Cristalization processes

These processes can be implemented on our supercritical fluid equipment 2802.

• RESS (Rapid Expansion of Supercritical Solution) Process

In this process, the FSC is used as the solvent.

The RESS process employs the solving power of a fluid put at its nearby or in higher critical datas conditions. This fluid, according to the temperature and the pressure, can reach significant densities that boosts the solvation phenomenon by decreasing the intermolecular lenghs and consequently the interactions that exist between the solvent molecules and the chemical specie inserted during the dissolution of a compound in a solvent.

In the RESS process, one or many substance(s) is (are) dissolved in the SCF, employed here as the solvent, at determined temperature and pressure conditions so that the solute/solvent mix be an homogeneous solution. Then, there is a sudden depressurization of the solution through a hole in a supplementary enclosure maintained at low pressure. This generates a highly fast diminution of the SC CO2 density which comes to gas (and so a fluid with a low solving power) and finally leads to a recristallization of the solved substance.

This process has multiple applications only when the produce has a solubility higher than 10-3kg/kg in the SC CO2 which limits the process to unpolar and small polar.

• SAS (Supercritical Anti–Solvent) Process and its variants

In these processes, the FSC is used as an anti-solvent.

Their major advantage is that they can be used with any molecule. Most of the time it’s possible to find a appropriate solvent/anti-solvent couple.

In most of the cases the anti-solvent is CO2, so the solvent choice is determinant. It has to be a good solvent of the molecule to be cristallized and to be miscible, at least partially, with the CO2.

In the continuous anti-solvent process, the solution and the anti-solvent bring together  at the expansion nozzle and are injected cocurrent. At the exception of the particles’ recuperation, the rest of the process can be continuously operated. The solvent can be recuperated downstream in the separators whereas the anti-solvent can be recycled through compression and heating.

A washing or extraction with pur CO2 step is recommended at the process end to eliminate the last solvent traces that could be in the cristallized particules.

After the reactor pressurization and the anti-solvent flow stabilization, the liquid organic solution containing the dissolved product is sprayed through a nozzle in fine droplets. The oversaturation is made by a double matter transfer. The solvent solute goes to the SCF with which it is at least partially miscible and the SCF goes to the solvent.