R05320801-mass-transfer-operations-ii

Set No. 1

Code No: R05320801

III B.Tech Supplimentary Examinations, Aug/Sep 2008 MASS TRANSFER OPERATIONS-II (Chemical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) What is the effect of pressure on packed tower height. (b) Is there any role molecular weight of solvent in absorption operation? (c) Why absorption operation may not be considered as isothermal operation? (d) Write short notes on ideal solutions. 2. Show that Z= HtoL NtoL for stripper.

[4+4+4+4] [16]

3. A feed solution containing 4000kg of water and 20kg of acetic acid is to be extracted with benzene solvent to recover 80% acetic acid by weight. The equilibrium data is: S.No x′ = gm acetic acid per kg water x′ = gm acetic acid per kg benzene 1 0.920 1.020 2 1.140 1.620 3 1.525 2.910 4 2.04 5.35 5 3.29 20.10 6 5.23 36.0 Calculate: (a) The number of cross - current stages required, if 1000 kg of benzene per stage is used and (b) The concentration of acetic acid in the combined extract.

[16]

4. Discuss continuous countercurrent multistage extraction and explain how it is shown on a triangular chart. Indicate how the quantities and compositions of extract and raffinate are computed. For a given separation indicate how the number of equilibrium stages required is found. [16] 5. (a) Explain the concept of HETP and HTU. (b) With the help of a neat sketch explain the construction and working of centrifugal extractor. [8+8] 6. (a) Discuss in detail about Adsorption equilibrium. (b) Explain about adsorption Hysterisis. (c) For adsorption from dilute liquid solutions in stagewise countercurrent operations, where the Freundlich equation describes the adsorption equilibrium, derive analytical expressions in terms of n,m, Yo and YN , for the minimum adsorbent/solvent ratio when fresh adsorbent is used. [4+4+8] 1 of 2

Set No. 1

Code No: R05320801

7. (a) Discuss fixed bed adsorption and its application in food industry. (b) Apply Freundlich equation for multi stage cross-current adsorption operation and derive (Y1 /Y2 )1/n - 1/n (Y0 /Y1 ) = 1-Yn [8+8] 8. Ground nut oil is extracted from granulated ground nut meal in a counter-current multi-batch arrangement using ether as solvent. The solids charge contains 0.35 kg oil/kg exhausted meal and it is desired to obtain a 90% oil recovery. How many theoretical stages are required if 50 kg ether is used per 100 kg untreated solids. The entrainment data are as below. [16] Concentration of oil 0.1 0.2 0.3 0.4 0.5 0.6 0.67 kg oil/kg solution Entrainment: 0.28 0.34 0.40 0.47 0.55 0.66 0.8 Kg solution/ Kg extracted meal ⋆⋆⋆⋆⋆

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Set No. 2

Code No: R05320801

III B.Tech Supplimentary Examinations, Aug/Sep 2008 MASS TRANSFER OPERATIONS-II (Chemical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Give the Kremser brown equation for the number of the theoretical plates in an absorption tower taking absorption factor as unity. What are the assumptions made in obtaining this equation? (b) Explain with suitable example about mass transfer with chemical reaction for absorption. [10+6] 2. An acetone-air mixture containing 0.025 mole fraction acetone has its acetone reduced to 1% of this value by counter current absorption in a packed tower. Gas flow rate of pure air is 1kg/m2 sec and water is1.6 kg/m2 . For this system the equilibrium diagram is given by Y=1.75X/(1-0.75X) where Y is kg moles of acetone /kg mole of air in gas phase and X is kg moles of acetone per kg mole of water in liquid phase. What is the tower required if height of overall transfer unit is HtoG =50 cm. [16] 3. Draw a neat sketch of multistage cross current extraction unit and make the material balance by using solvent free coordinates? Also explain how to estimate number of stages for given problem. [16] 4. (a) Write short notes on fractional extraction with the help of flow chart. (b) Explain the procedure for the estimation of number of stages for counter current extraction of immiscible liquids. [8+8] 5. An aqueous solution contains 25% acetone by weight together with a small amount of an undesired contaminant. For the purpose of later process, it is necessary to have the acetone dissolved in water without impurity. To accomplish this, the solution will be extracted counter currently with trichloroethane, which extracts the acetone but not impurity. The extract will then be counter currently extracted with pure water in a second extractor to give the desired product water solution and the recovered solvent will be returned to the first extractor. It is required to obtained 98% of the acetone in the final product. Water and trichloroethane are insoluble over the acetone concentration range involved, and the distribution coefficient (kg acetone /kg trichloroethnae)/(kg acetone /kg water) =1.65 = constant. (a) What is the largest concentration of acetone possible in the recovered solvent? (b) If the recovered solvent contains 0.005 kg acetone/kg trichloroethane, if 1 kg of trichloroethane /kg of water is used in the first extractor and if the packed height of the column in both the extractors is same what concentration of acetone in the final product will result? [16] 1 of 2

