Catalyst Deactivation Model Research Articles

Systematic Procedures for Interpretation and Modeling of Catalyst Deactivation Using Integral Fixed-Bed Reactors

The method of decreasing conversion, constant space−time (DCCST) is sometimes used for empirical determination of catalyst decay kinetics in fixed beds. The method of constant conversion, increasing space−time (CCIST) is used infrequently. Although it is well known that these methods are most readily applied to cases in which the deactivation is independent of the composition of the fluid phase, the ease with which they can be misapplied to concentration-dependent cases has not been studied systematically. In this work, the empirical determination of catalyst decay kinetics in fixed beds has been examined by numerical simulation. It has been shown that it is rather easy to generate an invalid concentration-independent decay model, either by fitting a dubious straight line to a limited range of data using the DCCST method or by fitting a good, or even perfect, straight line using the CCIST method. It has also been shown that both methods can, in principle, be used reliably for empirical determination of ca...

Modeling of Catalyst Deactivation in Catalytic Wet Air Oxidation of Phenol in Fixed Bed Three-Phase Reactor

Modeling of Catalyst Deactivation in Catalytic Wet Air Oxidation of Phenol in Fixed Bed Three-Phase Reactor

ChemInform Abstract: Modeling of Catalyst Deactivation by Coke Formation

ChemInform Abstract: Modeling of Catalyst Deactivation by Coke Formation

Modeling of catalyst deactivation in zeolite-catalyzed alkylation of isobutane with 2-butene

The deactivation of solid acid catalysts in liquid phase alkylation of isobutane with 2-butene was investigated. Since under liquid phase conditions the alkylation reaction is severely diffusion limited, effects of diffusion on the rate of reaction and deactivation pathways were considered. In the present work, an attempt has been made to implement more appropriate assumptions in order to properly model catalyst deactivation in a mixed reactor. Accordingly, spatial variation of diffusivity in the pores of the catalyst was considered as a function of time on stream. The effect of the pore mouth plugging was also investigated and it was found that this phenomenon had a pronounced effect on the deactivation behavior of the catalyst. An empirical order of deactivation was determined through a power-law expression for alkylation over a faujasite (FAU) zeolite.

Hydrotreated-LCO oxidation in a transport reactor-hydrocyclon system for a low-emission fuel oil production. II Catalyst deactivation and simulation model

The CuCr/IP (4-PVP) catalyst deactivation was studied using continuous stirred-tank reactor (CSTR) laboratory equipment at different temperatures during the oxidation of a tetralin- and fluorene-doped diesel. The concentration of naphtho-aromatics molecules was followed as a function of time on stream, and the catalyst properties analyzed at the beginning and end of run. A computational program was developed to simulate the operation of a continuous recirculation slurry-hydrocyclon-type reactor. The program uses a Runge Kutta Felberg numerical method to solve the mass and energy balance equations for gas, liquid, and solid. For this calculation, it uses a plug flow recycle reactor model for the riser and a plug flow for the downcomer, in agreement with previous fluid dynamic study. The deactivation results indicate a low catalyst deactivation that can be modeled by using an exponential function of the time on stream. The simulation results show that the most important operating variables affecting activity and selectivity are the gas/liquid ratio, the solid hold-up, and the initial temperature. The study confirms the effect of both fluid dynamics and kinetics model parameters in the diesel quality improvement

Time Decay of the Activity of the Reduction Reaction of NO by CO on a Pd/Al2O3 Catalyst

An experimental study is made of the time decay of activity of the CO–NO reaction on a Pd/Al2O3 looking at the effect on reaction order and apparent activation energy. The optimum kinetics parameters fitting the steady state data at moderate pressures are determined. The time decay curves are analyzed through various catalyst deactivation models.

Optimal Hydrogen Production through Revamping a Naphtha-Reforming Unit: Catalyst Deactivation

Generating the necessary volume of hydrogen to produce high-quality gasoline has become a critical issue in some refineries, where an important hydrogen source is an old semi-regenerative catalytic naphtha-reforming unit. We studied the possibility of redesigning this unit to obtain an additional ∼0.1 millon of standard cubic metric per day of hydrogen while fulfilling the 15 ppm sulfur specification with the refurbished naphtha hydrotreater. The reforming unit (which has three equal-size reactors in series) was simulated using a previously developed kinetic lump model and a new catalyst deactivation model. The constants for the apparent kinetics model were adjusted using commercial data from one cycle of operation. The deactivation model was developed on the basis of pilot-plant and commercial data from an operating unit. The constants for both models were obtained using a genetic algorithm. The integrated model was used to both estimate the impact of including a new reactor and optimize existing reactor...

