Supercritical fluid processing of materials from aqueous solutions : The application of SEDS to lactose as a model substance

The objective of the work was to study the factors influencing the crystallisation of alpha-lactose monohydrate from aqueous solution using the Solution Enhanced Dispersion by Supercritical Fluids (SEDS) technique. An aqueous solution of alpha-lactose monohydrate is dispersed with a homogeneous mixture of carbon dioxide-ethanol/methanol using a co-axial nozzle. Crystallised lactose particles were analysed for water content by Karl-Fisher analysis, anomeric composition by Differential Scanning Calorimetry (DSC) and characterised for crystallinity by powder X-ray diffraction and morphology by scanning electron microscopy. Water content in the lactose recrystallised with ethanol was higher compared to the product obtained with methanol as cosolvent. Rate of crystallisation could be altered by varying the CO2 flow thereby modifying the water content in the lactose. At low flow rates of CO2, the crystallisation occurred in a cosolvent rich antisolvent phase causing rapid crystallisation whereas high flow rates of CO2 favoured a much slower crystallisation mechanism in the water rich phase. As a consequence, the morphology changed from thin long bands to large agglomerated chunks with mean particle size between 5 and 31 microns. The SEDS process is an efficient method for forming micron sized particles of water-soluble compounds with controlled physico-chemical properties.