Giovanni Zuretti

Alkylation of phenol with methanol over zeolites

Abstract The reaction of phenol with methanol was carried out over five X-, six Y- and three ZSM-zeolites, in a fixed-bed continuous reactor at 250°C. Alkylation products were cresols (o>p>m), anisole, xylenols and methylanisoles. The highest conversion and the highest yields of o- and p-cresols were obtained within the initial 5 h on-stream. Selectivity to o,p-cresols in the range 40-50% at phenol conversion 40-50% was reached on some X- and Y-zeolites, the best catalyst being HY.

Kinetic studies for processes of liquid-phase alkylation of aromatics over solid acid catalysts

The liquid-phase alkylation of aromatics has been effected traditionally with catalysis by inorganic acids or AlCl3 and similar compounds. However the increasing importance of solid acid catalysts is changing the procedures in this field. One of the prerequisites for the development of relevant processes, and the design of reactors, is knowledge of the kinetic data in reactions catalyzed by solid acids. This review examines the information available on the kinetics of alkylations catalyzed by solid acids, mainly zeolites, supported metal chlorides and oxides, mesoporous (MCM) materials, and heteropolyacids, but also other less studied materials.

Toluene disproportionation catalysed by various zeolites

Abstract Toluene disproportionation in the gas/solid phase was performed in a flow reactor (carrier H 2 or N 2 ) over some partially exchanged X and Y zeolites and, more systematically, over decationated Y, ZSM-5 and ZSM-11 zeolites. Activity, selectivity and stability of the catalysts were tested at temperatures up to 500°C, but mostly in the range 350°–400°C. Two samples HZSM-5 showed a considerably different catalytic behaviour: with one of them, shape-selectivity effects, favouring p -xylene, were observed during progressive deactivation (carrier N 2 ); the other one, of higher and stable activity, gave xylenes in the equilibrium isomeric ratios. Using the latter zeolite, kinetic measurements were carried out in a differential reactor at 240°–300°C (carrier H 2 ). A few kinetic models were tested.

The reaction of naphthalene with benzyl alcohol over a Nafion-silica composite: a kinetic study

A Nafion-silica composite was employed as catalyst for the reaction, in a slurry batch reactor at 80 °C, of naphthalene (NA) with benzyl alcohol in cyclohexane. The products, the benzylnaphthalenes (M) and several dibenzyl derivatives (D), included dibenzyl ether that was itself shown to be a weak benzylating agent. However, dibenzyl ether has also been shown to be a critical factor in catalyst stability. The kinetics of both the reaction of benzyl alcohol to give dibenzyl ether, and the benzylation of naphthalene by benzyl alcohol or mixtures of alcohol and ether, were studied, and the measurements interpreted by kinetic models.

Dimerization of 1-butene over nickel zeolitic catalysts : a search for linear dimers

Abstract Catalysts based both on nickel and ZSM-5 zeolites have been prepared and used for the dimerization of 1-butene. The reaction was performed at 40 and 80 bar and 100 to 200°C in a fixed-bed flow reactor with gas-chromatographic (GC) determination of alkenes product fractions characterized by their C atom number. Hydrogenation and GC analysis of the alkane C 8 isomers allowed determination of the degree of branching and of the linear isomers content of the C 8 fraction. The reactions detected were isomerization of 1-butene to 2-butenes, dimerization and further oligomerization of butenes. Favoured C 8 products were in every case several dimethylhexenes; however, under appropriate conditions, considerable fractions of linear octenes were obtained.

Comparison of different samples of HZSM-5 as catalysts for toluene disproportionation

Abstract Toluene disproportionation was performed at 300°–360°C in a fixed-bad reactor (carrier H 2 ) over samples of HZSM-5 differing in surface acidity, organic compound used for the synthesis, crystal size and procedure used for decationation. Xylene isomers in the product were in equilibrium ratios. The catalyst activity was found to be clearly dependent on surface acidity. An interpretation is given, in terms of a slow toluene disproportionation within the zeolite pores, followed by fast xylene isomerization on the external surface. Measurements of the reaction rate at 300°C over one of the catalysts confirmed a kinetic model as previously suggested.

Screening of solid acid catalysts for the condensation of acetaldehyde with o-xylene

Condensation of acetaldehyde with ortho-xylene was carried out in the presence of solid acid catalysts, in spite of the strongly competitive autocondensation of acetaldehyde to give crotonaldehyde. A semibatch reactor, with a continuous feed of paraldehyde into a stirred system containing o-xylene and the catalyst, proved more convenient to obtain 1,1-bis(3,4-di-methylphenyl)ethane, because it assures a high o-xylene/acetaldehyde ratio. High selectivity was found in runs at 140°C, over zeolitic catalysts of type Y (dealuminated) or β. Some catalyst deactivation was observed and a partial regeneration was found possible.