Particle formation by rapid expansion from solution using near-critical dimethyl-ether

The present experimental work examines the use of dimethyl-ether (DME) in a process for formation of particulate materials. DME is used in the sub-critical liquid state as a solvent which partially vaporizes as it is sprayed through a nozzle and then evaporates to leave a fine, dry, solvent free powder. DME is an effective solvent for a range of polar compounds, including many pharmaceutical compounds, and good product throughput rates can be achieved. The spray characteristics are investigated here in terms of the hydrodynamics and thermodynamics of the depressurization step, and using a visual analysis of the profile of the spray. The process is demonstrated using acetaminophen as a model solute, and the resulting particles are characterized by SEM analysis and measurement of their dissolution rate in water. Measurements of the solubility of acetaminophen in DME are also reported.