Question

Draw the flow for manufacturer of H2SO4 by contact process

Answer 1

Lead Chamber process is one of the sulphuric acid production methods which gives only about 50-60 Be grade acid. The main principle behind the process is that the moist SO2 (sulphur dioxide) in presence of nitrogenous oxides (active catalyst) is oxidized to sulphur trioxide with the oxygenpresent in air. Sulphur trioxide is made to react with water to produce sulphuric acid. The reactions would be like below:

2SO2 + O2 → 2SO3SO3 + H2O → H2SO4

Description of Lead Chamber process:

 

Sulphur is burned with air to produce sulphur dioxide gas and due to excess air burning, oxygen and nitrogen are present along with the sulphur dioxide. By means of filters solid particles are filtered leaving out clean gas mixture. Now the gas mixture is passed from combustion chambers to Glower’s tower through nitre pots where NO2 and NO are mixed. Glower tower is brick made chamber which are acid resistance, Burner gases that are SO2,O2,N2,NO2 and NO are at the temperature 450-650oC are passed to the bottom of Glower tower. In counter-current to these gases dilute sulphuric acid scrub down the Glower tower, the gases are cooled down to 70-80oC.

The acid scrub collected the bottom of Glower tower is passed to air cooler to bring the temperature from 130-150oC to 40oC which is to maintained for the feed of the lead chambers. A parallel set of lead chambers are setup where the walls and roof of chamber is fitted with lead sheets. Low pressure steam and filtered water are introduced at top of the chamber through spray nozzles. The acid thus formed condenses on the wall and collected as chamber acid which is a dilute sulphuric acid. The reaction carried by the nitrogen oxides at nitre pots are

2ONOSO2OH + H2O → 2H2SO4 + NO + NO2SO2 + NO2 + H2O → H2SO4 + NO

The unabsorbed gases from lead chamber are ready to enter into the Gay-Lussac’s tower where dilute concentration HNO3 used to react the upcoming gases of nitrosyl sulphuric acid. The reaction take place in the tower would be HNO3 + NO.HSO4 → 2NO2 + H2SO4 The oxides of nitrogen are absorbed by the glower acid forming nitrosyl sulphuric acid. NO + NO2 + 2H2SO4 ↔ 2.NOHSO4 + H2O The whole set up is explained by the following flowsheet of lead chamber process.



Oldest sulphuric acid manufacturing technology

Concentration of sulphuric acid is tested from the outlet of the tower frequently to ensure the quality and it is conducted continuously by indirectmeasurement method called specific gravity. It is calculated as the ratio of sulphuric acid density and water density measured at same temperature. Twaddell scale is one of the famous scale used in hydrometer to find specific gravity of acids which is related to the weight percentage. The formula for calculation of degree of Twaddell of sulfuric acid using specific gravity is: 200(Sp.Gravity-1.0)

 

Answer 2

A brief summary of the Contact Process

The Contact Process:makes sulphur dioxide;convert the sulphur dioxide into sulphur trioxide (the reversible reaction at the heart of the process);converts the sulphur trioxide into concentrated sulphuric acid.Making the sulphur dioxideThis can either be made by burning sulphur in an excess of air:. . . or by heating sulphide ores like pyrite in an excess of air:In either case, an excess of air is used so that the sulphur dioxide produced is already mixed with oxygen for the next stage.Converting the sulphur dioxide into sulphur trioxideThis is a reversible reaction, and the formation of the sulphur trioxide is exothermic.Converting the sulphur trioxide into sulphuric acidThis can't be done by simply adding water to the sulphur trioxide - the reaction is so uncontrollable that it creates a fog of sulphuric acid. Instead, the sulphur trioxide is first dissolved in concentrated sulphuric acid:The product is known as fuming sulphuric acid or oleum.This can then be reacted safely with water to produce concentrated sulphuric acid - twice as much as you originally used to make the fuming sulphuric acid.