Role of gas bubbles in nucleation of solid solutes: A molecular simulation approach
Crystallization is an important method of separation and purification employed in a wide variety of industries including food, pharmaceutical, cosmetics, and biochemical industries, amongst others. The process of crystallization typically involves nucleation of solute particles and their subsequent growth. Broadly speaking, there are two modes of nucleation: homogeneous and heterogeneous. Homogeneous nucleation is known to lead to low particle size. Many studies have, however, suggested that heterogeneous nucleation is likely to be more common in industrial crystallization processes, due to the presence of foreign surfaces such as dust particles, impurities, vessel and impeller surfaces, etc. Recent studies suggest that gas bubbles may also promote heterogenous nucleation of solids, as evident from reduction in the induction time for their nucleation as well as of the metastable zone width observed in presence of gas bubbles. However, to date all the relevant studies have been experimental in nature, with practically no attempt on modeling the phenomenon using either classical nucleation theory or microscopic approaches. The present study will aim to employ an approach based on molecular simulation to understand the microscopic behaviour of systems where gas bubble-mediated precipitation of solids has been postulated to occur by several research groups. The study will also investigate the role of bubble size and flow rate, crystal-substrate contact angle, and interfacial energy in such nucleation processes.