Catalytic Pyrolysis of Gas Oil Derived from Canadian Oil Sands Bitumen

The catalytic pyrolysis behaviors of gas oil derived from Canadian oil sands bitumen over catalyst CEP-1 in a confined fluidized bed reactor have been investigated in the present paper. The effect of reaction temperature, catalyst-to-oil weight ratio, steam-to-oil weight ratio, and residence time of oil gas on product distribution was researched. The results show that the optimal reaction temperature, weight ratios of catalyst to oil and steam to oil, and residence time of oil gas are about 660 °C, 15, 0.55, and 2 s, respectively. Under the optimal operating conditions, the yield of total light olefins exceeds 38.0 wt %. A new five-lump kinetic model is developed for the catalytic pyrolysis of gas oil, and a catalyst deactivation model based on the coke content is also presented. Rate constants and apparent activation energies were estimated with the least-squares method. The effect test shows that the five-lump kinetic model can predict the yields of gasoline, light olefins, light alkanes, and coke very ...

Aromatization of light naphtha fractions on zeolites, 3: Model of coke formation

In previous papers [1,2], we reported on the reaction kinetic and catalyst deactivation models for the Zeoforming process. The significant coking of a catalyst takes place, and two types of coke are formed. In this work the equations of coke accumulation are derived and its relations with relative activities are presented and discussed.

Modelling coke formation and deactivation in a FCCU

In this paper we describe a new model of catalyst deactivation due to riser reactions in a FCCU. For this purpose, we analyse different coke types and model the formation of each type based on oil feed properties rather than considering all cokes as being equal like other authors do. Thereafter, we examine different deactivation kinetic equations and propose an alternative that describes catalyst deactivation against coke as opposed to against time as in conventional approaches. Although it is easier to model deactivation against time, our model is more flexible and intuitive since it can simulate special situations, such when the catalyst is partially regenerated.

Catalytic pyrolysis of heavy oils: 8-lump kinetic model

A new 8-lump kinetic model is proposed to describe the heavy oil catalytic pyrolysis process. The kinetic model contains 17 kinetic constants and one for catalyst deactivation. This paper also presents a new catalyst deactivation model, a function of feed properties and operating conditions, in which the deactivation constant doesn’t vary with reaction temperature. Kinetic constants and apparent activation energies were determined by the least square regression analysis of the experimental data, obtained in a confined fluidized bed reactor at temperatures of 600, 630, 660 and 700 °C. Most of the apparent activation energies are higher than 100 kJ/mol, between the apparent activation energies for catalytic cracking and those for thermal cracking. The predicted results indicate that catalytic pyrolysis of heavy oils had better be conducted at high temperature and short residence time of oil gas, and heavy oils with the aromaticity higher than 30% had better not be considered as the feeds of catalytic pyrolysis.

Dynamic Modeling of Catalyst Deactivation in Fixed-Bed Reactors: Skeletal Isomerization of 1-Pentene on Ferrierite

In this work, we have derived a general dynamic model for a fixed-bed reactor involving combined reaction kinetics and deactivation kinetics. Catalyst deactivation was treated as a surface reaction among the other reactions. The evolved system of partial differential equations (PDEs) was solved numerically by the method of lines. Several rival deactivation mechanisms for ferrierite catalyst in skeletal isomerization of 1-pentene were investigated. The model assuming two adsorbed n-pentene molecules as surface species forming coke explained the experimental results best.

An integrated dynamic model for reaction kinetics and catalyst deactivation in fixed bed reactors: skeletal isomerization of 1-pentene over ferrierite

Catalyst deactivation in fixed beds is a critical issue in many industrial processes. A general dynamic model for fixed bed reactors involving catalyst deactivation was presented and simplified. The simplifications were based on the pseudo-steady state hypothesis for the fluid phase. Catalyst deactivation was treated by a linear model with respect to surface intermediates. A semi-analytical solution was obtained for the surface intermediates. The approach was applied to skeletal isomerization of 1-pentene over ferrierite. The comparison of experimental results and model predictions revealed that the model is able to describe the essential features of catalyst deactivation in skeletal isomerization and it can be useful for process scale-up.