Set No. 2

Code No: R05320801

6. (a) Discuss briefly the difference between Vander Walls adsorption and Chemisorption. (b) An aqueous solution containing a valuable solute is colored by small amounts of an impurity which is to be removed by a single stage contact with the absorbent carbon, which adsorbs insignificant amount of principle solute. Color intensity is proportional to the concentration of colored substance. It is desired to reduce color to 10Y* =8.91 × 10−5 X 1.66 Where Y* = equilibrium color, units/kg of solution X = adsorbate concentration, units/kg carbon. [6+10] 7. (a) Write short notes on Ion Exchange. (b) A batch of water containing residual chlorine from a treating proess, at a concentration 12 ppm, is to be treated with activated carbon at 250 C to reduce the chlorine concentration to 0.5 ppm. The carbon consists of 30-mesh granules, density = 561 kg/m3 (35 lb/ft3 ) = mass of particle/gross volume of particle. Adsorbate diffusional resistance is expected to be small relative to that in the liquid. The equilibrium distribution coefficient = c*/X = 0.80 (kg Cl2 /m3 liquid)/(kgCl2 /kgC) = 0.05 (kg Cl2 /ft3 liquid)/(kg Cl2 /kg C). [8+8] 8. (a) Write a note on preparation of solids for leaching. (b) Write a note on various types of equilibrium diagrams for a solid-liquid system for leaching operation. (c) With a neat sketch, explain the working and operation of Bollman extractor. [4+6+6] ⋆⋆⋆⋆⋆

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Set No. 3

Code No: R05320801

III B.Tech Supplimentary Examinations, Aug/Sep 2008 MASS TRANSFER OPERATIONS-II (Chemical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) In absorption, what is a solute? (b) Can absorption be accompanied by a temperature change? Why? (c) What is the difference between physical absorption and chemical (reactive) absorption? Explain with suitable examples and also mention advantages and disadvantages. [4+4+8] 2. A soluble gas is to be absorbed in a counter current packed tower using a solute free liquid. The equilibrium relation ship is given by ye= mx. Obtain an expression for the number transfer units if the inlet and exit gas compositions are y1 and y2 respectively. If a recovery of 90% of the solute is required and the liquid rate is 1.5 times the minimum calculate the number of transfer units by graphical methods. [16] 3. (a) The coefficient of distribution of the solute C between two mutually immiscible liquids A (carrier) and B (solvent) is K=yc /xc =0.75. Draw the equilibrium curve using the right triangular coordinates. (b) Define selectionry. What are the paremeters to be considered for selection of a silrent in liquid-liquid extraction. [8+8] 4. A feed of one thousand kilograms aqueous solution of pyridine per hour (50% by mass) is to be extracted with pure benzene to reduce the solute content in the raffinate to 2%. Determine the number of ideal stages required if the solvent rate is 1.3 times the minimum. [16] Equilibrium data Water layer Pyridine, mass% Benzene, mass% 1.17 0.0 3.55 0.0 7.39 0.0 13.46 0.15 22.78 0.25 32.15 0.44 42.47 2.38 48.87 3.99 49.82 4.28 56.07 19.56 1 of 3

Set No. 3

Code No: R05320801 Benzene layer Pyridine, mass% Benzene, mass% 3.28 94.54 9.75 87.46 18.35 79.49 26.99 71.31 31.42 66.46 34.32 64.48 36.85 59.35 39.45 56.43 39.27 55.72 48.39 40.05 5. (a) Explain the concept of HETP and HTU.

