Deactivation Kinetic Research Articles

A framework for modeling of catalyst deactivation and coking free of main-reaction kinetics in methanol to gasoline process

Optimizing the methanol-to-gasoline technology necessitates a profound comprehension of catalyst deactivation and coke formation kinetics. However, conventional mathematical models cannot capture catalyst deactivation without relying on complex main-reaction kinetic models, and they treat the prediction of coking as a separate problem. Addressing these challenges, this research introduces a computational framework to identify the optimal model for the kinetics of deactivation and coking. The key novelty is leveraging the concept of active site loss to eliminate the requirement for main-reaction kinetic models while facilitating the prediction of coking according to the site loss model. Experimental data of an HZSM-5 catalytic bed under diverse operating conditions (WHSV: 10–100 h−1, temperature: 325–375 °C) were employed to validate method efficiency for predicting reactor outputs, including oxygenates, light olefins, and gasoline. The proposed approach demonstrates a 0.52 % Root-Mean-Square-Error in simulating product weights and a 66 % reduction in deactivation kinetic constants. This study reveals assuming a critical volume for each grown coke precursor justifies experimental data by R2 of 99.71 %. This volume was computed around 100 Å3 and exhibits a linear Arrhenius temperature dependency. These results highlight the high accuracy and extreme simplicity this framework offers. Moreover, the method transforms deactivated catalyst data at varying WHSVs into a larger unified dataset for the fresh catalyst at each isotherm. Hence, it also positively impacts the kinetic study of main reactions. Consequently, the developed framework is a promising tool for direct assessment of catalyst deactivation and coking in similar processes toward advancing catalyst design strategies and fuel production efficiency.

Controllable fabrication of persimmon wood-inspired macroporous (a%Co-Mn)1.5Al0.5Ox, high desulfurization performance and analysis of deactivation kinetic mechanism

The removal of H2S that seriously threaten the environment and human health is of great significance in enhancing coal cleaning utilization. Herein, a series of persimmon wood-inspired macroporous (a%Co-Mn)1.5Al0.5Ox (a = 0, 3, 6, 10, 15, 20) sorbents were constructed by the self-assembly of vacuum-assisted sol–gel procedure, and their desulfurization efficiency was evaluated on a fixed-bed reactor at 600–800 °C. Among cobalt-doping sorbents, the breakthrough sulfur capacity (BSC, 272.2 mg g−1) and effective utilization (EU, 81.5%) over (15%Co-Mn)1.5Al0.5Ox is greatly high than the value (138.08 mg g−1) over ZnCoO4/SAPO-34@SBA-15, and slightly lower than BSC (286.2 mg g−1) and EU (92.3%). The magnification SEM images of (15%Co-Mn)1.5Al0.5Ox revealed that regularly straight macroporous channel structure inherited from persimmon wood effectively promoted the rapid diffusion of H2S molecules and accelerated the rate of sulfur/oxygen exchange on the interface of the channel wall. In the meantime, the results studied by the deactivation kinetics model also confirm invariable rate constants (ka, kd) with high correlation coefficients due to higher stability and renewable ability of (15%Co-Mn)1.5Al0.5Ox.

A kinetic study of ethanol coupling with acetaldehyde to 1,3‐butadiene over Zr‐β zeolite: insight into deactivation

AbstractBACKGROUNDWith the improvements in bioethanol production, the process of converting ethanol to 1,3‐butadiene (ETB) has received substantial scholarly attention, whose industrialization has been constrained by the stability of the catalysts.RESULTSIn this work, the deactivation behavior of Zr‐β zeolite in the process of ethanol/acetaldehyde conversion to 1,3‐butadiene was investigated. In addition, the deactivation kinetics of ETB was studied using an isothermal differential microreactor. A kinetic model was developed and parametrized with the Langmuir–Hinshelwood mechanism, and the intrinsic kinetic equation was derived. The deactivation kinetic model of the ETB reaction was established from the active site content of the catalyst as a function of time on stream. The validity of the kinetic model was tested, and the results were found to be accurate.CONCLUSIONSCatalyst deactivation was mainly caused by coke species, which are mainly long‐chain unsaturated oxygenated organic compounds and aromatic compounds, covering Lewis acid sites in the microporous channels of the catalyst; nevertheless the zeotype topology and morphology were not destroyed. The kinetic data suggested that the reaction was of first order and the activation energy of the deactivation process was 75.59 kJ mol−1. © 2023 Society of Chemical Industry (SCI).

