Deactivation Kinetic Model Research Articles

Comparative study on a deactivation kinetic model based on fractional conversion of solid in fluid/solid heterogeneous processes

Comparative study on a deactivation kinetic model based on fractional conversion of solid in fluid/solid heterogeneous processes

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).

The mathematical catalyst deactivation models: a mini review.

Catalyst deactivation is a complex phenomenon and identifying an appropriate deactivation model is a key effort in the catalytic industry and plays a significant role in catalyst design. Accurate determination of the catalyst deactivation model is essential for optimizing the catalytic process. Different mechanisms of catalyst deactivation by coke and metal deposition lead to different deactivation models for catalyst activity decay. In the rigorous mathematical models of the reactors, the reaction kinetics were coupled with the deactivation kinetic equation to evaluate the product distribution with respect to conversion time. Finally, selective and nonselective deactivation kinetic models were designed to identify catalyst deactivation through the propagation of heterogeneous chemical reactions. Therefore, the present review discusses the catalyst deactivation models designed for CO2 hydrogenation, Fischer-Tropsch, biofuels and fossil fuels, which can facilitate the efforts to better represent the catalyst activities in various catalytic systems.

2D model of the transfer processes for CO2 methanation in a microchannel reactor

A dynamic two-dimensional model was developed for transfer processes in a microchannel reactor in an innovative plant concept for CO2 methanation. The model is based on balance equations together with deactivation and sulfidation submodels taking into account the chemisorption of impurity (H2S). The deactivation of the catalyst is described by Levenspiel’s deactivation kinetic model (LDKM). Sulfidation is defined by the shrinking core model (SCM) equation. Following the rate-determining step assumption, a simplified mechanism is derived for CO2 and CO methanation in a microchannel reactor with kinetic rate expressions. The developed 2D model adequately describes transient and steady-state behavior of the microchannel methanation reactor following the trend in experimental profiles available in the literature.

Batch and packed bed techniques for adsorptive aqueous phase removal of selected phenoxyacetic acid herbicide using sugar industry waste ash

Abstract Batch and packed bed adsorption of 4-chloro-2-methylphenoxyacetic acid (MCPA) herbicide was performed using bagasse fly ash (BFA) as an adsorbent. In batch process, characteristics of adsorbent, and the influence of adsorbent dosage, initial herbicide concentration, time, pH, particle size of adsorbent and temperature on adsorption were studied. Results disclose higher removal of MCPA on bigger particles of BFA owing to higher specific surface area because of greater carbon and lesser silica percentage in bigger particles. Application of isotherm models in present study indicates the best fitting of Langmuir and Temkin isotherms whereas the kinetic models suggest the suitability of pseudo second order and Elovich models. Thermodynamic study specifies the temperature preferred adsorption process. In packed bed technique, the effect of influent concentration, flow rate and bed height were investigated. The deactivation kinetic model which was previously considered only for studies in gas-solid adsorption is applied in this study to solid-liquid adsorption along with conventional packed bed models. In packed bed study, Bohart-Adams and Wolborska models are appropriate to explain the experimental data upto 60% saturation of the column. The deactivation kinetic model is found the best to elucidate the nature of breakthrough curves till the complete saturation of column. Batch capacity and packed bed capacity per m2 specific surface area of BFA is found about two and three times greater than the previously used adsorbents for MCPA respectively.

Catalyst deactivation in the hydrodechlorination of micropollutants. A case of study with neonicotinoid pesticides

