posted on 2023-05-26, 13:09authored byJiale Wu, Xianjing Zheng, Li Wan, Yuan Tao, Dang Cheng, Fener Chen
Solvent swap from high- to low-boiling solvents still
presents
a huge challenge in the development of multistep continuous-flow processing.
Herein, a miniaturized inline tube-in-tube solvent exchanger combining
intensified convective mass transfer with droplet evaporation is presented.
The design involves intimate contact between droplet and gas phases
in countercurrent mode within a mesofluidic tube. Its solvent removal
performance was evaluated by using pure solvents and binary mixtures.
The results revealed that the commonly used solvents with low to medium
boiling points (Tb < 100 °C) can
be completely evaporated at room temperature without the need of heating.
Significantly, high-boiling solvents can be efficiently removed at
temperatures much lower than their boiling points. Its capacity for
the separation of binary mixtures was corroborated by removing dichloromethane
from a 50:50 mol % dichloromethane–dimethylformamide mixture
and acetic acid from a 50:50 mol % p-nitroacetophenone–acetic
acid mixture. A computational fluid dynamics (CFD) model based on
the phase field approach was developed to quantitatively describe
the droplet evaporation process, providing indepth evaporation dynamics
and furthering our understanding on the concomitant phase change phenomenon.
The comparison with other types of evaporators highlights its superior
evaporative performance. To enable fast design and optimization of
this type of evaporators, a correlation model was proposed to calculate
the evaporation rate with good prediction performance. The usefulness
of this device was demonstrated by performing a two-step continuous-flow
synthesis of 4-aminoacetophenone. The combined experimental and CFD
studies demonstrate that this tube-in-tube device can serve as a convenient
and efficient tool for continuous solvent exchange, particularly from
high- to low-boiling solvents, in continuous-flow synthesis.