# UPTU Previous Year Question Papers

## Mass Transfer-2

1.  Attempt any four parts of the following :

(a) A mixture of A and B forms ideal solution. The pure component vapor pressures of A and B are given by

In P^at = 14.27- 2945 A                        t +224

In PgUt = 14.20 – 2973 B                       t + 209

where P^at, P^at = vapour pressures of A and B in kPa

t = temperatures in °C If the draw point of a certain mixture of A and B is 100°C at a total pressure of 101.325 kPa, find the composition of the first liquid drop that forms.

(b) Define relative volatility. Show that the relative volatility of an ideal binary mixture is equal to the ratio pf vapour pressures of components.

(c) A mixture of 50 mol water and 50 mol benzene is boiling at 101.325 kPa. Liquid benzene is immiscible in liquid water. Determine the boiling point of the mixture and the composition of the vapour. Which compound will first be removed completely from the still ?

 Temperature °C 35.3 52.7 72.6 80.1 Vapor pressure of water, mm Hg 43 106 260 356 Vapour pressure of benzene, mm Hg 150 300 600 760

(d) Derive the following equation for differential distillation of constant relative volatility (a)

In F x, W x W = a Zn F(1-xf) W(l-xw) where f = moles of feed W = moles of residual liquid xF, xw = mole fractions of more volatile component in feed and residual liquid, respectively.

(e) What is meant by positive and negative deviations from Raoult’s law and how is sign of the integral heat of solution related to positive and megative deviations from Raoult’s law ?

(f)  An open kettle contains 100 mol of an aqueous solution of methanol containing 1 mol % methanol at the bubble point. Steam is continuously sparged into kettle. The entering steam agitates the kettle contents so that they are always of uniform composition. The vapor produced which is always in equilibrium with the liquid, is led away. Assume adiabatic operation. For the concentrations encountered it may be assumed that the enthalpy of steam and evolved vapour are the same, the enthalpy of liquid in the kettle is essentially constant, and the relative volatility is constant at 7.6. Calculate the quantity of steam to be introduced in order to reduce the concentration of methanol in the kettle contents to 0.1 mol %.

2. Attempt any two parts of the following :

(a) Show that the minimum reflux ratio required to distill a binary mixture of constant relative volatility at as its bubble point in a continuous fractionating column is given by  xD a(l-xD) xF 1 – xF where a = relative volatility Xp, xD = mole fractions of more volatine component in feed and distillate, respectively.

(b) An equimolal mixture of A ar|d B with a relative volatility of 2.1 is to be separated into a distillate product with 98 percent A, a bottom product with 3 percent A and an intermediate liquid product which is 80 percent A and has 40 percent of the A fed.

(1) Derive the equation for the operating line in the middle section of the column and sketch the three operating lines on a Mecabse-Thiele diagram.

(2) Calculate the amounts of each product per 100 mol of feed and determine the minimum reflux rate if the feed is liquid at the boiling point.

(c) The following information is available from the records of a binary distillation column.

Feed =180 kmol/h (60% vaporized)

Distillate = 100 kmol/h with 0.98 mole fraction of more volatile component Reboiler steam demand= 420 kg/h R a-1

Latent heat of column liquid = 3 /10^ J/mol Latent heat of steam used in reboiler = 2200 kJ/kg Calculate the operating reflux ratio and the composition of vapour entering that plate in the enriching, section from which liquid overflow contains 0.7 mole fraction of the more volatile component.

3. Attempt any two parts of the following :

(a) The equilibrium data for the distribution of solute C between solvent A and the extracting solvent B is given below : In a countercurrent contact operation 10 kg/s of the feed containing 20 wt.% C in A is treated with pure solvent so as to reduce the solute concentration to 5wt.%. Calculate the solvent rate for operation with 2.5 times the minimum solvent rate.

(b) What is tie line ? Explain the difference between single stage, multistage cocurrent, multistage cross current and multistage counter current extractions with their relative merits and demerits.

(c)    It is proposed to extract acetic acid from aqueous solution using ethyl acetate as the solvent. It is known that ethyl acetate and acetic acid are completely miscible. If the initial composition of aqueous solution is given and the ratio of the rate of aqueous solution to the rate of solvent stream is fixed at a certain value, explain by making a sketch of a ternary, equilibrium diagram how you would proceed to determine the number of countercurrent contacts necessary for effecting the extraction if the raffmate liquor composition is specified for the above case.

4. Attempt any two parts of the following :

(a) A countercurrent multistage extraction system is to treat 50000 kg/h of wet sliced sugarbeets with fresh water as solvent. The beets have the following analysis.

Component                      Mass fraction

Water                                    0.48

Pulp                                       0.40

Sugar                                     0.12

The strong solution leaving the system is to contain 0.15 mass fraction sugar and 97 percent of the sugar in the sliced beets is to be recovered.

Determine the number of extraction stages required assuming equilibrium between underflow and overflow from each stage, if each kg of dry pulp retains 3 kg of solution.

(b) A seashore sand contains 85% insoluble sand, 12% salt and 3% water. 1000 kg of this mixture is to be extracted so that after drying it will contain only 0.2% salt. How many washings with 2000kg batches of pure water are required to give the desired purity ? The sand contains 0.5 kg of water per kg of insoluble sand.

(c) Define and explain leaching. Differentiate between moving-bed leaching and dispersed solid leaching.

5. Attempt any four parts of the following :

(a) What is adsorption isotherm ? Give equations for Langmuir and Freundlich adsorption isotherms.