Chemical Process Calculations

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JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD II B.TECH – I SEM SUPPLEMENTARY EXAMINATIONS, JUNE - 2010

CHEMICAL PROCESS CALCULATIONS (CHEMICAL ENGINEERING)

Time: 3hours Max.Marks:80

Answer any FIVE questions All questions carry equal marks

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1. A solution of Sodium Chloride in water contains 250 grams of NaCl per liter at 200C. The density of the solution at this temperature is 1.148 grams per cubic centimeter. Calculate:

a) Composition in weight percent b) Composition in mole percent c) Composition in atomic percent

d) Molality. [16]

2. Cracked gas from a petroleum refinery has the following composition by volume: Methane 45%, Ethane 10%, Ethylene 25%, propane 7%, propylene 8%, n-butane 5%. Find:

a) The composition by weight.

b) The specific gravity of the mixture at STP.

c) The average molecular weight. [16] 3. A solution contains 50 % Benzene, 30 % Toluene and 20 % Xylene by weight at

a temperature of 1000C. The vapors are in contact with the solution. Calculate the total pressure and the molar percent composition of liquid and the vapor. The vapor pressures and molecular weights are as follows:

Component VP at 1000C Mol wt Benzene 1340 mm Hg 78 Toluene 560 mm Hg 92

Xylene 210 mm Hg 106 [16] 4. A mixture of acetone vapor and N2 contains 15% acetone by volume. Calculate the

relative saturation and percentage saturation of the mixture at a temperature of 200C and a pressure of 745 mm Hg vapor pressure of acetone at 200C= 184.8 mm Hg. [16] 5. A gas containing only methane and nitrogen is burned with air yielding a flue gas

that analyzed to the following composition: CO2 = 8.7%, CO = 1%, O2 = 2% and

the rest is nitrogen. Calculate: a) The composition of fuel.

b) Percent excess air supplied. [8+8] 6. A saturated solution of MgSO4 at 800C is cooled to 300C in a crystallizer. During

cooling, mass equivalent to 4% solution is lost by evaporation of water. Calculate the quantity of the original saturated solution to be fed to the crystallizer per 1000 kg crystals of MgSO4.7H2O. Solubilities of MgSO4 at 300C and 800C are 40.8 and

64.2 kg per 100 kg of water respectively. [16]

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T

where p = vapor pressure in mm Hg and T is in kelvin. Estimate the heat of

vaporization of zinc at 9070C which is the normal boiling point. [3+3+10] 8.a) Calculate the standard heat of reaction for the following:

CH3Cl(g) + KOH(s) → CH3OH(l) + KCl(s)

Data:-

∆_{Hf for KOH(s) = -101780 cal} ∆ Hf for KCl(s) = -104175 cal ∆Hf for CO2 (g) = -94058 cal ∆ Hf for H2O(l) = -68317 cal ∆ Hf for HCl(aq) = -40023 cal ∆ Hc for CH3Cl(g) = -182810 cal ∆ Hc for CH3OH(l) = -173650 cal

b) Explain the procedure how to estimate heat of reaction at higher temperature. [10+6]

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1. The solubility of Sodium Chloride in water at 290 K is 36 kg / 100 kg of water. Express the solubility as the following:

a) Mass fraction and mass percent of NaCl b) Mole fraction and mole percent of NaCl

c) k mol NaCl per 1000 kg of water. [16] 2. A chimney gas has the following composition by volume

CO2-9.5%, CO-0.2%, O2-9.6%, N2 -80.7% Calculate:

a) Its composition by weight

b) Volume occupied by 1.0 lb of the gas at 800F and 29.5 in Hg pressure.

c) Average molecules weight [16] 3. Write briefly on the following:

a) Vapor pressure plots

b) Vapor pressure of immiscible liquids. [16] 4.a) If sufficient water is placed in a dry gas at 150C and 100 kPa to thoroughly

saturate it, what would be the pressure after saturation, the temperature and volume remaining constant.

b) Explain wet bulb & dry bulb thermometry.

Antoine equation for water vapour pressure is given by log₁₀ 7.3092 1791.30 35.05

p

T

= −

−

Where p in kpa & T in k. [16]

5. A coal containing 87% total carbon and 7% unoxidized hydrogen is burned in air. Air is used 40% in excess of that theoretically required.

a) Calculate the number of kg of air used per kg of coal burned.

b) Calculate the composition, by weight, of the gases leaving the furnace,

assuming complete combustion. [8+8]

6.a) How can you carry out crystallization in process industries?

b) What is the yield of Na2SO4.10H2O if 100 kg of a pure 32% Na2SO4 solution is cooled to 200C? Solubility of Na2SO4 in water at 200C is 19.4 kg per 100 kg

water. [6+10]

7.a) Discuss heat capacity of gases.

