(727c) The Characterization of Supported Molten Metal Membranes for Hydrogen Separation
Hydrogen separation membranes such as Pd, Pd alloys are being applied in the reformers as they prompt the reaction conversion and lower the working temperature which makes it more energy efficient, compact and highly selective towards hydrogen as compared to the traditional technologies. However, they are expensive, sensitive to poisons, and lack adequate durability. Therefore, the search for novel and cheaper materials to replace palladium is ongoing. We are, thus, developing entirely novel supported molten metal membranes (SMMMs) based on low melting metals and their alloys for their inherent ability to avoid sintering, hydrogen embrittlement, and thermal mismatch between the membrane and the support, and potentially their higher permeability. Since this molten metal as hydrogen separation was never investigated before, therefore, the attempt of hydrogen permeability characterization was performed via experiments and theoretical calculations. Also in this presentation, we will describe the promise of SMMM and the pitfalls we have so far encountered in this quest.
Before membrane characterizing, an understanding of developing thin and stable SMMMs is required. To build SMMMs, the wettability and reactivity between porous support and the molten metals are two major issues. This is a fine balance since some chemical interaction between the liquid metal and the support is necessary for adequate wetting, while too much of it dooms the membrane. Therefore, one of the goals of this work was to find a porous support material with both good wettability and stability. Dense Ga molten metal membrane was made using previously screened materials and showed that the hydrogen permeance of molten Ga is comparable to Pd membrane at 500-550. Since there is the lacking of Ga hydrogen permeance in the literature as well as its hydrogen solubility which makes it difficult to verify the credibility of experimental measurements. The attempt of calculating Ga hydrogen permeability using Margules type equations was also made in this work for comparison.