Non-traditional applications of NMR tomography

Koptyug, Igor V.; Sagdeev, R. Z.

doi:10.1070/rc2003v072n02abeh000744

Cited by 21 publications

(16 citation statements)

References 195 publications

(345 reference statements)

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“…Recently, space-resolved NMR thermometry was applied to monitor the temperature gradients along a fixed-bed reactor consisting of Pd/c-Al 2 O 3 beads during propylene hydrogenation [127]. Special applications using NMR tomography such as solid and gas imaging have been excellently described [107].…”

Section: Nmr/mrimentioning

confidence: 99%

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Space-Resolved Profiling Relevant in Heterogeneous Catalysis

Urakawa

Baiker

2009

Top Catal

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Knowledge of gradients involved in chemical processes, such as heterogeneously catalyzed reactions, on molecular as well as reactor scale is of paramount importance for understanding and optimizing such processes. This review highlights and discusses recent advances in spatially resolved methods for the detection of chemical (structural) and temperature gradients, with particular focus on in situ methods.

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Section: Nmr/mrimentioning

confidence: 99%

“…Magnetic resonance imaging (MRI) or alternatively called nuclear magnetic resonance tomography (NMRT), routinely employed in medical fields, has found its powerful application also in the field of heterogeneous catalysis [103][104][105][106]. Spatial resolution of 30 lm can be achieved [107].…”

Section: Nmr/mrimentioning

confidence: 99%

Space-Resolved Profiling Relevant in Heterogeneous Catalysis

Urakawa

Baiker

2009

Top Catal

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“…To estimate the degree of conversion, we assume that the rate of AMS hydrogenation in the liquid phase can be neglected in comparison with the rate of AMS hydrogenation in the gas phase; the AMS hydrogenation in the gas phase takes place in the dry surface layer of the pellet; the change in the hydrogen partial pressure along the thickness of the reaction catalyst layer is insignificant and is equal to the equilibrium pressure, (21) and the hydrogenation kinetics is described by the power law [15] …”

Section: Degree Of Ams Conversion In Vapor Hydrogenationmentioning

confidence: 99%

“…In magnetic resonance microimaging, spatial images are produced using pulsed magnetic field gradients [7][8][9][10][11]21]. The resonance frequency of an NMR signal depends linearly on the magnetic field applied to a sample; therefore, on application of a field gradient, the frequency becomes a unique function of the nuclear spin coordinate along the gradient direction.…”

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confidence: 99%

Self-oscillations on a partially wetted catalyst pellet in ?-methylstyrene hydrogenation: Experiment and mathematical modeling

Кириллов

Koptyug

Куликов

et al. 2005

Theor Found Chem Eng

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Catalytic reactions of hydrogenation of liquid hydrocarbons underlie many petrochemical processes. A feature of these reactions is high heat release, because of which components of the liquid phase can evaporate and the reactions can occur in both the liquid and the vapor-gas phases on wetted and dry catalyst pellets, respectively. The interplay between chemical and phase changes on an incompletely flooded pellet give rise to various types of steady-state heat modes.Experimental studies in this area were started [1, 2] with model reactions of hydrogenation of α -methylstyrene (AMS) and cyclohexene in a three-phase system. In steady-state experiments on cyclohexene hydrogenation on a single catalyst pellet [2], multiplicity of temperature and flooding states of the catalyst pellet was first observed, which were dependent on the initial impregnation of the pellet with liquid. In AMS hydrogenation [3], phenomena of the "ignition" and the "extinction" type were experimentally investigated for the first time in irrigation of various types of single catalyst pellets at different flow rates of the liquid reactant.Previously [4], we proposed a physical mechanism and developed several simple models for a monoporous pellet, which, by and large, explained the experimental data [3]. We also put forward a more complex mathematical model of AMS hydrogenation on a catalytic plate that is partially wetted on the surface and partially impregnated with the liquid reactant. This model took into account the pore size distribution, the pore filling distribution, and the reactions in the liquid and gas phases [5]. Using this model, by numerical methods, multiplicity of steady states and hystereses of temperature and the degree of pellet filling with the liquid were revealed.It is known that the interplay between physical steps of the process (impregnation of a pellet with the liquid, liquid evaporation, heat and mass transfer) and chemical reactions in the liquid and vapor-gas phases may lead to instability and self-oscillation modes in threephase systems [6]. Therefore, it seems necessary to study such modes further.The purpose of this work was to experimentally and theoretically investigate self-oscillation modes on an irrigated porous catalyst pellet in exothermic hydrogenation accompanied by liquid evaporation. For this purpose, the most promising experimental method is in situ NMR tomography (magnetic resonance microimaging) [7][8][9]. This method allows one, in particular, to obtain images of the liquid-phase distribution within the porous object and monitor the liquid-phase redistribution immediately during the process without destroying the object and without introducing any probes or molecular labels [10][11][12][13]. EXPERIMENTAL As a model reaction, we chose α -methylstyrene (AMS) hydrogenation to form cumene:C 6 H 5 C(CH 3 )=CH 2 + H 2 C 6 H 5 C(H)(CH 3 ) 2 . This reaction is most widely used as a model reaction in the experimental investigation of processes in trickle-bed reactors (in which there is a downward cocurrent g...

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“…The nuclear magnetic resonance imaging (MRI) technique is well known for its ability to visualize the internal structure of various liquid-containing objects, from humans to catalyst pellets and prewetted rock cores [1][2][3]. It is important, however, that image contrast in MRI is governed not only by the structural characteristics of an object under study, but also by a broad range of its other properties and the processes within it.…”

Section: Introductionmentioning

confidence: 99%

NMR imaging of mass transport processes and catalytic reactions

et al. 2005

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c Boreskov Institute of Catalysis, 5 Acad. Lavrentiev Pr., Novosibirsk 630090, Russia NMR imaging and spectroscopy techniques are applied to study flow and filtration of liquids, gases and granular solids in various geometries and to the in situ studies of the interplay of mass transport and catalytic reactions in porous media. In particular, quantitative spatially resolved maps of flow velocities of liquids and gases in the channels of monoliths have been obtained. A comparative study of the filtration of water and propane through model porous media has revealed that the dispersion coefficients for water are dominated by the holdup effects even in a bed of nonporous glass beads. Similar experiments performed with the gravity driven flow of liquid-containing fine solid particles through a porous bed have yielded the distributions of particle velocities for various flow rates. The NMR imaging technique was employed to visualize the propagation of autocatalytic waves for the Belousov-Zhabotinsky reaction carried out in a model porous medium. It was demonstrated that the wave propagation velocity decreases as the wave crosses the boundary between the bulk liquid and the flooded bead pack. The images detected during the catalytic hydrogenation of a-methylstyrene on a single catalyst pellet at elevated temperatures have revealed that the reaction and the accompanying phase transition alter the distribution of the liquid phase within the pellet.

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Non-traditional applications of NMR tomography

Abstract: For Abstract see ChemInform Abstract in Full Text.

Cited by 21 publications

References 195 publications

Space-Resolved Profiling Relevant in Heterogeneous Catalysis

Space-Resolved Profiling Relevant in Heterogeneous Catalysis

Self-oscillations on a partially wetted catalyst pellet in ?-methylstyrene hydrogenation: Experiment and mathematical modeling

NMR imaging of mass transport processes and catalytic reactions

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