline concentrations, and the ability to continuously desalinate, which make it a potential desalination technology. This work employed activated carbons as flow electrode materials for FCDI system to investigate not only the treatability of different saline concentrations, but also the effectiveness of FCDI system of addition of conductive materials (including carbon black, carbon nanotubes, or graphene (rGO)). Three sodium chloride concentrations (1, 10, and 30 g/L) were tested in the FCDI system with 5 wt% AC in short-circuit closed (SCC) mode for three hours. The removal efficiency of NaCl from 1 g/L NaCl can reach 99% in the FCDI system. Nevertheless, the ASRR was only 6.4·10-3 μmol/cm2/min since the majority of the ions were eliminated in less than three hours. Charging efficiency was poor (23.59%) and energy consumption was slightly high (8.4·10-2 kWh/mmol). The NaCl removal efficiency decreases to 47% while processing 10 g/L of NaCl, with a respective ASRR of 2.31*10-2 μmol/cm2/min; but, charge efficiency was enhanced to 72.1%. The NaCl removal efficiency and charge efficiency (55.2%) somewhat drop when the NaCl concentration was increased to 30 g/L; nevertheless, the ASRR was improved to 2.38·10-2 μmol/cm2/min, demonstrating that the FCDI system can deal with high saline concentrations and perform well with good desalination performance. The efficacy of the FCDI system to treat 10 g/L NaCl was tested by adding varying amounts (0.5, 1, 1.5, and 2 wt%) of carbon black to the 5 wt% activated carbons as flow electrode materials. NaCl removal efficiency can be enhanced by adding carbon blacks to activated carbons as flow electrode materials. The NaCl removal efficiency rose from 47% to 82% at a carbon black addition ratio of 2 wt%, and the ASRR increased from 2.3·10-2 μmol/cm2/min to 4.2·10-2 μmol/cm2/min. Carbon black, however, cannot effectively increase charging efficiency of FCDI system. The energy consumption increased slightly from 2.7·10-2 kWh/mol to 2.8·10-2 kWh/mol due to the addition of carbon black, while the charge efficiency was between 63 and 72%. The effectiveness of FCDI system to treat 10 g/L NaCl with adding carbon nanotubes (CNTs) in varying amounts (0.2, 0.5 wt%) with 5 wt% activated carbons as flow electrode materials were examined. With addition of 0.2 wt% CNTs, the removal efficiency of NaCl was slightly enhanced from 47% to 49.69%. Although there was not much increasing trend of NaCl removal efficiency, the charge efficiency improved significantly from 72% to 91.55%. Moreover, energy consumption dropped from 2.7·10-2 kWh/mol to 2.1·10-2 kWh/mol. Only 47.61% of the NaCl was removed after adding 0.5 wt% CNTs, which did not appreciably increase the NaCl removal efficiency. Nonetheless, there was an improvement in charge efficiency (87.85%) and a lower energy consumption (2.2·10-2 kWh/mol). The optimal ratio for introducing CNTs has been found to be 0.2 wt% with 5 wt% activated carbons as flow electrode materials. The performance of FCDI system to treat 10 g/L NaCl with 5 wt% activated carbons with addition of various amounts (0.2, 0.5 wt%) of graphene (rGO) as flow electrode materials were evaluated. The NaCl removal efficiency was increasing with higher ratios of rGO addition with activated carbons. The NaCl removal efficiency was enhanced from 47% to 55.6% with the addition of 0.5 wt% rGO. Adding rGO also raise the charge efficiency. The charge efficiency rose from 72.1% to 90%. Additionally, energy consumption decreased to 2.2·10-2 kWh/mol from 2.7·10-2 kWh/mol. Although adding carbon black to activated carbon flow electrodes can successfully boost NaCl removal efficiency, it has no discernible influence on energy consumption or charge efficiency. Carbon nanotubes can be added to activated carbon flow electrodes to improve energy consumption and charging efficiency, but has less impact on NaCl removal efficiency. The addition of graphene to activated carbon flow electrodes has shown to have positive impact on NaCl removal efficiency, charge efficiency, and energy consumption. These results suggest that graphene addition to activated carbon flow electrodes applied in FCDI systems has great potential.