以部分因素設計法最佳化電容去離子程序之研究

Abstract

電容去離子技術對半鹹水去除的能源成本較低且回收率高，模組結構簡單且可在常溫常壓下操作，只需將電場移除或倒極即可再生。活性碳為常見之電容去離子電極材料，具有大比表面積、便宜，且可利用添加導電碳黑之簡單的方式提高其電吸附效能，故本研究選用活性碳/碳黑複合電極探討其去離子表現並提升其效能。 本研究分為兩部分，第一部分為電容去離子操作程序之探討，在電容去離子操作過程中，所設定的操作參數會影響其電吸附表現，本研究以活性碳混合導電碳黑，再以黏著劑將其披覆於鈦網基材上製成之網狀複合電極，先針對活性碳粉末及電極特性進行分析，再分別探討各項操作參數對於電容去離子效能之影響；第二部分則以實驗設計法綜合評估操作參數對電容去離子效能之影響及其間之相關性，並找出提升效能之關鍵因素。 研究結果顯示，ACS之比表面積為1622 m2/g，其比電容值104.84 F/g，可提供足夠之離子吸附位，且在施加電壓1.5 V時電吸附容量達12.7 mg/g，相較ACL更適合作為電容去離子之電極材料；僅施加電壓及進流鹽類初始濃度對電吸附容量為正相關，進流流速、電極間距及電極層數等參數對電吸附容量皆為負相關。 由部分因素設計法得知，施加電壓、進流鹽類初始濃度及電極層數為影響電極效能之關鍵因素。其中，在施加電壓為高階水準、進流鹽類初始濃度及電極層數為低階水準時，可達到最高電吸附容量為16.636 mg/g。

Capacitive deionization (CDI) is a technology for salt recovery as well as desalination of brackish water with low energy consumption, high recovery rate, and easy assemble. CDI can be operated under room temperature, normal pressure, and is easily regenerated by short-circuit or reversed polarity. Activated carbon (AC) is one of the most common electrode materials for CDI applications because of its high specific surface area, low cost, and easy assemble. Recent studies have shown that the use of AC in CDI can also improve its electrosorptive performance of electrode by adding conductive carbon black. In this study, activated carbon (AC) mixing with carbon black (CB) were applied to fabricate electrodes to investigate their optimal conditions in the salt recovery of CDI process. This study has been divided into two parts. The first part is to investigate the effect of CDI operating parameters. The second part is to realize the comprehensive effect of CDI operating parameters by using fractional factorial design. In CDI process, the electrosorptive capacity plays an important role in deionization performance. Activated carbon (AC) was mixed with carbon black (CB) by using a polymer binder (PVdF). Then it was coated onto titanium mesh via dip coating method. Two types of AC/CB composite electrodes were fabricated by two kinds of activated carbons (ACS, China Steel Chemical; ACL, Sigma-Aldrich), and their characteristic and electrosorption performance were investigated. The effects of operating parameters were also included. The results show that the activated carbon, ACS, comprising higher specific surface area (1622 m2/g) and specific capacitance (104.84 F/g). Its eletrosorptive capacity reached 8.9 mg/g with applied voltage of 1.5 V. In CDI process, the increase of applied voltage and initial concentration could enhance the capacity of CDI process. However, that of flow rate, electrode distance, and electrode layers has shown the negative effect on deionization performance. By fractional factorial design approaching, it has been found that applied voltage, initial inlet concentration, and electrode layers are key factors of deionization performance in CDI. By statistical analysis, the results have also revealed that the highest electrosorptive capacity (16.636 mg/g) has been reached under the optimum operational conditions (ie, 1.5V of applied voltage, 3 mM of initial NaCl concentration, and one sheet of electrode layer)