The Experts below are selected from a list of 18087 Experts worldwide ranked by ideXlab platform
Ulrich Stimming - One of the best experts on this subject based on the ideXlab platform.
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unraveling complex electrode processes by differential electrochemical mass spectrometry and the rotating ring disk electrode technique
Journal of Physical Chemistry C, 2019Co-Authors: Wei Che, Ling We Liao, Ju Cai, Yanxia Che, Ulrich StimmingAbstract:The competition of oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) on pc-Pt electrode in weakly acidic solution (pH~3) under condition when both reactions are thermodynamically allowed are investigated using the rotating ring disc electrode (RRDE) technique and differential electrochemical mass spectrometry (DEMS). The partial currents of HER and ORR producing H2O2 or H2O are quantified. The results show that: i) ORR occurs preferentially in a diffusion-limited manner (either limited by the mass transfer of O2 or H+) and only the excess H+ not being consumed by the ORR can be converted to Had and H2; ii) At potentials negative of the onset for Had formation, the H2O2 production rate first increases then decreases with the increasing overpotential. Possible origins for H2O2 yield in HER region are suggested. Present results demonstrate that combining DEMS and RRDE techniques can be powerful for deriving the Intrinsic Kinetics of individual processes in a complex electrochemical system.
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unraveling complex electrode processes by differential electrochemical mass spectrometry and the rotating ring disk electrode technique
The Journal of Physical Chemistry, 2019Co-Authors: Wei Che, Ling We Liao, Ju Cai, Yanxia Che, Ulrich StimmingAbstract:The competition between the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) on a polycrystalline Pt (pc-Pt) electrode in weakly acidic solutions (pH ≈ 3) under the condition when both reactions are thermodynamically allowed is investigated using the rotating ring disk electrode (RRDE) technique and differential electrochemical mass spectrometry (DEMS). The partial currents of HER and ORR producing H₂O₂ or H₂O are quantified. The results show that (i) ORR occurs preferentially in a diffusion-limited manner (either limited by the mass transfer of O₂ or H⁺) and only the excess H⁺ not being consumed by the ORR can be converted to Hₐd and H₂ and (ii) at potentials negative of the onset of Hₐd formation, the H₂O₂ production rate first increases and then decreases with the increasing overpotential. Possible origins for the H₂O₂ yield in the HER region are suggested. Present results demonstrate that combining DEMS and RRDE techniques can be powerful for deriving the Intrinsic Kinetics of individual processes in a complex electrochemical system.
P R Bishnoi - One of the best experts on this subject based on the ideXlab platform.
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determination of the Intrinsic Kinetics of co2 gas hydrate formation using in situ particle size analysis
Chemical Engineering Science, 2005Co-Authors: Matthew A Clarke, P R BishnoiAbstract:Abstract The Intrinsic Kinetics of CO 2 hydrate formation were investigated using a semi-batch stirred tank reactor equipped with a focused beam reflectance method (FBRM) probe for in situ particle size analysis. Experiments were carried out at temperatures ranging from 274 to 279 K and pressures ranging from 1.6 to 3.0 MPa. The experiments were designed to obtain the Intrinsic rate constant using a modified version of the model of Englezos et al. (Chem. Eng. Sci. 42(1987a)2647) that incorporates the measured particle size data. It was found that the Intrinsic rate constant for CO 2 hydrate formation varied from 3.214 × 10 - 3 to 6.423 × 10 - 3 mol/m 2 Pa s, with the minimum value occurring at roughly 277 K.
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determination of the Intrinsic Kinetics of co2 gas hydrate formation using in situ particle size analysis
Chemical Engineering Science, 2005Co-Authors: Matthew A Clarke, P R BishnoiAbstract:Abstract The Intrinsic Kinetics of CO 2 hydrate formation were investigated using a semi-batch stirred tank reactor equipped with a focused beam reflectance method (FBRM) probe for in situ particle size analysis. Experiments were carried out at temperatures ranging from 274 to 279 K and pressures ranging from 1.6 to 3.0 MPa. The experiments were designed to obtain the Intrinsic rate constant using a modified version of the model of Englezos et al. (Chem. Eng. Sci. 42(1987a)2647) that incorporates the measured particle size data. It was found that the Intrinsic rate constant for CO 2 hydrate formation varied from 3.214 × 10 - 3 to 6.423 × 10 - 3 mol/m 2 Pa s, with the minimum value occurring at roughly 277 K.
