Mass transfer quiz 2015

MASS TRANSFER OPERATIONS QUIZ

Q. 1 A spherical naphthalene ball of 2 mm diameter is subliming very slowly in stagnant air at 25 ⁰C. The change in the size of the ball during the sublimation can be neglected. The diffusivity of naphthalene in air at 25 ⁰C is 1.1×10^-6 m²/s. The value of mass transfer coefficient is B×10^-3 m/s, where B (up to one decimal place) is......

Q. 2.Identify the WRONG statement amongst the following

Steam distillation is used for mixtures that are immiscible with water.
Vacuum distillation is used for mixtures that are miscible with water.
Steam distillation is used for mixtures that are miscible with water
Vacuum distillation columns have larger diameters as compared to atmospheric columns for the same throughput.

Q. 3 For binary mixture of components A and B, N_A, and N_B denote the total molar fluxes of components A and B, respectively. J_A and J_B are the corresponding molar diffusive fluxes. Which of the following is true for equimolar counter-diffusion in the binary mixture?

N_A + N_B =0 and J_A + J_B ≠ 0
N_A + N_B ≠0 and J_A + J_B = 0
N_A + N_B ≠0 and J_A + J_B ≠ 0
N_A + N_B =0 and J_A + J_B = 0

Q. 4 A binary mixture of components (1) and (2) forms an azeotrope at 130 ⁰C and X₁= 0.3. The liquid phase non-ideality is described by ln γ₁ = Ax₂ ² and γ₂ = Ax₁ ² , where γ₁ ,γ₂ are the activity coefficients, and x₁, x₂ are the liquid phase mole fractions. For both components, the fugacity coefficients, are 0.9 at the azeotropic composition. Saturated vapor pressure at 130 ⁰C are P₁ ^sat= 70 bar and P₂ ^sat= 30 bar. The total pressure in bars for the above azeotropic system(up to two decimal Places) is......

Q. 5 Benzene is removed from air by absorbing it in a non-volatile wash-oil at 100kPa in a counter-current gas absorber. Gas flow rate is 100mol/min, which includes 2 mol/min of benzene. The flow rate of wash-oil is 50mol/min. Vapor pressure of benzene at the column conditions is 50kPa. Benzene forms an ideal solution with the wash-oil and the column is operating at steady state. Gas phase can be assumed to follow ideal gas law. Neglect the change in molar flow rates of liquid and gas phases inside the column. For the process, the value of the absorption factor(up to two decimal places) is......

Q. 6 Adsorption on activated carbon is to be used for reducing phenol concentration in wastewater from 0.04mol/l to 0.008mol/l. The adsorption isotherm at the operating temperature can be expressed as q=0.025C^1/3,where q is the phenol concentration in solid (mol/g solid) and C is the phenol concentration in water(mol/l). The minimum amount of solid (in grams) required per liter of wastewater ( up to one decimal place) is ......

Q. 7 A binary feed consisting of 25 mol% liquid and 75mol% vapour is separated in a staged distillation column. The mole fraction of the more volatile component in the distillate product is 0.95. The molar flow rate of distillate is 50% of the feed flow rate and the McCable-Thiele method can be used to analyze the column. The q-line intersects the operating line of the enriching section at (0.35,0.5) on the x-y diagram. The slope of the stripping section operating line (up to one decimal place) is......

Q. 8 Consider a steady state mass transfer process between well-mixed liquid and vapour phases of a binary mixture comprising of components A and B. The mole fractions of component A in The bulk liquid(xA) and bulk vapour(yA) phases are 0.36 and 0.16, respectively. The mass transfer coefficients for component A in liquid and vapour phases are 0.1mol/(m².s) and 0.05mol/( m².s) respectively. The Vapour-liquid equilibrium can be approximated as y_A=2x_A,for x_A less than 0.4. The mole fraction of A in the liquid at the interface (up to two decimal places) is ......

Q. 9.A Multi stage, counter-current liquid-liquid extractor is used to separate solute C form a binary mixture(F) of A and C using solvent B. Pure solvent B is recovered from the raffinate R by distillation, as shown in the schematic diagram below.

Locations of different mixtures for this process are indicated on the triangular diagram below P is the solvent-free raffinate, E is the extract, F is the feed and D is the difference point from which the mass balance lines originate. The line PB intersects the binodal curve at U and T. The lines PD and FB intersect the binodal at V and W respectively.

The raffinate coming out of the extractor is represented in the diagram by the point:

T
U
V
W