Influence Of Catalyst Deactivation Research Articles

Three-phase trickle-bed reactor model for industrial hydrotreating processes: CFD and experimental verification

Catalytic hydrotreating (HDT) is a process used to remove impurities from refinery streams, reacting a given feed with hydrogen at high temperature and pressure in a trickle-bed reactor. In order to optimize the operation of such reactors, one needs information about the detailed performance of the reactor. However, mathematical models of such reactors have not received due attention in last decades. Therefore, this work aimed at revisiting a plug flow HDT model to predict the performance of industrial diesel hydrotreating reactor, which considers most of the HDT reactions, gas-liquid and liquid-solid mass transfer, as well as the influence of catalyst deactivation and quenches injection on model predictions. A fourteen pseudo-component reactional network was proposed and successfully used. Computational fluid dynamics (CFD) predictions verified the plug flow behavior of the industrial HDT reactor. Both the CFD and plug flow models were verified using real process plant data, inspecting residual sulfur content and temperature profiles, with maximum relative error of 14%. Pressure and species concentration profiles as well as the effect of inlet pressure and temperature on final sulfur content were predicted and discussed. Catalyst deactivation is an important factor for accurate prediction of industrial HDT over time of campaign.

Kinetics of carbon nanotubes growth on a Ni–Mg–Al catalyst by CCVD of methane: Influence of catalyst deactivation

In this work, we present the application of a phenomenological kinetic model to the analysis of experimental results obtained with a LDH-based Ni–Mg–Al catalyst during the CCVD of methane. This model takes into account all the main stages implicated in CNT growth: methane decomposition, metal surface carburization, carbon diffusion, CNT nucleation and growth. The main causes of growth cessation, catalyst deactivation and steric hindrance have also been considered. The effect of the main operational variables, reduction (activation) and reaction temperatures and feed composition (hydrogen and methane composition), have been studied. The model fits very well the data obtained with the studied catalyst at the different operating conditions. As a consequence of the application of the model to the kinetic results, we can describe the influence of the operating conditions on each of the individual stages involved in the CNT formation.

Influence of catalyst deactivation on N2O emissions from automobiles

Though estimates of the total N2O emitted by automobiles differ widely, automobiles are believed to be a significant source of non-agricultural anthropogenic N2O emissions. At the Third Conference of the Parties (COP-3) UN Framework Convention on Climate Change, held in Kyoto in 1997, N2O was designated as a greenhouse gas whose release into the atmosphere must be reduced. This action increased the need for more accurate estimates of automotive N2O emissions. The wide variation in estimates may be attributed to differences in emission test modes, types of catalysts, and levels of catalyst deactivation involved in the tests. In this study, we examined the influence of automotive catalyst deactivation on N2O emissions from the perspective of catalyst temperature frequency distribution. Using a model gas and deactivated three-way catalysts (TWCs), we applied the exhaust emission test modes of various countries. The results indicate that the factor behind the increase of N2O emissions following catalyst deactivation is not growth in N2O generation, but a decline in the N2O decomposition capability of the catalyst. It was also found that the effect of catalyst deactivation differs according to the catalyst composition and the emission test mode.

Behavior of a pilot plant fixed-bed reactor during catalyst deactivation

The behavior of an non-adiabatic, non-isothermal fixed-bed reactor used for the hydrogenation of toluene has been studied under the influence of catalyst deactivation caused by continuous addition of thiophene to the reactant feed. Axial and radial temperature and concentration profiles were measured during deactivation. In spite of significant radial temperature gradients (Biot number = 5.25), it was possible to describe the reactor behavior with a one-dimensional pseudohomogeneous model. Mean cross-sectional temperatures can be used since the measured radial profiles are parabolic. The activation energy for thiophene adsorption derived from the measured profiles (4.7 kJ/mole) agrees with previous direct determinations in the literature.

Zur dynamik des katalytischen festbettreaktors bei katalysator-desaktivierung—I.

The influence of catalyst deactivation on the dynamic behaviour of a catalytic fixed-bed-reactor is investigated. Using the spatially one-dimensional two-phase-model and an additional differential equation for the activity, profiles of temperature and activity are shown and compared to experimental results. It turns out that, due to deactivation, moving reaction zones can occur even at constant inlet conditions and that, in case of rapid deactivation, serious overheating of the reactor may result.