kinetic study of the support acidity effects of nimo sulfide catalysts on quinoline hydrodenitrogenation
Résumé
The improvement of hydrodenitrogenation (HDN) catalytic activity is important due to poisoning effects of nitrogen compounds on acidic catalysts and their inhibiting effects on hydrotreating reactions [1,2]. HDN reaction networks usually comprise a complex set of hydrogenation, ring opening and C-N bond breaking reactions. In order to understand how modifications of HDN catalysts act on this complex reaction network, a detailed kinetic analysis is necessary.
In this work we present a very detailed kinetic study of the HDN of quinoline in a batch reactor. The Langmuir-Hinshelwood model includes liquid-vapor mass transfer, which is essential for obtaining reliable kinetic parameters. Each catalyst is tested at different concentrations of quinoline and different temperatures. Thus, 981 experimental points are obtained, which allow the simultaneous estimation of 39 parameters, i.e. activation energies and heat of adsorption. The catalytic tests were carried out over NiMo(P) sulfide catalysts supported on γ-Al2O3 and SiO2-Al2O3. Table 1 summarizes the characteristics and catalytic properties of the two catalysts.
Table 1 â Characteristics and catalytic properties of the NiMo catalysts
NiMo(P)/Al2O3NiMo(P)/SiO2-Al2O3
Weight content of MoO3 / NiO, wt %18.6 / 3.8414 / 2.97
Cyclohexane isomerization conversion, %2288
NiMoS promoted phase content (mmol/g catal.)0.3260.205
Position of NiMoS band in IR Spectroscopy of adsorbed CO (cm-1)21292134
Effective rate constant of 14THQ â DHQ step (s-1)0.070.12
Effective rate constant of OPA â PB step (s-1)0.0460.173
Our kinetic modeling shows that the hydrogenation of 1,2,3,4-tetrahydroquinoline (14THQ) into decahydroquinoline (DHQ) is the determining rate step of the main reaction pathway for both catalysts. The NiMo(P)/SiO2-Al2O3 exhibits a higher rate constant in the hydrogenation of 14THQ and Csp2-N bond cleavage of o-propylaniline (OPA) into propylbenzene (PB). This is attributed to the modification of the electronic properties of promoted phase due to the higher acidity of NiMo(P)/SiO2-Al2O3, as confirmed by Infrared Spectroscopy of CO. The adsorption constants of nitrogen compounds are higher on NiMoP/SiO2-Al2O3 than on NiMoP/γ-Al2O3, which results in higher self-inhibition effects of quinoline and N compounds over NiMoP/SiO2-Al2O3. As a consequence of this higher self-inhibition, the overall activity of the silica-alumina supported catalyst becomes lower than for the alumina-supported catalyst.