Ultra-pure hydrogen is required in applications rang-ing

Chapter 14, Problem 14.28

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Ultra-pure hydrogen is required in applications rang-ing from the manufacturing of semiconductors topowering fuel cells. The crystalline structure of palla-dium allows only the transfer of atomic hydrogen (H)through its thickness, and therefore palladium mem-branes are used to filter hydrogen from contaminatedstreams containing mixtures of hydrogen and othergases. Hydrogen molecules (H2) are first adsorbedonto the palladiums surface and are then dissociatedinto atoms (H), which subsequently diffuse throughthe metal. The H atoms recombine on the opposite sideof the membrane, forming pure H2. The surface concen-tration of H takes the form CH?KspH20.5, where Ks?1.4 kmol/m3?bar0.5is known as Sieverts constant.Con-sider an industrial hydrogen purifier consisting of anarray of palladium tubes with one tube end connectedto a collector plenum and the other end closed. Thetube bank is inserted into a shell. Impure H2at T?600 K, p?15 bars, xH2?0.85 is introduced into theshell while pure H2at p?6 bars, T?600 K isextracted through the tubes. Determine the productionrate of pure hydrogen (kg/h) for N?100 tubes whichare of inside diameter Di?1.6 mm, wall thicknesst?75 ?m, and length L?80 mm. The mass diffusiv-ity of hydrogen (H) in palladium at 600 K is approxi-mately DAB7 ?? 0? m2/s.