Mechanistic Insights into the Induction Period of Methanol-to-Olefin Conversion over ZSM-5 Catalysts: A Combined Temperature-Programmed Surface Reaction and Microkinetic Modeling Study

Omojola, Toyin

doi:10.1021/acs.iecr.3c01401

Cited by 3 publications

(33 citation statements)

References 60 publications

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“…Ultrahigh purity water-free methanol (99.8%) was obtained from Sigma-Aldrich, while anhydrous dimethyl ether (99.999%) was obtained from CK Temperature-programmed surface reaction (TPSR) experiments were conducted in a temporal analysis of products (TAP) reactor. The experimental details have been described before 10,12,13 and are only described here briefly. ZSM-5 (25), ZSM-5 (36), and ZSM-5 (135) catalysts were decomposed, under vacuum conditions, in the temporal analysis of products reactor.…”

Section: Experimental Methodologymentioning

confidence: 99%

“…The kinetic scheme used has been described in previous publications (Scheme 1). 10,12 The methoxymethyl mechanism is loosely adapted from the work of Fan and co-workers. 27,28 The methoxymethyl mechanism was used for parameter estimation and optimization over fresh and working ZSM-5 catalysts.…”

Section: Experimental Methodologymentioning

confidence: 99%

“…The densities of acid sites for binding sites and active sites were obtained from our simulations. Previously, 12 we used eq 6 for calculating the distance between acid sites on the basis that each site ensemble covers the entire surface area. However, this leads to an overestimation of the distance between acid sites.…”

Section: Initial and Boundary Conditions Methanol Tpsrmentioning

confidence: 99%

“…Site-specific scaling relations were observed between these key descriptors and the barriers to methoxymethyl cation formation over ZSM-5 catalysts. 10,12,13 The novelty in this work is that, for the first time, site-specific volcano-plots and site-specific activity-maps of the induction period of propylene formation over ZSM-5 catalysts are presented. We observe an optimum site density of ca.…”

Section: Introductionmentioning

confidence: 99%

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Site-Specific Activity Maps Observed during Methanol-to-Olefin Conversion over ZSM-5 Catalysts

Omojola

2024

Ind. Eng. Chem. Res.

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The Sabatier principle has been applied to nonuniform site ensembles of ZSM-5 catalysts of different compositions (Si/Al = 25, 36, and 135) during the induction period of the conversion of methanol and dimethyl ether to propylene. For the first time, site-specific volcano-plots and site-specific activity-maps have been observed following microkinetic simulations of the temperature-programmed surface reaction of methanol and dimethyl ether over ZSM-5 catalysts in a temporal analysis of products reactor. The microkinetic simulations are constructed using coupled 1D nonlinear partial differential equations that connect reactions at the active site to convection and dispersion through the reactor. The methoxymethyl cation pathway predicts the formation of propylene from methanol and dimethyl ether via dimethoxyethane. Site-specific scaling relations are observed between the acid site density and the barriers of the dissociative desorption of dimethyl ether with the barrier of methoxymethyl cation formation during the induction period of propylene formation from methanol and dimethyl ether, respectively. During the induction period of methanol conversion to propylene, depending on the barrier to methoxymethyl cation formation, the active site density should not be too low such that site cooperation is inhibited and not too high such that site competition is promoted. The optimum site density is ca. 5 × 10–4 mmol g–1 of active sites over the high-temperature active sites of ZSM-5 (Si/Al = 36) catalysts. Over the high-temperature active sites on ZSM-5 (25) catalysts, we observe a maximum rate of propylene formation at an optimum site density of 7 × 10–4 mmol g–1 active sites. During the induction period of dimethyl ether conversion, the binding energies should not be too weak to activate dimethyl ether and not too strong to inhibit its release into the gas phase. The binding energy of methoxymethyl cation should be between −80 kJ mol–1 and −100 kJ mol–1 for maximum propylene formation over the low-temperature active sites of ZSM-5 (Si/Al = 36) catalysts. Over the medium-temperature active sites of ZSM-5 (Si/Al = 36) catalysts, the maximum rate constant of propylene formation is observed between a binding energy of dimethyl ether of −135 kJ mol–1 and −145 kJ mol–1. The site-specific activity maps show that the catalytic activity of methanol-to-olefin conversion varies across the different site ensembles. In each site-specific activity map, the direction of the maximum rate constant of propylene formation changes with zeolite composition and site-ensemble. The precision given by this site-specific control shows that the catalytic activity can be tailored to the site characteristics.

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Section: Experimental Methodologymentioning

confidence: 99%

Section: Experimental Methodologymentioning

confidence: 99%

Section: Initial and Boundary Conditions Methanol Tpsrmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Site-Specific Activity Maps Observed during Methanol-to-Olefin Conversion over ZSM-5 Catalysts

Omojola

2024

Ind. Eng. Chem. Res.

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“…Light olefins, e.g., ethylene, propylene, and butane, have received great attention as they are essential materials for the polymer industry. − With the gradual depletion of petroleum, there is an urgent need to use nonpetroleum as materials to replace traditional olefin production routes . Methanol to olefins (MTO) is an important process used to produce light olefins from coal. − The reaction kinetics model is crucial to describe the distribution of MTO reaction products. , It can meet the major demand for a cyber-physical systems (CPS) model base in the construction of an intelligent factory for the coal chemical industry in reactor simulation, design, scale-up, and optimization. Therefore, the formulation of an accurate and efficient MTO reaction kinetics model is a challenging issue.…”

Section: Introductionmentioning

confidence: 99%

Hybrid Modeling of Methanol to Olefin Reaction Kinetics Based on the Artificial Neural Network

Wang,

Sun

et al. 2024

Ind. Eng. Chem. Res.

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Methanol to olefin (MTO) is an important coalbased process to ensure olefin yield. The current reaction kinetics model as a crucial tool of process regulation lacks real-time, accuracy, and simplicity in describing the catalyst deactivation. To fill in the gap, a reaction kinetics hybrid model of MTO was developed by a machine learning approach. Specifically, a catalyst deactivation model was first built by an artificial neural network (ANN) and then integrated into a lump-based reaction kinetics model over a fresh SAPO-34 catalyst. Reaction kinetics parameters were estimated by the genetic algorithm. A priori knowledge was extracted by analyzing the deactivation experimental data and used in the training of ANN to enhance its extrapolability. The developed model of MTO agreed well with the kinetics experimental data considering the catalyst deactivation. The model provided a satisfactory predictive performance. Results show that a higher reaction temperature, longer reaction space time, and shorter catalyst residence time are beneficial to the yield of ethylene and propylene. The hybrid model developed in this work is expected to apply to the process control of MTO. The proposed hybrid modeling approach could be used as theoretical guidance for other catalytic reaction kinetics modeling.

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Enhancing the selectivity of light olefins through synergistic VOx/ZSM-5 composite in the oxidative cracking of hexane

Amusa,

Lateef,

Adamu

et al. 2024

Applied Catalysis A: General

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Mechanistic Insights into the Induction Period of Methanol-to-Olefin Conversion over ZSM-5 Catalysts: A Combined Temperature-Programmed Surface Reaction and Microkinetic Modeling Study

Cited by 3 publications

References 60 publications

Site-Specific Activity Maps Observed during Methanol-to-Olefin Conversion over ZSM-5 Catalysts

Site-Specific Activity Maps Observed during Methanol-to-Olefin Conversion over ZSM-5 Catalysts

Hybrid Modeling of Methanol to Olefin Reaction Kinetics Based on the Artificial Neural Network

Enhancing the selectivity of light olefins through synergistic VOx/ZSM-5 composite in the oxidative cracking of hexane

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