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analytical modelling of gas production from hydrates in porous media
Journal of Canadian Petroleum Technology, 2003Co-Authors: H Hong, Mehran Pooladidarvish, P R BishnoiAbstract:Gas hydrates are being considered as an alternative energy resource of the future since they exist in enormous quantities in permafrost and offshore environments. However, gas production potential from hydrate reservoirs through different production schemes has not been fully investigated yet. This work introduces a simple analytical model for simulating gas production from hydrate decomposition in porous media by a depressurization method. We consider the heat transfer to the decomposing zone, Intrinsic Kinetics of hydrate decomposition, and gas-water two-phase flow as the three primary mechanisms involved in hydrate decomposition in porous media. In this study, the relative importance of these mechanisms is compared over a realistic range of the physical properties. It is shown that for the cases studied, the effect of two-phase flow is significantly smaller than the heat transfer and the Intrinsic Kinetics of hydrate decomposition. Considering the rate-controlling mechanisms, an analytical model is developed'to predict the performance of decomposition of gas hydrates in porous media. The model is used to perform sensitivity studies to investigate the feasibility of commercial gas production from hydrate reservoirs. The results suggest that significant quantities of gas can be produced from gas hydrate reservoirs where the hydrate overlies the gas zone. Such reservoirs have been found in the permafrost regions of Siberia, Alaska, and Canada.
Wei Che - One of the best experts on this subject based on the ideXlab platform.
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unraveling complex electrode processes by differential electrochemical mass spectrometry and the rotating ring disk electrode technique
Journal of Physical Chemistry C, 2019Co-Authors: Wei Che, Ling We Liao, Ju Cai, Yanxia Che, Ulrich StimmingAbstract:The competition of oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) on pc-Pt electrode in weakly acidic solution (pH~3) under condition when both reactions are thermodynamically allowed are investigated using the rotating ring disc electrode (RRDE) technique and differential electrochemical mass spectrometry (DEMS). The partial currents of HER and ORR producing H2O2 or H2O are quantified. The results show that: i) ORR occurs preferentially in a diffusion-limited manner (either limited by the mass transfer of O2 or H+) and only the excess H+ not being consumed by the ORR can be converted to Had and H2; ii) At potentials negative of the onset for Had formation, the H2O2 production rate first increases then decreases with the increasing overpotential. Possible origins for H2O2 yield in HER region are suggested. Present results demonstrate that combining DEMS and RRDE techniques can be powerful for deriving the Intrinsic Kinetics of individual processes in a complex electrochemical system.
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unraveling complex electrode processes by differential electrochemical mass spectrometry and the rotating ring disk electrode technique
The Journal of Physical Chemistry, 2019Co-Authors: Wei Che, Ling We Liao, Ju Cai, Yanxia Che, Ulrich StimmingAbstract:The competition between the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) on a polycrystalline Pt (pc-Pt) electrode in weakly acidic solutions (pH ≈ 3) under the condition when both reactions are thermodynamically allowed is investigated using the rotating ring disk electrode (RRDE) technique and differential electrochemical mass spectrometry (DEMS). The partial currents of HER and ORR producing H₂O₂ or H₂O are quantified. The results show that (i) ORR occurs preferentially in a diffusion-limited manner (either limited by the mass transfer of O₂ or H⁺) and only the excess H⁺ not being consumed by the ORR can be converted to Hₐd and H₂ and (ii) at potentials negative of the onset of Hₐd formation, the H₂O₂ production rate first increases and then decreases with the increasing overpotential. Possible origins for the H₂O₂ yield in the HER region are suggested. Present results demonstrate that combining DEMS and RRDE techniques can be powerful for deriving the Intrinsic Kinetics of individual processes in a complex electrochemical system.
Matthew A Clarke - One of the best experts on this subject based on the ideXlab platform.
