CHEMICAL INDUSTRIES

Chapter 16

CHEMICAL INDUSTRIES

SOLVED TEST YOURSELFS

Test Yourself 16.1 (BASIC METALLURGICAL OPERATIONS)

  1. No. i. Define concentration process used in metallurgy of copper.

Answer. The process of removal of gangue from the ore is technically known as concentration and the purified ore is called the concentrate. The concentration process used in metallurgy of copper is froth flotation. It is based on the wetting characteristic of the ore and the gangue particles with oil and water, respectively.
The ore particles are preferentially wetted by oil and the gangue particles by the water. The whole mixture is agitated with compressed air. Hence, oil coated ore particles being lighter come to the surface in the form of a froth that can be skimmed as shown in figure below.

  1. No. ii. Why a small amount of coke is required in the smelting process?

Answer. Smelting is further heating the roasted ore with sand flu and coke in the presence of excess of air in a blast furnace. It is high exothermic process; therefore, a small amount of coke is required in| the process.

  1. No. iii. Differentiate between minerals and ores.

Answer. The solid natural materials found beneath the Earth’s surface, which contains compounds of metals in the combined state along with earthly impurities, are called minerals.

Those minerals from which the metals are extracted commercially at a comparatively low cost with minimum effort are called ores of the metals

  1. No.iv. Why lime is added in the smelting process?

Answer. Lime is added to remove excess of Si02. Lime decomposes to form CaO, which reacts with sand to form slag.

CaCO3            CaO + CO2

CaO + SiO2         CaSiO3

  1. No. v. How slag and matte are removed from the blast furnace?

Answer. Blast furnace is used for smelting of copper. In the furnace roasted ore is heated to oxidize ferrous sulphide to form ferrous oxide which reacts with sand to form iron silicate slag (FeSiO3). It being lighter rise to the top and is removed from the upper hole.

2 FeS(s) + 3O2(g)      2 FeO(s) + SO2(g)#

FeO(s) + SiO2(s)       FeSiO3(s)

On the other hand, cuprous sulphide also oxidizes to form cuprous oxide which reacts with unreacted ferrous sulphide to form ferrous oxide and cuprous sulphide. In this way, cuprous sulphide and ferrous sulphide form a mixture (Cu2S.FeS). This molten mixture is called matte.

It is withdrawn from the lower hole. It contains about 45% of copper.

2 Cu2S(1) + 3O2(g)     2Cu2O(1) + 2SO2(g)#

Cu2O(1) + FeS(1)       Cu2S(1) + FeO(1)

  1. No.vi. What is difference between slag and matte?

Answer. Matte is a mixture of cuprous sulphide along with un-reacted ferrous sulphide (Cu2S, FeS). It is a molten mixture that contains about 45% copper.

Ferrous sulphide is oxidized to ferrous oxide, which reacts with sand to form a fusible material iron silicate (FeSiOa) called slag. It is a lighter material.

FeO(s) + SiO2(8) ———> FeSiO3(s)

(i).      Matte is further heated in bessemer converted to blister copper

(ii).     Slag is an impurity that is removed away.

  1. No. vii. Mention the chemical reaction for the formation of metallic copper in the bessemerization process.

Answer. In the bessemerization process molten matte is further heated. Molten matte is mixed with sand and heated with a hot blast of air through tuyers. Ferrous sulphide is oxidized to form ferrous oxide. Which react with sand to form slag (FeSiO3) that float on the top.

2FeS(1) + 3O2(g)            2FeO2(g) + 2SO2(g)

FeO(1) + SiO2(1)            FeSiO3(slag)

On the other hand, cuprous sulphide is oxidized to form cuprous oxide, which again reacts with remaining cuprous sulphide to form metallic copper.

2Cu2S(1) + 3O2(g)           2Cu2O(1)+ 2SO2(g)

2Cu2O(1) + Cu2S(1)         6Cu(s)+ SO2(g)

  1. No. viii. What is blister copper?

Answer. The molten metal is shifted from the converter to sand moulds and is allowed to cool. The dissolved gases escape out forming blisters on the surface of the solid copper. Therefore, it is called blister copper. It is about 98% pure copper.

