Acid strength measurements of Amberlyst 15 resin, p-xylene-2-sulfonic acid and chlorosulfonic and sulfuric acid treated SiO2, Al2O3, TiO2 and MgO

The measurements of the minimum acid strength (HOmin) required for the initiation of cis-stilbene at 303 K and tert-butylbenzene at 313 K, 323 K and 333 K have enabled the establishment of a much more precise acid strength scale based on test reactions. HOmin values obtained were: − 9.0 (cis-stilbene, 303 K), − 9.3, − 9.5 and − 9.9 (tert-butylbenzene, 313 K, 323 K, 333 K). The updated method was used for the determination of the acid strength of different catalysts obtained in the reaction of chlorosulfonic and sulfuric acid on different oxide carriers. It was found that the acid strength values depended on the basicity of the studied supports. For the supports treated with chlorosulfonic acid the values of acid strength were: − 11.5 < HO ≤ − 10.8 in the case of the less basic SiO2 and − 9.3 < HO ≤ − 9.0 for the more basic TiO2, Al2O3 and MgO. For the supports treated with sulfuric acid the acid strength was: -9.3 < HO ≤ -9.0 for the less basic SiO2 and TiO2, − 9.0 < HO ≤ − 7.9 for the more basic Al2O3 and − 7.9 < HO ≤ − 6.9 for the most basic MgO. Silica treated with chlorosulfonic acid possesses higher acid strength than HZSM-5 and amorphous silicaalumina. The catalyst obtained in the modification of TiO2, Al2O3 and MgO with chlorosulfonic acid were of lower acid strength comparable to Amberlyst 15 and HZSM-5 (− 9.3 < HO ≤ − 9.0), but higher than p-xylene-2-sulfonic acid dihydrate (− 7.9 < HO ≤ − 6.9).