(b) With the help of a neat sketch explain the construction and working of centrifugal extractor. [8+8] 6. (a) Explain about various Industrial adsorbents. (b) Prove that for crosscurrent two-stage treatment of liquid solutions by contact filtration, when the adsorption isotherm is linear, the least total adsorbent results if the amounts used in each stage are equal. [6+10] 7. The sulfur content of an oil is to be reduced by percolation through a bed of adsorbent clay. Laboratory tests with the clay and oil in a representative percolation filter show the following instantaneous sulfur contents of the effluent oil as function of the total oil passing through the filter 10 m3 oil / kg clay 0 1.752 3.504 8.760 17.52 35.04 52.56 70.08 % Sulfur 0.011 0.020 0.041 0.067 0.0935 0.118 0.126 0.129 Assume that the specific gravity of the oil is unchanged during the percolating. The untreated oil has a sulfur content of 0.134%, and a product containing 0.090% sulfur is desired. (a) If the effluent from the filter is composited, what yield of satisfactory product can be obtained per kg of clay? (b) If the effluent from the filter is continually and immediately withdrawn and blended with just sufficient untreated oil to give desired sulfur content in the blend, what quantity of product can be obtained per kg of clay? [16] 8. Ground nut oil is extracted from granulated ground nut meal in a counter-current multi-batch arrangement using ether as solvent. The solids charge contains 0.35 kg oil/kg exhausted meal and it is desired to obtain a 90% oil recovery. How many theoretical stages are required if 50 kg ether is used per 100 kg untreated solids.

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Set No. 3

Code No: R05320801 The entrainment data are as below. Concentration of oil 0.1 0.2 0.3 kg oil/kg solution Entrainment: 0.28 0.34 0.40 Kg solution/ Kg extracted meal ⋆⋆⋆⋆⋆

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[16] 0.4

0.5

0.6

0.67

0.47

0.55 0.66 0.8

Set No. 4

Code No: R05320801

III B.Tech Supplimentary Examinations, Aug/Sep 2008 MASS TRANSFER OPERATIONS-II (Chemical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Write short notes on ideal and non-ideal solutions. (b) What is absorption factor? How is this related to stripping factor? (c) Discuss what factors should be considered in the selection of a solvent for absorption. [6+4+6] 2. A soluble gas is to be absorbed in a counter current packed tower using a solute free liquid. The equilibrium relation ship is given by ye = mx. Obtain an expression for the number transfer units if the inlet and exit gas compositions are y1 and y2 respectively. If a recovery of 90% of the solute is required and the liquid rate is 1.5 times the minimum calculate the number of transfer units by analytical methods. [16] 3. (a) Give a few examples of potential applications of solvent extraction for wastewater treatment. (b) Explain the representation of different co-ordinate systems in liquid-liquid extration with respect to solvent free basis.. (c) What is mixture rule.

[4+8+4]

4. Explain in detail for the estimation of number of stages for continuous counter current extraction with out reflux using rectangular graph sheets and also write the relevant equations. [16] 5. A 25% solution of dioxane in water is to be continuously extracted at a rate of 1000 kg/hr in a counter current fashion with benzene to remove 95% of the dioxane. What is the minimum solvent required? If 900 kg/hr of solvent is used, estimate the number of transfer units, NtoR . the equilibrium data was given below: Wt.% of dioxane in water : 5.1 18.9 25.2 Wt.% of dioxane in benzene : 5.2 22.5 32.0 [16] 6. A solution of washed, raw cane sugar, 48% sucrose by weight, is colored by the presence of small quantities of impurities. It is to be decolorized using an adsorptive solid in a contact filtration plant. The data for an equilibrium adsorption isotherm were obtained by adding various amount of the carbon to separate batches of the original solution and observing the equilibrium color reached in each case. The data, with the quantity of adsorbent expressed on the basis of the sugar content of the solution, are as follows:

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Set No. 4

Code No: R05320801

Kg carbon/kg dry sugar 0 0.005 0.01 0.015 0.02 0.03 Color removed, % 0 47 70 83 90 95 The original solution haws a color concentration of 20, measured on an arbitrary scale, and it is desired to reduce the color to 2.5% of its original value. (a) Convert the equilibrium data to Y* = color units /kg sugar, X= color units/kg carbon. Do they follow the Freundlich equation? If so, what are the equation constants? (b) Calculate the necessary dosage of fresh carbon, per 1000 kg of solution, for a single-stage process. [16] 7. (a) Explain the working of Higgin‘s contactor with a neat sketch. (b) Distinguish between fluidized and teeter beds.

[8+8]

8. (a) For a multistage counter current leaching operation show how by graphical method and composition of raffinate, extract cnbe obtained along with number of stages. (b) Write note on various types of equilibrium diagrams for a solid liquid systems fopr leaching operation. [8+8] ⋆⋆⋆⋆⋆

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