Evaluation of rotating packed beds for distillation

Abstract

In the chemical industry, centrifugal contactors have been proven to enhance separation processes, including distillation and absorption. Due to intensified mass and heat transfer, these contactors offer lower equipment volume, faster processing, and greater flexibility and performance. Rotating packed beds (RPBs), a centrifugal contactor, have been investigated for decades; however, their industrial implementation remains limited despite several benefits reported in the literature. One key limitation is the lack of a fundamental understanding of mass transfer within the packing and the absence of appropriate scaling rules. This work evaluates the rotating packed bed (RPB) technology for distillation by developing a fundamental understanding of mass transfer in RPB packings through comprehensive investigations. Firstly, a pilot plant was developed to facilitate large-scale distillation experiments and enable temperature measurements. It was automated using LabVIEW for instrumentation, control, and data acquisition. Secondly, total reflux distillation experiments were conducted at atmospheric pressure using conventional RPB packings, such as knit mesh and metal foam, with varying radial packing lengths, and without packing. Based on these results, a novel Zickzack packing was designed, resulting in slightly improved separation efficiency and easier scalability due to more homogeneous conditions inside the packing. Experiments with varying rotational speeds, vapor loads, and packing lengths demonstrate the flexibility of RPB operation while maintaining separation efficiency. Lastly, rotor telemetry was implemented for the first time to estimate the radial temperature profile and to develop an understanding of mass transfer within the packing, revealing that, in addition to the packing, the casing also contributes to the total separation efficiency of an RPB. Moreover, the separation efficiency of conventional RPB packings does not increase linearly with radial packing length, unlike Zickzack packing. The mass transfer performance was estimated using available correlations, and their limitations were identified. The key design and operational findings are summarized.