薄膜蒸餾於溶液氨氮移除與回收之實驗探討

Study on ammonia removal and recovery from aqueous solution by membrane distillation

李爾浩(Er-Hao Lee)

指導教授 ： 莊清榮

中原大學/工學院/化學工程研究所/碩士(2021年)

https://doi.org/10.6840/cycu202100694

摘要

當水體中氨氮濃度過高會造成優氧化，致使水中生物大量死亡，為防止此問題發生，現今已發展出許多技術用以處理廢水中的氨氮。其中，薄膜蒸餾法(MD)因操作上不受限於廢水中氨氮濃度高低，且在單位體積下提供較大的接觸膜面積等優點，應用於氨氮處理上甚有發展潛力。目前業界普遍使用直接接觸式薄膜蒸餾(DCMD)操作，以硫酸為吸收液，若能於脫氨程序中產製氨水或其他更具回收利用之產物，其工業應用之經濟價值將提高。本研究以空氣掃流薄膜蒸餾(SGMD)及真空式薄膜蒸餾(VMD)實驗，探討其脫除氨氮之速率及產製氨水與氯化銨的產物回收。
本研究首先針對以SGMD進行氨氮移除實驗，探討於不同操作條件下，對質傳係數、通量及進料槽中氨氮濃度之影響。以空氣掃流移除氨氮實驗，針對0.2μm之 PTFE薄膜，當進料pH=11而溫度由40增加至60℃，總質傳係數從6.59x10-6增加至9.48x10-6 m/s，但分離選擇率會因進料溫度上升而下降。增加掃流流率可提高總質傳係數與氨氮去除率，然而在過高的掃流流率下，對於質傳係數與氨氮去除率即不會有明顯的提升。以鹽酸氣體掃流之SGMD系統中，氨氣與鹽酸氣體反應形成之氯化銨結晶附著於表面，導致氨氮移除率降低。
另一方面，將移除之氨氮以氨水形式回收時，於本研究實驗設計之冷凝系統限制下，氨氮回收率僅約8~15%。而以氯化銨形式回收時，加裝過濾裝置之氨氮回收率會由15 % (未加裝過濾裝置) 提升至34 %。另外，以VMD形成氨水回收實驗時，由於冷凝系統溫度的限制以及氨氣於低溫低壓下溶解度極低，回收率僅約17 %，因此使用VMD回收氨水時，須降低冷凝系統溫度與提高氨氣滯留時間方能有效地回收氨水。

關鍵字

薄膜蒸餾 ； 氨氮移除 ； 氨氮回收

並列摘要

Ammonia nitrogen is one of the major pollutants in the water bodies in recent years, which is introduced by industrial, domestic and agricultural wastewater discharges. Many technologies have been developed to remove or recover the ammonia nitrogen from wastewaters. Among them, there are many advantages of using membrane distillation method (MD), one is no concentration limit of ammonia nitrogen in wastewaters and another is providing larger contact membrane area per unit volume. For these reasons, it has highly potential in ammonia nitrogen treatment application. At present, most industries use sulfuric acid as the absorption liquid in the MD operations. If ammonia water or other recyclable products can be produced in the deamination process, the economic value of its industrial application will be increased. In this study, sweeping gas membrane distillation (SGMD) and vacuum membrane distillation (VMD) experiments were carried out to investigate the rate of ammonia removal and the recovery of ammonia and ammonium chloride products.
In the first part, we focus on ammonia nitrogen removed by SGMD, and to examine the influence on the mass transfer coefficient, total flux and ammonia nitrogen concentration in the feed tank under different operating conditions. Experimental results of 0.2μm PTFE membrane show that when the feeds at pH=11 the overall mass transfer coefficient will increase from 6.59x10-6 to 9.48x10-6 m/s for temperatures in a range from 40 to 60℃, while the separation selectivity will decrease due to the water permeability ratio increases. When the sweep flow rate increases, the mass transfer coefficient and ammonia nitrogen removal rate will increase. Nevertheless, in the case of high flow rate, the mass transfer coefficient and ammonia nitrogen removal rate will not be improved significantly. Using hydrochloric acid as sweeping gas in the SGMD system, ammonia gas combines with hydrochloric acid while produce ammonium chloride crystals on the membrane pores, resulting in significantly lower ammonia nitrogen flux.
About the recovery of ammonia nitrogen, due to the limitation of the scale of the condensing system in the experimental design, the recovery rate of ammonia nitrogen is only from 8 to 15% when it is recovered in the form of ammonia water. When the recovery product is ammonium chloride, the recovery rate of ammonia nitrogen with a filter device will increase from 15% (without a filter device) to 34%. In addition, when using VMD to recover the ammonia, the recovery rate is only 17% due to the ammonia has very low solubility at low temperature and low pressure. Therefore, it is necessary to improve the condensing system and increase the residence times of ammonia to enhance the efficiency of ammonia recovery in using VMD.

並列關鍵字

Membrane distillation ； Ammonia removal ； Ammonia recovery

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