Nitric acid is a strong, corrosive mineral acid that is colorless, though older samples appear yellowish. It is produced commercially at 68% concentration through three main methods, including the arc process. The arc process involves passing air through an electric arc chamber where nitrogen and oxygen combine at high temperatures to form nitric oxide, which is then oxidized to nitrogen dioxide and absorbed to produce nitric acid.

1. NITRIC ACID
Prepared by- Mr. Vishal B. Thakare
(M.Tech, Chemical SVNIT Surat)
Assistant Professor PARUL UNIVERSITY
Vadodara
vishalbt88@gmail.com

2. NITRIC ACID
 Nitric acid (HNO3) is a highly corrosive strong mineral acid.
 The pure compound is colourless, but older samples are yellowish
in colour due to the accumulation of oxides of nitrogen.
 Commercially available nitric acid having concentration of 68%
HNO3, while the solution containing more than 86% HNO3, is
referred to as fuming nitric acid.
 Depending on the amount of nitrogen dioxide present, fuming nitric
acid is further characterized as white fuming nitric acid or red
fuming nitric acid, at concentrations above 95%.

3. Nitric acid is manufactured by three methods.
a) From Chile saltpetre or nitrate process
b) Arc process or Birkeland or eyde process
c) Ostwald's process or Ammonia oxidation process
b) Arc process or Birkeland or eyde process
Raw materials
Basis: 1000kg Nitric acid (98% yield)
Air = 198kg
Water = 145kg

4. Reaction
N2 + O2 2NO ΔH = + 43.2 kcals
2NO + O2 2NO2 ΔH = - 26.92 kcals
4NO2 + 2H2O + O2 4HNO3
Nitric acid

6. Air freed from CO2 and moisture is passed through electric arc
chamber having two copper electrodes which are continuously
circulated by cold water and are connected with AC dynamo.
A powerful electromagnet placed at right angles to the electrodes
spreads the arc in the form of a disc.
The chamber is also provided with inside suction pumps for rapid
circulation of air across the flame through holes of refractory fire
work.
Nitrogen and oxygen of air combines at 2000oC temperature to
form nitric oxide.

7. The hot exit gases (1000oC) leaving the chamber is passed through
tube fire boiler for steam generation.
The gases are allowed to pass through oxidation chambers made of
iron and lined inside with acid proof stone. Here, nitric oxide is
further oxidizing to nitrogen peroxide in presence of air.
The exit gases from oxidation towers are passed through series of
absorption tower filled with broken quartz through which cold water
or dilute nitric acid is continuously sprayed from top.
The gases which enter from the base of 1st tower are leave at the
top. Continuous counter current flow of gases in each tower is
maintained by centrifugal fan.

8.  The 3rd tower is fed with cold water and the dilute nitric acid is
collected at the base is re-circulated to the top of the preceding
tower. 50% HNO3 is obtained at the base of 1st tower.
The gases are allowed to pass through two wooden towers which are
sprayed down by dilute solution of soda ash. The solution at the base
of sodium carbonate tower is evaporated to collect crystal of sodium
nitrate.