A comparative study on H2SO4, HNO3 and HClO4 treated metakaolinite of a natural kaolinite as Friedel-Crafts alkylation catalyst

A natural kaolinitic clay from Padappakkara mine of Quilon District of Kera la, India, has been metakaolinized at 550 degrees C and activated separatel y with H2SO4, HNO3 and HClO4 of varying concentrations. The chemical compos ition. BET surface area, acidity distribution as well as alkylation activit y of these activated metakaolinites are studied. Silica to alumina molar ra tio, surface area and the number of strong acid sites increased on increasi ng the concentration of acid used for activation. Metakaolinite activated w ith 4 M HNO3 is found to possess the highest surface area and surface acidi ty. Alkylation of benzene with benzyl chloride at reflux was chosen as the test reaction. All the catalyst samples prepared were active for the benzyl ation reaction giving above 75 mol% conversion of the alkylating agent. Met akaolinite activated with 4 M HNO3 gave 87 mol% conversion of benzyl chlori de to diphenylmethane with 100% selectivity within 30 min of reaction time. This could be correlated well with the greater surface acidity of this sam ple. It is concluded that extremely efficient solid catalysts of remarkable acidic properties could be produced by the activation of metakaolinite wit h H2SO4, HNO3 and HClO4. (C) 1999 Elsevier Science B.V. All rights reserved .