以國內外椰殼製備具中孔性高比表面積活性碳之程序技術

活性碳(AC)為一種多孔性吸附材料，因具有甚高的比表面積而有高吸附容量，這些獨特的孔洞結構使其去除有機污染物應用上扮演相當重要的功能。本研究選用本國農業廢棄物椰子殼(DCS)及外國椰子殼(FCS)為製備活性碳的起始原料，探討以絕氧碳化及CO2活化的方式生產具有高比表面積集中孔性活性碳之可行性，並了解經高溫處理對活性碳的物理特性的影響。研究結果顯示，活化溫度及活化時間是椰子活性碳產出高比表面積及中孔體積的重要因素，國內外椰子殼經過碳化溫度500℃所產出的焦炭，再經850℃活化1小時，可製得最高之比表面積分別是1,152 m2/g。而由等溫吸脫附曲線和真密度測量發現，椰殼衍製活性碳之孔洞性質(包括中孔性)呈現上升趨勢。這是因為木質纖維素的碳化產物和CO2之間的氣化反應導致。本研究使用電子顯微鏡(SEM)及能量分散光譜儀(EDS)觀察所製備的活性碳表面外觀結構及元素含量均符合活性碳之正常值。此外藉由甲烯藍之動力吸附實驗數據及其假二階模式分析得知，本研究合成之活性碳的吸附量優於商業化粒狀活性碳，可見國內椰殼經CO2氣體活化，所製得活性碳產品皆能達商業級的水準。可作為日後研究椰殼活性碳或其他農業廢棄物活性碳一個有利的參考數據。

關鍵字

椰子殼；活性碳；物理活化；中孔洞；吸附

並列摘要

Activated carbon (AC) is a porous adsorbent, which exhibits a high adsorption capacity due to its large specific surface area. These unique pore structures play a very important role in many different applications for removal of organic pollutants. The purpose of this study was to investigate the liability for a preparation of mesoporous ACs with high surface area from coconut shell through oxygen-free carbonization and CO2 physical activation, and to realize the influence of high- temperature treatments on the physical properties of resulting ACs. The results indicated that activation time and activation temperature are two key factors to influence the pore properties of resulting ACs. Furthermore, the results showed that the pore properties (including mesoporosity) of resultant AC products, obtained from nitrogen adsorption-desorption isotherm and true density measurements, were on an increasing trend as activation temperature and holding time increased. These findings were attributable to the gasification between lignocellulose-based char and CO2. According to the maximal Brunauer-Emmet-Teller (BET) surface area of 1,152 m2/g, the optimal activation conditions should be performed at 850°C for a holding time of 60 min, but will result in a low yield (about 3%). In addition, the textural structures and elemental compositions of resulting ACs were viewed using the scanning electron microscopy – energy dispersive X-ray spectroscopy (SEM-EDS) and elemental analysis, showing consistent results as described above. Using the adsorption kinetics of methylene blue by the pseudo-second order model, the adsorption capacities of resulting ACs are higher than those of commercial AC. Therefore, coconut shell through CO2 activation can produce mesoporous ACs, having a high potential for removal of organic pollutants from effluents. This study provides an opportunity for producing ACs from coconut shell and other agricultural residues.