建立高效能的樹脂晶片電去離子技術進行鹹水淡化及其性能之研究

Abstract

本研究重點在於開發建立新型的高效能的樹脂晶片電去離子技術，將其淡室（dilute compartment）內的散裝的樹脂，用熱壓機壓制成固定的樹脂晶片（resin wafer）以使樹脂在各方向上分佈均勻，用以提高對低濃度的苦鹽水（brackish water）淡化的效率，降低其能耗。 借助掃描電鏡法以及傅裡葉轉換紅外光譜法分析方法，可以瞭解樹脂的材料在熱壓機前後的特性之改變。掃描電鏡法通過對材料表面資訊的捕獲，可以顯示材料表面之結構及組成。傅裡葉轉換紅外光譜法通過對不同波數下的特徵峰的資訊的捕獲，可以用於研究材料中所含有的官能基，並且對處理廢水前後的樹脂晶片的FT-IT圖形的比較，可以得出參與反應的官能基。 研究電壓、進水流量和進水濃度對苦鹽水淡化過程的影響。研究發現，新型電去離子技術在2小時內就能達到99%以上的去除效率，且電壓對去除效率的影響比進水流量更加顯著。此外，電壓，進水流量和進水濃度對電流效率都具有顯著的影響。離子去除速率可隨著電壓和進水流量的提高而增大。其中，電壓的提高增加了離子轉移的驅動力，而進水流量的增加則增加了離子與樹脂之間的質傳進而增加了吸附量，另一方面，流量的增加降低了水流在EDI中的停留時間，從而使得離子去除速率提高。而對EDI的反應動力學的研究，表明其符合擬一階反應動力學模式，且反應速率常數是關於電壓和進水流量的函數。 對5000 mg/L的氯化鈉溶液進行淡化實驗，當去除率達到90%以上時，得到其能耗為 0.493 ~ 2.361 kWh/m3，能源效率為21 ~ 48%，產量達到 16 ~ 42 L/(m2*hr)。相較於最廣泛使用的RO，在其去除率為80%時，其能耗為1.2 ~ 1.5 kWh/m3，而其能源效率僅為12 ~ 15%。表明RW-EDI在苦咸水淡化應用中具有前景。通過響應曲面法限定能耗和產量條件，可實現最優操作條件為 9.25 V電壓及490 mL/min流量，得到33 L/(m2*hr)的產量，及1.397 kWh/m3的能耗。 對RW-EDI和RO進行生命週期評估，發現RW-EDI的生命週期所引起的環境衝擊比RO小。同時以EDI濃縮廢水用作RPB飛灰碳捕捉溶劑，比自來水補碳明顯增強。

This study focuses on the development of energy-efficient resin wafer electrodeionization, of which resins in the dilute compartment is immobilized and fabricated into wafer by Hot-Press. Such changes could make the resins uniformly-distributed in both vertical and horizontal direction, which can enhance separation efficiency of RW-EDI for brackish water desalination and decrease energy consumption. The characteristics of resin wafer materials before and after hot-pressed can be detected via SEM and FT-IR. The application of SEM could help to obtain the information of surface topography and composition of resin wafer. The functional groups of the resin wafer could be detected by FT-IR to capture the peak at the specific wavenumber. By comparing FT-IT images of resin wafer before and after treating wastewater, the functional groups (SO32- and Quaternary Ammonium) participating in adsorption of ions could be determined. The investigation of effect of applied voltage, feed flow rate and influent concentration on performance of RE-EDI suggests that the removal efficiency of RW-EDI could reach more than 99% in 2 hours, indicating it very effective in treating brackish water. On the other hand, applied voltage has a more drastic influence on removal efficiency than feed flow rate. As for current efficiency, it could be significantly influenced by voltage, feed flow rate and influent concentration, of which higher voltage, lower flow rate and lower influent concentration corresponds to a lower current efficiency. Vice versa. It suggests that the ion removal rate will increase with both increased applied voltage and feed flow rate. On the one hand, the increased voltage enhances the driving force as static force to migrate ions from dilute compartment into concentrate compartment. On the other hand, the increased feed flow rate improves the mass transfer between mixed-resin bed and ions to enhance adsorption of ions, and the retention time of flow decreases, both of which accelerate the removal of ions. Above all, the removal kinetics of RW-EDI fits a pseudo first-order model well, of which the reaction rate constant is a function of applied voltage and feed flow rate. The energy consumption of this study for treating a NaCl solution with TDS of 5,000 mg/L are 0.493 ~ 2.361 kWh/m3, corresponding to productivity of 16 ~ 42 L/(m2*hr) with removal efficiency larger than 90% and energy efficiency of 21 ~ 48%. By comparison of reverse osmosis (RO) which is most applicable, its energy consumption for treating NaCl solution of the same concentration is 1.2 ~ 1.5 kWh/m3, of which the energy efficiency is only 12 ~ 15% and removal efficiency of 80%, indicating that RW-EDI is a promising desalination technology. By response surface methodology giving the limitation of energy consumption and productivity, the optimal operation conditions for treating brackish water with 5,000 mg/L NaCl are 9.25 V and 490 mL/min, corresponding to the best achievable energy consumption and productivity of 1.397 kWh/m3 and 33 L/(m2*hr), respectively. To assess the life cycle impacts of RW-EDI on environment with RO as business-as-usual scenario, it presents a less life-cycle impacts of RW-EDI on environment than RO. The utilization of concentrate wastewater from EDI in capturing CO2 via RPB shows a significant increase of captured CO2 compared with tap water, providing an approach to deal with wastewater from EDI.