b) What is the effect of pressure on heat capacity of gases?

c) Obtain an expression for mean heat capacity of gases if Cp = a + bT + CT2. [4+2+10] 8. In an effort to find an alternate source of fossil fuels, experiments were conducted

using methanol as a substitute for gasoline. The standard heat of combustion

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1. A gas mixture has the following composition by volume: Ethylene - 30.6 %, Benzene - 24.5 %, Oxygen - 1.3 %, Methane - 15.5 %, Ethane - 25.0 %, Nitrogen - 3.1 %. Find:

a) The average molecular weight of the gas mixture

b) The composition by weight and mole %. [16]

2. One gram mole of methyl chloride vapor is contained in a vessel at 1000C and 10 atm:

a) Use ideal gas law to estimate the system volume.

b) Suppose the actual volume of the vessel is 2.8 lit. What percentage error

results from assuming ideal gas behavior. [16]

3. Write briefly on the following:

a) Boiling point diagrams (T - x - y diagrams)

b) Equilibrium diagrams (x - y diagrams). [16]

4. On a particular day in Mumbai, a news paper reported the weather conditions of the previous day as 350C dry bulb, 80% relative humidity and barometric pressure of 100kPa. Using the psychrometric chart, find

a) The absolute humidity

b) The dew point

c) The percentage saturation and

d) The humid heat. [16]

5. 20 kg of propane is burned with 450 kg of air to produce 44 kg of carbon dioxide and 12 kg of carbon monoxide. Calculate the percent excess air. [16] 6.a) It is desired to make 100 kg of a 25% solution by weight of caustic soda. The

method of making this is as follows:

In a dissolution tank 50 wt% caustic soda solution is prepared. Then it is fed to a dilution tank where water is added to produce the desired solution. Assuming no evaporation loss in the dissolution tank, calculate the amount of water by passed to the dilution tank.

b) Explain Recycle with a neat flow diagram. [8+8]

7.a) Write Kopp’s rule. How this rule is useful in energy balance calculations. b) The heat capacity of SO2 is given by

Cp = a + bT-1 + CT-2.

Obtain an expression for mean heat capacity for sulfur dioxide. [6+10] 8.a) Explain adiabatic reaction temperature.

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∆ Hc for CH3Cl(g) = -182810 cal [6+10]

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1. Assume that a dry gas contains 21 % oxygen and 79 % nitrogen by volume. Calculate the following:

a) The composition in weight and mole percent

b) The average molecular weight of dry air. [16]

2.a) Ten cubic feet of air at 700F and 1 atm is heated to 6100F and compressed to 2.5 atm. What volume does the gas occupy in its final state?

b) An ideal gas mixture at 10 atm absolute contains 50 wt%H2 and 50 wt%N2.

Is the partial pressure of H2 less than, equal to, or greater than 5 atm. [16] 3. The vapor pressure of benzene is measured at two temperatures and results are as

follows:

T1 = 7.60C P1* = 40 mm Hg T2 = 15.40C P2* = 60 mm Hg

Calculate the latent heat of vaporization and the vapor pressure P* at 42.20C

using Clausius - clapeyron equation. [16]

4. Air at a temperature of 200C and a pressure of 750 mm Hg. has a relative humidity of 80%.

a) Calculate the molal humidity of the air.

b) Calculate the weight of water condensed from 1000 m3 of this air when it is cooled to 100C and its pressure increased to 35 psi.

Vapor pressure of water : 17.5 mm Hg. at 200C

9.2 mm Hg. at 100C. [16]

5. Pure sulfur is burned with 30% excess air. 15% of the sulfur burned is converted to sulfur trioxide and the remaining is converted to sulfur dioxide. What is the

composition of the flue gases? [16]

6.a) A crystallizer is charged with 500 kg of a hot aqueous solution that contains 30% by weight of anhydrous sodium sulphate. The solution is cooled. During cooling operation 4% of water originally present is lost. The resulting crystals are Na2SO4.10H2O. The mother liquor is found to contain 18% by weight of anhydrous salt. Calculate the yield of crystals and quantity of mother liquor.

b) Explain by pass with neat flow diagram. [10+6]

7.a) How do you obtain the heat capacities of solids, liquids and solutions? b) Calculate the amount of heat required to heat 1 g of each of the following

liquids from 0 to 500C.

i) Acetone

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8.a) Write down the laws of thermo chemistry.

b) Calculate the standard heat of reaction for the following: CaC2(s) + 2H2O(l) → Ca(OH)2(s) + C2H2(g)

Data:-

∆ Hf for CaC2(s) = -15000 cal ∆ Hf for Ca(OH)2(s) = -235800 cal ∆ Hf for CO2 (g) = -94058 cal ∆ Hf for H2O(l) = -68317 cal

∆ Hc for C2H2(g) = -310615 cal [6+10]