(76a) Production of Functionalized Powders Using Effervescent Spray Drying

Spray drying of rheological complex food liquids is a challenging industrial task due to the lack of technically feasible processing concepts. To reduce costs and improve yield, the water content of the feed is desired to be decreased. The resulting higher solids fraction may lead to higher viscosities, which renders the rheological behavior more complex, especially for multiphase feeds. A higher viscosity increases spray unsteadiness, spray drop size and consequently the necessary drying time. Hence, larger particles cannot be thoroughly dried and exhibit high stickiness, which impairs the yield due to sticking to the spray tower wall. Therefore, pneumatic atomizers with external mixing would be beneficial but are often avoided due to their high gas consumption.

In order to avoid these problems, this research project focuses on the application of a special two-fluid nozzle with an internally mixing atomizer, also called effervescent atomizer. The atomizing gas occupies a relevant proportion of the cross-sectional flow area, which reduces the liquid dimensions in the exit orifice. Furthermore, it shatters the feed liquid at the nozzle exit during the expansion of the gas. Due to the high kinetic energy of the atomizing gas, simultaneous foaming during spray drying is enabled and clogging of highly viscous liquids can be avoided. This allows to process complex non-Newtonian fluids with higher viscosities and enables to tailor foamed powder particles with desired properties, such as high porosity, dissolution rates and specific texture characteristics. Different cellulose derivatives were chosen as biopolymers due to their specific hydrophobicity, molecular weight and influence on viscosity. In a first step, spray drying parameters with a lab scale spray dryer were identified for biopolymer suspensions of different viscosities. For the analytical evaluation of the sprayed suspensions, the Sauter mean diameter was measured with a laser diffraction spectroscopic device and showed an increase with higher viscosity while bulk density decreased. The shape of the spray dried powder particles was investigated with light microscopy and SEM revealing the surface properties and their porous structure. DSC showed changes in glass transition temperatures and melting behavior of the spray dried powders compared to their original state.

These findings can help not only to reduce production costs by decreasing gas consumption but also to improve the yield and efficiency of spray drying and thus making this process step more sustainable. Process regimes and suitable parameters can now be defined for a stable atomization of complex fluids with high viscosities. The conversion of heat-sensitive liquids into an engineered powder with enhanced shelf life offers a broad variety of possibilities for new product characteristics in various fields. A detailed description of the process setup will be given together with results from the spray drying experiments.