  1. No. ix. Why anode is eaten up in electro-refining process?

Answer. Electro-refining of copper carried out in an electrolytic tank. It consists of two electrodes; anode of impure copper and cathode of pure copper metal. In the process oxidation takes place at anode. As a result, copper atoms of the anode lose two electrons at the anode and copper ion (Cu2+) dissolves into the solution.

Cu ———> Cu2+ + 2e;

Simultaneously, Cu2+ ions from the solution reduce and deposit at the cathode. The process continues by dissolving of anode and depositing of Cu2+ ions at cathode. Meanwhile, ultimately the anode is eaten up.

  1. No. x. What do you mean by anode mud?

Answer. In the electro-refining, of copper, anode is made of impure copper metal. It consists of impurities like gold and silver. When oxidation takes place at anode, there metallic ions dissolve in the solution. Cu2+ ions reduce and deposit at cathode while gold and silver impurities settle down as anode mud.

Test Yourself.16.2 (MANUFACTURE OF SOOIUM CARBONATE BY SOLVAY’S PROCESS)

  1. No. i. Why only NaHCO3 precipitates when CO2 is passed through the ammonical brine?

Answer. When CO2 is passed through an ammonical solution of NaCl called ammonical brine only NaHCO3 precipitate due to its lowest solubility at 15°C in the presence of excess of CO2.

Na+(aq) + HCO3(aq)         NaHCO3(s)

  1. No. ii. Which raw materials are required for the formation of sodium carbonate?

Answer.   Raw   materials   required   for   the   formation   of sodium carbonate are:

  1. sodium chloride or brine
  2. lime stone
  3. ammonia gas,
  1. No. iii. How CO2 is prepared in the Solvay’s process?

Answer. CO2 is prepared by heating limestone in a lime kiln. Then it is carried to carbonating tower.

CaCO3 ———> CaO + CO2

  1. No.iv. Give the reaction of formation of ammonia in the process.

Answer. It is prepared by the Haber’s process. One volume of nitrogen (from air) and three volumes of hydrogen (obtained by passing methane and steam over heated nickel catalyst) are passed over iron catalyst at 450°C and 200 atm pressure.

N2 + 3H2               2NH3

  1. No. v. Give the advantages of Solvay’s Process.

Answer. Solvay’s process has the following advantages:

(i)       It is a cheap process as raw materials are available at very low prices.

(ii)      Carbon dioxide and ammonia are recovered and reused.

(iii)     Process is pollution free, because the only waste is calcium chloride solution.

(iv)     Sodium carbonate of very high purity is obtained.

(v)      Consumption of fuel is very less since no solution is to be evaporated.

Test Yourself 16.3 (MANUFACTURE OF UREA)

  1. No. i. What happens when ammonium carbonate is heated with steam?

Answer. When ammonium cabana is evaporated with the help of steam, it dehydrates to form urea.

NH2COONH4 ———>NH2CONH2 + H2O

  1. No. ii. How many stages are involved in formation of urea?

Answer. Three stages are involved in the formation of urea. These stages are:

  1. Reaction of ammonia and carbondioxcide.
  2. Urea formation.

iii. Granulation of urea.

  1. No. iii. What is percentage of nitrogen in urea?

Answer. Percentage of nitrogen in urea is 46%.

Test Yourself 16.4 (PETROLEUM INDUSTRY)

  1. No. i. Define petroleum.

Answer. Petroleum is a natural product found under the Earth’s crust trapped in rocks. Petroleum means rock oil. It is a complex mixture of several gaseous, liquid and solid hydrocarbons having water, salts and earth particles with it. It is lighter than water and is insoluble in it.

  1. No. ii. How petroleum is extracted?

Answer. Petroleum is extracted by drilling holes (oil wells) into Earth’s crust where the oil is found. When a well is drilled through the rocks, natural gas comes first with a great pressure. For some time crude oil also comes out by itself due to gas pressure. When gas pressure subsides, then crude oil is pumped out as shown in figure.

Occurrence of petroleum

  1. No. iii. What is principle of fractional distillation?

Answer. The principle of fractional distillation is based upon separation of substances depending upon their boiling points. The substances having low boiling points boil out first leaving behind others. Then next fraction of slightly higher boiling point boils out. This process remain continue until a residue is left behind. The vapours of each fraction are collected and condensed separately.

  1. No.iv. In how many fractions crude oil is separated?

Answer. Crude oil is separated into six fractions:

  1. Petroleum gas b. Petroleum ether   c. Gasoline or petrol        d. Kerosene oil e. Diesel oil               f. Fuel oil
  1. No. v. What do you mean by a fraction of petroleum?