Deactivation kinetic study on vapor phase Beckmann rearrangement of cyclohexanone oxime and design of the multi-layer inclined channel bionic reactor

The optimal design of the reaction system of a large-scale industrial vapor phase Beckmann rearrangement of cyclohexanone oxime to caprolactam process requires both deactivation kinetics and reactor optimization. The deactivation kinetics was study in a micro fluidized bed reactor with online catalyst particle sampling system. An empirical coke formation rate equation was obtained based on time evolution of coke amounts. A Langmuir-Hinshelwood kinetics with deactivation factor based on coke amount was developed. Based on the obtained deactivation kinetics, a Multi-layer Inclined Channel Bionic Reactor was designed as a substitute of the conventional fixed-bed reactor. The hierarchical structure has four levels with inclined channel implementation in the third and fourth level to reduce the pressure drop and improve the flow distribution uniformity. The optimized massive structure of the Multi-layer Inclined Channel Bionic Reactor designed for 200 thousand tons of CPL productivity has a total pressure drop lower than 2kPa, and the maximal relative difference of the bed infiltration velocity is about 11 %.

Green process of fuel production under porous γ-Al2O3 catalyst: Study of activation and deactivation kinetic for MTD process

One of the methods of industrial dimethyl ether production is the catalytic dehydration of methanol. In this research work, methanol dehydration reactor has been modeled using continuous model and its results have been compared with experimental works and Voronoi pore network model. A 1D heterogeneous dispersed plug flow model was utilized to model an adiabatic fixed-bed reactor for the catalytic dehydration of methanol to dimethyl ether. The mass and heat transfer equations are numerically solved for the reactor. The concentration of the reactant and products and also the temperature varies along the reactor, therefore the effectiveness factor would also change in the reactor. We used the the effectiveness factor that was simulated according to the diffusion and reaction in the catalyst pellet as a Voronoi pore network model. Sensitivity analysis was performed to determine the influence of T, P and weight hourly space velocity on performance of the chemical reactor. Acceptable agreement was reached between the measured and the model data. The results showed that the maximum reaction conversion was obtained about 90 % at WHSV = 10 h−1 and T = 560 K, while the inlet temperature (Tinlet) had a greater effect on methanol conversion. In addition, the effect of water in the feed on methanol conversion was quantitatively studied. Also, the deactivation kinetics of γ-Al2O3 heterogeneous-acidic catalyst in methanol to dimethyl ether dehydration process was studied using integral analysis method. Based on independent deactivation kinetics, a second order was found that accurately fitted the experimental conversion time data. The main reaction activation energies and catalyst deactivation energies were 143.1 and −102.1 kJ/mol, respectively.

Modulation of KV7 Channel Deactivation by PI(4,5)P2.

The activity of KV7 channels critically contributes to the regulation of cellular electrical excitability in many cell types. In the central nervous system, the heteromeric KV7.2/KV7.3 channel is thought to be the chief molecular entity giving rise to M-currents. These K+-currents as so called because they are inhibited by the activation of Gq protein-coupled muscarinic receptors. In general, activation of Gq protein-coupled receptors (GqPCRs) decreases the concentration of the phosphoinositide PI(4,5)P2 which is required for KV7 channel activity. It has been recently reported that the deactivation rate of KV7.2/KV7.3 channels decreases as a function of activation. This suggests that the activated/open channel stabilizes as activation persists. This property has been regarded as evidence for the existence of modal behavior in the activity of these channels. In particular, it has been proposed that the heteromeric KV7.2/KV7.3 channel has at least two modes of activity that can be distinguished by both their deactivation kinetics and sensitivity to Retigabine. The current study was aimed at understanding the effect of PI(4,5)P2 depletion on the modal behavior of KV7.2/KV7.3 channels. Here, it was hypothesized that depleting the membrane of P(4,5)P2 would hamper the stabilization of the activated/open channel, resulting in higher rates of deactivation of the heteromeric KV7.2/KV7.3 channel. In addressing this question, it was found that the activity-dependent slowdown of the deactivation was not as prominent when channels were co-expressed with the chimeric phosphoinositide-phosphatase Ci-VS-TPIP or when cells were treated with the phosphoinositide kinase inhibitor Wortmannin. Further, it was observed that either of these approaches to deplete PI(4,5)P2 had a higher impact on the kinetic of deactivation following prolonged activation, while having little or no effect when activation was short-lived. Furthermore, it was observed that the action of either Ci-VS-TPIP or Wortmannin reduced the effect of Retigabine on the kinetics of deactivation, having a higher impact when activation was prolonged. These combined observations led to the conclusion that the deactivation kinetic of KV7.2/KV7.3 channels was sensitive to PI(4,5)P2 depletion in an activation-dependent manner, displaying a stronger effect on deactivation following prolonged activation.

Deactivation kinetics of individual C6-C9 aromatics' generation from methanol over Zn and P co-modified HZSM-5.

A deactivation kinetic model has been determined for the methanol to aromatic process over a HZSM-5 zeolite catalyst (SiO2/Al2O3 = 30) modified by 1.0 wt% ZnO and 2.0 wt% P, in which the generation rates of C6–C9 aromatics are treated individually while olefins and paraffins are lumped as intermediate and byproduct, respectively. The time-dependent catalytic activity is described by a deactivation coefficient related to the concentration of both methanol and products. The established kinetic model is able to predict the product distribution along with on-stream time under various conditions and is identified to be valid by a model significance test. The effect of operating conditions on catalyst behavior was also investigated: deactivation rate increases dramatically with methanol partial pressure and temperature; higher feed methanol content leads to less aromatics and more paraffin; increasing temperature reduces paraffin generation and results in higher aromatic yield, especially benzene and toluene.

Deactivation kinetics with activity coefficient of the methanol to aromatics process over modified ZSM-5

A lumped kinetic model for methanol to aromatics (MTA) process was investigated using modified ZSM-5 industrialized catalyst. The deactivation kinetic behavior of MTA was studied by developing a 5-lump kinetic model to describe the product distributions. The feedstock and products are divided into five lumps by simplifying reaction network, including oxygenates (methanol and dimethyl ether), C1 (CO, CO2, CH4 and H2), aliphatic hydrocarbons, light aromatics (C6-C8) and heavy aromatics (C9+). The catalytic activity was reflected by activity coefficient a. The deactivation model kinetic parameters were estimated using simplex and nonlinear least squares methods. This model can be used to predict key products and their compositions of MTA industrial process.

Deactivation Kinetics for the Carbonylation of Dimethyl Ether to Methyl Acetate on H-MOR

The carbonylation of dimethyl ether (DME) to methyl acetate (MA) is one of the crucial steps in an indirect synthesis route of ethanol from syngas (CO+H2). The H-MOR zeolite exhibits excellent activity and selectivity at mild conditions. However, the catalyst suffers rapid deactivation due to the carbonaceous deposits on Bronsted acid sites. In this study, the deactivation kinetics for the carbonylation of DME to MA on the H-MOR zeolite was investigated. Based on the fitting results and in situ FTIR analysis, a model taking into account the composition concentration was established. This deactivation kinetic model allows simulating the concentration of different compounds in the reaction medium with time on stream under different experimental conditions. In this model, coke is considered to be derived from DME and CO. Moreover, CO remarkably accelerates the coke formation, and the effect of its concentration on the deactivation rate is quantified. The establishment of deactivation kinetics will be conduct...

Deactivation kinetics for the conversion of dimethyl ether to olefins over a HZSM-5 zeolite catalyst

A deactivation kinetic equation for the conversion of dimethyl ether (DME) to olefins (DTO process) has been established. The catalyst has been prepared with a HZSM-5 zeolite (SiO2/Al2O3 ratio of 280) agglomerated with boehmite (mesoporous matrix of weak acidity). The experimental data have been obtained in an isothermal fixed bed reactor in a wide range of operating conditions: temperature, 573–673K; space time, 0.2–6gcathmolC−1; time on stream, 18h; and different dilutions of DME (with He, methanol and water). The main cause of the catalyst deactivation is the coke deposition, being DME the principal precursor and the presence of water in the medium a key parameter in its attenuation. The kinetic model considers these effects and its use together with the kinetic model at zero time on stream results suitable to simulate the reactor over the whole range of operating conditions experimentally studied.

Investigation of the performance and deactivation behavior of Raney-Ni catalyst in continuous dehydrogenation of cyclohexane under multiphase reaction conditions

The performance and deactivation behavior of Raney-Ni catalyst in continuous dehydrogenation of cyclohexane under multiphase reaction conditions were investigated in this paper. The experimental results showed that Raney-Ni had excellent catalytic activity for dehydrogenation of cyclohexane. Without assistance of any sweeping or carrier gas, the highest hydrogen evolution rate per unit reaction area could reach 0.20mmolcm−2min−1 at 322°C with a cyclohexane feeding rate of 8.5mmolmin−1 and Raney-Ni catalyst dosage of 3g. However, the deactivation of Raney-Ni catalyst was also observed during the course of reaction. The deactivation kinetics of Raney-Ni was studied, and the orders of deactivation at different reaction temperatures were determined, which showed that the decay of Raney-Ni catalyst was parallel deactivation. The equations of hydrogen evolution rates at different reaction temperatures were deduced from the deactivation kinetic equations. Due to the strong purging effect caused by the rapid evaporation of liquid organics on the catalyst surface under multiphase reaction conditions, the dehydrogenation reaction was confined to the outer layers of catalyst pallet and an ultralow apparent activation energy of 20.60kJmol−1 was obtained.

