Questions and Answers of Separation Process Principles Chemical

A colored substance (B) is removed from a mineral oil by adsorption with clay particles at 25C. The original oil has a color index of 200 units/100 kg oil, while the decolorized oil must have an
A vapor mixture of equal volumes NH3 and N2 is contacted at 20οC and 1 atm (760 torr) with water to absorb some of the NH3. If 14 m3 of this mixture is contacted with 10 m3 of water, calculate the %
Fifty mol% propylene in propane is separated with silica gel. The products are to be 90 mol% propylene and 75 mol% propane. If 1,000 lb of silica gel/lbmol of feed gas is used, can the desired
A liquid of 30 mol% toluene, 40 mol% ethylbenzene, and 30 mol % water is subjected to a continuous flash distillation at 0.5 atm. Assuming that mixtures of ethylbenzene and toluene obey Raoult’s
Devise an interlinked cascade like Figure 5.2e, but with three columns for separating a four-component feed into four products.
What is a separation cascade? What is a hybrid system?
What is the difference between a countercurrent and a crosscurrent cascade?
What is the limitation of a single-section cascade? Does a two-section cascade overcome this limitation?
What is an interlinked system of stages?
Which is more efficient, a crosscurrent cascade or a countercurrent cascade?
Under what conditions can a countercurrent cascade achieve complete extraction?
Why is a two-section cascade used for distillation?
(a) When rinsing clothes, would it be more efficient to divide the water and rinse several times, or should one use all the water in one rinse? Explain. (b) Devise a washing machine that gives
What is a group method of calculation?
An aqueous acetic acid solution containing 6.0 mol/L of acid is extracted with chloroform at 25οC to recover the acid (B) from chloroform- insoluble impurities in the water. The water (A) and
What is the Kremser method? To what type of separation operations is it applicable? What are the major assumptions of the method?
What is an absorption factor? What is a stripping factor?
In distillation, what is meant by reflux, boilup, rectification section, and stripping section?
Under what conditions is a membrane cascade of multiple stages in series necessary?
Why are hybrid systems often considered?
Give an example of a hybrid system that involves recycle.
Explain how a distillation–crystallization hybrid system works for a binary mixture that exhibits both an azeotrope and a eutectic.
When solving a separation problem, are the number and kind of specifications obvious? If not, how can the required number of specifications be determined?
Solve Example 5.3 with the addition of a heat exchanger at each stage so as to maintain isothermal operation of the absorber at: (a) 125οF and (b) 150οF. What is the effect of
Can the degrees of freedom be determined for a hybrid system? If so, what is the easiest way to do it?
In absorption, the absorbent is stripped to an extent that depends on its K-value. In stripping, the stripping agent is absorbed to an extent depending on its K-value. In Figure 6.1, it is seen that
What is the difference between physical absorption and chemical (reactive) absorption?
What is the difference between an equilibrium-based and a rate-based calculation method?
What is a trayed tower? What is a packed column?
Bubble-cap trays were widely used in towers prior to the 1950s. Today sieve and valve trays are favored. However, bubble-cap trays are still specified for operations that require very high turndown
What are the three most common types of openings in trays for the passage of vapor? Which of the three is rarely specified for new installations?
In a trayed tower, what is meant by flooding and weeping? What are the two types of flooding, and which is more common?
Volatile organic compounds (VOCs) can be removed from water effluents by stripping with steam or air. Alternatively, the VOCs can be removed by carbon adsorption. The U.S. Environmental Protection
What is the difference between random and structured packings?
For what conditions is a packed column favored over a trayed tower?
In general, why should the operating pressure be high and the operating temperature be low for an absorber, and the opposite for a stripper?
For a given recovery of a key component in an absorber or stripper, does a minimum absorbent or stripping agent flow rate exist for a tower or column with an infinite number of equilibrium stages?
What is the difference between an operating line and an equilibrium curve?
What is a reasonable value for the optimal absorption factor when designing an absorber? Does that same value apply to the optimal stripping factor when designing a stripper?
When stepping off stages on an Y–X plot for an absorber or a stripper, does the process start and stop with the operating line or the equilibrium curve?
Why do longer liquid flow paths across a tray give higher stage efficiencies?
What is the difference between the Murphree tray and point efficiencies?
What is meant by turndown ratio? What type of tray has the best turndown ratio? Which tray the worst?
Fuel cell automotive systems are being considered that will require hydrogen of 95% purity. A refinery stream of 800,000 scfm (at 32οF, 1 atm), containing 72.5% H2, 25% CH4, and 2.5% C2H6, is
What are the three contributing factors to the vapor pressure drop across a tray?
The absorber of Examples 6.1 and 6.4 is being scaled up by a factor of 15, so a column with an 11.5-ft diameter will be needed. Because of the 30% efficiency for the original tray, a new design has
What is the effective diffusivity?
Why is diffusion in crystalline solids much slower than diffusion in amorphous solids?
What is Fick’s second law of diffusion? How does it compare to Fourier’s second law of heat conduction?
Molecular diffusion in gases, liquids, and solids ranges from slow to extremely slow. What is the best way to increase the rate of mass transfer in fluids? What is the best way to increase the rate
What is the defining equation for a mass-transfer coefficient? How does it differ from Fick’s law? How is it analogous to Newton’s law of cooling?
For laminar flow, can expressions for the mass-transfer coefficient be determined from theory using Fick’s law? If so, how?
What is the difference between Reynolds analogy and the Chilton–Colburn analogy? Which is more useful?
