(144g) A Study of Axial Mixing Influence on the Mass Transfer Transferability from Absorption to Distillation Conditions

Our paper assesses success of the recalculation of the mass-transfer data from absorption to distillation conditions for the Mellapak 250Y structured packing and two random packings (Pall rings 25mm and Intalox saddles 25mm). The tests of the recalculation procedure are namely focused on the effect of taking into the account of the axial mixing of the liquid phase or acceptance of the usual assumption of the plug flow. The absorption data in the form of the volumetric mass-transfer coefficients were either overtaken from the literature or were measured in the absorption column of inner diameter of 0.29m using proven aqueous test systems. The distillation data in the form of the HETP were measured under the total reflux in the 0.15m atmospheric column using C₆/C₇ and methanol/n-propanol systems.

The recalculation of the acquired absorption mass-transfer coefficients to the distillation conditions was performed through utilization of the model proposed by Billet and Schultes (1999). The raw absorption data were used for optimization of the all six packing specific constants of the model. The hydraulic/hydrodynamic data necessary for the evaluation were also measured.

The measurement of the hydrodynamic parameters revealed significant degree of the liquid-phase axial mixing for all the packings, while the total liquid hold-up were found to be comparable. The most significant axial mixing was found for the Intalox saddles.

The HETP prediction based on the recalculated mass-transfer coefficients led to poor results for all packings. However, the disagreement is not addressed to the fundamental impropriety of the test systems or the inability of the BS model to transfer the data from absorption conditions to distillation ones. We demonstrate that reasonably accurate values of HETP can be obtained when the influence of the liquid phase axial mixing is involved into the HETP prediction. Therefore we suggest as a reasonable further development step of the process simulation software incorporation of the more sophisticated hydrodynamic models.