Answer. Fraction of petroleum means a part of petroleum that is a mixture of hydrocarbons having different number of carbon atoms in it. Each fraction has its specific name, boiling range and usage in daily life.

MULTIPLE CHOICE QUESTIONS

Put a (√) on the correct answer.

  1. Concentration is a:
  2. mixing technique. b. separating technique,
  3. boiling technique. d. cooling technique.
  1. Froth flotation process is used to concentrate:
  2. oxide ores. b. nitrate ores,
  3. sulphide ores. d. carbonate ores.
  1. Matte is a mixture of:
  2. FeS and CuS b. Cu20 and FeO
  3. Cu2S and FeS    d. CuS and FeO
  1. In the bessemerization process:
  2. roasted ore is heated. b. molten matte is removed,
  3. molten matte is heated. d. molten matte is recovered.
  1. Concentration of the copper ore is carried out by:
  2. calcinations. b. roasting.
  3. forth flotation.         d. distillation.
  1. When CO is passed through the ammonical brine the only salt that precipitates is
  2. NaHCO3      b. NH4HCO3
  3. Na2CO3                    d. (NH4)2C03
  1. In Solvay’s process slaked lime is used to:
  2. prepare CO2. b. prepare quicklime,
  3. recover ammonia. d. form Na2CO3.
  1. When NaHCO3 is heated it forms:
  2. CO2                               b. Ca (OH)2
  3. CaCO3                      d. CaO
  1. Formula of urea is
  2. NH2COONH4 b. NH2COONH2
  3. NH2CONH4 d. NH2CONH2
  1. Crude oil is heated in the fractionating furnace up to
  2. 300°C b. 350°C
  3. 400°C d. 450°C
  1. When crude oil is heated in the fractionating tower
  2. vapours of higher boiling point fraction condense first in the

lower part of the tower

  1. vapours of lower boiling point fraction condense first in the

lower part of tower

  1. vapours of higher boiling point condense later in the upper

part of tower.

  1. vapours of higher boiling point never condense.
  1. Which one of the following is a fraction of crude oil?
  2. paraffin wax                           b. asphalt
  3. fuel oil  d. petroleum coke
  1. Which one of the followings is not a fraction of petroleum?
  2. kerosene oil b. diesel oil
  3. alcohol              d. petrol
  4. The nitrogen present in urea is used by plants to synthesize
  5. sugar                         b. proteins
  6. fats d.DNA
  1. Which one of the following organic compounds is found in gasoline?
  2. C2H4 b. C3H8
  3. C8H18               d. C12H26

ANSWER MCQs

  1. b 2. c 3. c       4. c       5. c       6. a       7. c       8. a
  2. d 10. c 11.a       12. a     13. c      14. c     15. b      16. c

ANSWERS TO THE SHORT QUESTIONS

  1. No.1. What role is played by pine oil in the concentration process?

Answer. In the concentration process of copper ore, pine oil is added. Pine oil wets the ore particles and being lighter, they float over the surface in the form of a froth that can be skimmed. While, the gangue particles are moisturized by water. They settle down at the bottom. Hence the pine oil plays the role of separator of ore particles from gangue particles.

  1. No.2. Name the various metallurgical steps.

Answer. The important metallurgical steps are:

concentration of the ore;

ii   extraction of the metal, and

iii   refining of the meta

  1. No.3. How roasting is carried out?

Answer. Roasting: It is a process of heating the concentrated ore to a high temperature in excess of air. For example; copper pyrite (CuFeS2) is strongly heated in excess of air to convert it into a mixture of cuprous sulphide and ferrous sulphide (Cu2S + FeS). While impurities sulphur, phosphorus arsenic etc. react with oxygen to form volatile oxides. Such as

2 CuFeS2(s) + O2(g) ———> Cu2S(s)+ 2FeS(s)+ SO2(g)

  1. No.4. Explain process of electro refining.

Answer. Refining the impure metal by electrolysis is the most widely used process of refining metals. The impure slab of the metal is made the anode, while a pure thin sheet of metal is made the cathode. For example, electrolytic refining of copper is carried out in an electrolytic tank having copper sulphate solution as shown in figure below:

On passing the electric current through the solution, anode (impure copper) dissolves to provide Cu2+ ions to the solution. These Cu2+ ions are discharged by gaining of electrons from the cathode.

