Abstract
A clustered countercurrent-flow micro-channel reactor (C-CFMCR) has been assembled by the numbering-up of its single counterpart (S-CFMCR). Its micromixing performance was then studied experimentally using a competitive parallel reaction system, and the micromixing time was calculated as the micromixing performance index. It was found that the micromixing time of C-CFMCR was ranged from 0.34 to 10 ms according to its numbering-up times and the operating conditions of the reactor, and it was close to that of S-CFMCR under the same operating conditions, demonstrating a weak scaling-up effect from S-CFMCR to C-CFMCR. The C-CFMCR was then applied to prepare ultrafine manganese dioxide in a continuous manner at varying micromixing time. It showed that the micromixing time had a major effect on the particle structure. More uniform and smaller MnO2 particles were obtained with intensified micromixing. By building a typical three electrode system to characterize their performance as a supercapacitor material, the MnO2 particles prepared by both S-CFMCR and C-CFMCR under optimal conditions displayed a specific capacitance of ~175 F·g−1 at the current density of 1 A·g−1, with a decline of ~10% after 500 charge-discharge cycles. This work showed that C-CFMCR will have a great potential for the continuous and large-scale preparation of ultrafine particles.
Highlights
Precipitation is an extensive process in chemical industries for the preparation of particles of various size distributions, morphologies and other properties, in which the achievement of supersaturation— thermodynamically controlled phase transition—is significant because of the highly nonlinear dependency of both nucleation and growth rates on supersaturation [1]
The characteristic micromixing time scale must be low enough to be theoretically able to compete with the characteristic reaction time scale as well as the precipitation time scale [3]
The precipitate suspension flowing out of the countercurrent-flow micro-channel reactor (C-CFMCR) shell was collected into a stirred container and further stirred at room temperature for 0.5 h
Summary
Precipitation is an extensive process in chemical industries for the preparation of particles of various size distributions, morphologies and other properties, in which the achievement of supersaturation— thermodynamically controlled phase transition—is significant because of the highly nonlinear dependency of both nucleation and growth rates on supersaturation [1]. Many devices for strengthening the micromixing performance have been developed, such as confined impinging jets reactor [4], rotor-stator mixer [5], Y-type micro-channel reactor [6], microporous tube-in-tube micro-channel reactor [7], etc All of these equipment suffer from two important drawbacks: Most of them are difficult to manufacture and scale up due to their complicated structures; and, as to precipitation processes, low throughput and severe blocking problems have greatly restricted their applications [8,9], which allows only small-scale production. The C-CFMCR was applied for the precipitation of ultrafine MnO2 at varying micromixing time and the performance of the prepared MnO2 as a supercapacitor material was evaluated by building a typical three electrode system, the influence of micromixing time on the particle properties will be assessed
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