Kinetics of the Liquid Phase Hydrogenation of Di- and Trisubstituted Alkylbenzenes over a Nickel Catalyst

Abstract

The liquid phase hydrogenation kinetics of five di- and trisubstituted alkylbenzenes, xylenes, mesitylene, and p-cymene were determined in a semibatch reactor operating at hydrogen pressures of 20−40 atm and at temperatures of 95−125 °C. Commercial preactivated catalyst particles of nickel−alumina were used in all experiments. The hydrogenation activity of the aromatic compound was affected by both the number of substituents and their relative positions in the benzene ring. The trisubstituted benzene (mesitylene) had a lower reaction rate than the disubstituted compounds (xylenes). The activity of the different substituent positions decreased in the order para > meta > ortho. The main reaction product was always the completely hydrogenated cycloalkane; no cycloalkenes were detected. The hydrogenation rates were virtually constant at low and intermediate conversions of the aromatics, but at high conversions the rates decreased. Rate equations based on the formation of partially hydrogenated surface complexes were derived, and the kinetic parameters were estimated from a heterogeneous reactor model with nonlinear regression analysis. The rate equations were able to describe the features of the experimental data.

Hydrogenation of alkylaromatics over Rh/silica

“…In general the rate of hydrogenation decreases as the length of the substituent increases, while for the xylenes the para-isomer has been found to be the most active [5,6,9]. Toppineen et al [14,15] investigated in detail the hydrogenation of five aromatics (di-and tri-substituted alkyl benzenes, xylenes, mesitylene, and p-cymene) over Ni/Al2O3. They also concluded that the reaction rate is affected by the number, length and position of the substituent.…”

Single‐Face/All‐cis Arene Hydrogenation by a Supported Single‐Site d0 Organozirconium Catalyst

“…[1] Of particular interest for many applications is the selective creation of more saturated product stereoisomers, however these can be difficult to purify.A lkyl-substituted arenes such as xylenes have been the subject of extensive studies,a sb uilding blocks for more complex systems.I nvestigations with conventional heterogeneous hydrogenation catalysts such as Ni, Rh, Ru, Pt, and Pd have explored the scope and mechanism of both liquid phase and vapor-phase transformations. [2] Several studies reported promising selectivities (> 90 %) for the thermodynamically less favored ciscyclohexanes,h owever these catalysts require harsh reaction conditions (> 50 bar H 2 , > 50 8 8C, acid solvents). [3] To date,an allylcobalt system is ar are example of ah omogenous arene hydrogenation catalyst with excellent cis selectivity (> 95 %), however it undergoes rapid deactivation with < 15 %c onversions achieved.…”

Dynamic non-isothermal trickle bed reactor with both internal diffusion and heat conduction: Sugar hydrogenation as a case study

“…These kind of flux terms have been earlier used for semi-batch cases (Toppinen et al, 1996a(Toppinen et al, , 1996b.…”

“…The reaction kinetics for the verification case was a Langmuir-Hinshelwood expression, that is typical of hydrogenation studies (Toppinen et al, 1996a(Toppinen et al, , 1996bCrezee et al, 2003) including a correction (˛) for catalyst deactivation, Eq. (11).…”