反应详情

The technical 3-sulphobenzoic acid melt, preferably not diluted, and the concentrated aqueous sodium hydroxide solution are pumped simultaneously into a mixing tube, the mixing tube being so designed that complete mixing takes place solely as a result of the turbulent flow produced. If desired the mixing process can also be assisted by internal fitments in the mixing tube, but this measure is not absolutely necessary. For example, 2,000 to 5,000 ml per hour of technical sulphonation melt can be mixed with corresponding quantities of sodium hydroxide solution in a mixing tube 500 mm in length and 5 mm in diameter, and can be conveyed into the reaction vessel for the subsequent pressure hydrolysis. This variant also can be carried out under normal pressure or under an elevated pressure, this elevated pressure being limited, if desired. If the initial temperatures of the components are suitably chosen, for example 150° to 180° C. for the sulphonation melt and 100° to 180° C. for the sodium hydroxide solution, a reaction temperature which is advantageous for the reaction to give 3-hydroxybenzoic acid, for example 270° to 320° C., will be reached at the end of the mixing tube. It can also be advantageous to carry out the mixing operation at a lower temperature or to limit the resulting steam pressure by blowing off steam. This process constitutes a partially continuous process in which the mixing operation in the mixing tube constitutes the continuous part of the process and the subsequent completion of the reaction in an autoclave constitutes the discontinuous part. However, since the reaction between the 3-sulphobenzoic acid and the alkali metal hydroxide becomes increasingly rapid in the upper part of the temperature range of 220° to 450° C. mentioned, it is also possible to complete the conversion into 3-hydroxybenzoic acid and thus the total reaction in a continuous form in the mixing tube itself, if the temperature is sufficiently high, for example in the region of 400° C. and if the corresponding pressure is maintained.

1. additionpreferably not diluted
2. additionthat complete mixing
3. customa result of the turbulent flow
4. customproduced
5. customcan be conveyed into the reaction vessel for the subsequent pressure hydrolysis
6. customa reaction temperature which is advantageous for the reaction