For mass transfer across a phase interface, what is the difference between the film, penetration, and surface-renewal theories, particularly with respect to the dependence on diffusivity?
What is the two-film theory of Whitman? Is equilibrium assumed to exist at the interface of two phases?
What advantages do the Maxwell–Stefan relations provide for multicomponent mixtures containing charged biomolecules, in comparison with Fick’s law?
How do transport parameters and coefficients obtained from the Maxwell–Stefan relations compare with corresponding values resulting from Fick’s law?
A cooling-tower packing was tested in a small column. At two points in the column, 0.7 ft apart, the data below apply. Calculate the overall volumetric mass-transfer coefficient Kya that can be used
Estimate the steady-state concentration profile for an aqueous solution of cytochrome C(12 x 103 Da; xA0 = 1 X 10 -6 VA = 0.75 cm3/g) subjected to a centrifugal
Two large bulbs, A and B, containing mixtures of H2, N2, and CO2 at 1 atm and 35οC are separated by an 8.6-cm capillary. Determine the quasi-steady-state fluxes of the three species for the
What are the limitations of the Gibbs phase rule? How can it be extended?
When a liquid and a vapor are in physical equilibrium, why is the vapor at its dew point and the liquid at its bubble point?
What is the difference between a homogeneous and a heterogeneous azeotrope
What two types of equations are used for single equilibrium stage calculations?
A liquid mixture containing 25 mol% benzene and 75 mol% ethyl alcohol, in which components are miscible in all proportions, is heated at a constant pressure of 1 atm from 60C to 90C. Using the
How do intensive and extensive variables differ?
What is meant by the number of degrees of freedom?
Why do azeotropes limit the degree of separation achievable in a distillation operation?
What is the difference between an isothermal and an adiabatic flash?
Why is the isothermal-flash calculation so important?
When a binary feed is contacted with a solvent to form two equilibriumliquid phases, which is the extract and which the raffinate?
Why is the right-triangular diagram easier to construct and read than an equilateral-triangular diagram? What is, perhaps, the only advantage of the latter diagram?
What are the conditions for an ideal, equilibrium leaching stage?
In crystallization, what is a eutectic? What is mother liquor? What are hydrates?
The stream below is flashed adiabatically across a valve. Conditions upstream are 250F and 500 psia, and downstream are 300 psia. Compute using a process simulator the: (a) Phase condition
What is the difference between adsorbent and adsorbate?
The feed below enters a distillation column as saturated liquid at 1.72 MPa. Calculate the bubble-point temperature using the K-values of Figure 2.4.
In adsorption, why are adsorbents having a microporous structure desirable?
Given the isothermal-flash algorithm and Table 4.4, propose algorithms for the following flash calculations, assuming that expressions for K-values and enthalpies are available. Given hr, P hr,
In Figure 4.40, a mixture is heated and expanded before entering a distillation column. Calculate, using a process simulator, mole percent vapor and vapor and liquid mole fractions at locations
Does a solid have a vapor pressure?
A feed of 13,500 kg/h is 8 wt% acetic acid (B) in water (A). Removal of acetic acid is to be by liquid–liquid extraction at 25C. The raffinate is to contain 1 wt% acetic acid. The following four
What is the maximum number of phases that can exist at physical equilibrium for a given number of components?
In a rigorous vapor–liquid–liquid equilibrium calculation (the so-called three-phase flash), is it necessary to consider all possible phase conditions, i.e., all-liquid, all-vapor,
A mixture of chloroform (CHCl3) and acetic acid at 18οC and 1 atm (101.3 kPa) is extracted with water to recover the acid. Fortyfive kg of 35 wt% CHCl3 and 65 wt% acid is treated with 22.75 kg of
A total of 6,000 lb/h of a liquid solution of 40 wt% benzene in naphthalene at 50οC is cooled to 15οC. Use Figure 4.22 to obtain the weight of crystals and the flow rate and composition of mother
What is the secondary dew point? Is there also a secondary bubble point?
A liquid mixture consisting of 100 kmol of 60 mol% benzene, 25 mol% toluene, and 15 mol% o-xylene is flashed at 1 atm and 100C. Assuming ideal solutions, use vapor pressure data from a process
The feed stream in the table below is to be separated into four nearly pure products. None of the components is corrosive and, based on the boiling points, none of the three separations is difficult.
A solution at 107οC contains 50 mol% water (W) and 50 mol% formic acid (F). Using (2-72) with vapor pressure data and the van Laar equation with AWF = -0.2935 and AFW = 0.2757: (a) Compute the
The ABE biochemical process makes acetone, n-butanol, and ethanol by an anaerobic, submerged, batch fermentation at 30C of corn kernels, using a strain of the bacterium Clostridia acetobutylicum.
Which of the following K-value expressions are rigorous? For the nonrigorous expressions, cite the assumptions. (a) K (b) K (c) K (d) K Ki (e) K (f) _K (g) K = Φ/Φιν = Φ/Φιν = dit =
Prove that, in a triangular diagram where each vertex represents a pure component, the composition of the system at any point inside the triangle is proportional to the length of the respective
Give examples of separation operations used for the steps in a bioprocess.
In an energy balance, what are the two most common references (datums) used for enthalpy and entropy? Does one have an advantage over the other?
How does availability differ from Gibbs free energy?
Why is fugacity used in place of chemical potential to determine phase equilibria? Who invented fugacity?
How is the K-value for vapor–liquid equilibria defined?
How is the distribution coefficient for a liquid–liquid mixture defined?
What are the definitions of relative volatility and relative selectivity?

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