本實驗以一系列自製的矽分子篩作為線上濃縮揮發性有機污染物(volatile organic compounds,VOCs)的媒介，測試其吸附捕捉的特性，並與商業化碳分子篩比較。 以各種分子篩捕捉一內含21種大小不同VOCs的自製標準氣體，經由過篩選擇吸附後，接著熱脫附至GC-FID，可以GC層析圖譜具體表現分子篩之間孔洞特性的差異，此自製標準氣體所含物種範圍為C2~C12的VOCs。而以行之多年的商業化碳多重床(Carbotrap+Carboxen1000+ Carboxen1003)作為捕捉大範圍VOCs濃縮材料的基準，與之比較，1003撘配MCM-48製成二重床可以有效彌補中孔徑MCM-48對於C3~C5這些較小分子捕捉效率不佳的缺點。而自製微孔徑的矽分子篩ZSM-5能夠以單一材料對C3~C12的VOCs大範圍的捕捉，在吸附量上接近商業化碳分子篩，熱脫附所需溫度比碳分子篩低，經過耐熱實驗，也顯示矽骨幹分子篩耐熱性比碳分子篩高，所以其使用壽命更長，應用範圍更廣，惟此自製ZSM-5含有Al金屬在熱脫附時會使某些VOCs發生觸媒反應，使標準氣體的成分改變，造成分析結果略差於碳分子篩，但是自製ZSM-5的結構特性提供未來開發VOCs線上濃縮吸附材料一個明確的指引方向。 This research investigates the use of a series of self-made silica molecular sieves as in-line trapping media for the enrichment of ambient volatile organic compounds (VOCs). A standard mixture containing 22 VOCs from C2 to C12 is employed as the target compounds to be captured by sorbents and thermally desorbed into gas chromatograph/flame ionization detection (GC/FID) for assessment. A combination of 3 commercially available carbon based molecular sieves are employed which are either individually or collectively formulated into multi-sorbent bed which the silica materials can reference to. While the mesoporous silica MCM-41 is know to only capture heavier VOCs (> C8), the combination of a microporous carbon sorbent (Carboxen 1003) and MCM-41 provide an expected complementary merit by fullfilling the entire sorption range. Despite the obvious merit, the thermally liable carbon sorbents still cause a concern in terms of the lifetime of the in-line trap. In light of this deficiency, several micro-porous silica molecular sieves are explored as possible candidates due to their suitable pore sizes and high thermal stability. Among these selections, ZSM-5, an Al/Si = 67 mixed silica, shows an extremely satisfactory trapping efficiency across the entire VOC range. This single compound can meet the criteria of e.g., full range trapping, high thermal stability, low thermal desorption temperatures, fine mechanical properties, etc. The only drawback with ZSM-5 lies in its catalytic activity which has been shown to alter the integrity of certain VOC composition. For instance, 1-butene, can be catalytically converted into other butene isomers during thermal desorption. Nevertheless, the above mentioned structural advantages of ZSM-5 provide clear guidelines for further improving the existing ZSM-5 to a metal-free silica with similar porous properties.
