Introduction:
Sulfuric acid is one of the most widely used and important
industrial chemicals. It is highly corrosive and used in the
production of fertilizers, dyes, detergents, waste water treatment
and many other products. The manufacturing process of sulfuric
acid involves several steps that transform sulfur or sulfur-
containing compounds into sulfuric acid.
Raw Material – Sulfur:
Sulfur is the primary raw material used to make sulfuric acid.
Sulfur is a non-metallic element, chemically it is bonded with 2
Hydrogen, 1 Sulphur and 4 atoms of Oxygen. It is widely found in
nature in the form of underground deposits, as well as in crude
oil, natural gas, and other petroleum products. The sulfur is
typically extracted from underground deposits or recovered from
various sources using different processes.
Different process used for extraction and production of Sulphuric
acid are as follows:
Frasch Process
Claus Process
Contact Process
Frasch Process:
The Frasch process is a method of extracting sulfur from
underground deposits. It is the only method of extracting Sulphur
from elemental deposits. The process involves drilling down to the
sulfur deposit, injecting superheated water into the sulphur
deposit, and pumping out molten sulfur. The molten sulfur is then
transported to a storage facility, where it can be used as a raw
material for the production of sulfuric acid. Sulphur obtained can
be very pure (99.7 - 99.8 %).
In this process, three concentric tubes are introduced into sulphur
deposit. Superheated water at 165°C is injected through the
outermost tube which melts the sulphur (m.p. 115 °C) and it flows
into middle tube. Water pressure alone is unable to force the
sulphur due to molten sulphur’s greater density, so hot air is
introduced through innermost tube to froth the sulphur making it
less dense and pushing to the surface.
FRASCH
PROCESS
However, the Frasch process is expensive and is not now
currently in use because of the high cost of fuel needed to heat
water, therefore not suitable for for large-scale sulfur production.
CLAUS PROCESS:
The Claus process is widely used to recover sulfur from various sources such as
natural gas or hydrogen sulfide (H2S) containing gas streams. The process involves
burning the sulfur-containing gas with air to form sulfur dioxide and then
converting the sulfur dioxide to sulfuric acid by multiple reactions. The process is
energy-efficient, and it can recover sulfur from various sources
CONTACT PROCESS:
The Contact process is used to convert sulfur dioxide to sulfur trioxide (SO3). The
process involves the oxidation of SO2 in the presence of a catalyst, vanadium
pentoxide (V2O5). The oxidation reaction is carried out at a temperature of
around 450°C and a pressure of around 2 atmospheres. Excess air is also used in
the process to ensure complete oxidation of SO2. The reaction produces a
mixture of SO2 and SO3, which is then cooled and purified to obtain pure SO3.
Oleum:
Oleum is a solution of sulfur trioxide in sulfuric acid, and it is a vital
intermediate in the manufacturing process of sulfuric acid. The oleum is
produced by mixing SO3 and sulfuric acid in a reaction vessel. The reaction
is highly exothermic, and it is carried out at a temperature of around 100°C.
The oleum is used to make fuming sulfuric acid (oleum mixed with SO3),
which is used in some industrial applications.
Absorption Tower:
The absorption tower is the final stage in the sulfuric acid production
process. The tower is used to absorb the SO3 produced in the Contact
process. The tower contains a series of packed beds where sulfuric acid is
sprayed, and the SO3 is absorbed to form sulfuric acid. The reaction is
highly exothermic and generates a large amount of heat. To control the
temperature, the sulfuric acid is cooled by circulating water around the
packed beds.
Dilution:
The final step in the process is to dilute the concentrated sulfuric acid to
the desired strength. The concentrated sulfuric acid is highly corrosive and
can cause severe burns. Therefore, it is necessary to dilute the
concentrated sulfuric acid before use. The dilution is done by slowly adding
the concentrated sulfuric acid to water while stirring. The resulting solution
is highly exothermic, and it can generate a large amount of heat. Therefore
making Sulfuric Acid
