Solved: Iso-octane is produced in the reaction of

Chapter 4, Problem 4.82

(choose chapter or problem)

Iso-octane is produced in the reaction of isobutane and butylene in an emulsion with concentrated sulfuric acid: i-C4H10 C4H8 ! i-C8H18 DISTILLATION COLUMN Product DECANTER REACTOR Emulsion recycle Acid recycle Fresh feed Isobutane recycle n-Butane Iso-octane The fresh feed to the process flows at a rate of 60,000 kg/h and contains 25.0 mole% isobutane, 25.0% butylene, and 50.0% n-butane, which is chemically inert in this process. The fresh feed combines with three separate recycle streams, as shown in the flowchart, and the combined stream enters the reactor. Essentially all of the butylene fed to the reactor is consumed. A portion of the reactor effluent is recycled to the reactor inlet and the remainder passes to a decanter, in which the aqueous (sulfuric acid) and hydrocarbon phases are allowed to separate. The acid is recycled to the reactor, and the hydrocarbons pass to a distillation column. 207 WEBC04 06/04/2015 20:35:2 Page 208 The overhead from the column contains iso-octane and n-butane, and the bottoms product, which is recycled to the reactor, contains only isobutane. The stream entering the reactor contains 200 moles of isobutane per mole of butylene, and 2 kg of 91 wt% H2SO4(aq) per kg of hydrocarbon. The stream obtained by combining the fresh feed and isobutane recycle contains 5.0 moles of isobutane per mole of butylene. You wish to determine the molar flow rates (kmol/h) of each component of the fresh feed, the product stream, and the emulsion, isobutane, and acid recycle streams. (a) Draw and completely label a flowchart of the process, perform degree-of-freedom analyses on the overall process and subprocesses, and write the equations you would use to determine the required flow rates. (Suggestion: Begin by calculating the total molar flow rate of the fresh feed stream.) (b) Perform the calculations. (c) List the assumptions in this problem that are not likely to be fully satisfied in practice.