Experimental investigation of effective gas-liquid specific interfacial area in a rotor-stator reactor
Graphical abstract
Comparison of experimental and predicted effective gas-liquid specific interfacial area in a rotor-stator reactor.
Introduction
The need for intensification of mass transfer and micromixing processes has led to the invention of a variety of multiphase reactors. A typical example of such reactors is a rotating packed bed (RPB), a Higee device which was invented by P. G. Schmidt in 1913 [1]. In an RPB, the rotation of the packing creates a large centrifugal force which spreads and splits aqueous reactants flowing through the packing into small droplets or thin films. Consequently, the surface renewal rate and micromixing efficiency are greatly intensified, resulting in a significant increase in gas-liquid interfacial area and mass transfer coefficient [2,3]. As a result, RPBs have extensively been used to enhance micromixing and mass transfer in gas-liquid systems [4,5], liquid-liquid systems [6], and liquid-solid systems [7].
Nonetheless, further researches have revealed some drawbacks of RPBs such as the need for gas seal especially in gas-liquid systems and lack of even circumferential distribution of liquid in the packing [8]. On the basis of an RPB, a rotating zigzag bed (RZB) with a zigzag channel rotor but without liquid distributors and packing has been designed for continuous distillation process [9,10]. The structure of an RZB allows for zigzag flow of gas and liquid streams [11,12]. In comparison with an RPB, an RZB exhibits excellent operability with a higher turndown ratio while its mass transfer efficiency is roughly the same as that of an RPB [13].
A novel rotor-stator reactor (RSR) was also developed on the basis of an RPB [14]. The main difference of RSR from RPB is that the conventional packed rotor is replaced by several layers of circular rotors and pin-like stators, which function as disturbing parts and cause the redistribution of fluids when they pass these stators. Therefore, better circumferential distribution of liquid and higher micromixing efficiency can be achieved in RSR. It was reported by Chu et al. [15] that the micromixing time of RSR can be as low as 10−5 s, which is much less than that of 10−4 s in RPB. Our previous studies have also showed good performance of RSR in the intensification of gas-liquid-liquid reaction [16,17], nanoparticle preparation [18], deoxygenation [19], absorption [20] and ozonation [21] processes.
The effective gas-liquid specific interfacial area (ae) is a vital parameter in the design of a mass transfer equipment. Although there have been many studies on RSR and its applications, to the best of our knowledge there is no report on its effective gas-liquid specific interfacial area (ae). This work therefore aimed to experimentally determine the effective gas-liquid specific interfacial area in an RSR by chemisorption of CO2 into NaOH solution. The variation of ae with different operating conditions of rotation speed, liquid volumetric flow rate and gas volumetric flow rate is also presented. A correlation for ae as a function of the various operating conditions was also established and validated experimentally.
Section snippets
Structure and characteristics of RSR
Structure of the RSR employed in this study is demonstrated in Fig. 1. The RSR comprises five layers of rotor rings and four layers of stator rings. These rotor and stator rings are arranged alternately. Centrifugal force is produced by the rotation of the rotor-rings driven by a motor, while the stator-rings are fixed on an end cover. The inner diameters of the five rotor-rings are 40, 54, 68, 82, 96 mm respectively, while the inner diameters of the stator-rings are 49, 63, 77, 91 mm
Effect of rotation speed
The effect of rotation speed on ae is illustrated in Fig. 3. It is evident that ae increases with an increase in rotation speed. Higher rotation speed of the rotor can bring about a larger shear force and stronger turbulence of the gas and liquid streams. As a result, liquid is split into smaller liquid droplets and thinner films, as was observed in our previous study where a high-speed camera was used to obtain continuous and clear images of liquid flow inside an RSR [27], leading to a larger
Conclusions
This work aimed to determine the ae in an RSR by chemisorption of CO2 into NaOH solution and to establish its correlation. The variations of ae under different operating conditions such as rotation speed, liquid volumetric flow rate and gas volumetric flow rate were studied. The experimental results show that ae increases with an increase in rotation speed and volumetric flow rates of both liquid and gas streams. The significant rise of ae with an increasing rotation speed indicates that the
Declaration of interests
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (Nos. 21676008, 21406009).
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