Dynamic MRI visualization of two‐phase flow in a ceramic monolith

Abstract

Regular and irregular catalyst packings are extensively used in the chemical industry for promoting mass transfer and chemical reaction between gas and liquid. Traditionally, randomly packed beds of catalyst particles operating in co-current downflow operation, often termed trickle-bed reactors, have been used because of the high mass-transfer rates achievable. More recently, structured supports are increasingly considered for use because of the potential improvements they offer with respect to, for example, the decoupling of heat-and mass-transfer phenomena, operation under reduced pressure drop conditions and at much higher gasrliquid Ž flow rates, and a greater resistance to attrition Irandoust and Andersson, 1988a,b; Irandoust et al., 1998; Kapteijn et al., . 1999 . Monoliths, which comprise a metal or ceramic structure with a large number of straight or parallel channels, are an example of such structured supports, and their use in solid-catalyzed gas-phase chemical reactions is well established. One example is the monolithic exhaust converter used throughout the automotive industry. In contrast, the application of monoliths to gas-liquid reactions is not well advanced and a significant research activity exists to provide the necessary understanding to enable reliable scale-up for process op-Ž . eration Nijhuis et al., 2001 . Undoubtedly, such efforts would be significantly aided if it were possible to develop an in-situ probe of the multiphase transport and reaction phenomena occurring within these porous structures. Magnetic resonance techniques show particular promise in this regard because of their ability to provide chemically-specific information on both the internal phase distribution and transport processes Ž . occurring within three-dimensional 3-D optically opaque systems.Visualization of gas-liquid flow in ceramic monoliths has Ž . previously been attempted by Mewes et al. 1999 using the capacitance tomography technique. While temporal resoluCorrespondence concerning this article should be addressed to L. F. Gladden. Ž tion of capacitance tomography is high 100 images per sec-. ond can be achieved , spatial resolution is relatively low with typical in-plane resolutions being 5᎐10% of the diameter of the system under investigation, thereby making impossible visualization of phase distribution within a single channel. In Ž . contrast, magnetic resonance imaging MRI has the poten-Ž . tial for relatively high spatial resolution say, 30᎐200 m , but the temporal resolution obtained for gas-liquid flow has to date been far too slow to visualize dynamic processes occurring in reactors. Time-averaged visualizations of singleand two-phase flow have been reported with data acquisition Ž times of minutes to hours Sederman et al., 1998;Tallarek et al. 1998;Johns et al., 2000; Sederman and Gladden, 2001; . Mantle et al., 2001 . Fast velocity imaging techniques have been reported which are able to acquire liquid velocity im-Ž ages in several minutes Seifert et al., 2000; Scheenen et al., . 2000 , but ...

Operating Characteristics and Performance of a Monolithic Downflow Bubble Column Reactor in Selective Hydrogenation of Butyne‐1,4‐diol

“…De TezanosPinto et al [10] have previously revealed that the liquid flow plays an important role in forcing the bubbles to enter the channels. Dynamic visualization by MRI technique also suggests that the proposed system allows achieving good distribution of gas-liquid flow in the monolith channels [16]. It is important since our work was focusing on obtaining a simple monolith reactor with good gas-liquid distribution.…”

“…Therefore, it is believed that the bubbles entered the monolith channels separated from each other by liquid plugs then creating a segmented gas-liquid flow or Taylor flow inside the channels. This phenomenon was revealed by means of visualization of gas-liquid flow in the same reactor setup (air-water system) using magnetic resonance imaging (MRI) technique [16]. Observation of flow revealed the development of a stable gas-liquid dispersion above the monolith, and the dispersion level was easily controlled to introduce gas-liquid flow that allowed the establishment of Taylor flow inside the monolith channels.…”

Viscous co‐current downward Taylor flow in a square mini‐channel

“…In technical multichannel applications, however, uniform Taylor flow is hardly achieved, because the bubble generation often leads to a distribution of bubble sizes. 13 For a better understanding of the basic hydrodynamic phenomena, experiments on Taylor flow are often performed in visually accessible single channels. Thulasidas et al…”

Prozessintensivierung heterogen katalysierter Gas/Flüssig‐Reaktionen mit Monolithreaktoren

“…Monolithreaktoren haben das Potenzial, die herkömmlichen Dreiphasenreaktoren aufgrund einer besseren Leistungscharakteristik, einer reduzierten Reaktorgröûe und einer erhöhten Sicherheit bei mindestens gleicher Produktivität zu verdrängen [6] [17].…”