Abstract
A study was conducted in enhancing the measurement of volumetric liquid phase mass transfer coefficients (KLa) in packed columns, by re-considering the application of conventional desorption and absorption of oxygen and carbon dioxide. The cost-effectiveness of this well-established system is hampered by reagent costs, in the form of oxygen and nitrogen, as well as plant footprint requirements. Therefore, aqueous desorption of isobutyl acetate into air (ADIBAA) is proposed as alternative to the conventional system. This ADIBAA-method utilises continuous dosing of isobutyl acetate with on-line ultraviolet quantification. This decreases reagent costs as only the desorbed component is dosed, thereby limiting related losses. Additional benefits of the newly proposed ADIBAA-method include minimal environmental impact and short experimental evaluation times, in the order of 20-30 min.
The ADIBAA-method was experimentally verified in a 400 mm ID column with a 1.1 m bed height. FlexiRings® sizes 1.5” and 2”, and Intalox® Ultra™ size A, were evaluated over liquid loadings ranging from 6 to 96 m3.m 2.h 1 and vapour flow factors between 0.6 and 2 kg.m-0.5.s-1. Liquid phase mass transfer coefficients (KLa) ranging from 0.0032 to 0.168 s-1 and 0.004 to 0.02 s-1 were measured for the 1.5” and 2” FlexiRings®, respectively. This is in agreement with the literature, with deviations limited to ca 10%. The liquid phase mass transfer coefficient evaluations of the Intalox® Ultra™ size A, yielded KLa values ranging from 0.00482 to 0.0242 s-1. These results confirm the manufacturer statement that modern Intalox® Ultra™ packing provides similar mass transfer efficiency to smaller, and therefore higher apparent interfacial area packing from the second and third generations. This implies comparative mass transfer efficiencies between Intalox® Ultra™ A and 1” FlexiRings®, while providing decreased pressure drop and increased hydraulic capacity.
