Understanding the impact of convective ethanol humidity on the precipitation behaviour of dissolved lactose in a water droplet

Abstract

• Crystallization behaviour during ethanol-vapour precipitation drying was studied. • Internal composition profiles of lactose-containing droplets were investigated. • High ethanol humidity promotes the formation of dendritic crystallites. • Nonuniform droplet shrinkage is due to randomly packed structures. Crystalline lactose particles, composed of agglomerated ultrafine crystallites, were produced using the antisolvent vapour precipitation technique. This technique exposes a single suspended aqueous lactose droplet to a convective stream laden with ethanol vapour. Manipulating simultaneous ethanol absorption and water evaporation from the droplet by adjusting the ethanol vapour humidity, led to various crystallite morphologies. Within the intermediate and high ranges of the ethanol humidity tested, higher humidity led to finer and more dendritic-like crystallites. Surprisingly, low ethanol humidity (20% ERH) led to a relatively high rate of ethanol concentration increment in the droplet but inadvertently exhibited a low nucleation potential. Thus, the crystallization potential of a lactose droplet under antisolvent vapour precipitation conditions will need to be evaluated in terms of the rate of ethanol concentration increment as well as the solute concentration-ethanol concentration history. These factors will be important in controlling or scaling up the antisolvent vapour precipitation technique.