Hydrotreating Residue Deactivation Kinetics and Metal Deposition

Introducing a fractional type of time-varying activity coefficient, the residue hydrotreating catalyst deactivation kinetic model was established. On the basis of the operating conditions and data collected from a commercial residue hydrotreating units, the kinetic parameters such as the reaction order, activation energy, reaction rate constant, and the activity coefficient were estimated, and the time-varying equations of the activity coefficient were obtained. By timely measuring the metal content of inlet and outlet flows of the catalytic bed, and through its material balance of each period, the amount of metal deposition accumulating on the catalyst was determined. The relationship between the metal deposition and the activity coefficient was analyzed and discussed. It was found that the amount of metal deposition was linearly related with the activity coefficient in the stable operation period, this feature indicated that the reaction rate was controlled by pore diffusion in this stage. Combining the...

Deactivation kinetics of platinum-based catalysts in dehydrogenation of higher alkanes

The deactivation of promoted Pt-Al 2O 3 catalyst in dehydrogenation of C 10–C 14 normal paraffins to the corresponding mono-olefins was studied. Two models based on reversible and irreversible main reaction and nth order, concentration-independent deactivation kinetic was used. The kinetic parameters were obtained by utilizing non-linear estimation functions of industrial plant time–temperature trajectory data. The reversible reaction model showed a better fit to the plant data. The results were also checked through integral analysis of experimental data. The results of both approaches were consistent and showed a second-order decay law. The activation energies of the dehydrogenation and catalyst decay were found to be E A = 90 kJ/mol and E d = 140 kJ/mol, respectively. The larger activation energy for catalyst deactivation compared to that of main reaction implies that catalyst decay is much more temperature sensitive than main reaction.

Deactivation kinetics of immobilized glucose oxidase for production of calcium gluconate in an external loop airlift bioreactor

In our previous works, the immobilized glucose oxidase (GO) plus manganese dioxide (MnO 2) were prepared and efficiently used at 30 °C for production of calcium gluconate (CaG) in an external loop airlift. In the gel beads occurred the three reactions: (1) the GO-catalyzed air oxidation of glucose to produce gluconic acid (GA) and hydrogen peroxide (P) which inactivated GO, (2) the MnO 2-catalyzed decomposition of P and (3) the neutralization of GA with calcium hydroxide added continuously resulting in accumulation of CaG at a constant pH. In this work, the stabilities of the immobilized GO and MnO 2 activities to various operating conditions are observed and analyzed to develop an efficient prolonged use of GO plus MnO 2 entrapped. The well-known first-order kinetics is assumed to analyze the deactivation of either GO or MnO 2 since its stability is affected by a complicated interaction among the operating variables. The first-order deactivation rate constant for GO, k d,E is determined from the progressive decrease in the apparent effectiveness factor for GO, α app based on the initial GO concentration C E,0 in the gel beads. This is because the decrease in the GO concentration, C E is too difficult to measure but approximately directly proportional to α app. The k d,E value under any set of operating conditions is determined from the two values of α app at the start and end of the 24 h reaction. To obtain the k d,E values for the prolonged times, the repeated 24 h reactions are carried out with the same gel beads. Examining the data on k d,E obtained under the various operating conditions gives an empirical correlation of k d,E with the pH value and the P concentration C P which is the time-averaged P concentration during every 24 h reaction. The other variables such as the glucose and gel beads concentrations and the superficial air velocity are found to exert almost no influence on the k d,E value. On the other hand, the deactivation rate constant for MnO 2, k d,M is determined from the two values of the intrinsic P decomposition rate constant, k P in the same 24 h reaction as above since the k P value, which is proportional to the MnO 2 concentration C M, can be calculated from its apparent value based on the effectiveness factor theory. The k d,M values are empirically correlated with the pH value only. The above two deactivation kinetic models are combined with our previous reaction and mass transfer model for the gel beads in the airlift to simulate the CaG production process in a prolonged batch bioreactor operation. A fair agreement obtained between the observed and calculated time courses of the process suggests the validity of the deactivation models developed. An application of the simulation model also predicts an optimal ratio of the amounts of GO and MnO 2 immobilized in the gel beads.

