Set No: Code No: NR-210803 II-B.Tech I-Semester Supplementary Examinations May /June, 2004 MATERIAL AND ENERGY BALANCE (Chemical Engineering) Time: 3 hours Max. Marks: 80 Answer any FIVE questions All questions carry equal marks --1. What are the various methods employed for expressing composition of mixtures and solutions? Explain them giving examples.

b)

3. a) b)

Calculate the volume occupied by 13.6 kg of chlorine at a pressure 743 mm Hg and 21.1C. Calculate the weight of 3 cu.m of water vapor, measured at a pressure of 15.5 mm Hg and 23C.

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State Raoult’s law. What are its limitations? Estimate the vapor phase composition at 60C in equilibrium with a liquid mixture containing 40 mole% benzene and 60 mole% toluene. Also calculate the composition of the liquid mixture, which boils at 90C and 101.32 kPa. Vapor pressure data is given as:

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Temp. C Vapor pressure of Benzene, kPa Vaporpressure of toluene,kPa 60 51.3 18.7 90 135.05 54.4

A continuous drier is operated under such conditions that 115 kg of water are removed per hour from the stock being dried. The air enters the drier at 79.5oC and a pressure of 765 mm Hg. The dew point of the air is 4.5oC. The air emerges from the drier at 35°C, a pressure of 755 mm Hg and 90% relative humidity. Vapour pressure ofwater at 4.5oC is 6.1 mm Hg. (i) How many m3 of original air must be supplied per hour? (ii) How many m3 of air emerge from the drier per hour? 2000 kg of wet solids containing 70% solids by weight are fed to a tray drier where it is dried by hot air. The product finally obtained is found to contain 1% moisture by weight. Calculate : i) kg of water removed from wet solids (ii) kg of product obtained . b) An aqueous solution of pyridine containing 27% by weight of pyridine and 73% water is to be extracted with chlorobenzene. The feed and solvent are mixed well in a batch extractor and the mixture is then allowed to stand for phase separation. The extract phase contains 11% pyridine, 88.1% chlorobenzene and 0.9% water by weight. The raffinate phase contains 5% pyridine and 95% water by weight. Calculate : i) The quantities of the two phases (ii) The weight ratio of solvent to feed based on 100 kg feed. Contd…2

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Code No: NR-210803

.2.

Set No: 1

The orsat analysis of the flue gas from an oil fired furnace is CO2 8%, CO 3%, O2 4%, and N2 85% (by volume) . An analysis indicates that the oil contains 78% by weight carbon and the remainder being combustible hydrogen and moisture. Air enters at 300C and 101325 N/m2. Assuming the air to be dry calculate (a) The percent excess air used (b) The carbon hydrogen weight ratio in the fuel (c) The volume of air used per kg of oil fired (d) The kg of moisture in the flue gas per kg of oil fired

7.

Write notes on (a) Kopp's rule (c) Humid heat capacity of air

(b) Kistyakowsky equation (d) Clapeyron equation

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When benzene (liquid) is completely burnt to CO2 (gas) and H2O (liquid) the standard heat of combustion is –3263.5  103 kJ/kg mol. The standard heat of combustion of H2 (gas) to H2O (liquid) is –285.8  103 kJ/kg mol, that of carbon (solid) to CO2 (gas) is –393.3  103 kJ/kg mol. Calculate the standard heat of formation of liquid benzene at constant volume neglecting the volume of water formed and initial volume of benzene.

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Set No: Code No: NR-210803 II-B.Tech I-Semester Supplementary Examinations May /June, 2004 MATERIAL AND ENERGY BALANCE (Chemical Engineering) Time: 3 hours Max. Marks: 80 Answer any FIVE questions All questions carry equal marks --1. a) An aqueous solution of sulphuric acid has 36.8 mole percent H2SO4. The density of the solution at 20oC is 1.681 gm/cc. Express the concentration of the solution in the following terms: percentage of H2SO4 by weight, g-moles of H2SO4 per 100 gram of water, grams of H2SO4 per 100 cc solution at 20oC, normality. b) A gas mixture contains 20% CO2, 5% CO, 10% O2 and the rest N2 by volume. Calculate the composition of the gas mixture in weight percent and average molecular weight.

b)

3. a) b)

Write a brief note on Raoult’s law. Explain how to compute the entire vaporliquid equilibria for a binary mixture behaving ideally, using Raoult’s law. The following table gives the vapor pressures of pure hexane and pure heptane. 69 70 75 80 85 90 95 99.2 Temperature C VP Hexane mm Hg 760 780 915 1060 1225 1405 1577 1765 VP Heptane mm Hg 295 302 348 426 498 588 675 760 Assuming that the Raoult’s law is valid, use the above data to calculate for each of the above temperatures the mole per cent x of hexane in the liquid and the mole per cent y of hexane in the vapor, at a total pressure of 760 mm Hg. Discuss wet and dry bulb thermometry. Define wet bulb temperature and dry bulb temperature. The percent absolute humidity of air at 30 °C and a total pressure of 750 mm Hg is 20%. The vapor pressure of water vapor at 15.55 oC is 31.8 mm Hg. Calculate, (i) The percent relative humidity. (ii) The partial pressure of the water vapor in the air.