Thereby copper atoms deposit on the cathode, making it thick block of pure copper metal as is shown in figure. The impurities like gold and silver settle down as anode mud.

Electro-refining of copper

  1. No.5. What are advantages of Solvay’s process?

Answer.

(i)       It is a cheap process as raw materials are available at very low prices.

(ii)      Carbon dioxide and ammonia are recovered and reused.

(iii)     Process is pollution free, because the only waste is calcium chloride solution.

(iv)     Sodium carbonate of very high purity is obtained.

(v)      Consumption of fuel is very less since no solution is to be evaporated.

  1. No.6. What is the principle of Solvay’s process?

Answer. Principle of Solvay’s Process lies in the low solubility of sodium bicarbonate at low temperature, i.e. at 15°C. As a result it precipitates when CO2 is passed through an ammonical solution of NaCl called ammonical brine.

Na+(aq) + HCO3(aq)         NaHCO3(s)

  1. No.7. What happens when ammonical brine is carbonated?

Answer. Ammonical brine is fed into carbonating tower and carbon dioxide is passed through it. Following reactions take place in the carbonating tower.

CO2(g) + NH3(g) + H2O                NH4HCO3(1)

NH4HCO3(1) + NaCl (brine)            NaHCO3(1) + NH4Cl(s)

The temperature of the mixture is lowered to 15°G and precipitates of NaHCO3 are obtained.

  1. No.8. How NaHCO3 is converted to Na2CO3?

Answer. The precipitates of sodium bicarbonate are filtered, washed with cold water and heated to form sodium carbonate.

2NaHCO3 ———> Na2CO3 + CO2 + H2O

  1. No.9. How ammonia is recovered in the Solvay’s process?

Answer. Ammonia is recovered from ammonium chloride solution produced in the carbonated tower and calcium hydroxide formed in lime kiln. Both of these are pumped to the top of the ammonia recovery tower. Steam is introduced from the base of the tower for heating purposes. Ammonia is recovered from NH4C1 as:

2NH4C1 + Ca(OH)2 ———> 2NH3 + CaCl2 + 2H2O

  1. No.10. How ammonia is prepared for the synthesis of urea?

Answer. It is prepared by the Harber’s process. One volume of nitrogen (from air) and three volumes of hydrogen (obtained by passing methane and steam over nickel catalyst) are passed over iron catalyst at 450 °C and 200 atm pressure

N2(g)+ 3H2(g) ———> 2NH3(g)

Q.No.11. Describe the formation of petroleum.

Answer. Petroleum was formed by the decomposition of dead plants and animals buried under Earth’s crust millions of years ago. It is believed that millions of years ago living plants and animals in the seas died. Their bodies sank and buried under mud and sand. Then decomposition process took place in the absence of air because of high pressure, temperature and bacterial effects. This process took millions of years for completion. Thus, remains of dead plants and animals were converted into a dark brownish viscous crude oil.

  1. No.12.What is refining of petroleum and how it is carried out?

Answer. Refining process is the separation of crude oil mixture into various useful products (fractions). It is carried out by a process called fractional distillation in a fractionating tower. The crude oil is heated in a furnace up to a temperature of 400°C under high pressure. Then vapours are passed through a fractionating column from near its bottom, hot vapours rise up in the column and gradually cool down and condense. Such that vapours of higher boiling point fraction (350— 400°C) condense first in the lower part of the tower, while vapours of medium and lower boiling point fractions rise upwards in the tower and condense gradually with respect their boiling points at different levels. In this way crude oil is separated into six hydrocarbon fractions as discussed below. Each fraction has its specific boiling range, composition and uses.

  1. No.13. Give a use of kerosene oil.

Answer. Kerosene oil is used as domestic fuel a special grade of it is used as an aeroplane fuel.

  1. No.14. Describe the difference between diesel oil and fuel oil.

Answer. Diesel oil consists of C13 to C15 carbon atom while fuel oil consists of C15 to C18. The boiling range of diesel oil varies from 250°C to 350°C. While, boiling range of fuel oil varies from 350°C to 400°C. Diesel oil is used as a fuel in buses, trucks, railway engines, tube well engines and other heavy transport vehicles. While, fuel oil is used in ships and industries to heat up boilers and furnaces

  1. No.15. Write down the names of four fractions obtained by the fractional distillation of residual oil.

Answer. Four fractions obtained from the fractional distillation of residual oil are:

  1. Lubricants b. Paraffin wax
  2. Asphalt d. Petroleum coke
  1. No.16. What is the difference between crude oil and residual oil?

