光催化環氧化丙烯之研究

Abstract

近年來有許多學者致力於環氧化反應的研究，然而在大多的反應情形中，都伴隨著廢水廢熱問題，且產物需要經由分離再純化，經濟效益也不高，且最大的問題在於反應形成環氧丙烷的轉化率和選擇率都仍然很低。從經濟效益和環境保護的觀點來看，氧氣是相當理想的氧化劑，可用來跟丙烯選擇性反應生成環氧丙烷，已經有一些研究致力於發展這樣的乾淨製程，藉由提供光能給光觸媒材料，便可輔助氣相原料間的直接氧化反應產生環氧丙烷，這是相當具有前景的化學品生產途徑。 本研究目標在研究不同種類的光觸媒於室溫下進行光催化環氧反應，希望能提升目標產物環氧丙烷(PO)的選擇率。負載金的TiO2和釩的SiO2光觸媒是分別由光沉積法和含浸法製得，TS-1則是經由水熱結晶法製備。在多組實驗結果中，最佳反應條件為使用TS-1觸媒，在50oC一大氣壓下照射強度1W/cm2 之UVA紫外光，進料流速3000ml/h，反應四小時可得PO產率28.75μmol.g-cat−1.h−1，且PO選擇率達43.2%。此外，在相同條件下若使用Au(0.1 wt%)/TS-1觸媒，可進一步觀察到反應生成PO的平均產率能維持在24-26 μmol.g-cat–1.h–1達15小時，失活情形大為減少。

In recent years, there has been great research focus on epoxidation; however, in most case, we face the disposal, separation, and economic problems. In addition, the propylene conversion and the selectivity to propylene oxide (PO) are still very low. Molecular oxygen is an ideal oxidant for a selective epoxidation of propylene from the environmental and economic viewpoints. A major research effort has been made in the development of alternative direct epoxidation processes for the production of propylene oxide. The aim is to develop a process for the direct gas-phase photo epoxidation. With the aid of light energy and heterogeneous photocatalyst, it is promising for chemicals production. Therefore, this research explores the photo selective catalytic epoxidation of propylene via O2. The key is using photo-energy to achieve higher epoxidation products selectivity at room temperature over series of photocatalysts. The catalysts used in this research are the supported gold on TiO2, vanadium loaded SiO2 and titanium silicalite (TS-1) prepared by photo-deposition method, impregnation method and hydrothermal crystallization of gel, respectively. The most favorable photocatalytic epoxidation, with 28.75μmol.g-cat−1.h−1 highest PO specific rate and 43.2% PO selectivity obtained on stream after 4 hrs, was TS-1 photocatalysts under the 3,000 ml.h−1, 1W/cm2 UVA irradiation and very mild conditions (50oC and atmospheric pressure). In addition, the epoxidation was conducted over Au(0.1 wt%)/TS-1 with significant improvement on the lifetime and still achieved ~ 24-26 μmol.g-cat–1.h–1 PO specific rate on stream after 15 hrs.