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It is desired to compress 4.536 kg of carbon dioxide to a volume of 0.5664 cu m. Calculate the pressure in atmospheres that is required at a temperature of 30 C, assuming the applicability of the ideal-gas law. Assuming the applicability of the ideal gas law, calculate the maximum temperature to which 4.536 kg of nitrogen, enclosed in a 0.849 cu m chamber, may be heated without the pressure exceeding 10.2 atmospheres.

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Code No: NR-210803

b)

Set No: 2

A dryer system handles 1000 kg/day of wet solids. The wet solids containing 50% solids and 50% water are fed to the first drier. From the first drier the product that comes out has 20% moisture. This is admitted to the second drier from which the product coming out has 2% moisture. Calculate i) the % of original water that is removed ii) The final weight of the product. Formaldehyde is produced from Methanol in a catalytic reactor by the reaction CH3OH  HCHO + H2. If the conversion of methanol is 65% calculate the required feed rate of methanol if the production rate of formaldehyde is 1000 kg/hr.

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.2.

Limestone containing (by weight) CaCO3 84.5%, MgCO3 11.5% and the rest inert is mixed with coke containing (by weight) 76% carbon 21% ash 3% moisture and is burnt in a kiln. The calcination of CaCO3 (CaCO3  CaO + CO2) is only 95% complete and that of MgCO3 (MgCO3  MgO +CO2) is 90%. The carbon in the coke is completely burnt to CO2. The furnace is fed with one kg of coke for every 5 kg of limestone. If 200 % excess air is used calculate a) The composition of lime leaving the furnace b) The composition of the flue gas leaving the furnace

7.

What is the final temperature when 800 kJ of heat are added to 10 mol of ethylene initially at 200 oC in a steady flow heat exchanger operated at atmospheric pressure Cp = 2.83 + 28.6 x 10-3T – 8.72 x 10-6T2.

8.

Discuss in detail about the effect of pressure and temperature on heat of reaction.

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Set No: Code No: NR-210803 II-B.Tech I-Semester Supplementary Examinations May /June, 2004 MATERIAL AND ENERGY BALANCE (Chemical Engineering) Time: 3 hours Max. Marks: 80 Answer any FIVE questions All questions carry equal marks --1. a) A mixture of gases with an average molecular weight 43 contains by volume 40% CO2, 20% CO, 5% O2 and rest an inert gas. What is the molecular weight of the inert gas? b) For a two-component mixture, prove mathematically that the compositions on mole basis and weight basis are the same only when their molecular weights are equal. Give an example of this case.

3. a)

b)

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Air is assumed to contain 79% nitrogen and 21% oxygen by volume. Calculate its density in grams per liter at a temperature of 21C and a pressure of 741mm Hg. It is desired to market oxygen in small cylinders having volumes of 0.01 m3 and each containing 0.4536 kg of oxygen. If the cylinders may be subjected to a maximum temperature of 49 C, calculate the pressure for which they must be designed, assuming the applicability of the ideal-gas law. Determine the boiling temperature of the benzene-water mixture using the following data given in table. The pressure maintained above the liquid surface is 0.9803 bar. Benzene and water may be treated essentially as immiscible. V.P. Benzene bar V.P. Water bar Temperature C 60 0.5133 0.1975 65 0.6053 0.2500 68 0.6711 0.2830 70 0.7238 0.3092

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Write short notes on (i) Dalton’s law (ii) Amagat’s law. Describe the humidity chart with its application. A mixture of air and benzene is found to have a 50% relative saturation at 27 °C at an absolute pressure of 110 kPa. What is the mole fraction of benzene in the air? The vapor pressure of benzene at 27 °C is 103.5 mm Hg.

5.

1000 kg /hr of a mixture containing equal parts by mass of benzene and toluene is distilled to get an overhead product containing 95% benzene (by weight). The flow rate of the bottom stream being 512 kg/hr calculate i) the percentage of toluene in the bottom product (by weight) ii) flow rate of the overhead product and its molar composition iii) molar percentage of benzene in the feed Contd…2

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Code No: NR-210803

Set No: 3

A producer gas made from coke has the following composition by volume CO 28% CO2 3.5% O2 0.5% N2 68% This gas is burned with such a quantity of air that the oxygen from the air is 20% in excess of the net oxygen required for complete combustion. If the combustion is 98% complete, calculate the weight and composition in volumetric per cent of the gaseous products formed per 100 kg of gas burned.

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.2.

