DELOS process: a crystallization technique using compressed fluids: 1. Comparison to the GAS crystallization method

The depressurization of an expanded liquid organic solution (DELOS) crystallization technique is a new one-step process, which uses a compressed fluid (CF) (e.g. CO2), for the straightforward production of sub-micron- or micron-sized crystalline particles. The driving force of a DELOS crystallization process is the fast, large and extremely homogeneous temperature decrease experienced by a solution, which contains a CF, when it is depressurized from a given working pressure to atmospheric pressure. In contrast to other already reported high-pressure crystallization techniques (RESS, GAS, PCA, PGSS), in a DELOS process the CF behaves as co-solvent over the initial organic solution of the solute to be crystallized. Through a DELOS process it is possible to produce fine powders of a compound provided that a system ‘compound/organic solvent/CF’ in a liquid one-phase state is found. In order to compare DELOS and gas anti-solvent (GAS) procedures, 1,4-bis-(n-butylamino)-9,10-anthraquinone has been crystallized from ‘acetone/CO2’ mixtures by both methods. The crystallization results obtained have been analyzed upon the solubility behavior of 1,4-bis-(n-butylamino)-9,10-anthraquinone in ‘acetone/CO2’ mixtures with different composition. It will be seen how important is the knowledge of the solute solubility behavior in the CO2-expanded solvent in order to choose the most convenient crystallization technique (GAS like or DELOS) and the best operational parameters. Finally, it has been experimentally determined which are the operational parameters that control the temperature decrease experienced in a DELOS crystallization. The results obtained have been corroborated through thermodynamic considerations.