Raoult's Law and Distillation
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Raoult's Law and Distillation

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Questions and Answers

Why should the solvent used in liquid extraction not have high latent heat of vaporisation?

  • It cannot be recovered by distillation.
  • It will decompose while recovering by distillation.
  • The pressure drop and hence the pumping cost will be very high.
  • Its recovery cost by distillation may be prohibitatively high. (correct)

    • What is the order of liquid diffusivity in cm2/second?

  • 0.01
  • 0.1
  • >1
  • 10^-5 to 10^-6 (correct)

    • What is the effect on the pressure drop in a packed tower being irrigated with liquid compared to a dry packed tower?

  • It is unpredictable
  • It is less
  • It remains the same
  • It is more (correct)

    • Which of the following is an example of a maximum boiling azeotrope?

    <p>Water-hydrochloric acid</p> Signup and view all the answers

    In option (ii) as compared to option (i), which of the following is true?

    <p>More number of trays are required and the residue composition is more dilute in methanol</p> Signup and view all the answers

    What is the law followed by the partial pressure distribution of an ideal gas diffusing through another stagnant ideal gas at steady state?

    <p>Linear</p> Signup and view all the answers

    Why is it necessary to consider the composition of the residue in liquid extraction?

    <p>To determine the composition of the extract</p> Signup and view all the answers

    What is the effect of using a solvent with high latent heat of vaporization in liquid extraction?

    <p>It makes the recovery cost by distillation prohibitively high</p> Signup and view all the answers

    What type of resistance controls the liquid phase in wet bulb?

    <p>Liquid phase resistance</p> Signup and view all the answers

    What happens to the separation efficiency as the reflux ratio decreases?

    <p>It becomes less efficient</p> Signup and view all the answers

    What is the relationship between drying time and moisture content within the constant rate period?

    <p>Directly proportional</p> Signup and view all the answers

    Which equation applies to diffusivities in liquids?

    <p>Wilke and Chang equation</p> Signup and view all the answers

    What is the main difference between a packed tower and a plate tower for a particular mass transfer operation?

    <p>Packed towers have a higher mass transfer efficiency</p> Signup and view all the answers

    Which equipment is not used for gas dispersion?

    <p>Heat exchangers</p> Signup and view all the answers

    What happens to the composition of the flash vapor when Raoult's law is obeyed?

    <p>It changes with changes in feed composition</p> Signup and view all the answers

    What is the effect of increasing the reflux ratio on the number of plates in a distillation column?

    <p>The number of plates increases</p> Signup and view all the answers

    Raoult's law is applicable to which of the following types of solutions?

    <p>Non-ideal solutions only</p> Signup and view all the answers

    In distillation columns, the number of bubble caps per tray primarily depends on which factor?

    <p>Allowable liquid velocity</p> Signup and view all the answers

    What does a sharp decrease in pressure drop indicate in a distillation column?

    <p>Flooding in the distillation column</p> Signup and view all the answers

    Which of the following methods is more accurate for determining theoretical stages in non-ideal binary systems?

    <p>Ponchan-Savarit method</p> Signup and view all the answers

    In distillation, what does the overhead product usually contain?

    <p>Two components</p> Signup and view all the answers

    What components are used in determining relative volatility when Raoult's and Dalton's laws are obeyed?

    <p>Vapour pressure of component A to that of component B</p> Signup and view all the answers

    Which type of distillation is suitable for separating components with very close boiling temperatures?

    <p>Fractional distillation</p> Signup and view all the answers

    Which factor is not critical in determining the efficiency of a distillation column?

    <p>Temperature of the feed</p> Signup and view all the answers

    Which color of paint would heat up the maximum by radiation from the sun?

    <p>Black paint</p> Signup and view all the answers

    What device is typically used to separate liquid droplets from vapor in evaporators?

    <p>Entrainment separator</p> Signup and view all the answers

    What does the Prandtl number represent?

    <p>Thermal diffusivity to mass diffusivity</p> Signup and view all the answers

    How is the fouling factor for a heat exchanger defined?

