Crystallisation behaviour of sugars precipitated by supercritical fluids

Aqueous solutions of common saccharides and polyols used by the pharmaceutical industry were spray dried in various concentrations with a co-current flow of supercritical carbon dioxide enriched with ethanol in a pressurised precipitation vessel, while keeping all other process conditions constant. The dry powders were recovered from a filter after pressure release. The residual water content was measured and the particle morphology and crystallinity were observed. Sucrose and mannitol were readily crystallised, but the trehalose was amorphous. The effect of viscosity and of hydrate formation is discussed.