On the Modeling of the Kinetics of the Selective Deactivation of Catalysts. Application to the Fluidized Catalytic Cracking Process

The deactivation of a solid catalyst may affect in different ways each reaction taking place in a complex network. This creates a variation with time on stream of the product distribution at the reactor exit. To handle data from this common situation, a selective deactivation kinetic model fits the data much better than a nonselective one. Selective deactivation kinetic models are scarcely used because they are often complex and difficult to handle. They also introduce more deactivation kinetic parameters than the nonselective models. Nevertheless, selective deactivation kinetic models are a refinement and are a step forward in the modeling of deactivation kinetics. They might also improve the existing macrokinetic models for commercial reactors. In this paper, several new concepts and ideas are given relating to selective deactivation kinetic models. These concepts are applied to the kinetics of the deactivation of commercial fluidized catalytic cracking catalysts with commercial feedstocks. It is also proven how the kinetics of cracking of the feedstock (heavy oils) is much more affected by the catalyst deactivation than the cracking of the gasoline. A discussion of the results is included.

Kinetics of Pyruvate Decarboxylase Deactivation by Benzaldehyde

Based on experimental data, a kinetic model for the deactivation of partially purified pyruvate decarboxylase (PDC) by benzaldehyde (0–200 mM) in MOPS buffer (2.5 M) has been developed. An initial lag period prior to deactivation was found to occur. With first order dependencies of PDC deactivation on exposure time and on benzaldehyde concentration, a reaction time deactivation constant of 2.64×10−3 h−1 and a benzaldehyde deactivation coefficient of 1.98×10−4 mM−1 h−1 were determined for benzaldehyde concentrations up to 200 mM. The PDC deactivation kinetic equations established in this study are an essential component in an overall model being developed to describe the enzymatic biotransformation of benzaldehyde and pyruvate to produce the pharmaceutical intermediate (R)-phenylacetylcarbinol (R-PAC).

Catalyst deactivation kinetics from variable space-velocity experiments

Reliable estimates of catalyst deactivation parameters are difficult to get from conventional experiments at constant space velocity where conversion declines with time on stream, or when temperature is adjusted to compensate for the loss of catalyst activity. An alternate technique, where space velocity is adjusted to maintain constant conversion, is shown here to give reliable rate information for both the catalyst deactivation and the primary catalytic reactions. This technique, at constant temperature, provides kinetics data on a deactivating catalyst in which the catalyst is exposed to reactant and product concentrations that are relatively constant. In principle, the kinetics of deactivation are obtained directly as the kinetic regime remains unchanged. This technique is used quite successfully for many catalytic processes of industrial significance. In this paper, the variable-space-velocity experimental technique is demonstrated for the methanol to hydrocarbons process on a ZSM-5 catalyst. The deactivation kinetic parameters were determined at several temperatures in a fixed-bed reactor. This rate information was then used to determine the temperature-time policy for maintaining constant reactor outlet conversion at a fixed space-velocity. The predicted temperature-time policies are in good agreement with experimental data on fixed-bed and fluid-bed reactors. Mathematical analysis of interpreting experimental data, as well as predicted temperature-time policies for practical applications, is illustrated.

Studies on deactivation kinetics of a heterogeneous catalyst using a concentration-controlled recycle reactor under supercritical conditions

A concentration-controlled continuously operated recycle reactor was applied to study the deactivation kinetics of the heterogeneous catalytic disproportionation of ethylbenzene (EB) under supercritical conditions. First the possibility of this method was studied by simulation. On the basis of this simulation it was experimentally realised, thanks to the slow deactivation of the catalyst under supercritical conditions and high feed mole fraction, to determine directly the catalyst activity vs. time on stream. The method seems to be superior to classical methods based on the stationary kinetics of the reaction system. A model for the deactivation kinetic is presented.

The modeling of the kinetics of deactivation of a commercial hydrocracking catalyst in the reaction of cumene disproportionation

The mechanism of coke formation on a commercial hydrocracking catalyst is studied. The data by R. P. L. Absil J. B. Butt, and J. B. Dranoff ( J. Catal. 85, 415, 1984) for cumene disproportionation have been analyzed using the theory and developments of J. Corella and J. M. Asua ( Ind. Eng. Chem. Process Des. Dev. 21, 55, 1982). Several coke formation mechanisms are presented and their Langmuir-Hinshelwood kinetic equations are deduced. Only the mechanisms with two active sites in the controlling step or with deactivation order 1.5 fit the data. The chemical mechanism of coke formation in this process is presented and a reasonable mechanistic explanation for the empirical deactivation kinetic equations given previously is presented.