Miniaturized Measuring Cells as Scale-Down Tools for Absorption Column Design: CO2-Based Characterization of Liquid-Side Mass Transfer in Structured Packings

Abstract

Reliable liquid-side mass-transfer data are essential for the design of packed absorption columns, but their experimental determination in conventional pilot-scale columns requires considerable apparatus size, liquid inventory, and operating effort. This study investigates whether carbon dioxide (CO2) desorption from water into air can be used to characterize liquid-side mass transfer in a miniaturized measuring cell equipped with Montz-Pak B1-250.45 structured packing. The experiments were evaluated using the HTU/NTU concept to determine overall liquid-side HTUOL values and liquid-side volumetric mass-transfer coefficients βLaeff. In addition to integral sump sampling, the liquid leaving the packing core and the wall zone was collected separately to assess the contribution of different liquid pathways. The calculated HTUOL values ranged from approximately 0.22 to 0.33 m and showed a weak dependence on gas load in the preloading regime, especially for the lowest liquid load, followed by a more pronounced decrease when the loading region was approached. Compared with pilot-scale data obtained in a DN288 column with the same packing, the miniaturized measuring cell produced HTUOL values in the same order of magnitude, but approximately 15–30% lower at comparable operating points. The derived βLaeff values were within the range of established correlations and literature data for structured packings. Separate liquid sampling showed substantially higher HTUOL values in the wall zone than in the packing core, while the integral sump values remained close to the core values. These results indicate that the measuring-cell response is predominantly governed by the active packing core. The study demonstrates the potential of miniaturized measuring cells as complementary tools for early-stage liquid-side mass-transfer characterization in packed absorption columns, while highlighting the need to account for packed height, wall flow, inlet and outlet effects, and sampling configuration when transferring results to conventional column geometries.