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sensitivity analysis of parameters governing the recovery of methane from natural gas hydrate reservoirs
Energies, 2014Co-Authors: Carlos Giraldo, Matthew A Clarke, Jens Klump, Judith M SchicksAbstract:Naturally occurring gas hydrates are regarded as an important future source of energy and considerable efforts are currently being invested to develop methods for an economically viable recovery of this resource. The recovery of natural gas from gas hydrate deposits has been studied by a number of researchers. Depressurization of the reservoir is seen as a favorable method because of its relatively low energy requirements. While lowering the pressure in the production well seems to be a straight forward approach to destabilize methane hydrates, the Intrinsic Kinetics of CH 4 -hydrate decomposition and fluid flow lead to complex processes of mass and heat transfer within the deposit. In order to develop a better understanding of the processes and conditions governing the production of methane from methane hydrates it is necessary to study the sensitivity of gas production to the effects of factors such as pressure, temperature, thermal conductivity, permeability, porosity on methane recovery from naturally occurring gas hydrates. A simplified model is the base for an ensemble of reservoir simulations to study which parameters govern productivity and how these factors might interact.
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determination of the Intrinsic Kinetics of co2 gas hydrate formation using in situ particle size analysis
Chemical Engineering Science, 2005Co-Authors: Matthew A Clarke, P R BishnoiAbstract:Abstract The Intrinsic Kinetics of CO 2 hydrate formation were investigated using a semi-batch stirred tank reactor equipped with a focused beam reflectance method (FBRM) probe for in situ particle size analysis. Experiments were carried out at temperatures ranging from 274 to 279 K and pressures ranging from 1.6 to 3.0 MPa. The experiments were designed to obtain the Intrinsic rate constant using a modified version of the model of Englezos et al. (Chem. Eng. Sci. 42(1987a)2647) that incorporates the measured particle size data. It was found that the Intrinsic rate constant for CO 2 hydrate formation varied from 3.214 × 10 - 3 to 6.423 × 10 - 3 mol/m 2 Pa s, with the minimum value occurring at roughly 277 K.
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determination of the Intrinsic Kinetics of co2 gas hydrate formation using in situ particle size analysis
Chemical Engineering Science, 2005Co-Authors: Matthew A Clarke, P R BishnoiAbstract:Abstract The Intrinsic Kinetics of CO 2 hydrate formation were investigated using a semi-batch stirred tank reactor equipped with a focused beam reflectance method (FBRM) probe for in situ particle size analysis. Experiments were carried out at temperatures ranging from 274 to 279 K and pressures ranging from 1.6 to 3.0 MPa. The experiments were designed to obtain the Intrinsic rate constant using a modified version of the model of Englezos et al. (Chem. Eng. Sci. 42(1987a)2647) that incorporates the measured particle size data. It was found that the Intrinsic rate constant for CO 2 hydrate formation varied from 3.214 × 10 - 3 to 6.423 × 10 - 3 mol/m 2 Pa s, with the minimum value occurring at roughly 277 K.
Tapio Salmi - One of the best experts on this subject based on the ideXlab platform.
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modelling of the interaction of Kinetics and external transport phenomena in structured catalysts the effect of reaction Kinetics mass transfer and channel size distribution in solid foams
Chemical Engineering Science, 2021Co-Authors: Tapio Salmi, Vincenzo Russo, Adriana Freites AguileraAbstract:Abstract The increasing use of structured reactors and catalysts, particularly solid open foams requires a new touch to the interaction of Intrinsic chemical Kinetics and mass transfer. In spite that the internal mass transfer resistance in the catalyst pores is efficiently suppressed because of thin washcoat layers on structured catalysts, the low flow velocities applied in many liquid-phase processes impair the mass transfer efficiency at the outer surface of the catalyst layer inside the channels of monoliths and open foams. The coupling of external mass transfer resistance and Intrinsic Kinetics was considered for various power-law and adsorption Kinetics in tubular reactors filled with structural catalysts. The relevant mass balance equations were derived and solved numerically and the behaviors of single-channel systems were illustrated in the parameter spaces of Damkohler numbers. The single-channel model was successfully extended to a system of parallel channels with a distribution of channel sizes. The effect of the channel size distribution on the Reynolds and Sherwood numbers was illustrated by numerical simulations. The proposed approach is a potential tool for the design of structured catalysts.
