陰離子交換與中和作用的動力學探討

Abstract

純水不論用於洗滌、冷卻或是充當溶劑，都是製程中不可或缺的。尤其在半導體工業上的應用，不僅需求量大，在純度上的要求更是嚴苛。一般超純水製造系統，為達到確實去除水中陰陽離于之目的，其去除離子化程序最常採用離子交換法。因此，以陰離子交換樹脂做去離子化已被廣泛的應用，但是在定量分析及伴隨中和作用的動力學探討方面，卻鮮少有文獻做有系統的記載。本研究的目的，即為陰離子交換與中和作用的動力學探討。 在動力學探討方面採用分批式操作系統，針對不同化學計量比、攪拌速率、樹脂顆粒大小等影響反應速率的因素，設計10個OH-Cl系統的實驗。同時，為了瞭解不同交換離子對反應速率的影響，設計了3個OH-SO4系統的實驗。在應用方面採用固定床式操作系統，針對OH-Cl、OH-SO4及OH-Cl-SO4系統設計了5個實驗。 將實驗結果加以分析，發現在分批式操作系統中：1.較大化學計量比的反應有較高的反應速率。2.提高攪拌速率可以降低固一液界面薄膜厚度，得到較快之反應速率。3.樹脂顆粒愈小反應速率愈快，且在本稀薄溶液的離子交換系統，可以用薄膜擴散控制來描述。4.雖然強鹼性陰離子交換樹脂，對硫酸根離子比對氯離子有較高之選擇係數，但因氯離子有較大之擴散係數，所以OH-Cl系統有較快之反應速率。在固定床式操作系統中：1.因為強鹼性陰離子交換樹脂，對二價之硫酸根離子比一價之氯離子有較高之選擇係數，所以當樹脂床貫穿時，氯離子會被硫酸根離子取代而先行排出。2.進流液流速愈慢，則貫穿曲線愈陡峭，樹脂利用率愈高。 本研究從理論的觀點出發，經由各種不同操作條件的實驗，得到許多伴隨中和作用之離子交換反應動力學數據。此數據將可應用於純水製造系統，供離子交換塔之設計及操作參考，並期望本研究對工業應用上有所助益。

The use of pure water, whether for washing, cooling or as solvent, is essential in the process industry. This is especially true in the field of semi-conductor where the purity requirement for water is severe and its consumption is in large quantity. Ion exchange is known to be the most effective method of deionization as one of several steps carried out in purifying water. There has been few studies on the kinetics of ion exchange accompanied by chemical reaction. The aim of this work is to carry out the study on the kinetics of anion ex- change accompanied by chemical reaction. Batch system is employed in the kinetics study. Ten experiments on Cl-OH exchange were conducted for the purpose of studying the effect of stoichiometric ratio/stirring rate and resin size. To examine the kinetics of heterovalent exchange, three experiments for SO4-OH exchange were also carried out. For consideration of practical application, five column runs with pure HCl, pure H2SO4 and mixture of HCl and H2SO4 as feed solution. Results of batch experiments indicate 1. Increase the stoichiometric ratio of resin and solution results in higher rate. 2. Increasing stirring rate tend to reduce film thickness and hence increase the rate of exchange. 3. Smaller resin particle yields higher rate, this is consistent with the film diffusion model employed in this study. 4. Rate of SO4-OH exchange is higher than Cl-OH due to the larger value of Dnci compared to DH2SO4. The exchange being irreversible, higher selectivity of sulfate ion over chloride ion has no effect on the rate of exchange. Results of column runs show : 1. Due to the higher selectivity of sulfate ion, the chloride ion is displaced and break-through occurs earlier. 2. The lower the flowrate employed, the sharper the breakthrough curve hence higher resin utilization. This study is undertaken with the use of theoretical derived equations and experiments conducted under various operating conditions. The kinetics data and parameters as determined in this work will be useful in the application of manufacturing pure water by fixed bed ion exchange.