Properties a N D Catalytic Activity of a C I D - M O D I F I E D M O N T M O R I L L O N I T E a N D Vermiculite

-The acidic properties of acid-modified montmorillonite and vermiculite were determined by pyridine and ammonia adsorption to correlate with the alkylating and dehydrating activity of the activated samples. Treatment of the minerals with different concentrations of hydrochloric acid results in the variation of overall acidity and density of acidic sites. Infrared (IR) spectral and differential scanning calorimetric analyses have revealed the presence of Bronsted and Lewis acid sites on the activated samples. The catalytic activity towards the above reaction has been correlated to the acid strength and density of Lewis acid sites. Treatment of montmorillonite with hydrochloric acid in the range of 0.1 and 0.3 M and vermiculite with 0.2 to 0.3 M seemed to be suitable for the conversion of methanol into olefin-rich hydrocarbons. Acid-activated montmorillonite catalyzed the isopropylation of benzene to a maximum extent of 16%, whereas acid-activated vermiculite gave a maximum conversion of only 4%. Key Words--Acidity, Benzene, Catalyst Characterization, Hydrocarbons, Isopropylation, Methanol Dehydration, Montmorillonite, Vermiculite. I N T R O D U C T I O N Modified smectites exhibit attractive properties as solid acids (Pinnavaia 1983). These modified clay minerals have attracted considerable attention as acid catalysts for petroleum refining (Occelli 1983) and other acid-catalyzed reactions (Occelli et al. 1985; Burch and Warburton 1986). Hydroxyl groups on the surface of the layer aluminosilicates are very important with respect to the use of these solids in catalysis or adsorption. Treatment of clays with acid has been reported to replace exchangeable cations with H ions and leaching A1 and other cations out of both tetrahedral and octahedral sites, but leaving the SiO4 groups la rgdy intact (Theochaffs et al. 1988). The present study was undertaken to modify montmorillonite and vermiculite by treatment with hydrochloric acid. Acid treatment produces an increase in surface area and acidity. The nature, strength and density of acidic sites on activated samples have been investigated by IR spectroscopy and differential scanning colorimetry using pyridine and ammonia as probe molecules. The dehydration of methanol and alkylation of benzene (cumene synthesis) were carried out as test reactions for the acid-activated clay minerals. The effect of temperature and concentration of the acid used for the preparation of the catalyst also have significant influence on the catalytic activity. E X P E R I M E N T A L Montmori l loni te (Fluka) and vermicul i te (Tamil Nadu, Minerals , India) were treated with hydrochloric acid solutions at different concentrat ions in the range of 0.1 to 3 M (30 g clay/L). The suspensions were maintained at 100 ~ with stirring for 4 h. The samples were cooled to room temperature, col lected over a illter funnel and washed with double distil led water until free of excess acid. The samples were dried at 100 to 120 ~ for 12 h and calcined at 250 ~ for 2 h. The samples activated with 0.1, 0.2, 0.3, 0.4, 0.7, 1.0, 2.0 and 3.0 M hydrochloric acid are denoted as M1, M2, M 3, M 4, M 5 and M 6 for montmori l loni te (no 2.0 or 3.0 M samples) and V1, V2, V3, V4, Vs, V6, V7 and V8 for vermiculi te , respectively.