Cross Current Extraction Exercise 11
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Questions and Answers

In the separative absorption of a species from a gas by a liquid, the equilibrium line is represented by:

  • A zigzag line in the loading diagram
  • A curved line in the loading diagram
  • A straight line in the loading diagram (correct)
  • A parabolic line in the loading diagram

    • What does the balance line represent in the loading diagram?

  • The variation in the gas flow rate with respect to the liquid flow rate
  • The variation in pressure along the absorption column
  • The variation in the liquid flow rate with respect to the gas flow rate (correct)
  • The variation in temperature along the absorption column

    • What is the effect of a smaller height of the liquid stream on the theoretical number of separation stages?

  • The number of stages becomes undefined
  • The number of stages remains the same
  • The number of stages decreases
  • The number of stages increases (correct)

    • What happens when the balance and equilibrium lines intersect each other?

    <p>The number of theoretical stages becomes infinity</p> Signup and view all the answers

    What is a requirement for the washing liquid in the separative absorption process?

    <p>High solubility for species to be separated</p> Signup and view all the answers

    How can the loading of the washing liquid be calculated from the partial mass balance of ammonia?

    <p>$N_{H2O} \cdot (X_{in} - X_{out}) = N_{air} \cdot (Y_{in} - Y_{out})$</p> Signup and view all the answers

    What allows for the construction of the equilibrium line in separative absorption?

    <p>The given equilibrium data</p> Signup and view all the answers

    What does a smaller slope of the balance line indicate in the desorption process?

    <p>Smaller inert gas flow rates</p> Signup and view all the answers

    How can the number of theoretical stages be evaluated in separative absorption?

    <p>By calculating the ratio of liquid and gas streams</p> Signup and view all the answers

    What is represented by a straight line in the loading diagram?

    <p>Balance line</p> Signup and view all the answers

    In the context of cross current extraction, which property is NOT a requirement for the solvent?

    <p>High miscibility with the carrier phase B</p> Signup and view all the answers

    What is the purpose of extraction in the preparation of soil samples from armament sites?

    <p>Volume reduction for safety purposes</p> Signup and view all the answers

    Which statement accurately describes the role of extraction in bioseparation?

    <p>To carefully separate valuable materials by avoiding denaturation of proteins</p> Signup and view all the answers

    What is the key reason for using extraction in the concentration of metals in aqueous solutions in metallurgy?

    <p>To separate valuable metals from the aqueous solution</p> Signup and view all the answers

    Which scenario necessitates the use of extraction in thermal process engineering?

    <p>When decomposition at higher temperature makes distillation impractical</p> Signup and view all the answers

    In the context of cross-current extraction, what is the basis of Nernst's distribution theorem?

    <p>The selective transport of the solute to the solvent</p> Signup and view all the answers

    What is the key purpose of a multi-stage cross-flow system in cross-current extraction?

    <p>To ensure equilibrium between the raffinate and extract phases in each stage</p> Signup and view all the answers

    What factor determines the number of stages required in cross-current extraction?

    <p>The extent to which the raffinate phase should be free of acetone</p> Signup and view all the answers

    What does it mean when it is stated that 'the extract and raffinate phases are in equilibrium in each stage' in cross-current extraction?

    <p>The mass fractions of the extract phase remain constant in each stage</p> Signup and view all the answers

    What role does 1,1,2-trichloroethane play in the process of cross-current extraction?

    <p>Solvent that favors selective transport of solute A</p> Signup and view all the answers

    Study Notes

    Separative Absorption

    • The equilibrium line in the loading diagram represents the balance between the concentration of the species in the gas and liquid phases.
    • A smaller height of the liquid stream results in an increase in the theoretical number of separation stages.

    Balance and Equilibrium Lines

    • When the balance and equilibrium lines intersect, it indicates that the concentration of the species in the liquid phase is equal to the concentration of the species in the gas phase.

    Washing Liquid Requirements

    • The washing liquid in the separative absorption process must be free of the absorbed species.

    Loading Calculation

    • The loading of the washing liquid can be calculated from the partial mass balance of ammonia.

    Equilibrium Line Construction

    • The equilibrium line in separative absorption can be constructed using the Henry's law constant and the partial pressure of the species.

    Balance Line Slope

    • A smaller slope of the balance line in the desorption process indicates a faster desorption rate.

    Theoretical Stages Evaluation

    • The number of theoretical stages in separative absorption can be evaluated using the Kremser equation.

    Loading Diagram

    • A straight line in the loading diagram represents the equilibrium line.

    Cross-Current Extraction

    • In cross-current extraction, the solvent does not require to be miscible with the feed.
    • The purpose of extraction in the preparation of soil samples from armament sites is to separate and purify the analytes.
    • Extraction plays a crucial role in bioseparation as a separation technique to isolate and purify biomolecules.
    • The key reason for using extraction in the concentration of metals in aqueous solutions in metallurgy is to separate and purify the metals.
    • In thermal process engineering, extraction is necessary when a substance needs to be separated from a mixture based on differences in solubility or boiling point.
    • Nernst's distribution theorem is based on the distribution coefficient, which is the ratio of the concentrations of the species in the two phases.
    • A multi-stage cross-flow system in cross-current extraction is used to increase the separation efficiency.
    • The number of stages required in cross-current extraction is determined by the distribution coefficient and the flow rates of the phases.
    • When the extract and raffinate phases are in equilibrium in each stage, it means that the concentrations of the species in the two phases are equal.
    • 1,1,2-Trichloroethane is used as a solvent in cross-current extraction.

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    Description

    This exercise involves extracting a 50% aqueous acetone solution using pure 1,1,2-trichloroethane to achieve a raffinate phase with no more than 10 mol% acetone. The multi-stage cross-flow system with specified throughput and solvent usage requires determining the necessary stages and mass fractions of the extract phase.

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