# Ultra-pure hydrogen is required in applications ranging from the manufacturing of semiconductors to powering fuel cells. The crystalline structure of palladium allows only the transfer of atomic hydrogen (H) through its thickness, and therefore palladium membranes are used to filter hydrogen from contaminated streams containing mixtures of hydrogen and other gases. Hydrogen molecules (H 2 ) are first adsorbed onto

Chapter 14, Problems #27

Ultra-pure hydrogen is required in applications ranging from the manufacturing of semiconductors to powering fuel cells. The crystalline structure of palladium allows only the transfer of atomic hydrogen (H) through its thickness, and therefore palladium membranes are used to filter hydrogen from contaminated streams containing mixtures of hydrogen and other gases. Hydrogen molecules (H2) are first adsorbed onto the palladium's surface and are then dissociated into atoms (H), which subsequently diffuse through the metal. The H atoms recombine on the opposite side of the membrane, forming pure H2. The surface concentration of H takes the form CH = KspH20.5, where Ks ≈ 1.4k mol/m3 ∙ bar 0.5 is known as Sievert's constant. Consider an industrial hydrogen purifier consisting of an array of palladium tubes with one tube end connected to a collector plenum and the other end closed. The tube bank is inserted into a shell. Impure H2 at T = 600 K, p = 15 bars, XH2 = 0.85 is introduced into the shell while pure H2 at p = 6 bars, T = 600 K is extracted through the tubes. Determine the production rate of pure hydrogen (kg/h) for N = 100 tubes which are of inside diameter Di = 1.6 mm, wall thickness t = 75μm, and length L = 80 mm. The mass diffusivity of hydrogen (H) in palladium at 600 K is approximately DAB = 7 x 10-9 m2/s.