Mass Transfer Operations I — Winter 2022

Classify the mass transfer operations based on direct contact of two immiscible phases with examples.

Explain Fick’s law in brief and prove D = D AB BA

Atube 1 cm in inside diameter that is 20 cm long is filled with CO and H22 at a total pressure of 2 atm at 0°C. The diffusion coefficient of the CO –2 Hsystem under these conditions is 0.275 cm2/s. If the partial pressure of2 CO is 1.5 atm at one end of the tube and 0.5 atm at the other end, determine2 flux for: i) steady state equimolar counter diffusion, ii) steady state counter diffusion where N = -0.75 N , iii) steady state diffusion of CO through B A stagnant H2

Define: Elusion, Solutropic solutions, Plait point

Deduce an equation for molar flux for diffusion of component Athrough non-diffusing component Bin case of steady state molecular diffusion for liquid phase.

Enlist the tower internals for packed tower and explain their roles. Discuss about few types of packing. Also compare Tray tower with Packed tower.

With neat sketch, explain spray tower and sparged vessel as G-L equipment in brief.

At high temperature, two pair partially soluble liquid system behaves like one pair partially soluble liquid system. Agree or not? Support the answer.

Explain various equilibrium curves with reference to leaching.

If 8000 kg/h of an acetic acid (C)- water (A) solution, containing 30% acid is to be counter currently extracted with isopropyl ether (B) to reduce the acid concentration to 2% in the solvent-free raffinate product, determine (a) the minimum amount of solvent which can be used and (b) the number of theoretical stages if 20 000 kg/h of solvent is used. Data is given as (% wt): Aqueous phase Ether phase Acetic acid water Ether Acetic acid water Ether 0.69 98.1 1.2 0.18 0.5 99.3 1.41 97.1 1.5 0.37 0.7 98.9 2.89 95.5 1.6 0.79 0.8 98.4 6.42 91.7 1.9 1.93 1 97.1 13.3 84.4 2.3 4.82 1.9 93.3 25.5 71.1 3.4 11.4 3.9 84.7 36.7 58.9 4.4 21.6 6.9 71.5 44.3 45.1 10.6 31.1 10.8 58.1 46.3 37.1 16.5 36.2 15.1 48.71

Cite few industrial examples of liquid-liquid extraction with appropriate solvent. Discuss selectivity as selection parameter for solvent and for single stage, find distribution coefficient if feed, pure solvent and extract amounts are 500, 400 and 600 kg respectively. Feed and extract has 45% and 30 % solute respectively.

Explain how pre-treatment and agitation affect the leaching operation? Also justify the statement “High temperature is not always preferable for leaching.”

Explain absorption and stripping by stating appropriate industrial examples. Also differentiate between physical and chemical absorption.

Discuss selection criteria for solvent in liquid-liquid extraction.

State various theories of mass transfer co-efficient and discuss film theory at length. Also derive its equation.

With reference to absorption, discuss minimum liquid to gas ratio.

Brief about the working of rotating disc contactor.

Discuss interphase mass transfer. Explain in detail about Overall and individual mass transfer coefficients. Also derive interrelationship between these.

Define: Absorption factor, HETP, NTU

Define super saturation and discuss Mier’s theory.

Agas stream (1 kmol/s) containing 90 mol% Nand 10% CO is passed22 through an absorber, in which pure and cool water at 5 ⁰C is used as a solvent. The operation is assumed to be isothermal at 5 ⁰C and isobaric at 10 atm. The liquid flow rate is 1.5 times the minimum liquid flow rate. Determine the number of equilibrium stages required to absorb 92 % of CO . Equilibrium relation is y = 87.6x.2

With reference to crystallization, explain nucleation and crystal grown.

The solubility of copper sulphate in water at 80 °Cis 55 g CuSO per 1004 g of water and that at 30 °Cis 25 g CuSO / 100 g water. One ton of4 saturated solution at 80 °Cis slowly cooled down to 30 °C. 5 % water is lost by evaporation. Determine weight of crystals and mother liquor. Hydrated form is represented as CuSO ·5H O.42

Agas containing 4 % cyclohexane and rest inert has to be treated with non volatile absorption oil in a packed tower. It is required to remove 98 % of cyclohexane of the gas. The feed solvent is free from cyclohexane. If the feed gas rate is 80 kmol/hour, calculate the minimum solvent rate. Equilibrium relation is given Y = 0.2X / (1+0.8X)