觸媒填充床內微米至毫米尺度的微結構對乙烯進行氧氯化反應之影響

Abstract

本論文使用顯微電腦斷層以2.734 μm的解析度掃描圓環狀乙烯氧氯化觸媒(FOC, AKZO, *Akzo and Nobel merged as AkzoNobel in 1994; AkzoNobel’s catalyst division sold to Albemarle in 1999)，獲得觸媒內部的孔隙度分布情形，並使用計算流體力學(Computational Fluid Dynamics, CFD)計算觸媒內部結構於不同孔隙度下的滲透率。研究結果顯示觸媒內的孔隙度為徑向距離的函數，平均孔隙度為0.537；分析三方向的觸媒滲透率與孔隙度的關係，發現相同孔隙度下，徑向與切向滲透率的數值相近，而軸向滲透率較徑向與切向滲透率小，整體滲透率介於1E-13至1E-11 m2之間，以半對數直線型函數可良好描述滲透率與孔隙度的關係。 研究創建三種觸媒放置方向的單顆觸媒填充床模型，圓環狀觸媒之軸心與z軸夾角分別為0、45、90度，並使用離散元素法(Discrete Element Method, DEM)隨機堆疊生成14顆觸媒填充床。研究將顆粒解析毫米尺度CFD與觸媒內部微米結構滲透率結合，探討473 K及523 K下，單顆觸媒填充床於不同放置角度下及14顆觸媒填充床進行乙烯氧氯化反應的流態、熱傳、反應等物理化學現象。單顆觸媒填充模型中，0度放置模型在觸媒內有最大的平均流速，進料溫度為523 K下，乙烯氧氯化反應的反應速率約為473 K下的4.4倍。三種觸媒放置模型中，45度放置模型在觸媒內有最高的局部溫度及平均反應速率，在進料溫度為473 K下各為492.8 K及0.0293 kmol/m3-s，乙烯轉化率為2.53E-4。在14顆觸媒填充模型中，進料溫度為473 K下，反應器內14顆觸媒的平均反應速率為0.0269 kmol/m3-s，乙烯轉化率為2.20E-3。

The internal structure of a hollow cylindrical ethylene oxychlorination catalyst (FOC, AKZO, *Akzo and Nobel merged as AkzoNobel in 1994; AkzoNobel’s catalyst division sold to Albemarle in 1999) was obtained by micro-computed tomography scanning with a resolution of 2.734 μm. Computational Fluid Dynamics (CFD) is then used to calculate the permeability of the catalyst through the porosity distribution from these scanning images. The results show that the porosity in the catalyst is a function of the radial position, and the average porosity is 0.537. The overall permeability in the catalyst ranges from 1E-13 to 1E-11 m2. The relationship between the permeability and porosity can be well described by a semi-logarithmic linear function. In the location with the same porosity values, the radial and tangential permeability values are similar, and the axial permeability is smaller. Three catalyst orientations are studied in a single catalyst in reactor column model. The angles between the axis of the hollow cylindrical catalyst and the column z-axis are 0, 45, and 90 degrees. The 0-degree orientation model has the largest average flow rate within the catalyst. When the ethylene feeding temperature is 523 K, the oxychlorination reaction rate is 4.4 times larger than that using the feeding temperature of 473 K. When the ethylene feed temperature is 473 K, the 45-degree orientation model has the highest local temperature of 492.8 K and highest average reaction rate of 0.0293 kmol/m3-s. The conversion of the ethylene is 2.53E-4. Discrete Element Method (DEM) is used to create a 14-catalyst packed bed. Coupling the particle-resolved CFD and the catalyst’s permeability the average reaction rate of 14-catalyst in reactor model is 0.0269 kmol/m3-s and the conversion of ethylene is 2.20E-3 when the feed temperature is 473 K.