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

Purpose, The objective of the work was to study the factors influencing the crystallisation of alpha-lactose monohydrate from aqueous solution using t he Solution Enhanced Dispersion by Supercritical Fluids (SEDS) technique. Methods. 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 K arl-Fisher analysis, anomeric composition by Differential Scanning Calorime try (DSC) and characterised for crystallinity by powder X-ray diffraction a nd morphology by scanning electron microscopy. Results. Water content in the lactose recrystallised with ethanol was highe r compared to the product obtained with methanol as cosolvent. Rate of crys tallisation 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 crystallisati on whereas high flow rates of CO2 favoured a much slower crystallisation me chanism in the water rich phase. As a consequence, the morphology changed f rom thin long bands to large agglomerated chunks with mean particle size be tween 5 and 31 microns. Conclusions. The SEDS process is an efficient method for forming micron siz ed particles of water-soluble compounds with controlled physico-chemical pr operties.