    <p>U1 - U2</p> Signup and view all the answers

    Which term defines the effect of elevation on the boiling point of a solution?

    <p>Liquid head</p> Signup and view all the answers

    What is the relationship represented by conductance?

    <p>x/KA</p> Signup and view all the answers

    Which number describes the ratio involving mass and thermal diffusivity?

    <p>Peclet number</p> Signup and view all the answers

    What determines the impact of temperature on solution boiling points?

    <p>Liquid head</p> Signup and view all the answers

    What is the range for the higher shell side heat transfer coefficient in a multipass shell and tube heat exchanger?

    <p>10 to 100</p> Signup and view all the answers

    The LMTD correction factor for a multipass shell and tube heat exchanger is always:

    <p>&gt;1</p> Signup and view all the answers

    Which of the following must be true for heat transfer to a fluid flowing through a tube?

    <p>Suspended solids content is negligible</p> Signup and view all the answers

    To find the mass of moisture removed when drying 1000 kg of wet solids from 60% to 20% moisture, which calculation is correct?

    <p>400 kg</p> Signup and view all the answers

    Which method is best for the concentration of highly concentrated solutions?

    <p>Vacuum evaporation</p> Signup and view all the answers

    What should be the phase relationship in a plane wall made of two different solids at steady state?

    <p>Both solids reach an equal temperature</p> Signup and view all the answers

    For fluids flowing through a heat exchanger, which exit condition typically indicates optimal heat transfer?

    <p>Exit fluid temperature &lt; wall temperature</p> Signup and view all the answers

    Which Graetz number condition implies that heat transfer may be limited in a flow scenario?

    <p>Graetz number &gt; 100</p> Signup and view all the answers

    Study Notes

    Raoult's Law and Distillation

    • Raoult's law pertains to all liquid solutions and non-volatile solute behaviors in ideal systems.
    • In distillation columns, the number of bubble caps on each tray is influenced by allowable liquid and gas velocities, as well as feed composition.
    • A sharp pressure drop in a distillation column indicates flooding, a sign of operational failure.

    Distillation Products

    • The overhead product in distillation typically contains two components, not just one.
    • Relative volatility in a binary system adheres to Raoult's and Dalton's laws, expressed as the ratio of vapor pressures of components.

    Diffusivity and Extraction

    • Liquid diffusivity is typically in the range of 10^-5 to 10^-6 cm²/second.
    • Solvents used in liquid extraction should have low latent heat of vaporization to minimize costs and risks during recovery.

    Packed vs. Plate Towers

    • Packed towers often provide higher heat transfer coefficients compared to plate towers during mass transfer operations.
    • The pressure drop in a packed tower with liquid irrigation is lower than in a dry packed tower.

    Drying Processes and Vaporization

    • The drying time during the constant rate period increases with the square root of the thickness of the solid.
    • For flash vaporization of a binary mixture, changing feed composition affects the outcome when Raoult's law is applicable.

    Heat Transfer and Exchange

    • The LMTD correction factor for a multipass shell and tube heat exchanger is always greater than one.
    • The Nusselt number relates heat transfer to fluid flow characteristics, indicating efficiency.

    Radiation and Fouling Factors

    • A black-painted tank absorbs maximum solar radiation, whereas white reflects it.
    • Fouling factors in heat exchangers are derived from the difference in heat transfer coefficients between dirty and clean surfaces.

    Conductance and Concentration Techniques

    • Conductance is calculated using thickness, heat flow area, and thermal conductivity parameters.
    • Vacuum evaporators are suitable for concentrating highly concentrated solutions due to their efficiency.

    Miscellaneous Concepts

    • The partial pressure distribution of an ideal gas diffusing through another gas follows exponential law behavior.
    • Prandtl number represents the ratio of mass diffusivity to thermal diffusivity, critical in assessing heat transfer performance.

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    Related Documents

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    Description

    This quiz deals with Raoult's Law and its application in different scenarios, including ideal and non-ideal solutions. It also touches on distillation and the comparison of methods used in it.

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