Stability of Nanocrystals: Thermodynamic Analysis of Oxidation and Re-reduction of Cobalt in Water/Hydrogen Mixtures

The stability of nanosized materials differs significantly from the stability of bulk materials. In this study a thermodynamic analysis on the simultaneous oxidation and re-reduction of small metallic cobalt crystallites in the presence of water and hydrogen as a function of the crystallite diameter was performed as a model for catalyst deactivation in the Fischer-Tropsch synthesis. It is shown that spherical cobalt crystallites with a diameter less than 4.4 nm are likely to be oxidized under realistic Fischer-Tropsch synthesis conditions (p(H)(2)(O)/p(H)(2) < 1.5, T = 493 K).

Bisphenol A synthesis – modeling of industrial reactor and catalyst deactivation

Bisphenol A is an important starting material for production of epoxy resins and polycarbonates, which is manufactured by ion exchanger resin catalyzed condensation of acetone and phenol. Much higher reaction rate is achieved when in the reaction environment are present meracpto-group containing compounds. Alternatively, the promoter can be either dissolved in the reaction mixture or immobilized in the resin catalyst. Important problem of the process using the promoted catalyst is relatively rapid catalyst deactivation. Analysis of the reactor operation and mathematical modeling of its behavior indicate that the cause of the deactivation is a poison in the reaction mixture inhibiting the promoter. Proper design of laboratory experiments allows investigation of the deactivation process within acceptable time period and testing of possible preventive actions.

Model-Based Fault Detection for Three-Way Automotive Catalyst Systems

A model-based three-way automotive catalyst monitoring and fault detection strategy is presented in this work. A simplified oxygen storage and reversible catalyst deactivation model is employed to predict the measured postcatalyst air fuel ratio. A fault is assumed to be present in the system when the current distribution of the post-catalyst air fuel ratio prediction error differs from the base operating distribution. Changes in the post-catalyst air fuel ratio prediction error distribution are indicative of both long-term catalyst poisoning effects and short-term emission control device failures. These changes are detected based on the results of a Kolmogorov-Smirnov test Using sampled cumulative distribution functions. A moving horizon approach is used to determine the current error distribution.

Catalyst deactivation and engineering control for steam reforming of higher hydrocarbons in a novel membrane reformer

The catalyst deactivation and reformer performance in a novel circulating fluidized bed membrane reformer (CFBMR) for steam reforming of higher hydrocarbons are investigated using mathematical models. A catalyst deactivation model is developed based on a random carbon deposition mechanism over nickel reforming catalyst. The results show that the reformer has a strong tendency for carbon formation and catalyst deactivation at low steam to carbon feed ratios (<1.4 mol/mol) for high reaction temperatures (>700 K) and high pressures (>506.5 kPa) . The trend is similar for the cases without and with hydrogen selective membranes. Based on this preliminary investigation, an engineering control approach, i.e., in-site control with a concept of critical/minimum steam to carbon feed ratio, is proposed and used to determine the carbon deposition free regions for both cases without and with hydrogen membranes. The comparison between the reported data and model simulation shows that the critical steam to carbon feed ratio predicted by the model agrees well with the reported industrial/experimental operating data.

Hydrogen Production and Carbon Formation during the Steam Reformer of Heptane in a Novel Circulating Fluidized Bed Membrane Reformer

Hydrogen production and carbon formation during the steam reforming of heptane over nickel-based catalyst are investigated in a circulating fluidized bed membrane reformer (CFBMR) at 723−823 K and 101.3−2026 kPa. A random carbon deposition and catalyst deactivation model is developed to account for the effect of carbon deposition on the overall reforming kinetics. The results show that the deposited carbon can be efficiently gasified by steam, hydrogen, carbon dioxide, or oxygen in this novel CFBMR, making carbon-free operation practically possible, especially when steam to carbon feed ratio is higher than 2.5 mol/mol. The use of hydrogen permselective membranes breaks the equilibrium barriers associated with the reversible re-forming reactions and increases the hydrogen yield significantly. The introduction of oxygen into the adiabatic reformer can efficiently supply the heat necessary for the endothermic steam reforming through the exothermic oxidation, making an autothermal condition possible for the e...

Aromatization of light naphtha fractions on zeolites: 2. Model of catalyst deactivation

A model of catalyst deactivation in the "Zeoforming" process was developed. The deactivation rate constants and activation energies were estimated. The role of adsorbed oligomers in the reaction and the deactivation kinetics were examined. The model is intended for further modeling and optimization of the process.

Mathematical model of fcc catalyst deactivation

A model is proposed that explains both lab-scale and commercial unit FCC catalyst deactivation, taking vanadium mobility between particles into account. Equilibrium catalyst density fractionation is also simulated, helping in the interpretation of the commercial unit results.