奈米黏土改質方法及其吸油和儲能應用

Abstract

本研究旨在探討奈米黏土之改質與應用。天然奈米黏土，例如蒙脫土為一親水性層狀結構，黏土表面帶負電荷，而其層間或黏土邊緣帶有不同價數的陽離子，例如: 鈉離子、鎂離子、鋁離子等以維持電荷平衡。由於蒙脫土具有 1.2 mequiv./g 之陽離子可交換當量，故可藉由將有機胺鹽或磷酸鹽酸化等方式，與黏土層間之鈉離子進行離子交換，使奈米黏土層間具有親油性質。 蒙脫土經有機胺鹽離子交換進行插層後，有機胺鹽彼此間之立體障礙及疏水性排斥力，使得奈米黏土層間距可由原本 12 Å 增大至 52 Å~ 74 Å 不等。由於經插層改質後的奈米黏土之層間具親油性，故可吸引有機或油性物質進入黏土層間距，而此時奈米黏土之層間距可再進一步增大甚至達無序脫層狀態。 利用奈米黏土經有機插層而具親油性，以及插層和吸附有機物質後其層間距可進一步增大而可容量更多有機物質的特性，本研究主軸為將有機改質後的奈米黏土作為一奈米容器，探討經不同插層劑改質之蒙脫土對於原油吸附與回收之效果，另亦將之用以吸附相轉變材料，作為一儲熱奈米容器。本研究總共分三部分，其目標分述如下。 第一部分將蒙脫土以高分子有機胺鹽進行插層，比較不同胺基數目及分子量的高分子有機胺鹽插層後的有機黏土對於水中原油吸附效果。此外，此研究中所選用之有機胺鹽具有低臨界相轉變溫度，於低溫下可藉由分子間氫鍵均勻分散於水中並吸附原油；當溫度升高至相轉變溫度時，氫鍵遭破壞而有機黏土將聚集成團，利用此溫度變化而相轉變特性，吸附原油後之有機黏土可容易地進行回收。實驗結果發現高分子有機黏土吸附原油之最佳效能可達有機黏土重量之 15 倍。 第二部分則選用小分子有機胺鹽 (十八烷基胺) 對於蒙脫土進行插層並探討其吸附原油效能。以十八烷基胺鹽插層後之有機黏土對原油吸附最佳效能可達 6 倍之有機黏土重。和第一部分高分子胺鹽插層有機黏土不同的是十八烷基胺鹽改質之蒙脫土於室溫下吸附原油後，不需經溫度轉換即可自動產生聚集而從水相分離。除同樣具有容易回收之特性外，吸附原油後的有機黏土可藉由萃取將吸附於層間的原油分離出來而不破壞有機黏土本身結構。故此有機黏土可再次進行使用，實驗結果發現此有機黏土重覆使用之吸附效能具有高度穩定性，且有機黏土萃取後之回收率可高達九成以上，為一環境友善之原油除污材料。 第三部分同樣使用十八烷基胺鹽插層之有機黏土，此部分研究中將有機黏土作為一儲熱奈米容器。實驗結果發現此有機黏土對於石蠟 (固－液相轉變材料) 之吸附效能可達 5.6 倍，可將石蠟固定於黏土層間中，即使加熱至高溫，石臘亦未見因相轉變而瀉出現象。此有機黏土除可固定石蠟外，石蠟之熱焓值轉化效能可高達 100% ，故其可作為一優異的儲熱奈米容器，未來可應用於建材等需求上。

The object of this research is studying the modification method and applications of nanoclays. The primary unit of MMT is comprised by layered stacks, and contains 8 to 10 sheets per stack. The dimension of nature clay, for example, montmorillonite (MMT) with layered structure is 1 x 100 x 100 nm3 for each sheet. There are large amounts of cations existing in clay layers, such as sodium ions, magnesium ions, calcium ions, and aluminum ions. The cationic exchange capacity of MMT is 1.2 mequiv./g. Hence, the MMT can be modified by acidifying organic ammonium salts and exchanging with sodium ions. After the organic ammonium salts intercalation, the d spacing of MMT could be expanded from 12 Å to 52 Å or to 74 Å. The organic intercalation would introduce the hydrophobic characteristic into clay layers and make the modified MMT has hydrophobic affinity which can absorb organic materials into clay spacing. In this case, the d spacing of intercalated MMT could be further expanded. Thus, the hydrophobic affinity and layered expandable characteristics make organoclay could be used as an organo-container to absorb and store organic materials. In this research, the organic modified MMT was treated as an organo-container to absorb crude oil and paraffin. For the crude oil absorption, the organoclay was intercalated by poly(oxyalkylene) amines. To compare with mono-amine or di-amine with different molecular weight, the highest crude oil absorption efficiency is the organoclay which was intercalated by mono-amine and the efficacy is up to 15 folds weight over organoclay. Except for the high absorption efficiency, there is another unique characteristic, lower critical solubility temperature (LCST) of these organoclays. The poly(oxyalkylene) ammonium salts intercalated organoclay could be homogeneously dispersed with crude oil and water under lower temperature, and aggregated into lumps and clearly separated from water phase that the crude oil could be removed easily. Furthermore, we used n-Octadecyl amine (ODA) to modify MMT and used to absorb crude oil. The absorption efficiency of ODA/MMT is 6 folds over organoclay. The ODA/MMT would be self-aggregated after absorbing crude oil and clearly separated from water phase under ambient temperature. The most important thing is that the ODA/MMT could be recovered from toluene extraction which the crude oil can be removed without destroying the structure of ODA/MMT. The ODA/MMT could be reused for several times with stably performance and the recovery was up to 90%. Thus, the ODA/MMT can be used as an environment friendly materials to remedy the water contaminant. In the third section, we used ODA/MMT as a heat storage organo-container. The ODA/MMT was used to absorb octadecane, a kind of phase change material (PCM). The absorption efficiency is 5.6 folds over organoclay when using 1.0 CEC intercalated ODA/MMT. The phase transition temperature of octadecane is about 25－29 °C, and the shape of octadecane could be fixed when absorbing by ODA/MMT. Moreover, the enthalpy transition of ODA/MMT/Paraffin reaches to 100%. Hence, the ODA modified organoclay is an excellent organo-container which can be used as a heat storing material.