Material and Energy Balances - Process Calculations - Chemical Engineering Previous Year Questions

1

2008 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2008

A 35 wt% Na\(_2\)SO\(_4\) solution in water, initially at 50°C, is fed to a crystallizer at 20°C. The product stream contains hydrated crystals Na\(_2\)SO\(_4\)·10H\(_2\)O in equilibrium with a 20 wt% Na\(_2\)SO\(_4\) solution. The molecular weights of Na\(_2\)SO\(_4\) and Na\(_2\)SO\(_4\)·10H\(_2\)O are 142 and 322, respectively. The feed rate of the 35% solution required to produce 500 kg/hr of hydrated crystals is

A

403 kg/hr

B

603 kg/hr

C

803 kg/hr

D

1103 kg/hr

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2

2008 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2008

600 kg/hr of saturated steam at 1 bar (enthalpy 2675.4 kJ/kg) is mixed adiabatically with superheated steam at 450°C and 1 bar (enthalpy 3382.4 kJ/kg). The product is superheated steam at 350°C and 1 bar (enthalpy 3175.6 kJ/kg). The flow rate of the product is

A

711 kg/hr

B

1111 kg/hr

C

1451 kg/hr

D

2051 kg/hr

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3

2009 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2009

A dehumidifier (shown below) is used to completely remove water vapor from air.
Which ONE of the following statements is TRUE ?

A

Water is the ONLY tie component

B

Air is the ONLY tie component

C

BOTH water and air are tie components

D

There are NO tie components

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4

2010 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2010

A new linear temperature scale, denoted by °S, has been developed, where the freezing point of water is 200°S and the boiling point is 400°S. On this scale, 500°S corresponds, in degrees Celsius, to

A

100°C

B

125°C

C

150°C

D

300°C

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5

2010 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2010

A saturated solution at 30°C contains 5 moles of solute (M.W.=50 kg/kmol) per kg of solvent (M.W.=20 kg/kmol). The solubility at 100°C is 10 moles of the solute per kg of the solvent. If 10 kg of the original solution is heated to 100°C, then the weight of the additional solute that can be dissolved in it, is

A

0.25 kg

B

1 kg

C

2 kg

D

3.34 kg

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6

2010 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2010

The products of combustion of methane in atmospheric air (21% O₂ and 79% N₂) have the following composition on a dry basis.

Products	Mole %
CO₂	10.00
O₂	2.37
CO	0.53
N₂	87.10

The ratio of the moles of CH₄ to the moles of O₂ in the feed stream is

A

1.05

B

0.60

C

0.50

D

0.45

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7

2011 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2011

The following combustion reactions occur when methane is burnt. \( CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O \) \( 2CH_4 + 3O_2 \rightarrow 2CO + 4H_2O \) 20 % excess air is supplied to the combustor. The conversion of methane is 80 % and the molar ratio of CO to \( CO_2 \) in the flue gas is 1:3. Assume air to have 80 mol % \( N_2 \) and rest \( O_2 \). The \( O_2 \) consumed as a PERCENTAGE of \( O_2 \) entering the combustor is

A

20

B

62.5

C

80

D

83.3

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8

2011 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2011

An aqueous sodium chloride solution (10 wt %) is fed into a single effect evaporator at a rate of 10000 kg/hr. It is concentrated to a 20 wt % sodium chloride solution. The rate of consumption of steam in the evaporator is 8000 kg/hr. The evaporator capacity (kg/hr) and economy are

A

5000, 0.625

B

10000, 0.625

C

5000, 1.6

D

10000, 1.6

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9

2011 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2011

P, Q, R and S are four types of dangerous microbes recently found in a human habitat. The area of each circle with its diameter printed in brackets represents the growth of a single microbe surviving human immunity system within 24 hours of entering the body. The danger to human beings varies proportionately with the toxicity, potency and growth attributed to a microbe shown in the figure below:
A pharmaceutical company is contemplating the development of a vaccine against the most dangerous microbe. Which microbe should the company target in its first attempt?

A

P

B

Q

C

R

D

S

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10

2011 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2011

A container originally contains 10 litres of pure spirit. From this container 1 litre of spirit is replaced with 1 litre of water. Subsequently, 1 litre of the mixture is again replaced with 1 litre of water and this process is repeated one more time. How much spirit is now left in the container?

