Papers by Author: Isamu Yasuda

Abstract: The alloying effects of Pd on the hydrogen solubility and the resistance to hydrogen embrittlement are investigated for Nb-xmol%Pd-ymol%Zr (x=0~19; y=0, 1) alloys. The hydrogen solubility at 673 K is found to decrease with increasing Pd content in the alloys. Both pure Nb and Nb-Pd alloys possessed ductility in vacuum at 673 K. However, severe hydrogen embrittlement occurs in pure Nb when it is tested under the hydrogen pressure even as low as 0.01 MPa. In view of the small punch (SP) absorption energy, the addition of Pd into Nb improves the resistance to hydrogen embrittlement by decreasing the hydrogen solubility in the alloy, although brittle fracture is still observed in the Nb-15mol%Pd alloy tested under a hydrogen pressure of 0.015 MPa at 673 K.

Abstract: A membrane reformer is composed of a steam reformer equipped with palladium-based alloy modules in its catalyst bed, and can perform steam reforming reaction and hydrogen separation processes simultaneously, without shift converters and purification systems. It thus can be configured much more compactly and can provide much higher efficiency than the conventional technologies. We have manufactured and tested a world-largest scale membrane reformer with a rated hydrogen production capacity of 40 Nm3/h. The operation test has successfully been proceeding for over 3,000 hours in one of the hydrogen refueling stations in Tokyo, which has demonstrated the potential advantages of the membrane reformer: simple system configuration as benefited by single-step production of high-purity (99.999% level) hydrogen from natural gas, compactness and energy efficiency as high as 70 to 76% under both the rated and partial-load operating conditions. The system has thus been proved to give the highest efficiency in producing hydrogen from natural gas among various competing technologies. The paper will present the latest achievements and the future plan of the membrane reformer technology development.

Abstract: Niobium metal is one of the promising material for hydrogen purification because of its high hydrogen permeability. In order to design and develop a new palladium-free hydrogen permeable membrane, it is important to understand the effects of alloying elements on the hydrogen permeability through metals. However, to the niobium metal, the alloying effects still remain unclear. In the present study, using a DC-polarization technique under the diffusion limiting condition, the hydrogen permeability of Nb-5mol%M alloys were investigated in high precision at 573K. Here, M’s were 4d transition metals, Zr, Mo, Ru and Pd. The permeability of niobium is found to be varied with the addition of a small amount of alloying element. For example, the hydrogen permeability of niobium increases by the addition of Zr but decreases by the addition of Ru.