Monolith multiphase flow

The low density of gases makes it more difficult to keep the bubbles dispersed. The bubbles will move to the low-pressure areas, that is, behind the impellers, in the trailing vortices close to the impeller, behind the baffles, and at the inner side after a bend. The bubbles will coalesce in these areas with high gas holdup. It is very difficult to design reactors without low-pressure regions where the low-density fluid will accumulate. One such reactor is the monolith reactor for multiphase flow [32, 33]. 

N. Reinecke, D. Mewes, Oscillatory transient two-phase flows in single channels with reference to monolithic catalyst supports, Int. J. Multiphase Flow 25 (6-7) (1999) 1373-1393. 

Monolith multiphase chemical reactors are another example of microfluidic multiphase flow applications. The slug flow pattern enhances the mass transfer in the liquid-solid process. There is also low-pressure drop for a given specific contact area. Machado et al (1999) have patented the use of monolith reactors for fast and highly exothermic nitroaromatic hydrogenation. In this process, the product is recycled through the reactors several hundreds of times, and the low-pressure-drop monolith reactor is therefore preferred. 

Kreutzer, M.T. et al. (2005) Multiphase monolith reactors chemical reaction engineering of segmented flow in microchannels. 7th International Conference on Gas-Liquid and Gas-Liquid-Solid, 2005,... 

An attractive property of monolithic reactors is their flexibility of application in multiphase reactions. These can be classified according to operation in (semi)batch or continuous mode and as plug-flow or stirred-tank reactor or, according to the contacting mode, as co-, counter-, and crosscurrent. In view of the relatively high flow rates and fast responses in the monolith, transient operations also are among the possibilities. 

The flow regimes in capillaries have been investigated extensively, and the reported results provide a good basis for imderstanding the hydrodynamics of multiphase operation of monoliths. Figure 11 shows the well-known two-phase flow patterns observed in tubes (16,17). 

A recent example is the optical fiber monolith reactor, reported by Lin and Valsaraj (208). They used a monolith for photocatalytic wastewater treatment with the channels of the monolith completely filled with flowing liquid. The monolith structure was used merely as the distributor of the optical fibers, but the benefits of monolith, such as low-pressure drop and excellent mass transfer characteristics for multiphase systems, were not fully exploited. 

Kreutzer, M. T., Kapteijn, F., Moulijn, J. A., Heiszwolf, J. J. (2005). Multiphase monolith reactors Chetnieal reaetion enginetaing of segmented flow in microchatmels. Chemical Engineering Science, 60, 5895—5916. 

M.T. Kreutzer, F. Kapteijn, J.A. Moulijn, J.J. Heiszwolf, Multiphase monolith reactors Chemical reaction engineering of segmented flow in microchannels. Chemical Engineering Science, 2005, 60, 5895-5916. 

J. Heiszwolf, Multiphase monolith reactors chemical reaction engineering of segmented flow in microchannels,... 

The multiphase nature of the flow inside the monolith channels influences hydrodynamics and mass transfer. We briefly review the main aspects related with modeling of monolith reactors with Taylor flow. Particular attention is devoted to the consequences from using gas-liquid flow in contact with a catalytic surface as a reactor ... 

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