Answer. Crude oil is the dark brownish viscous liquid formed by decomposition of remains of dead plants and animals in the absence of air because of high pressure, temperature and bacterial effects. When it is heated in a furnace up to 400°C under high pressure it gives important fraction of petroleum.

While, residual oil is the left behind residue of crude oil that does not vaporize when crude oil is seated in a furnace up to 400°C under high pressure. Residual oil is collected from the fractionating volume and is heated above 400°C to obtain four fractions; lubricants, paraffin wax, asphalt and petroleum coke.

  1. No.17. Which petroleum fraction is used in dry cleaning?

Answer. The fraction of petroleum used in dry cleaning is gasoline or petrol.

ANSWERS TO THE LONG QUESTIONS

  1. No.1. Describe in detail the various processes involved in the concentration of ore. Explain your answer with the help of diagrams.

Answer. The process of removal of gangue from the ore is technically known as concentration and the purified ore is called the concentrate. Concentration of the crushed ore is carried out by the following methods:

(a) Gravity separation

Gravity separation is based on the differences in densities of the metallic ore and the gangue particles.

In the process, the powdered heavy met

al bearing ore settles down on agitation in a stream of water, while the lighter gangue particles are carried away by the water as shown in figure below:

Water

Water +

Gangue

Concentrated

Ore

(b) Froth flotation process

Froth flotation process is based on the wetting characteristic of the ore and the gangue particles with oil and water, respectively.

The ore particles are preferentially wetted by the oil and the gangue particles by the water. Hence ore particles come to the surface in the form of a froth that can be skimmed as shown in figure below:

 

 

Fig.16.2. Froth floatation process

(c) Electromagnetic separation

Electromagnetic separation is based on the separation of magnetic ores from the non-magnetic impurities by means of electro­magnets or magnetic separators. The powdered ore is dropped over a leather belt moving over two rollers, one of which is magnetic. The ore gets attracted and is collected nearer to the magnet while the non­magnetic impurities fall further away as shown in figure below:

 

  1. No.2. Explain the process of roasting with reference to copper.

Answer. Roasting: It is a process of heating the concentrated ore to a high temperature in excess of air. For example; copper pyrite (CuFeS2) is strongly heated in excess of air to convert it into a mixture of cuprous sulphide and ferrous sulphide (Cu2S + FeS). While impurities sulphur, phosphorus arsenic etc. react with oxygen to form volatile oxides. Such as

2 CuFeS2(8) + O2(g)   ———> Cu2S(s) + 2FeS(s) + SO2(g)

  1. No.3. Write a detailed note on Ammonia Solvay process.

Answer. Principle of Solvay process lies in the low solubility of sodium bicarbonate at low temperature i.e. at 15°C. When CO2 is passed through an ammonical solution of NaCl called ammonical brine, only NaHCO3 precipitates.

Na+(aq) + HCO3(aq)         NaHCO3(s)

Raw Materials:

The raw materials needed for this process are cheap and easily available. They are in abundance, such as,

(i) Sodium chloride (NaCl) or brine.

(ii) Limestone (CaCOa3).

(iii) Ammonia gas (HN3)

Basic Reactions:

The process consists of the following steps:

(i) Preparation of ammonical brine:

First -of all ammonical brine is prepared by dissolving ammonia gas in sodium chloride solution (brine),

(ii) Carbonation of ammonical brine:

Ammonical brine is fed into carbonating tower and carbon dioxide is passed through it. Following reactions take place in the carbonating tower.

CO2(g) +  NH3(g) + H2O                NH4HCO3(1)

NH4HCO3(1) + NaCl (brine)            NaHCO3(1) + NH4Cl(s)

The temperature of the mixture is lowered to 15°C and precipitates of NaHCO3 are obtained.

 

 

(iii) Filtration of precipitates

The milky solution from the carbonating tower is filtered to get sodium bicarbonate. It is used as a baking soda.

(iv) Formation of sodium carbonate

Sodium carbonate is heated to get sodium carbonate.

