Impact of water film thickness on kinetic rate of mixed hydrate formation during injection of <scp>CO</scp><sub>2</sub> into <scp>CH</scp><sub>4</sub> hydrate

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. AbstractThe catalytic ozonation of VOCs is a promising approach for degradation of indoor VOCs, such as gaseous toluene. However, the mechanism and relevant kinetic steps involved in this reaction remain unclear. In this study, the catalytic ozonation of toluene over MnO 2 /graphene was investigated using the empirical power law model and classic Langmuir-Hinshelwood single-site (denoted as L-H s ) mechanism. The apparent activation energy determined using the power law model was 29.3±2.5 kJ mol −1 . This finding indicated that the catalytic ozonation of toluene over MnO 2 /graphene was a heterogeneous reaction, and the Langmuir-Hinshelwood mechanism was applicable. However, the L-H s mechanism did not fit the experimental data, suggesting that the reaction was non-single-site governed. A novel Langmuir-Hinshelwood dual-site (denoted as L-H d ) mechanism was then proposed to explain the experimental observations of the catalytic ozonation of toluene over MnO 2 /graphene through a steady-state kinetic study. This mechanism was based on the hypothesis that MnO 2 was responsible for ozone decomposition and toluene adsorption on graphene; these two types of adsorption were coupled by an adjacent attack. Furthermore, XPS results confirmed the presence of a strong connection between MnO 2 and graphene sites on the surface of MnO 2 /graphene. This connection allowed the adjacent attack and validated the dual-site mechanism. The L-H d model was consistent with the predicted reaction rate of toluene removal with a correlation coefficient near unity (r 2 = 0.9165). Moreover, the physical criterion was in accordance with both enthalpy and entropy of toluene adsorption constraints. Fulfillment of mathematical and physical criteria indicated the catalytic ozonation of toluene over MnO 2 /graphene can be well described by the L-H d mechanism. This study helps understand the catalytic ozonation of toluene over MnO 2 /graphene in a closely mechanistic view.

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“…5 at each temperature point. The correlation coefficient (r 2 ) was then used to intuitively distinguish the derived model [40,41].…”

Section: Discussionmentioning

confidence: 99%

Novel mechanistic view of catalytic ozonation of gaseous toluene by dual-site kinetic modelling

Yao

Hui

et al. 2017

Chemical Engineering Journal

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“…In the Ignik Sikumi test on hydrate production [8,9,11] large amounts of N 2 were added and the thermodynamic driving force for creating a new CO 2 hydrate was practically lost [9]. Instead of mechanically, breaking the hydrate films with efficient surfactants can keep the water/CO 2 interface free of blocking hydrate and permit for more continuous hydrate formation from the injected CO 2 .…”

Section: Hydrate Formation From Water and A Separate Phase Containingmentioning

confidence: 99%

“…Hydrate saturation is the percentage of available pore volume that is filled with hydrate. For temperatures in the liquid water region another mechanism [10,11] than solid state conversion is possible. Injected CO 2 will form new hydrate with free pore water.…”

Section: Introductionmentioning

confidence: 99%

Stages in the Dynamics of Hydrate Formation and Consequences for Design of Experiments for Hydrate Formation in Sediments

et al. 2019

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Natural gas hydrates in sediments can never reach thermodynamic equilibrium. Every section of any hydrate-filled reservoir is unique and resides in a stationary balance that depends on many factors. Fluxes of hydrocarbons from below support formation of new hydrate, and inflow of water through fracture systems leads to hydrate dissociation. Mineral/fluid/hydrate interaction and geochemistry are some of the many other factors that determine local hydrate saturation in the pores. Even when using real sediments from coring it is impossible to reproduce in the laboratory a natural gas hydrate reservoir which has developed over geological time-scales. In this work we discuss the various stages of hydrate formation, with a focus on dynamic rate limiting processes which can lead to trapped pockets of gas and trapped liquid water inside hydrate. Heterogeneous hydrate nucleation on the interface between liquid water and the phase containing the hydrate former rapidly leads to mass transport limiting films of hydrate. These hydrate films can delay the onset of massive, and visible, hydrate growth by several hours. Heat transport in systems of liquid water and hydrate is orders of magnitude faster than mass transport. We demonstrate that a simple mass transport model is able to predict induction times for selective available experimental data for CO2 hydrate formation and CH4 hydrate formation. Another route to hydrate nucleation is towards mineral surfaces. CH4 cannot adsorb directly but can get trapped in water structures as a secondary adsorption. H2S has a significant dipole moment and can adsorb directly on mineral surfaces. The quadropole-moment in CO2 also plays a significant role in adsorption on minerals. Hydrate that nucleates toward minerals cannot stick to the mineral surfaces so the role of these nucleation sites is to produce hydrate cores for further growth elsewhere in the system. Various ways to overcome these obstacles and create realistic hydrate saturation in laboratory sediment are also discussed.

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“…Many experimental and numerical studies have been performed to understand the CH 4 -CO 2 replacement [27]. Baig et al in [28] stated that conversion of CH 4 hydrates in CO 2 hydrates occurs according to two mechanisms: new CO 2 hydrate formation starting from gaseous CO 2 and free water surrounding hydrates and a direct conversion in the solid state.…”

Section: Introductionmentioning

confidence: 99%

Energy and Environmental Analysis of Membrane-Based CH4-CO2 Replacement Processes in Natural Gas Hydrates

et al. 2019

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Natural gas hydrates are the largest reservoir of natural gas worldwide. This paper proposes and analyzes the CH4-CO2 replacement in the hydrate phase and pure methane collection through the use of membrane-based separation. The investigation uses a 1 L lab reactor, in which the CH4 hydrates are formed in a quartz sand matrix partially saturated with water. CH4 is subsequently dissociated with a CO2 stream supplied within the sediment inside the reactor. An energy and environmental analysis was carried out to prove the sustainability of the process. Results show that the process energy consumption constitutes 4.75% of the energy stored in the recovered methane. The carbon footprint of the CH4-CO2 exchange process is calculated as a balance of the CO2 produced in the process and the CO2 stored in system. Results provide an estimated negative value, equal to 0.004 moles sequestrated, thus proving the environmental benefit of the exchange process.

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Impact of water film thickness on kinetic rate of mixed hydrate formation during injection of CO₂ into CH₄ hydrate

Cited by 36 publications

References 42 publications

Novel mechanistic view of catalytic ozonation of gaseous toluene by dual-site kinetic modelling

Novel mechanistic view of catalytic ozonation of gaseous toluene by dual-site kinetic modelling

Stages in the Dynamics of Hydrate Formation and Consequences for Design of Experiments for Hydrate Formation in Sediments

Energy and Environmental Analysis of Membrane-Based CH4-CO2 Replacement Processes in Natural Gas Hydrates

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Impact of water film thickness on kinetic rate of mixed hydrate formation during injection of CO2 into CH4 hydrate

Cited by 36 publications

References 42 publications

Novel mechanistic view of catalytic ozonation of gaseous toluene by dual-site kinetic modelling

Novel mechanistic view of catalytic ozonation of gaseous toluene by dual-site kinetic modelling

Stages in the Dynamics of Hydrate Formation and Consequences for Design of Experiments for Hydrate Formation in Sediments

Energy and Environmental Analysis of Membrane-Based CH4-CO2 Replacement Processes in Natural Gas Hydrates

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Impact of water film thickness on kinetic rate of mixed hydrate formation during injection of CO₂ into CH₄ hydrate