Abstract
This study aims to develop a continuous antisolvent crystallization technique using a novel non-submerged triple impinging jet mixer for multiple feeding volume ratios to perform the direct procession of a flow acetylsalicylic acid (ASA) reaction mixture. The impinging jet mixer was supplemented by an overflow mixed suspension mixed product removal (MSMPR) crystallizer to provide a longer aging period for the crystals. The effect of temperature, residence time, and antisolvent to ASA solution ratio on product purity, yield, productivity, crystal size, and crystal size distribution was examined applying a 23 two-level full factorial experimental design. It was found that due to the intensive initial mixing achieved with triple impinging jet significantly smaller crystal size (<180 µm) with narrower unimodal crystal size distribution and higher maximum yield (83.1%) could be obtained compared to the conventional MSMPR technique. Furthermore, the developed continuous crystallization was accomplished in smaller equipment with the same productivity. Consequently, the processing of the ASA reaction mixture using a triple impinging jet mixer system enables the morphology modification and the direct connection of flow synthesis with continuous crystallization step.
Highlights
Rapid, homogeneous, and efficient mixing is essential for continuous crystallization especially in the case of fast crystallization processes with high supersaturation, such as antisolvent and reactive crystallizations where highly miscible fluid components have to be agitated
Besides acetylsalicylic acid (ASA) the reaction mixture contained various impurities, such as salicylic acid (SA) (
The widely used impinging jet mixers and an in-house devel oped triple impinging jet mixer were tested for mixing unequal streams
Summary
Homogeneous, and efficient mixing is essential for continuous crystallization especially in the case of fast crystallization processes with high supersaturation, such as antisolvent and reactive crystallizations where highly miscible fluid components have to be agitated. The IJ mixers rapidly impinge two liquid streams at a very high velocity (1.0–15.0 m/s) to produce a homogeneous system without external mechanical mixing [13]. In many publications, this technique is called a dual impinging jet (DIJ) [13], or a two-impinging-jet mixer (TIJ) [14]. Liu et al [15] tested the collision of parallel fluid jets at a 4:1 volume ratio They reported the shift of the stream meeting point to the jet outlet of fluid with a lesser amount of feed and a smaller diameter, which caused gradually the product accumulation on this tube outlet and its clogging. Zhang et al tested a free triple impinging jet mixer with two horizontal opposite and a perpendicular jet configuration to study the turbulent behavior of mixing by unequal liquid streams in a liquid-liquid reaction [16]
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