*Manufacture of sulphuric* acid
Sulphuric acid is manufactured by contact process.
The process involves the following steps: {text:bookmark-start} {text:bookmark-end}
*1. Production of sulphur* dioxide
It is carried out by burning powdered sulphur or roasting of sulphur rich ores.
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{text:bookmark-start} {text:bookmark-end} *2. Oxidation of sulphur* dioxide
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This step is the key step in the manufacture of sulphuric acid. By applying Le-Chatelier's principle, the following conditions can be worked out for the better yield of sulphur trioxide. {text:bookmark-start} {text:bookmark-end}
Temperature
As the reaction is exothermic, a low temperature favors the forward reaction. An optimum temperature is maintained between 673-723 K.
{text:bookmark-start} {text:bookmark-end} Pressure
A high pressure favors the process. Thus, the optimum pressure of 1.5 - 2 atm. is maintained.
{text:bookmark-start} {text:bookmark-end} Catalyst
At such a low temperature the reaction is slow. Therefore, a catalyst is used.
d) Purity of gases
To prevent the poisoning of catalyst, the gases must be free from the impurities of As2O3 dust particles and moisture.
{text:bookmark-start} {text:bookmark-end} e) Excess of oxygen
To have a better yield of SO3, O2 is used in excess.
Conversion of SO3 into H2SO4 - SO3 is absorbed in conc. H2SO4 to get oleum. {draw:frame}
Oleum may then be diluted with calculated quantity of water to get H2SO4 of required concentration.
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The flow diagram of the plant used is as shown below.
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fig 8.7 - Flow diagram for the manufacture of sulphuric acid
The plant consists of:
{text:bookmark-start} {text:bookmark-end} *1. Sulphur* burner -
Here, sulphur dioxide is produced.
{text:bookmark-start} {text:bookmark-end} 2. Purification unit
This unit is an assembly of various parts like, a) Dust...