Kinetics of deactivation

The observed rate varies with time and the catalyst activity decreases with all the variables of the system constant. The activity a is defined as the ratio between the observed reaction rate and the initial rate (when the catalyst is virgin), i.e.  

We take a simple case assuming an irreversible first-order reaction as  

Samples tested in the ethanol conversion at the indicated temperature 

It is assumed that the first-order kinetics, however, considering that the catalyst particles are porous, there may be diffusion effects. This initial rate or reaction rate of the virgin catalyst can be represented by  

The reaction rate is given by mass of catalyst, and in this case, the specific surface area of the particles Sg must be known. 

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If proteins are used as biocatalysts the reason for deactivation is often not quite as important as the rate of deactivation. The kinetics of deactivation over time under constant conditions of temperature, substrate, and product concentration can be determined analogously to other kinetics, most easily by following residual activity over time. In many cases, a simple negative exponential law [Eq. (5.72)] is found to describe deactivation. 

J.Coreila,A-Monzon,J.B.ButlrR.PlAt)S4l The modelling of the Kinetics of Deactivation of a Commercial Hydrocracking Catalyst in ihe Reaction of Cumene Disproportionation J.CatalysJs 100(1986)149... 

R Mantha.S.Bathia.M.S.Rao Kinetics of Deactivation In Methylation of Toluene over H-ZSM-5 and Hydrogen Mordenite Catalysts itKtEng.Chem.Res. 30 (1991) 281... 

Conversion and coke formation during catalytic ethene oligomerization catalyzed by HZSM-5 have been investigated in the TEOM and in a conventional gravimetric microbalance under similar conditions (2). The results show that the TEOM is a powerful tool for determination of the kinetics of deactivation of catalysts, with a design that makes determination of the true space velocity (or space time) easy. The TEOM combines the advantages of the conventional microbalance with those of a fixed-bed reactor, and the same criteria can be used to check for plug flow and differential operation. 

Deactivation caused by coke formation (coking rates, kinetics of deactivation,... 

J.N. Beliramini and R. Datta, React. IQnetics and Catalysts Ijetters, in press. J.N, Beltramini, T.J. Wessel, and R. Datta, Kinetics of Deactivation of FVAtaOg-Cl catalysts by Coking During Methylcyclopentane Reforming, submitted for publication. 

The independent variable in the deactivation kinetic equation at least 3 different types of kinetics of deactivation can be envisaged a-t, a-Cc and Cc-t. The mean residence time (or, in reality, the space-time) of the gas (tg) in the riser reactor can be calculated know ing the expansion factor (Ea) if cracking. But since the value of the slip... 

Goud et al.141 studied the kinetics of deactivation of Pd/Zr02 catalyst in the steam reforming of n-hexadecane. A first-order kinetic model, with first-order deactivation rate, was used to obtain the best fit values for the reaction rate constant and the deactivation rate constant as a function of S/C ratio, temperature, and sulfur loading. They noticed that the reaction rate was enhanced by an increase in temperatures and S/C ratios, but decreased by the presence of sulfur. The catalyst deactivation was more rapid in the presence of sulfur, at low S/C ratios and at lower temperatures. 

By studying a series of Rh/Ti02 catalysts of varying metal dispersion, we noticed that the deactivating effect of HTR for ethane hydrogenolysis could be better correlated with the extent of interfacial perimeter around the metal particle than with the extent of interfacial metal-support contact area. In addition, we found that the kinetics of deactivation followed a square root of time dependence, which is generally observed for diffu-... 

The simplifications realized in equation (6-130) arise from the isothermality, hence Ti = T, and so on. If it is wished to retain generality in the model where the mechanism (and kinetics) of deactivation is concerned, then... 

Fig. 1 shows one kinetic of deactivation of the hydrolysis activity obtained in fully uncoupled conditions and in the absence of added nucleotides in the medium. The initial rates of ATP-hydrolysis are in this case measured in the presence of pyruvate kinase (15U/ml) and PEP (O.SmM) to recycle the new- synthesized ADP. In these conditions the deactivation process is biphasic with half times of 17 [Pg.2040]

FIGURE 1. Kinetic of deactivation of the hydrolysis activity in fully uncoupled conditions and in the absence of exogenous nucleotides. 

Kinetics of hydroprocessing reactions, as well as kinetics of deactivation over carbon supported catalysts have been investigated under a wide range of... 

Intrinsic Kinetics of Coke Burn-Off The intrinsic kinetics of deactivation and regeneration of a reforming catalyst have been studied by Kern et al. (Kern, 2003 Kem and Jess, 2005 Ren et al., 2002). The main results are ... 

Corella, J. andMenendez, M., "The Modelling ofthe Kinetics of Deactivation of Monofunctional Catalysts with an Acid Strength Distribution in their Non-homogeneous Surface. Application of the Deactivation of Commercial Catalysts in the FCC Process", Chem. Eng. Sci., 41(7), 1817-1826 (1986). 

Recent theoretical studies of deactivation in individual particles have focused on bifunctional catalysts (19,20), on apparent overall kinetics of deactivation ( ), deactivation in nonisother-mal particles ( ), and the effect of nonuniform distribution of the catalytic function within the particle on deactivation (22,23, 24). ... 

An important development over the past few years is the large increase in those investigators who have been willing to determine the kinetics of deactivation in various reaction systems, mostly by coking, and then incorporate this information into appropriate models to interpret or predict integral reactor performance. Most of this has been done for fixed beds but important examples treat moving and fluidized beds as well. 

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