Kinetic study of the selective hydrogenation of styrene over a Pd egg-shell composite catalyst

Abstract

This is a study on the kinetics of the liquid-phase hydrogenation of styrene to ethylbenzene over a catalyst of palladium supported on an inorganic-organic composite. This support has a better mechanical resistance than other commercial supports, e.g. alumina, and yields catalysts with egg-shell structure and a very thin active Pd layer. Catalytic tests were carried out in a batch reactor by varying temperature, total pressure and styrene initial concentration between 353-393 K, 10-30 bar, and 0.26-0.60 mol L -1 , respectively. Kinetic models were developed on the assumptions of dissociative hydrogen chemisorption and non-negligible adsorption of hydrogen and styrene. Final chemical reaction expressions useful for reactor design were obtained. The models that best fitted the experimental data were those ones that considered the surface reaction as the limiting step. In this sense a two-step Horiuti-Polanyi working mechanism with half hydrogenation intermediates gave the best fit of the experimental data. The heats of adsorption of styrene and ethylbenzene were also estimated.

Modeling Styrene Hydrogenation Kinetics Using Palladium Catalysts

“…Corvaisier et al (2013) also estimated 23 kJ/mol as the apparent activation energy for a Langmuir-Hinshelwood model with the same hypotheses of the model D_I_SEH. However, the results of 14.947 kJ/mol obtained by Rojas and Zeppieri (2014) and 76.2 kJ/mol estimated by Betti et al (2016) differ from those obtained in this work. For the other models, the values calculated are too small and inconsistent with the apparent activation energy of a chemical reaction (Nijhuis et al, 2003).…”

“…For the heat of hydrogen adsorption, the result of model D_I_SEH was comparable to the studies of Abreu et al (2013) and Betti et al (2016), who found -177 kJ/mol and -108.9 kJ/mol, respectively. Reference values for the heat of ethylbenzene adsorption were found only in the work of Betti et al (2016) as -54.4 kJ/mol, a result relatively close to those of the models ND_I_SE and D_II_SEH. …”

“…The model ND_I_SEH, however, gave results similar to those of Zhou et al (2007;2010), which were -10.71 kJ/mol and -13.412 kJ/mol, respectively. The models D_I_SE and D_I_SEH were close to Betti et al (2016), which obtained -54.0 kJ/mol. For the heat of hydrogen adsorption, the result of model D_I_SEH was comparable to the studies of Abreu et al (2013) and Betti et al (2016), who found -177 kJ/mol and -108.9 kJ/mol, respectively.…”

“…These authors obtained a good fit with a Langmuir-Hinshelwood model considering the dissociative adsorption of hydrogen and only one type of catalytic site was tested. Betti et al (2016) investigated styrene hydrogenation using a palladium catalyst supported on an inorganic-organic composite. Horiuti-Polanyi and Langmuir-Hinshelwood mechanisms were considered for hydrogenation and adsorption, respectively.…”

Determination of mass transfer resistances of fast reactions in three‐phase mechanically agitated slurry reactors

“…Many researchers have studied the hydrogenations of unsaturated organic compounds by varying the hydrogen partial pressure but they have not manipulated the overall mass transfer resistance against the square root of hydrogen concentration in gas-liquid interface, C H 2 ;i = MTR H2 vs. C H2;i 0:5 . 3, 4 Tiwari et al 5 used the plot of C H2;i = MTR H2 vs. C H2;i to calculate the reaction rate constant of the surface reaction of 3,4-dimethoxyphenone, but they assumed negligible external mass transfer resistance in their model. Joshi et al 6 used also these kind of plots to calculate the reaction constants of homogeneously catalysed styrene hydrogenation.…”