氟化蒙脫石固體酸特性與其應用於生質柴油催化之研究

Abstract

固體酸觸媒活性與固體酸本身之酸特性息息相關，因此如何改善固體酸酸特性確實是一重要課題，氟化法即是改良固體酸酸性其中之一種方法，因氟元素具有較大陰電性，可在固體酸內發生吸引電子行為造成固體酸表面酸性提昇。本研究目的在於以氫氟酸氟化法改質蒙脫石，提高並改善蒙脫石固體酸酸特性，並試圖與一般鹽酸、溴酸、硫酸與磷酸酸處理蒙脫石做比較。以EDX (Energy Dispersive X-ray Spectrometer)分析蒙脫石組成之改變，以XRD (X-ray diffraction)分析蒙脫石結構之改變，以SEM (Scanning Electron Microscope)觀察蒙脫表面型態之改變，以氨氣預先吸附固體酸後DRIFT (diffuse-reflectance infrared Fourier-transform)光譜分析固體酸酸特性。EDX分析結果顯示隨著氫氟酸量或者濃度之增加，蒙脫石含氟量隨之增加，其中以50.0%氫氟酸處理之蒙脫石含氟量最高，可達43.2 wt%。固體酸酸性分析結果顯示，氫氟酸氟化法改質之蒙脫石隨著含氟量之增加固體酸酸性隨之提升，表現在Brønsted與Lewis酸特性峰面積積分之增加；一般酸處理只會提升蒙脫石Brønsted酸性。隨著氫氟酸量或濃度之增加蒙脫石層狀結構有被破壞之情形發生，在XRD分析結果顯示蒙脫石(001)、(002) 與(005)特性峰有顯著下降，在SEM分析結果顯示蒙脫石經過腐蝕表面形態變得較為破碎。初步以改質蒙脫石催化黃豆油熱裂解實驗顯示，加入改質蒙脫石有助於黃豆油熱裂解，所得之熱裂解產物產率增加，且產物碳數較低，熱裂解油性質接近生質柴油。

Catalytic activity of solid acid is strongly associated with its acidity of solid acid. Apparently, how to promote the acidity of solid acid is the major issue to enhance it’s practical application. Here, the fluorination method was used to augment the acidity. Due to larger electronegativity of the fluorine atom has, it will attract electron in the solid acid, causing the improvement of surface acidity. This study tended to use hydrofluoric acid via the fluorination method to improve the solid acid acidity of montmorillonite (MMT). This study also compared with other modified MMT treated with hydrochloric acid, hydrobromic acid, sulfuric acid, and phosphoric acid for the feasibility assessments. To reach the goal, EDX (Energy Dispersive X-ray Spectrometer) was used to analyze changes in compositions of MMT as well as related properties. For practical uses in diverse fields, XRD (X-ray diffraction) analysis showed herein the structural change of MMT. The characteristics in morphology of MMT was inspected by SEM (Scanning Electron Microscope). Solid acid pre-adsorbed ammonia gas was applied to analyze the acidity of solid acid with DRIFT (diffuse-reflectance infrared Fourier-transform) spectra. The result of EDX showed that the fluorine content of MMT was increased with an increase of hydrofluoric acid concentration. Among all, the highest fluorine content of MMT was 43.2 wt% for the case treated with 50.0% hydrofluoric acid. The analysis of solid acid acidity also showed that the acidity of solid acid was increased with the fluorine content of hydrofluoric acid modified MMT, indicating rises in integrated area of Brønsted and Lewis peak. Comparison with general acid treated MMT, this study could improve Brønsted acidity of MMT. When the hydrofluoric acid amount or concentration increased, the original layer structure of MMT was gradually destructed. Peaks (001), (002), and (005) peaks of MMT in XRD diagram became progressively weaker. In addition, after etching surface morphology of MMT became lost as indicated in scanning electron micrograph. Preliminarily pyrolysis of soybean oil with modified MMT catalyst showed that with aid of the modified MMT catalyst the yield of pyrolysis product increased, carbon number of product could be lower, and the properties of pyrolysed oil was close to that of biodiesel.