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5.21: Untitled Page 118

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  • Chapter 5

    will reduce the salt concentration in the organic stream to 0.1, 0.01 and 0.001

    times the original salt concentration. The aqueous and organic phases are to be considered completely immiscible, i.e., only salt is transferred between the two phases. In addition, the amount of material transferred is so small that the volumetric flow rates of the two streams can be considered constant.

    5‐25. In this problem, we examine the process of recovering fission materials from spent nuclear fuel rods. This is usually referred to as reprocessing of the fuel to recover plutonium (Pu) and the active isotope of uranium ( U



    Reprocessing can be done by separation of the soluble isotope nitrates from a solution in nitric acid by a solvent such as a 30% solution of tributyl phosphate (TBP) in dodecane ( C H ) in which the nitrates are preferentially soluble.



    Industrial reprocessing of nuclear fuels is done by countercurrent operation of many liquid‐liquid separation stages. These separation stages consist of well-mixed contacting tanks, where UO (NO ) is exchanged between two 2

    3 2

    immiscible liquid phases, and separation tanks, where the organic and aqueous phases are separated. A schematic of a separation stage is shown in Figure 5.25a.

    Figure 5.25a. Liquid‐liquid separation stage for reprocessing In this process an aqueous solution of uranil nitrate [ UO ( NO ) ] is one of the 2

    3 2

    feed streams to the separation stage, and the mass flow rate of the aqueous feed phase is, m

      400 kg/h . The second feed stream is an organic solution of tributyl 1

    phosphate (TBP) in dodecane ( C H ) which we assume to be a single 12


    component. The organic and inorganic phases are assumed to be immiscible, thus only the uranil nitrate is transferred from one stream to the other. The


    Two‐Phase Systems & Equilibrium Stages


    process specifications are indicated in Figure 5.25b, and for this problem it is the mass flow rates that you are asked to determine.

    Figure 5.25b. Specified stream variables

    5‐26. A gas stream consisting of air with a small amount of acetone is purified by contacting with a water stream in the contacting device illustrated in Figure 5‐7.

    The inlet gas stream (Stream #2) contains one percent acetone and has a molar flow rate of 30 kmol/h. The molar flow rate of the pure water stream (Stream #1) is 90 kmol/h. The process operates at constant temperature and pressure, and the process equilibrium relation is given by

    Process Equilibrium Relation:

    ( y )


    ( x )


    A 3


    A 4

    where K


    2 53 . Assume that water and air are immiscible and that the molar eq,A

    flow rates entering and leaving the equilibrium stage are constant. In this problem you are asked to

    (i) Determine the absorption factor for this equilibrium stage.

    (ii) Determine the mole fractions of acetone in the two exit streams.

    5‐27. The concept of an equilibrium stage is a very useful tool for the design of multi‐component separations, and a typical equilibrium stage for a distillation column is shown in Figure 5.27. A liquid stream, S1, flowing downward encounters a vapor stream, S2, flowing upward. We assume that the vapor