2NaHCO3(1) ——— > Na2CO3(s) + CO2(g) + H2O(1)

CO2 is again used in tower. It is about half of CO2 needed in the process.

(v) Preparation of carbon dioxide and slaked lime:

CO2 is prepared by heating limestone in a lime kiln. Then it is carried to carbonating tower

CaO3(s)            CO2(g) + CO2(g)

Quick lime (CaO) formed in lime kiln is slaked with water. Then, it is pumped to the ammonia recovery tower.

CaO(g) + H2O(1) ——— > Ca(OH)2

(Slaked lime)

(vi) Ammonia recovery tower

Ammonia is recovered in this tower from ammonium chloride solution produced in the carbonated tower and calcium hydroxide formed in lime kiln.

2NH4Cl(s) + Ca(OH) 2(1)  ——— 2NH3(g) + CaCl2(s) + 2H2O(1)

In fact, all ammonia is recovered in this tower and is reused in the process. There are minor losses of ammonia in the process which are compensated by using some fresh ammonia.

 

Flow sheet diagram of Solvay’s Process for the manufacturing of

Sodium carbonate

Advantages of Solvay’s process

(i). It is a cheap process as raw materials are available at very low prices.

(ii). Carbon dioxide and ammonia are recovered and reused.

(iii). Process is pollution free, because the only waste is calcium chloride solution.

(iv). Sodium carbonate of very high purity is obtained.

(v). Consumption of fuel is very less since no solution is to be evaporated.

(vi). Pakistan is self-sufficient as far as demand of sodium carbonate is concerned.

Imperial Chemical Industries (ICI) Khewra (Distict Jhelum) is producing enough sodium carbonate. This unit was established in 1944 in Khewra because abundant raw material sodium chloride is available here. A Sindh alkali limited was established near Karachi in 1966. Sodium carbonate and sodium bicarbonate are important industrial chemicals and are used by many industries.

  1. No.4. Write a note on fractional distillation of petroleum.

Answer. The crude oil is refined in the refineries. Refining process is the separation of crude oil mixture into various  useful  products

(fractions). It is carried out by a process called fractional distillation. The principle of fractional distillation is based upon separation of substances depending upon their boiling points. The substances having low boiling points boil out first leaving behind others. Then next fraction of slightly higher boiling point boils out. This process remain continue until a residue is left behind. The vapours of each fraction are collected and condensed separately. The fractional distillation of petroleum is carried out in a tall fractionating tower as shown in figure below:

The crude oil is heated in a furnace up to a temperature of 400°C under high pressure. Then vapours are passed through a fractionating column from near its bottom as shown in figure. Hot vapours rise up in the column and gradually cool down and condense. Such that vapours of higher boiling point fraction (350—400°G) condense first in the lower part of the tower, while vapours of medium and lower boiling point fractions rise upwards in the tower and condense gradually with respect to their boiling points at different levels. In this way crude oil is separated into six hydrocarbon fractions as discussed below. Each fraction has its specific boiling range, composition and uses.

  1. No.5. How urea is manufactured? Explain showing the flow sheet diagram.

Answer. Manufacture of Urea

Urea is nitrogenous fertilizer. It consists of 46.6% nitrogen. It is white crystalline compound, highly soluble in water. It is used for the manufacturing of important chemicals, but its major (about 90%) use is as a fertilizer.

The raw materials for the manufacturing of urea are:

(i) Ammonia (NH3)      (ii) Carbon dioxide (CO2)

Ammonia is prepared by the Haber’s process. One volume of nitrogen (from air) and three volumes of hydrogen (obtained by passing methane and steam over heated nickel catalyst) are passed over iron catalyst at 450°C and 200 atm pressure.

450°C

N2(g) + 3H2(g)         2NH2(g)

200atm

Manufacturing of urea involves three stages:

(i)       Reaction of ammonia and carbon dioxide; Carbon dioxide is passed through liquid ammonia under high pressure to form ammonium carbonate

2NH3 + CO2 ——— > NH2COONH4

Ammonium carbonate

(ii)      Urea formation; When ammonium carbonate is evaporated with the help of steam, it dehydrates to form urea.

NH2COONH4 ———>NH2CONH2 + H2O

(Urea)

(iii)    Granulation of urea: At this stage, liquid urea is evaporated to form granules. When liquid urea is sprayed from top of a tower under pressure and a hot current of air is introduced from the base, it evaporates to form granules. This is stored to be marketed.