This work aims to analyse the effectiveness of catalytic hydrodechlorination (HDC) for the degradation of the neonicotinoid pesticides listed in the EU Watch List (Decision 2018/840): acetamiprid (ACT), imidacloprid (IMD), clothianidin (CLT), thiacloprid (THC) and thiamethoxam (THM). With the exception of THC, all neonicotinoid pesticides (1000 μg L−1) were completely removed in 30 min at 25 °C, using 0.25 g L−1 of a commercial Pd/Al2O3 (1 wt. %) catalyst and 50 N mL min−1 H2 flow rate. Strikingly, the micropollutant nature played a critical role on the activity and stability of the catalyst. The sulphur-bearing structures (CLT, THC and THM) showed the slowest degradation rates and led to a progressive deactivation of the catalyst. TEM/EDS and elemental analyses confirmed that the selective interaction of sulphur species on Pd active sites was the main reason for catalyst deactivation. The position of the heteroatom in the pesticide structure also influenced the catalytic deactivation. The catalyst showed a constant activity upon its sequential use in the HDC of ACT and IMD when these compounds were treated individually. Nevertheless, the interaction of the sulphur-containing compounds with the catalyst was remarkably favoured when the five micropollutants were treated in a mixture. A deactivation kinetic model in a long-term experiment was proposed with THC. To overcome catalyst deactivation, a regeneration procedure, based on a simple catalyst washing with a diluted NaClO solution, was developed. The process suitability was finally demonstrated in successive HDC-regeneration runs.

Effect of n-butanol cofeeding on the deactivation of methanol to olefin conversion over high-silica HZSM-5: A mechanism and kinetic study

The co-reaction of methanol and n-butanol that instantaneously dehydrated into 1-butene at the inlet was performed to evaluate the effect of co-feeding olefin on the catalyst deactivation from coke deposition over HZSM-5 with Si/Al = 200 at 460 °C, a practical situation encountered by commercial methanol to propylene (MTP) process. It was revealed that the deactivation was an autocatalytic process depending on both methanol and products. In particular, increasing inlet methanol fraction would dramatically accelerate activity attenuation, and the co-feeding butanol significantly reduces activity loss by promoting methanol conversion. The deactivation is generally non-selective to methanol transformation and product generation, except for methane. A possible deactivation mechanism was proposed with the coke precursor originated from the methylation of lower polymethylbenzenes to higher tardy ones. A deactivation kinetic model was then developed, which gave fairly good prediction to the experimental results in a wide range of feed composition.

Walnut wood-derived hierarchically 3D self-assembly of (a%Ce–Mn)yAl2−yOx and rapid diffusion character of straight micron channel during hot coal gas desulfurization

Refined design of sustainable sorbent demands to tackle the strong dependence for additional mesoporous support and low utilization in hot coal gas desulfurization. Unlike the well-established preparation of loading sorbents supported on zeolites, a vacuum-assisted self-assemble strategy tapping into the ordered channels of walnut wood is proposed to facilely fabricate three-dimensional (3D) (a%Ce–Mn)yAl2−yOx desulfurizers with anisotropy which provides a desirable macroporosity for rapid diffusion of H2S. Benefiting from the inherent straight channle in micron scale, the obtained (8%Ce–Mn)1.5Al0.5Ox presents the highest breakthrough sulfur capacity (289.79 mg g−1) and effective utilization (88.42%) at 700 °C. The favorable rapid diffusion of gases in micro/macropores improves greatly the H2O-resistance and anti-interference ability of 3D (8%Ce–Mn)1.5Al0.5Ox for high steam and concentration of reducing gas. The fast mass transport in sulfidation reaction at 700 °C is described perfectly by the improved deactivation kinetics model. This study opens a novel design of the ideal 3D desulfurizers with micron porosity inherited from hierarchical architecture of walnut wood for industrialization utilization in the near future.

Online estimation for catalyst activity of acetylene hydrogenation reactor

AbstractIn the ethylene industry, the high purity of the ethylene product depends on hydrogenation in acetylene hydrogenation reactor. Because the catalyst deactivation leads to the moving of the operating point, the operation scheme must be adjusted continually according to the catalyst activity. It is necessary to estimate the catalyst activity online. Based on the discrete dynamic model of the acetylene hydrogenation reactor, the extended Kalman filter (EKF) is used to build the soft sensor for catalyst activity. Considering that EKF involves the large computation costs, we propose a method that estimates the parameters of the time‐varying deactivation kinetics model for the tradeoff of accuracy and complexity. The method is effective to reduce computation complexity of estimation, and simultaneously, the accuracy satisfies the process requirement.

