應用磁性吸附劑吸附環境荷爾蒙-以鄰苯二甲酸二甲酯為例

Adsorption of Environmental Hormones Using Magnetic Adsorbent: A Case Study of Dimethyl Phthalate

盧德笙(De-Sheng Lu)

指導教授 ： 張慶源

國立臺灣大學/工學院/環境工程學研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.02012

摘要

鄰苯二甲酸二甲酯(DMP)屬於環境荷爾蒙，其存在濃度極低，同時其極低濃度的暴露量即可對生化與細胞作用機制造成巨大的改變。故本研究以吸附的方式濃縮DMP，欲達到提高單位體積的汙染物濃度，以利於氧化、降解或其他處理處置程序。
本研究以化學共沉法製備四氧化三鐵，再以懸浮聚合法的方式合成之磁性聚醋酸乙烯酯(M-PVAC)，最後進行表面改質形成吸附劑磁性聚乙烯醇(M-PVAL)。其飽和磁化強度分別為57.2、26.0和43.2 emu g-1。皆具有超順磁性。吸附劑屬於微米等級而其粒數平均粒徑為0.75 μm。
以完全攪拌槽進行動力實驗，整體性動力學部份，分別以假性一階動力方程式、假性二階動力方程式和Elovich rate equation。傳統動力學部分以孔擴散及表面擴散模式進行探討。結果顯示隨著初始濃度越高，固液之間濃度梯度越大，其達到平衡的時間越快。
等溫吸附曲線實驗分為不調整初始pH值、初始pH值為5及7三組，皆以Langmuir等溫吸附方程式、Freundlich等溫吸附方程式及Dubinin-Radushkevich (D-R)等溫吸附方程式進行模擬。三組實驗之Langmuir isotherm之單層飽和吸附量qL分別為5.21、4.01和4.22 mg g-1。三組之Freundlich isotherm之異質性常數nF值分別為2.19、2.59、2.59，皆大於1。顯示本DMP/M-PVAL系統屬於有利吸附。三組實驗由D-R等溫方程式推估之每莫耳吸附質吸附的自由能EF值分別6.48、7.04和7.19 kJ mol-1，其EF皆小於8 kJ mol-1，整體的吸附程序是屬於物理自然發生的形式。
調整含有甲醇比例為0、10 及50 vol.%進行等溫吸附實驗，其qL值分別為5.21、4.03及1.18 mg g-1。顯示甲醇之含量越高，則M-PVAL之qL值越低。同時三組之EF值分別為6.48、5.89和4.68 kJ mol-1，顯示甲醇與DMP可形成良好之鍵結，以致親合力較吸附劑為高。利用此特性以50 vol.%甲醇進行脫附實驗，經過兩次脫附單元後，其脫附效率高達95%。

關鍵字

環境荷爾蒙 ； 鄰苯二甲酸二甲酯 ； 吸附 ； 磁鐵礦 ； 懸浮聚合 ； 聚乙烯醇 ； 吸附動力

並列摘要

Dimethyl phthalate (DMP) is a member of environmental hormones. It exists with low concentration and is harmful to biological and cell`s mechanism even with a very low exposed concentration. Adsorption is chosen to remove and concentrate DMP for further oxidizing, degrading or other treating processes.
Fe3O4 (M) is prepared by precipitation method and then synthesized to magnetic polyvinyl acetate (M-PVAC) by suspension polymerization. Its surface is modified by alcoholization to produce a polymer adsorbent of magnetic polyvinyl alcohol (M-PVAL). The saturated magnetizations of particles M, M-PVAC and M-PVAL are 57.2, 26.0 and 43.2 emu g-1 with super-para-magnetism, respectively. The average particle size of M-PVAL by number is 0.75 μm in micro size.
Global kinetic expressions are simulated by pseudo-first-order equation, pseudo-second-order equation and Elovich rate equation in completely stirred tank reactor (CSTR) system. Traditional kinetic models of pore and surface diffusions are also employed. As a result, time to reach equilibrium is faster when the initial concentration of DMP is higher because of the high gradient of concentrations between solid and liquid.
The isotherm experiments include three cases: (1) with no adjustment of initial pH (pH0) of solution, (2) pH0 = 5 and (3) pH0 = 7. The results are simulated by Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms. The saturated amounts of adsorption of unimolecular layer (qL) of Langmuir isotherm are 5.21, 4.21 and 4.22 mg g-1 in these three cases and the values of heterogeneity factor nF of Freundlich isotherm are 2.19, 2.59 and 2.59 which are greater than 1. It reveals the DMP/M-PVAL system is belong to favorable adsorption. The values of adsorption activation energy per mole (EF) of D-R isotherm in these cases are 6.48, 7.04 and 7.19 kJ mol-1which are less than 8 kJ mol-1, indicating that the adsorption process is belong to the form of physical nature.
The values of qL for the adsorption of DMP in three solutions containing 0, 10 and 50 vol.% alcohol are 5.21, 4.03 and 1,18 mg g-1, respectively. It shows the more content of methnol the less the concentration in solid M-PVAL (qL). The values of EF in these three experimental sets are 6.48, 5.89 and 4.68 kJ mol-1 , indicating that stable bond forms between the methanol and DMP so that the affinity between them is better than that between the adsorbent and DMP. Using the characteristics between methanol and DMP to desorption process, the desorption efficiency is as high as 95 % by twice desorption units applying 50 vol.% methnol.

並列關鍵字

environmental hormones ； dimethyl phthalate ； magnetite ； polyvinyl alcohol ； suspended polymerization ； adsorption isotherm ； adsorption kinetic

參考文獻

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