A

7.58 litres

B

7.84 litres

C

7 litres

D

7.29 litres

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11

2013 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2013

A reverse osmosis unit treats feed water (F) containing fluoride and its output consists of a permeate stream (P) and a reject stream (R). Let C_F, C_P, and C_R denote the fluoride concentrations in the feed, permeate, and reject streams, respectively. Under steady state conditions, the volumetric flow rate of the reject is 60 % of the volumetric flow rate of the inlet stream, and C_F = 2 mg/L and C_P = 0.1 mg/L. The value of C_R in mg/L, up to one digit after the decimal point, is

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12

2014 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2014

Carbon monoxide (CO) is burnt in presence of 200% excess pure oxygen and the flame temperature achieved is 2298 K. The inlet streams are at 25 °C. The standard heat of formation (at 25 °C) of CO and CO₂ are −110 kJ mol⁻¹ and −390 kJ mol⁻¹, respectively. The heat capacities (in J mol⁻¹ K⁻¹) of the components are
\(C_{P_{O_2}} = 25 + 14 \times 10^{-3} T\)
\(C_{P_{CO_2}} = 25 + 42 \times 10^{-3} T\)
where, T is the temperature in K. The heat loss (in kJ) per mole of CO burnt is __________

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13

2017 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2017

An aqueous salt-solution enters a crystallizer operating at steady state at 25°C. The feed temperature is 90°C and the salt concentration in the feed is 40 weight %. The salt crystallizes as a pentahydrate. The crystals and the mother liquor leave the crystallizer. The molecular weight of the anhydrous salt is 135. The solubility of the salt at 25°C is 20 weight %.

The feed flowrate required for a production rate of 100 kg/s of the hydrated salt, rounded to the nearest integer, is __________ kg/s.

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14

2017 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2017

Reaction A → B is carried out in a reactor operating at steady state and 1 mol/s of pure A at 425°C enters the reactor. The outlet stream leaves the reactor at 325°C. The heat input to the reactor is 17 kW. The heat of reaction at the reference temperature of 25°C is 30 kJ/mol. The specific heat capacities (in kJ/mol.K) of A and B are 0.1 and 0.15, respectively.

The molar flowrate of B leaving the reactor, rounded to 2 decimal places, is __________ mol/s.

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15

2018 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2018

The ammonia (NH_3) oxidation process occurs over a catalyst as

4 NH_3 + 5O_2 \rightarrow 6H_2O + 4 NO

Air is supplied such that oxygen (O_2) is 20% in excess of that required for complete conversion of NH_3. The mole fraction of O_2 in inlet gas mixture (NH_3 + air) is __________ (rounded off to third decimal place)

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16

2019 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2019

100 kg of a feed containing 50 wt.% of a solute C is contacted with 80 kg of a solvent containing 0.5 wt.% of C in a mixer-settler unit. From this operation, the resultant extract and raffinate phases contain 40 wt.% and 20 wt.% of C, respectively. If E and R denote the mass of the extract and raffinate phases, respectively, the ratio E/R is

A

1/4

B

1/2

C

2/3

D

1

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17

2021 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2021

Formaldehyde is produced by the oxidation of methane in a reactor. The following two parallel reactions occur.
\( CH_4 + O_2 \longrightarrow HCHO + H_2O \)
\( CH_4 + 2O_2 \longrightarrow CO_2 + 2H_2O \)
Methane and oxygen are fed to the reactor. The product gases leaving the reactor include methane, oxygen, formaldehyde, carbon dioxide and water vapor.
60 mol s^-1 of methane enters the reactor. The molar flowrate (in mol s^-1) of CH₄, O₂ and CO₂ leaving the reactor are 26, 2 and 4, respectively. The molar flowrate of oxygen entering the reactor is __________ mol s^-1.

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18

2023 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2023

Burning of methane in a combustor yields carbon monoxide, carbon dioxide, and water vapor. Methane is fed to the combustor at 100 mol.hr^-1, of which 50 % reacts. The theoretical oxygen requirement (in mol.hr^-1) is __________ (rounded off to one decimal place).

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19

2023 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2023

Wet air containing 10 mole percent water vapor is dried by continuously passing it through a column of \( CaCl_2 \) pellets. The pellets remove 50 percent of water from wet air entering the column. The mole percent of water vapor in the product stream exiting the column is ______ (rounded off to two decimal places).

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20

2023 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2023

Orsat analysis showing the composition (in mol %, on a dry basis) of a stack gas is given in the table below. The humidity measurement reveals that the mole fraction of \( H_2O \) in the stack gas is 0.07. The mole fraction of \( N_2 \) calculated on a wet basis is ______ (rounded off to two decimal places). | Species | \( N_2 \) | \( CO_2 \) | CO | \( O_2 \) | |---------|-------|--------|----|-------| | mol % | 65 | 15 | 10 | 10 |

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