Kinetic Study of Coal Char Thermal Deactivation

As one of the significant properties in char combustion, char reactivity has been widely investigated. However, the previous deactivation kinetic models are unable to predict the char reactivity fo...

Lattice substitution and desulfurization kinetic analysis of Zn-based spinel sorbents loading onto porous silicoaluminophosphate zeolites

Green Zn-based spinel sorbents for hot coal gas desulfurization have been developed with the assistance of optimization procedures. The pilot study highlights an outstanding ordered mesoporous support (SBET = 323 m2 g−1, Da = 4.3 nm) of SAPO-34@as-prepared SBA-15 (SS) for loading active metal oxides. ZnCo2O4 spinel loaded onto SS (ZnCo2/SS) exhibits a prominent desulfurization performance compared to other sorbents whose partial Co is substituted by Mn or Fe in spinel B-site, owing to the slight effect of PO43− in SS. After systematic evaluation on role of sulfidation condition, 50 wt% ZnCo2/SS sorbent possesses the sulfur storage capacity of 138.08 mg g−1at550 °C and little loss of active species in 5 desulfurization-regeneration cycles. Results of high resolution transmission electron microscopy (HRTEM), Brunauer–Emmett–Teller (BET), X-ray photoelectron spectroscopy (XPS) etc. demonstrate that 70.42% of initial sulfur capacity of ZnCo2/SS presented in the 2nd utilization is associated with zinc evaporation, existence of high stable sulfides and partial sintering. The improved deactivation kinetic model suitably describes that the H2S concentration distribution relates with the spatial position of fixed-bed reactor and desulfurization time.

Modeling of Reaction and Deactivation Kinetics in Methanol-to-Olefins Reaction on SAPO-34

A new kinetic model is proposed for the methanol-to-olefins (MTO) reaction over SAPO-34. The resulting products in this model are divided into 7 lumps: methane, ethylene, propylene, butene, propane...

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 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...

Kinetic Analysis of H2S Removal over Mesoporous Cu–Mn Mixed Oxide/SBA-15 and La–Mn Mixed Oxide/KIT-6 Sorbents during Hot Coal Gas Desulfurization Using the Deactivation Kinetics Model

Kinetic analysis was investigated using the deactivation kinetics model, where the reaction order of each species based on the experimental data was estimated for H2S removal over mesoporous Cu–Mn mixed oxide/SBA-15 and La–Mn mixed oxide/KIT-6 sorbents during hot coal gas desulfurization in a fixed-bed reactor. The reaction orders, rate constants, apparent activation energy (Ea), and deactivation energy (Ed) were calculated as the kinetic parameters. The calculated reaction orders, α, β, and γ, were 1, 1, and 1 for Cu–Mn mixed oxide/SBA-15 and 0.6, 1.2, and 1 for La–Mn mixed oxide/KIT-6. The obtained Ea and Ed for Cu1Mn9 mixed oxide/SBA-15 were 33.02 and 46.34 kJ mol–1 and for La3Mn97 mixed oxide/KIT-6 were 48.98 and 56.10 kJ mol–1 , respectively. This model offered the H2S breakthrough curves for the whole duration of the desulfurization reaction, with errors less than 5% between calculated and experimental data.

Comparative evaluation of packed-bed performance of biomass ashes as adsorbents for removal of diuron from aqueous solution

The packed-bed performance of biomass ashes (BMA), namely rice husk ash (RHA) and bagasse fly ash (BFA), was investigated for adsorptive removal of diuron (herbicide) under dynamic conditions. The effects of influent concentration (10–30 mg/L), flow rate (1–3 mL/min), and bed height (3–11 cm) were studied at 30°C and results were analyzed using various packed-bed models. The saturation time and capacity of the BFA bed were found to be approximately 1.5 and 1.6 times higher due to higher BET surface area than that of RHA bed. However, the bed utilization of RHA was higher because of smaller mass transfer zone. At a constant influent concentration (20 mg/L) and flow rate (1 mL/min), the maximum volume of diuron treated was 1,325 and 1,685 mL using RHA (bed height 10 cm) and BFA (bed height 11 cm), respectively. Among the packed-bed models applied, the BDST model revealed the inconsistent MTZ and complex mechanism involving more than one rate-controlling step for the adsorption of diuron on both ashes. The kinetics in the initial part of the breakthrough curve was governed by external mass transfer according to the Bohart–Adams and Wolborska models. Better agreements between experimental and predicted values of bed capacities for each ash and the higher bed capacity of BFA than RHA were demonstrated by the Thomas model. The Yoon–Nelson model was found to be superior for BFA rather than for RHA to estimate 50% saturation time. However, the deactivation kinetic model, previously discovered and applied only for gas–solid adsorption, was found to be the best for the diuron–BMA (liquid–solid) adsorption system in this study.