(Unreacted NH3, CO2 & H2O)

Flow sheet diagram of manufacturing of urea

  1. No.6. How crude oil is refined? Explain the important fractions of petroleum along with their usage.

Answer.   Crude   oil   is   refined   by   fractional   distillation   in   a fractionating tower.

Important Fractions of Petroleum

Each fraction is not a single compound. Rather each one is a mixture of hydrocarbons having different number of carbon atoms in it. The name of each fraction, its molecular composition, boiling range and uses are given in the following Table 16.2:

Table 16.2 Fractions of Petroleum

 

 

 

 

 

 

 
Name

 

Composition

 

Boiling

range

 

 Uses

 

Petroleum

 

C1 to C4

 

up to

 

As a fuel, as such in the form
Gas

 

 

 

25°C

 

of     LPG,     used     for     the

 

 

 

 

 

 

 

production   of  carbon   black

 

 

 

 

 

 

 

(needed in tyre industry) and

 

 

 

 

 

 

 

hydrogen gas (needed to form

 

 

 

 

 

 

 

NH3   used    to    manufacture

 

 

 

 

 

 

 

fertilizer)

 

Petroleum Ether

 

C5toC7

 

30 to 80°C

 

Used as laboratory solvent and for dry cleaning purposes.

 

 

 

Name

 

Composition

 

Boiling range

 

    Uses
Gasoline or Petrol

 

 

C7 to C10

80 to 170°C

 

Used as fuel in motor cycles, motor cars and other light vehicles. It is more volatile than kerosene oil. It is also use for dry cleaning.

 

Kerosene oil

 

C10 to C12 170 to 250°C

 

Used as domestic   fuel,   a special grade of it is used as aeroplane fuel.

 

Diesel oil

 

C13 to C15 250 to

350°C

 

Fuel for buses, trucks railway engines,       ships,    tube well engines    and    other    heavy vehicles.

 

Fuel oil

 

C15 to C18

 

350 to 400%°C Used in industries to heat oilers and furnaces.

 

  1. No.7. Write a note in detail on smelting and bessemerization, giving a specific example’

Answer. Smelting: It is further heating the roasted ore with sand flux and coke in the presence of excess of air in a blast furnace as shown in figure. It is highly exothermic process therefore; a small amount of coke is required in the process. In the process, first ferrous sulphide oxidizes to form ferrous oxide which reacts with sand to form iron silicate slag (FeSiO3). It being lighter rise to the top and is removed from the upper hole.

2 FeS(s) + 3O2(g)             2 FeO(s) + SO2(g) #

FeO(s) + SiO2(s)                  FeSiO3(s)

On the other hand, cuprous sulphide also oxidizes to form cuprous oxide which reacts with unreacted ferrous sulphide to form ferrous oxide and cuprous sulphide. In this way, cuprous sulphide and ferrous sulphide form a mixture (Cu2S.FeS). This molten mixture is called matte.

It is withdrawn from the lower hole. It contains about 45% of copper.                      2 Cu2So(1) + 3O2(g) ———> 2Cu2O(1) + 2SO2(g) #

   Cu2O(1) + FeS(1) ———> CU2S(1) + FeO(1)

Gases

Matte

Blast furnace for smelting of copper

Bessemerization: It is the further heating of the molten matte in a pear shaped bessemer converter as shown in figure below. It is fixed on a pivot, so that it can be tilted in any direction. Molten matte is mixed with sand and heated with a hot blast of air through tuyers. Ferrous sulphide is oxidized to form ferrous oxide. Which reacts with sand to form slag (FeSiO3) that float on the top?

2 FeS(s) + 3O2(g)             2 FeO(s) + 2SO2(g)

FeO(s) + SiO2(s)                  FeSiO3(slag)

On the other hand, cuprous sulphide is oxidized to form cuprous oxide, which again reacts with remaining cuprous sulphide to form metallic copper.

2 Cu2S(1) + 3O2(g) ———> 2Cu2O(1) + 2SO2(g) #

                     2Cu2O(1) + Cu2S(1) ———> 6Cu(s) + SO2 (1) #

Steel

-Air

Metallic copper

Pivot

Bessemer converter used for bessemerization of copper.

 

 

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