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modelling of Kinetics mass transfer and flow pattern on open foam structures in tubular reactors hydrogenation of arabinose and galactose on ruthenium catalyst
Chemical Engineering Science, 2021Co-Authors: Ali Najarnezhadmashhadi, Kari Eranen, Dmitry Yu Murzin, Johan WärnÅ, Heather L Trajano, Tapio SalmiAbstract:Abstract Open foam structures are very beneficial as heterogeneous catalysts for three-phase processes, because they have high efficiency and low pressure drop. A mathematical model for open foam catalyst structures was developed. It was based on the concept of axial dispersion as flow pattern, on liquid-solid mass transfer effects and Intrinsic Kinetics on the active sites of the catalyst. Rate equations were presented for the hydrogenation of individual sugars and binary sugar mixtures on Ru/C catalysts and they were implemented in the mass transfer and flow models of the open foam catalyst. The flow pattern in the foam structure was confirmed with step change experiments with an inert tracer. The multiphase model was applied on the hydrogenation of arabinose and galactose in a laboratory-scale open foam catalyst bed. The model was able to reproduce the main features of the experimental observations, both for individual sugars and binary sugar mixtures.
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Kinetics of aqueous extraction of hemicelluloses from spruce in an intensified reactor system
Industrial & Engineering Chemistry Research, 2011Co-Authors: Henrik Grenman, Kari Eranen, Jens Krogell, Stefan Willfor, Tapio Salmi, Dmitry Yu MurzinAbstract:The aqueous extraction of hemicelluloses has gained increasing interest with new emerging applications for hemicelluloses in the modern forest-based biorefinery concept. The extraction Kinetics play a key role in their industrial utilization. The traditional kinetic studies and models for the selective dissolution of softwoods, however, always incorporate high concentrations of sodium hydroxide and sodium sulfide relevant to pulping, and the Kinetics in pure water is left outside the scope of these investigations. Aqueous extraction of hemicelluloses from spruce sapwood was investigated with a new cascade reactor setup, which was developed for intensified investigation of solid−liquid dissolution Kinetics. The experiments were performed at 150−170 °C with a particle size of 1.25−2 mm and solid loads of about 6.25 g of dry wood/L in the kinetic regime of Intrinsic Kinetics. The pH of the liquid phase was measured during the reaction. The selectivity of the dissolution and degradation of hemicelluloses was ...
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Interaction of Intrinsic Kinetics and internal mass transfer in porous ion-exchange catalysts: Green synthesis of peroxycarboxylic acids
Chemical Engineering Science, 2009Co-Authors: Sébastien Leveneur, Tapio Salmi, Dmitry Yu Murzin, Johan WärnÅ, Lionel EstelAbstract:Description of the interactions between Intrinsic Kinetics and internal mass transfer is one of the central issues in chemical reaction engineering. A general model was developed, comprising the kinetic and mass transfer effects in porous particles reacting in batch reactors. The catalyst particle size distribution was included in the model. A numerical algorithm and software was developed to solve the model for simulation and parameter estimation purposes. The model was applied to an industrially relevant case of green chemistry: synthesis of peroxycarboxylic acids from carboxylic acids and hydrogen peroxide. Due to the potential industrial applications, the present study was focused on the acetic and propionic acid perhydrolysis. The concentrations in the bulk phase and inside the catalyst particles were predicted by the model. It turned out that the smallest ion-exchange resin particles operated under kinetic control, whereas the largest particles (higher than 300 µm ) are influenced by diffusional limitation. Thus the combined effect of reaction and diffusion along with the particle size distribution are essential ingredients in the model.
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interaction of Kinetics and internal diffusion in complex catalytic three phase reactions activity and selectivity in citral hydrogenation
Chemical Engineering Science, 2006Co-Authors: Jeannette Aumo, Tapio Salmi, Johan WärnÅ, Dmitry Yu MurzinAbstract:Abstract Kinetics and mass transfer effects were studied for the complex catalytic liquid-phase hydrogenation in a semi-batch reactor, where finely dispersed and larger catalyst particles were used. Citral was used as a model molecule. The Intrinsic Kinetics was determined with crushed catalyst particles at 60 ∘ C and at pressures ranging from 10 to 40 bar. A kinetic model was proposed and successfully fitted to the experimental data. In order to elucidate the influence of internal diffusion on the selectivity and activity in complex reactions, citral hydrogenation was performed with larger catalyst pellets, in a pressurized autoclave equipped with a catalyst basket. As expected, the activity decreased with increasing catalyst particle size. The product distribution was shifted from the primary hydrogenation product (citronellal) to the fully hydrogenated end product (3,7-dimethyloctanol) as the catalyst particle size was increased. The concentrations of the secondary hydrogenation products were minor throughout the experiment. A complete reaction–diffusion model was developed for large pellets and complex reactions systems.
