Chemical products are ubiquitous in our daily lives, including various fibers to fabricate the clothes, the ingredients in cosmetics and toothpastes, the cathode and anode materials in batteries of electric vehicles, etc. All these chemicals are produced by chemical processes consisting of chemical reactions and a series of mixing and separation units.
It is known that effective collisions among reactant molecules can accelerate chemical reactions, besides the influences of temperature, catalyst, reactant concentration, etc. Recently, significant intensification effects of high-speed shearing on the chemical reactions were reported by the Chemical Process Intensification Innovation Team, School of Chemical Engineering &Technology, Tianjin University. This study was published in Frontiers of Chemical Science and Engineering on 21 March, 2022.
In the high shear mixer, the high tangential speed can be achieved due to the high-speed rotation of the rotor. And there is a great speed gradient in the narrow gap between the stator and the rotor. As shown in Fig. 1, changing the feeding location of one reactant in the experiment, the occurrence of the reaction will be restricted by the effect of the mass transfer and mixing. The mixing of the reactant molecules can be enhanced by the high shearing force, consequently resulting in higher reaction rate. It is indicated that the optimal feeding position of the reactant is close to the shear gap of high shear mixer.
CFD simulation results (Fig. 2) indicate that the fluid velocity in the high-shear area is high, and the outlet velocity of the feeding pipe is low, which results in the flow back of reactant A into the feeding pipe, i.e., a poor mixing condition. Therefore, when a high-shear mixer is used to intensify the chemical reaction, the backflow phenomenon in the feeding pipe can be eliminated by adjusting the diameter of the feed pipe and the feed rate.
This work shows that high shear mixers exhibit promising applications to intensify the industrial chemical reaction processes involving pharmaceuticals, cosmetics, food, chemicals, etc., since the unique feature of a narrow spacing (0.1–3 mm) between the stator and rotor, high tip speed of the rotor (10–50 m·s−1), high shear rate and turbulent energy dissipation rate in the gap.
