Aroma absorption in rapeseed oil using rotating packed bed

Abstract

An increasing consumers’ call for natural aromas fuels the development of biotechnological aroma production. Although aroma fermentation is quite advantageous, especially severe product losses of volatile compounds through the bioreactor off‐gas may challenge the downstream processing. The application of novel process intensification methods to overcome the common drawbacks of conventional apparatuses might be helpful on a way to commercial competitiveness of biotechnological aromas. This study explored the suitability of rotating packed bed (RPB), a rotating mass transfer enhancing machine, for the absorption of model aroma compounds in rapeseed oil. Increasing the rotation speed from 500 to 2750 rpm led to two‐ to threefold higher absorption efficiencies at elsewise constant conditions. Aiming for an enriched aromatic intermediate, 2.5 L of rapeseed oil was processed in a recycle for 200 minutes, and a final concentration of benzaldehyde of 0.323 ± 0.026 g/Loil was achieved. Compared to packed columns, the RPB outperforms at equal packing depth or requires less packing area to deliver same efficiency. Especially, the use of custom 3D‐printed spiral packing with elaborated wall film flow combined with rotation supported liquid distribution allows using absorbents with viscosities as high as 100 mPa·s at low pressure drop increase. However, small dimensions severely limit the performance of a laboratory‐scale RPB as the casing contributes disproportionally to mass transfer.

Radial Temperature Profile Measurements to Understand Mass Transfer in Rotating Packed Bed Distillation

“…However, adding packing material lowers the rotational speed at which the maximum separation efficiency is reached. These results can be supported by the investigations reported by Lukin et al 25 that the total wetted surface area of the empty rotor (without packing) and the casing is approximately in the range of 69−88% of the surface area generated in an RPB when the packing is used. 25 Therefore, it appears that the available conventional RPB packings need to be further improved to efficiently utilize their high specific surface areas efficiently.…”

“…Nevertheless, the results of the current research can be supported by experiments on ethanol dehydration conducted by Qammar et al , using a metal foam with varying outer radii as well as with an empty rotor having the same F -factor and RPB design as in the current study. They showed that even with no packing, there is a certain amount of separation in an RPB, which leads to the observation that there might not be a significant contribution of the end-zone to the overall mass transfer; instead, it might be the result of mass transfer on empty rotor plates and the mass transfer in the casing as also supported by the wetted area observations made by Lukin et al in an RPB (height to packing radius = 0.2) with and without packing. Table indicates that almost half of the separation is achieved even with no packing compared to the separation with a packing length of 0.19 m. If a few centimeters of the packing is added to the empty rotor, then it only increases the Nth by half a stage, and so on.…”

“…In Figure 8, the contribution of the empty rotor is smaller than the casing contribution indicating that mass transfer resulting from the flying droplets in the casing and these droplets striking the casing walls and running down contributes more to the mass transfer than the film mass transfer on the empty rotor plate. 25 The overall separation efficiency of a rotor equipped with knit mesh is almost 0.7 theoretical stages better than that of an empty rotor. However, adding packing material lowers the rotational speed at which the maximum separation efficiency is reached.…”

“…As indicated in our previous investigations 8,9,17 that packing is not the only place where the mass transfer is happening; there is a substantial contribution of the casing to the overall mass transfer in an RPB reported by other studies as well. 19,25 The results of temperature measurements at the rotor indicate that by increasing the rotational speed, the separation efficiency of the packing decreases and the separation efficiency of the casing goes through a maximum. Similar results were also observed by Guo et al 26 and Sang et al 27 The packing contribution at maximum separation efficiency for knit mesh packing is 2.1 Nth, and the maximum casing contribution is almost equivalent to one theoretical stage to the overall mass transfer in the RPB.…”