Nitric acid is a colorless, corrosive liquid used to make fertilizers, explosives, dyes, and other chemicals. It is produced via three main processes: Ostwald, HNO3 conversion, and dual pressure. These processes involve oxidizing ammonia to nitrogen oxides, absorbing the oxides in water to form nitric acid, and concentrating and purifying the acid. Understanding nitric acid production's unit operations and flow sheets provides insight into industrial chemical processes.

1. N I T R I C AC I D

2. I N T R O D U C T I O N
• Nitric acid is a colourless, highly corrosive liquid with a pungent odor.
• It is commonly used in the production of fertilizers, explosives, dyes, and other
chemicals.
• Nitric acid is also used in the manufacturing of metals, such as steel and brass, and
in the etching of metals and glass.

3. I M P O R TA N C E A N D U S E S
• Nitric acid is an important chemical in the manufacturing industry, as it is used in
the production of a wide range of products.
• It is used in the production of fertilizers, such as ammonium nitrate, which is used to
improve crop yields. It is also used in the manufacturing of explosives, such as
dynamite & TNT.
• It is used in the production of dyes, such as indigo, and other chemicals, such as
adipic acid, which is used in the production of nylon. It is also used in the
manufacturing of metals, such as steel and brass, and in etching of metals & glass.

4. R AW M AT E R I A L S
• Ammonia
• Oxygen
• Nitrogen Oxides

5. F L O W S H E E T D I AG R A M S

6. O S T W A L D P R O C E S S
• In this process, ammonia is oxidized to form nitrogen oxides, which are then
absorbed in water to form nitric acid.
The flow sheet diagram for the Ostwald process is as follows:
1. Oxidation of ammonia to form nitrogen oxides
2. Absorption of nitrogen oxides in water to form nitric acid
3. Concentration and purification of nitric acid

7. H N O 3 C O N V E R S I O N P R O C E S S
• In this process, ammonia is first oxidized to form nitrogen oxides, which are then
converted to nitric acid using concentrated nitric acid.
The flow sheet diagram for the HNO3 conversion process is as follows:
1. Oxidation of ammonia to form nitrogen oxides
2. Catalytic conversion of nitrogen oxides to nitric acid using conc. nitric acid
3. Concentration and purification of nitric acid

8. D U A L P R E S S U R E P R O C E S S
• The dual-pressure process is a variation of the Ostwald process.
• In this process, ammonia is first oxidized to form nitrogen oxides, which are then
absorbed in water to form dilute nitric acid.
• The dilute nitric acid is then concentrated using a dual-pressure system.

9. D U A L P R E S S U R E P R O C E S S
The flow sheet diagram for the dual-pressure process is as follows:
1. Oxidation of ammonia to form nitrogen oxides
2. Absorption of nitrogen oxides in water to form dilute nitric acid
3. Concentration of the dilute nitric acid using distillation under high pressure
4. Purification of the concentrated nitric acid to remove impurities
5. Concentration of the purified nitric acid using distillation under low pressure

10. U N I T O P E R AT I O N S & U N I T
P RO C E S S E S

11. O X I DAT I O N O F A M M O N I A
• It involves the reaction of ammonia and oxygen to form nitrogen oxides, which are
then used in the production of nitric acid.
• The oxidation of ammonia can be achieved using various methods, including
catalytic oxidation and arc oxidation.
4 NH3 + 5 O2 → 4 NO + 6 H2O
• This reaction is typically carried out in the presence of a platinum or rhodium
catalyst at temperatures between 800-900°C.

12. C ATA LY T I C C O N V E R S I O N O F
N I T R O G E N O X I D E S
• The catalytic conversion of nitrogen oxides is a unit process used in the HNO3
conversion process.
• It is the secondary oxidation.
• The catalytic conversion of nitrogen oxides can be achieved using various types of
catalysts, including platinum and rhodium gauze.
2 NO + O2 → 2 NO2

13. A B S O R P T I O N O F N I T R O G E N O X I D E S
• The absorption of nitrogen oxides is the second unit process in the production of
nitric acid.
• In this process, the nitrogen oxides produced in the oxidation of ammonia are
absorbed in water to form dilute nitric acid.
• The absorption of nitrogen oxides can be achieved using various methods,
including single-stage absorption and multistage absorption.
NO2 + H2O → HNO2 + HNO3

14. C O N C E N T R AT I O N A N D P U R I F I C AT I O N
O F N I T R I C AC I D
• The concentration and purification of nitric acid is the final unit process in the
production of nitric acid.
• In this process, the dilute nitric acid produced in the absorption of nitrogen oxides
is concentrated to the desired strength using various methods, including distillation
and absorption.
• The concentrated nitric acid is then purified to remove impurities, such as nitrogen
oxides and metals.

15. C O N C L U S I O N

16. C O N C L U S I O N
• The production of nitric acid involves various flow sheet diagrams, unit operations,
and unit processes, which are used to convert raw materials into the desired
product.
• The choice of flow sheet diagram and unit operations depends on various factors,
including the availability of raw materials, energy efficiency, and environmental
impact.
• By understanding the flow sheet diagrams and unit operations used in nitric acid
production, students can gain a better understanding of the chemical processes
involved in industrial manufacturing.