Chemometrics applied to the optimization of the preparation of hydrotropes for detergents starting from BTX fraction of natural gas

Manufacturers of cleaning products use hydrotopes to increase the solubility of surfactants in concentrated liquid detergents. In contrast to benzenesulfonate, alkylbenzenesulfonates with short chains (n < 4) are used as hydrotopes. In this paper, we present the results obtained from the preparation of toluenesulfonic and xylenesulfonic acids by selective sulfonation of toluene and xylenes present in the BTX fraction (benzene, toluene, xylenes) of the Tunisian natural gas MISKAR deposit. Chemometrics were applied to determine the optimal experimental conditions for the selective sulfonation of toluene and xylenes, we use a 2 IV 6-2 fractional factorial design in addition to several analytical methods (GC, HPLC, FTIR...). These conditions were found to be: the use of concentrated sulfuric acid as sulfonating agent, the azeotropic elimination of water during the reaction, a temperature of 110 °C, a duration of 9 hours and a molar ratio of sulfuric acid to toluene plus xylenes of 0.8. The application of all of these experimental conditions gives an aqueous phase with a composition that can be used very effectively as hydrotope agent in liquid detergents. This conclusion was the outcome from comparing the effect of our product on the clear point of a typical premium formulation of a liquid detergent to that of sodium xylenesulfonates, the most important hydrotope for light duty liquids.