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 (T_g), while allowing the particle temperature (T_p) to reach higher values by using an insulated drying chamber. The results showed that higher T_p − T_g, 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.

Keywords:

• Crystallization
• Humid air
• Lactose
• Spray drying
• Stickiness barrier