Advancing Nanobubble-Assisted Crystallization as a Green and Sustainable Technology

Crystallization is a key process in the chemical industry for manufacturing, separation, and purification. However, precise control over the crystal properties remains challenging. Ultrasound-assisted crystallization has been widely used to overcome these issues, but its continuous use can cause thermal degradation, reactor corrosion, and high energy consumption, limiting industrial scalability. Nanobubbles offer a green, sustainable alternative due to their high surface-to-volume ratio and strong negative surface charge, which promote nucleation and control crystal growth. This study compares ultrasound and nanobubbles in cooling crystallization. A theoretical analysis using a modified Gibbs free-energy equation showed that increased nanobubble surface charge reduces nucleation energy barriers by providing a relation of Δ G k B T ∝ Q r * . Experimentally, nanobubbles shortened induction times, increased yield, and reduced crystal size from 171 to 83 μm. The variation in operating parameters for nanobubble production resulted in optimum conditions for crystallization. Overall, nanobubbles present a viable, non-invasive alternative to ultrasound, offering effective crystallization control without significant energy input, making them suitable for industrial-scale applications.