Holdup and Wetting in Trickle Flow

Trickle-bed reactors usually consist of a fixed bed of catalyst particles, contacted by a gas liquid two-phase flow, with co-current downflow as the most common mode of operation. Such reactors are particularly important in the petroleum industry, where they are used primarily for hydrocracking, hydrodesulfurization, and hydrodenitrogenation other commercial applications are found in the petrochemical industry, involving mainly hydrogenation and oxidation of organic compounds. Two important quantities used to characterize a trickle-bed reactor are 

Prior to the use of MR to investigate holdup and wetting, while direct measurements of macroscopic holdup could be made gravimetrically, only indirect measurements of surface wetting had been reported. Such indirect measurements of wetting include chemical methods based on reaction rates (90) and tracer (91), 

Extension of this methodology to porous packing elements (e.g., catalyst support pellets) is not straightforward. The challenge arises because the signal we wish to measure is associated with the liquid (water) in the bed. However, the signal intensity acquired from a specific region of water depends on its local environment, because the nuclear spin relaxation times of water in different physical environments will vary. In this system, the different environments will be (i) free water in the bulk of the inter-pellet space, (ii) water within the intra-pellet pore space, and 

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