Manufacture of Sulphonating Agents Such as 25 and 65 % Oleums as well as Liquid Sulphur Trioxide

Abstract

In order to produce gaseous as well as liquid trioxide it is essential that manufacture of oleums by absorption of sulphur trioxide from plant gases producing sulphuric acid. Pure (99 % +) sulphur trioxide can be produced by boiling 25 % oleum. This can be liquefied or used for producing 65 % oleum. Until the mid-50s all sulphonations were carried out by use of Sulphuric Acid of different strengths. The reactions carried out by Sulphuric Acid were not able to give the conversion efficiencies that were economical, especially in the manufacture of detergents. In certain dye intermediates the higher strength Sulphuric Acid was found to be an essential part of the chemical reaction. This led to many of the Sulphuric Acid plants to manufacture “Fuming Sulphuric Acid” popularly known as Oleums. The initial product was in the range of 20–25 % Oleum which meant 20–25 % free SO₃ dissolved in Sulphuric Acid. The basic reaction carried out in the Oleum Tower is absorption of SO₃ in the Sulphuric Acid to form an adduct ${\text{H}}_{ 2} {\text{SO}}_{ 4} + {\text{SO}}_{ 3} = {\text{H}}_{ 2} {\text{S}}_{ 2} {\text{O}}_{ 7}$.