Highly selective aromatization of light naphtha using mesoporous aluminosilicate catalysts and theoretical model for predicting activity

In this work, various non-zeolitic catalysts were studied for the conversion of light naphtha into aromatics using a down-flow fixed bed reactor in a continuous mode operation. The physicochemical properties of the catalysts were determined using powder X-ray diffractometer, N2 sorption, atomic absorption spectroscopy, high-resolution transmission electron microscopy, NH3-temperature programmed desorption and thermogravimetric analysis techniques. Among the several non-zeolitic catalysts such as Al-SBA-15, mesoporous silica-alumina, SAPO-34, and calcined K-10 montmorillonite clay, Al-SBA-15 exhibited high light naphtha conversion of about 45% with 55% selectivity for aromatics. The rest of the catalysts though gave lower conversion, showed higher selectivity of > 90% for aromatics with a very low formation of cracking side products. The catalytic performance of non-zeolitic catalysts was compared with that of HZSM-5. The synergistic effect of physicochemical parameters such as acidity, pore volume, and pore diameter on the aromatic yield was theoretically deduced by constructing a non-linear model using the combination of the catalyst properties. To explore nature and to understand the responsible active sites involved in the mechanism for the light naphtha transformation to aromatics, the model compounds such as n-pentane, n-hexane, and cyclohexane were tested over mesoporous silica-alumina catalyst. The reaction parameters, viz. temperature, ratio of carrier gas to hydrocarbon, and weight hourly space velocity were optimized for obtaining a high aromatic yield. The 24 h time on stream study showed that the catalyst is resistant to coking and was able to retain its activity and selectivity for aromatics.