Micromixing efficiency in a multiphase reactor with a foam block stirrer

Abstract

A rotating foam reactor (RFR), which comprises a solid foam block stirrer as opposed to the agitator blade in stirred tanks, has recently received a significant amount of research interest due to its high mass transfer rates. For a deeper insight into the RFR the work herein investigated the micromixing efficiency of the RFR in terms of segregation index (X s ) using the iodide-iodate reaction system. The effects of various operating parameters including injection time, rotational speed, acid concentration, volume of liquid, volumetric ratio, and gas flow rate on segregation index were systematically examined. Results showed that the segregation index remained constant when injection time exceeded 100 s. Moreover, the X s increased with an increase in acid concentration but decreased with an increase in rotational speed, volume of liquid, volumetric ratio, and gas flow rate. Micromixing time was also calculated based on the incorporation model and was established to range from 1.1 Â 10 À3 -4.5 Â 10 À2 s, which is much shorter than that of conventional reactors. The results herein demonstrate that an RFR exhibits excellent micromixing efficiency and has a significant potential for use in chemical industries.

Image‐based measurement of engulfment vortex to quantitatively assess micromixing efficiency in a gas–liquid stirred tank

“…At the Position 1 above the impeller, X S decreases with the impeller speed regardless of the gas flow rate, which means the micromixing efficiency is improved by stirring. It is consistent with previous reports that the more energy input, the stronger turbulence level, and the better micromixing 51,61,67 . When the gas flow rate increases at a fixed impeller speed, X S rises in Q G <2 L/min and then decreases in Q G >2 L/min.…”

“…The micromixing time is typically solved by some mathematical models of micromixing based on the chemical process of test reactions in a semi‐batch reactor, 59–61 such as the E model and incorporation model. In the E model, the volume of an eddy V grows exponentially with time t : where E is the engulfment rate and its reciprocal is accepted as an index to the micromixing time t m on account of the same dimension ( t m ≈ E −1 ).…”

“…The micromixing time is typically solved by some mathematical models of micromixing based on the chemical process of test reactions in a semi-batch reactor, [59][60][61] such as the E model and incorporation model. In the E model, the volume of an eddy V grows exponentially with time t:…”

“…It is consistent with previous reports that the more energy input, the stronger turbulence level, and the better micromixing. 51,61,67 When the gas flow rate increases at a fixed impeller speed, X S rises in Q G <2 L/min and then decreases in Q G >2 L/min. This nonmonotonic relationship also has been found previously, 68 and the rise of X S is attributed to a negative effect of gas-induced agitation to the mixing.…”

Intensification of Liquid–Liquid Emulsification Process in a Rotating Solid Foam Stirrer Tank: Experiments and Modeling

“…The key feature of a RSFST is that a strong centrifugal force and shear force are induced simultaneously from the mechanical rotation of the porous foam packing, which shows a strong ability to intensify the gas–liquid contact and increase the interfacial area. In recent years, the reactor shows promising potential in various gas–liquid processes such as catalytic oxidation of glucose, catalytic hydrogenation of styrene, mass transfer of ozone, degradation of acidic red B by a foam-packed loaded catalyst in a semi-intermittent operation, degradation of acidic red B and p -nitrophenol by ozone in a continuous operation, micromixing efficiency, , and liquid–solid mass transfer . Moreover, the commercial application of RSFST exists.…”