Method for producing 2-acrylamido-2-methylpropane sulphonic acid

A production process for 2-acrylamido-2-methylpropane sulfonic acid including at least the following successive steps:

• 1) mixing of acrylonitrile with at least one compound contributing SO3 at a temperature included between −80 and 30° C. for at least one second in order to obtain a sulfonating mixture;
• 2) placing in contact and mixing isobutylene and the sulfonating mixture with a molar ratio of SO3 to isobutylene included between 0.2:1 and 2:1 and a molar ratio of acrylonitrile to isobutylene included between 3:1 and 60:1 at a temperature included between −40 and 100° C. for a time included between 10 seconds and 300 minutes in order to obtain a reaction mixture;
• 3) solid/liquid separation of the reaction mixture and isolation of the solid particles contained in the reaction mixture in the form of a composition 1 in which the solid particles represent 50 to 99% by weight of the composition 1;
• 4) mixing composition 1 at the end of step 3) with an aqueous solution A for at least 10 minutes at a temperature included between −20 and 70° C. in order to obtain a suspension 1 of 2-acrylamido-2-methylpropane sulfonic acid crystals;
• 5) solid/liquid separation of the suspension 1 and isolation of the crystals in the form of a composition 2 in which the crystals represent between 40 and 99% by weight of the composition 2.