) Problem 18D8 (parts a, b, c, d), page 905 , with the following modifications: feed is 6.0 vol \% helium and 94.0 vol \% hydrogen at 4.0 tm. The active portion of the membrane is 1.4 micron thick. Permeate pressure is 0.9atm. D8. A perfectly mixed membrane module is used to concentrate helium in retentate. Feed is 5.0vol% helium and 95.0vol% hydrogen at 5.0atm. Membrane is natural rubber of the type used by Nakagawa (Table 18-2), and operation is at 25.0C. The active portion of membrane is 1.0 micron thick. Permeate pressure is 1.0atm. Assume gases are ideal. a. If ypHe=0.025, what are cut and yrHe ? b. If =0.75, what are ypHe and yrHe ? c. If yrHe=0.06, what are cut and ypHe ? d. For part a, what membrane area is required for a feed of 100.0m3(STP)/h