Liquid-Phase Hydrogenation Kinetics of Aromatic Hydrocarbon Mixtures

Abstract

The liquid-phase hydrogenation kinetics of one multiaromatic mixture and five binary aromatic mixtures of toluene, ethylbenzene, xylenes, and mesitylene were determined in a semibatch reactor operating at a pressure of 40 bar and a temperature of 125 °C. Commercial preactivated catalyst particles of nickel−alumina were used in the experiments. In mixtures, the aromatic compounds reacted in queues so that the most reactive components started to react immediately while the least reactive components did not react until the most reactive components had been hydrogenated completely. This type of reactivity decreased with the increasing number of substituents, i.e. in the order monosubstituted > disubstituted > trisubstituted. The relative positions of the substituents affected the reaction rate so that the reactivity decreased in the order ortho > para > meta. The queue effect was described with a kinetic model based on the rapid adsorption of aromatic compounds and hydrogen and sequential addition of hydrogen to the aromatic nucleus, the first hydrogen addition step being rate determining. The kinetic parameters were estimated from a heterogeneous reactor model with nonlinear regression analysis. The kinetic model was able to describe hydrogenation kinetics of the binary aromatic mixtures.

Hydrogenation of alkylaromatics over Rh/silica

“…The variations in the activity from the competitive reactions suggest that the strength of bonding is ortho > para > meta. This agrees with the order of reactivity found by Toppinen et al [15] in their study of xylene competitive hydrogenation. The higher cis:trans ratio for the 1,2-dimethylcyclohexanes is expected as the higher aromatic concentration would tend to inhibit re-adsorption to allow for isomerisation.…”

“…The competitive reaction between toluene and ethylbenzene reveals an increase in hydrogenation rate for both species (table 2). A previous study by Toppinen et al [15] gave different results in that no increase in rate was observed but the general behaviour was similar. This enhanced rate behaviour is unusual but has been observed before in the competitive reaction of pentynes [22] and pentenes [23].…”

“…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.…”

Comparison of sorbents and isotherm models for NH3‐gas separation by adsorption

“…Therefore, the estimated parameters of all isotherm models Ž were evaluated by established statistical methods Froment and Bischoff, 1990; see also Ronnback et al, 1994;Lehtonen . et al, 1995;Toppinen et al, 1996Toppinen et al, , 1997 . The accuracy of fit was evaluated on the basis of several standard statistical val-Ž 2 .…”

Measurement of Micro Kinetics of Hydrogenation in Liquid Phase Using Raman Spectroscopy

“…The influence of solvent on the obtained kinetics is well documented in the literature [9][10][11]. An extensive study of liquid-phase hydrogenation kinetics in the absence of a solvent was done by Toppinen et al [12][13][14][15] who investigated the hydrogenation kinetics of benzene and substituted alkylbenzenes. Battsengel [16] determined the hydrogenation kinetics of 1-octene, which is the test system for the validation of the experimental setup proposed in this article.…”