An Experimental Study of Local Mass Transfer Measurements in a Bubble Column Reactor Using an Electrochemical Technique

Abstract

An electrochemical method was used to follow chemisorption of carbon dioxide from a gaseous mixture (nitrogen, carbon dioxide) in Benfield solution (potassium carbonate and diethanolamine; DEA) in a bubble column (methacrylate column of 6 cm × 6-cm rectangular section and 103-cm height). Measurements were conducted at various molar concentrations of absorbent (0.5, 1.0, 1.5, 2.0, and 2.5 M), molar concentration of the promoter (diethanolamine; 0, 0.2, and 0.3 M), and the mole fraction of carbon dioxide in a gaseous mixture (0.1, 0.15, and 0.2). The volumetric mass transfer coefficient, KLa, is modeled as: The local volumetric mass transfer coefficient, KLa, was found to vary significantly in the axial direction. It decreases with an increase in the electrode-to-sparger distance (HC/DC), and this decrease will be faster in the case of promoted potassium carbonate (promoted with 0.2 and 0.3 M DEA) because of bubble shrink. The variation of the local volumetric mass transfer coefficient, KLa, with the axial position indicates that the assumption of a constant mass transfer coefficient throughout the Bubble column reactor is erroneous and may lead to large errors in designing and scaling up Bubble columns. It was found that the volumetric mass transfer coefficient, KLa, can be related to the electrode-to-sparger distance (HC/DC) by the following empirical model: