利用零價鐵流體化床處理聚乙烯醇之研究

Treatment of polyvinyl alcohol by ZVI process in up-flow fluidized bed reactor

許哲榮(Che-Jung Hsu)

指導教授 ： 陳孝行

國立臺北科技大學/工程學院/環境工程與管理研究所/碩士(2012年)

https://doi.org/10.6841/NTUT.2012.00338

摘要

聚乙烯醇為一種親水性高分子聚合物，氫氧基連接每個碳鍵，結構簡單但聚合度高，因此被視為難分解的有機污染物。用途非常廣泛，可用作漿料、塗料、黏著劑、穩定劑、分散劑、乳化劑、增厚劑、感光劑和填充材料等，由於工業所需，估計全球每年聚乙烯醇產量可高達600,000噸。雖然聚乙烯醇對生物的毒性不高，但是由於分子量大且容易水解之特性，經由生態圈中的食物鏈易造成生物累積之現象。排放到河川及湖泊中則是會使水體的黏度上升並產生發泡的現象。因此如何有效處理聚乙烯醇的排放成為了工業上的一大課題。
本研究經由實廠利用之考量，設置一組實驗室規模之零價鐵流體化床程序，以符合工業上實廠連續使用之原則。在零價鐵流體化床處理聚乙烯醇的實驗中，分別測是四種由文獻得知之零價鐵流體化床操作因子，其包括濾床零價鐵添加量(ZVI dosage)、水力停留時間(HRT)、反應酸鹼值控制(pH)及反應槽溶氧量(DO)。首先由文獻參考並分別測試四種ZVI dosage (5 g/L, 20 g/L, 30g/L, and 40g/L)，實驗結果指出當ZVI dosage由5 g/L增加至30 g/L時，聚乙烯醇去除效率可提升19.22%，ZVI dosage由30 g/L增加至40 g/L時已無法明顯提升聚乙烯醇去除效果。在三種不同HRT的測試中可以發現，當HRT由30分鐘延長至60分鐘時，聚乙烯醇的去除效果可提升10.09 %，再由60分鐘延長至90分鐘時只提升0.86%之聚乙烯醇去除率。由三種不同pH的測試中可以發現，當零價鐵反應控制於pH 2之酸性狀態時能達到較佳去除效果。在零價鐵消耗測試試中發現，增加ZVI dosage至30 g/L以上雖然無法明顯提升去除效果，卻可以延長零價鐵濾床的使用期限。最後由上述操作參數搭配不同曝氣包括氮氣、空氣及氧氣，其實驗結果指出，當曝氮氣且進流聚乙烯醇水溶液濃度為100 mg/L、濾床零價鐵劑量為40 g/L、pH值為2及水力停留時間為60分鐘之厭氧條件下，聚乙烯醇的去除率為15.80%；在相同的實驗參數下，當曝空氣且溶氧為5.59 mg/L時，聚乙烯醇的去除率為78.47%；將溶氧以曝純氧的方式提升至20.00 mg/L時，聚乙烯醇及總有機碳的去除率則分別可達到80.23%及12.77%。
零價鐵反應動力學方面，當進流聚乙烯醇濃度為100mg/L、反應pH 2、零價鐵30g/L、曝純氧(100mL/min)及水力停留時間30分鐘時之反應速率常數4.5798 hr-1為最高。單位容積鐵去除聚乙烯醇方面，當進流聚乙烯醇濃度為100mg/L、反應pH 2、零價鐵30g/L、曝純氧及水力停留時間30分鐘時之13.9 mg PVA / g ZVI最高。由複合迴歸結果可以得知，pH及溶氧於單位容積鐵去除聚乙烯醇及反應速率常數上具有較大的影響力，過量的零價鐵劑量及過度的水力停留時間則不具有明顯正面影響。在聚乙烯醇之反應副產物的評估中可以發現，雖然總有機碳的去除效能不盡理想，但是結果也證明了巨大分子的聚乙烯醇確實降解成小分子化合物。

關鍵字

聚乙烯醇 ； 零價鐵 ； 流體化床

並列摘要

Polyvinyl alcohol is a common hydrophilic polymer having an OH group at every other-carbon in the backbone chain and well-known recalcitrant environmental pollutants. It is widely used as a sizing agent and an ophthalmic lubricant in the textile and pharmaceutical industries, respectively. The global production of PVA is estimated to be more than 600,000 tons/year, and the large amount of PVA discharged from industrial effluents has posed a serious threat to local ecosystem health.
A fluidized zero valent iron (ZVI) reactor is examined for polyvinyl alcohol (PVA) removal. Fluidized zero valent iron process was adopted to degrade PVA in low pH for two reasons: (1) low pH of the wastewater favoring the ZVI reaction; (2) higher ZVI utilization for fluidized process due to abrasive motion of the ZVI. The results showed that the degradation of PVA was greatly enhanced under acidic pH, longer hydraulic detention time (HRT) and presence of dissolved oxygen (DO).
In the experiment of ZVI dosage, results indicate the PVA removal was enhanced 19.22 % via increasing ZVI dosage from 5 g/L to 30 g/L as iron, but the removal efficiency had no significant promotion while ZVI dosage increased to 40 g/L. In the effect of HRT, the data shows that to extend the HRT from 60 min to 90 min was redundant on PVA removal. When pH was controlled at 2 in fluidized reactor, the efficiency of PVA removal was better than pH 3 and pH 4. Three different ZVI dosages were tested in the part of ZVI durability, and the result indicates that the life of ZVI was extended on PVA removal although ZVI dosage higher than 30 g/L had no significant improvement. Ultimately, three different type of aeration were tried with factors above-mentioned on PVA removal. Without addition of oxygen, 15.8 % of PVA was removed at pH 2, ZVI dosage of 40 g/L and HRT 60 min. With 5.59 mg/L of DO, 78.47 % of PVA was removed for the same experimental condition. With 20 mg/L of DO, PVA and TOC removal efficiencies were reached 80.23 % and 12.77 % respectively for the same experimental condition. The presence of oxygen/ZVI initiated a Fenton type reaction to reduce concentration of PVA. The fluidized ZVI process removed only 12 % as TOC in optimum condition, but the result also indicated the main pollutant as PVA was degraded to compound lower molecular weight, and CO2.
The highest reaction rate constant and ZVI capacity for PVA removal were found on parameters with influent PVA concentration of 100 mg/L, ZVI dosage of 30g/L, HRT 30 min, and DO of 20 mg/L for pH 2.

並列關鍵字

Polyvinyl alcohol ； Zero Valent Iron (ZVI) ； fluidized bed

參考文獻

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