CO2 SORPTION USING NA2CO3/AL2O3 SORBENT WITH VARIOUS FLOW PATTERNS OF FIXED/FLUIDIZED BED REACTORS

In this study, the carbon dioxide sorption using solid sorbent (sodium carbonate supported on alumina) in fixed and fluidized bed reactors was investigated. The key objective was to examine the carbon dioxide concentration profile or breakthrough curve (as well as capture capacity) and carbon dioxide sorption kinetic parameters with various flow regimes/flow patterns. The basic information for the sorption kinetic parameter computation was the breakthrough curve under different flow operating conditions. From the results, all the breakthrough curves were constant at the beginning stage then it decreased with the sorption time. The fixed bed gave longest sorption time. All the carbon dioxide gas was not captured in the fast fluidization flow regime. The turbulent fluidization flow regime exhibited highest carbon dioxide capture capacity. In addition, the employed deactivation kinetic model fitted well with the obtained experimental information. The initial sorption and deactivation reaction rate constants were the highest at the turbulent fluidization flow regime.

Agro-industrial waste: a low cost adsorbent for effective removal of 4-chloro-2-methylphenoxyacetic acid herbicide in batch and packed bed modes.

The present work describes the aqueous phase removal of 4-chloro-2-methylphenoxyacetic acid herbicide by rice husk ash (RHA) using batch and packed bed adsorption techniques. The effects of dosage, initial concentration, time, pH, temperature, and particle size of adsorbent in batch compared with effects of influent concentration, flow rate, and bed height in packed bed were studied. The particle size effect reveals that the removal is dependent on chemical composition (silica and carbon content) together with BET surface area of RHA. The aptness of Langmuir isotherm to batch data indicates the favorable adsorption whereas that of Temkin isotherm informs the heterogeneous nature of RHA. The kinetics of adsorption follows the pseudo-second order and Elovich models while thermodynamics of process indicates the exothermic adsorption. Among the models applied in packed bed study, the deactivation kinetic, Yoon-Nelson and bed depth service time (BDST) models are suitable to explain the packed bed adsorption. The adsorption capacity of RHA in packed bed study is found greater than that in batch. The adsorption capacity of RHA determined by the BDST model is 3019mg/L for 90% saturation of bed. The adsorption capacity of RHA based on weight is ∼2.3 times and that based on surface area is ∼55.55 times greater than that of granular activated carbon.

Correlations of kinetic parameters with various system operating conditions for CO2 sorption using K2CO3/Al2O3 solid sorbent in a fixed/fluidized bed reactor

The kinetic parameters for carbon dioxide sorption using potassium carbonate supported on an alumina oxide solid sorbent in a fixed/fluidized bed reactor were investigated using a deactivation kinetic model. The initial parameters of the deactivation model were explored by comparison of the obtained results with experimental data. Then, the effects of varying the three key system operating conditions (inlet gas velocity, sorption temperature and water vapor content) on the kinetic parameters were considered. The obtained breakthrough curves were used for calculation of the kinetic parameters. Finally, the relationship between the obtained kinetic parameters and the system operating conditions were summarized. The selected deactivation model was found to fit well with the experimental data. The reaction rate constant was highest in a turbulent fluidization flow pattern and the initial sorption and deactivation rate constant were dependent on the water vapor content except with excess water vapor content.