Spray Drying and Crystallization of Lactose with Humid Air in a Straight-Through System

Abstract

The effects of different humidities on process yields and degrees of crystallinity have been studied for spray-dried powders from the spray drying of lactose with humid air in a straight-through system. According to Williams-Landel-Ferry (WLF) kinetics, it was suggested that a higher particle temperature and lower glass transition temperature would increase the crystallization rates of the particles during the spray-drying process. Freshly humidified air produced by a Buchi-B290 spray dryer as a humidifier before the main spray dryer decreased the particle glass transition temperature (Tg), while allowing the particle temperature (Tp) to reach higher values by using an insulated drying chamber. The results showed that higher Tp − Tg, as a result of applying humid air, improved the process yield from 21 ± 4% to 26 ± 2% and the lactose crystallinity by decreasing the latent heat of crystallization for the powder products from 43 ± 1 J/g to 30 ± 11 J/g. It has been found in this study that the humidity of the inlet air should be adjusted in such a way as to not exceed relative and absolute humidities of 2.7–3% and 65–70 g/kg DA, respectively, at the outlet of the drying chamber, to give the most crystalline particles.