In any biochemical processes, lactose is used as a nutrient, which is oxidized as follows: C12H22O11(s) + 12O2 (g)  12CO2(g) + 11H2O(l) The heat of combustion  Hc at 25oC is –5648.8 x 103 J/g mol. Calculate the heat of complete oxidation (combustion) at 37oC, which is the temperature of many biochemical reactions. The Cpm of solid lactose is 1.20 J/g.K, and the molecular weight is 342.3. Cpm of O2(g) = 29.38 J/g.K Cpm of H2O(l) = 18.02 J/g.K Cpm of CO2(g) = 37.45 J/g.K.

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7. a) Explain how reference substances plots could be used to estimate heat of vaporization of a substance b) Estimate the heat of vaporization of freon-12 at 90 oC from the following data:

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Set No: Code No: NR-210803 II-B.Tech I-Semester Supplementary Examinations May /June, 2004 MATERIAL AND ENERGY BALANCE (Chemical Engineering) Time: 3 hours Max. Marks: 80 Answer any FIVE questions All questions carry equal marks ---

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Two students are calculating the average molecular weight of a gas mixture containing N2 and other gases. One student using the correct molecular weight of nitrogen calculates the average molecular weight as 36. Another student using an incorrect molecular weight of nitrogen as 14, calculates the average molecular as 29. This is the only mistake in computations. Calculate the composition in nitrogen in mole percent and weight percent.

2.

A chimney gas has the following composition by volume: CO2 9.5%, CO 0.2%, O2 9.6%, N2 80.7% Using the ideal-gas law, calculate: a) Composition by weight. b) Volume occupied by 0.4536 kg of the gas at 27C and 29.5 in. Hg pressure. c) Density of the gas in kg/m3 at the conditions of part b. d) Specific gravity of the mixture.

3.

A binary of A and B components have the following temperature and vapour pressure characteristics (vapour pressure in mm Hg) 38.5 42 46 50 54 58 62 TC Vapour pressure 400 458 532 615 708 812 948 A mm Hg Vapour pressure 160 185 217 254 295 342 400 B mm Hg Calculate the P-x-y & T-x-y diagrams for the above system at 50C and 400 mm Hg pressure respectively.

4.

If the atmosphere in the afternoon during a humid period is 32.2 oC with a relative humidity of 80 at a barometer reading of 738 mm Hg, and while at night it is at 20 °C at a barometer reading of 745 mm Hg. What percent of water in the afternoon air is deposited as dew at night? Vapor pressure of H2O at 32.2 oC = 36.1 mm Hg Vapor pressure of H2=O at 20 °C = 17.5 mm Hg

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Contd…2

Code No: NR-210803

6. a)

b)

A feed containing 60 mole % A, 30% B and 10% inerts enters a reactor. The product stream leaving the reactor is found to contain 2 mole % of A. The reaction taking place is 2A + B  C. Find the percentage of original A getting converted to C A wet solid containing 20% moisture is to be dried to a water content of 1% by passing hot air over them. The fresh air contains 0.018 kg water vapor per kg dry air and the exhaust air contains 0.095 kg water vapor per kg dry air. Calculate the volumetric flow rate of fresh air for drying 1000 kg/hr of wet solids if it is available at 300 K and 101.325 kPa pressure.

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b)

Set No: 4

A produces has the following composition by percent at NTP: CO = 23.0% CO2 = 4.4% O2 = 2.6% N2 = 70.0% Calculate the composition of gases leaving the burner assuming complete combustion when the gas is burnt with 20% excess of oxygen. Pure methane is burnt completely to CO2 and water vapour in a furnace. Air is oxidizing agent and is supplied 50% extra. Calculate the amount of flue gases produced and the composition of gases by volume.

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.2.

5000 kg/hr of a hot oil are cooled in a heat exchanger from 200 oC to 50 oC. Liquid water at ambient temperature is abundantly available and is used as the cooling medium. Average specific heat of the oil is 0.6cal/kg-K. Calculate (a) the water requirement if the rise in the temperature of water is 22 oC and (b) the rise in water temperature if 5000 kg/hr of water is used

8.

The waste gas from a process of 1000 g mol/h of CO at 473 K is burned at 1 atm pressure in a furnace using air at 373 K. The combustion is complete and 90% excess air is used. The flue gas leaves the furnace at 1273 K. Calculate the heat removed in the furnace. The standard heat of combustion at 25 oC and 1 atm absolute = -282.989  103 kJ/kg mol. The mean molar heat capacities between 298 and T K in kJ/kg mol K are as follows: CO = 29.38, air = 29.29, CO2 = 49.91, O2 = 33.25, N2 = 31.43.

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Set No:

II-B.Tech I-Semester Supplementary Examinations May /June, 2004 · MATERIAL .... VP Hexane mm Hg 760 780 915 1060 1225 1405 1577 1765 · VP Heptane ...

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