製備複合鈀/陽極氧化鋁/多孔陶瓷結構作為氫氣分離膜應用

Abstract

本論文研究主要是複合膜結構（鈀/陽極氧化鋁/多孔陶瓷）的製備，得以再高溫環境下將氫氣和二氧化碳分離。而基材的選擇大多是選用多孔的陶瓷結構，當基材孔洞愈大時，氣體通透性較好，但所覆蓋在基材上的鈀合金所需厚度也愈大，最後的總通透量也隨之下降，於成本上也較高。而小孔洞的基材，雖然鈀合金所需的厚度較小，但在高溫時容易受流體黏滯力的影響，而且基材本身也有一些閉孔的結構，使得氣體通透性變差。而陽極氧化鋁可由電化學參數來達到控制孔徑大小、密度及厚度，但機械強度也較差。此實驗就是在在多孔陶瓷基材上進行陽極氧化處理，以得到兼具高通量與機械強度的基材。 在氣體測試的部分是使用氣相層析儀來進行，在室溫下以氦氣進行測漏，發現約有0.455 ( ml•cm2•min-1 )的漏氣狀況發生，而在後續的氫氣通量測試後，扣除從孔洞漏氣的量，在600 ℃還有0.612 ( ml•cm2•min-1 )的流量。在50％H2 - 50％CO2氣氛下測試一小時，流量僅剩0.286( ml•cm2•min-1 )，此是H2跟CO2競爭鈀金屬上的吸附位置所致。

This work is concerned with the fabrication of a composite membrane structure (Pd/alumina oxide/porous ceramic) that enables the separation of hydrogen from a mixture of hydrogen and carbon dioxide at elevated temperature. The porous ceramic containing a variety of pores is adopted as the substrate where thin layers of alumina oxide and Pd are deposited sequentially. Large pores in the ceramic substrate facilitate hydrogen transports but they require thick layers of Pd to cover those exposing pores which wastes Pd unnecessarily. Hence, a thin layer of aluminum is thermally deposited onto the porous ceramic substrate followed by an anodization treatment to form hexagonal-structured porous alumina oxide. This effectively reduces the diameter of the open pores that allows a thin Pd deposit to function. For permeability test, a gas chromatograph is employed to determine the amount for leakage and hydrogen permeation. At room temperature, the leakage is estimated at 0.455 ml• cm2•min-1. In contrast, the hydrogen flux after deducting the amount of leakage at 600 °C is around 0.612 ml•cm2•min-1. In addition, after 60 min of operation in 50％H2-50％CO2 atmosphere, the hydrogen flux is decreased to 0.286 ml•cm2•min-1. This notable reduction in hydrogen permeation is caused by the competing adsorption of H2 and CO2 that limits the effective Pd surface for hydrogen permeation.