**5. Conclusions**

Special properties of supercritical CO2 as solvent power similar to liquids but high diffusivities similar to gases, resulting in higher mass transfer rates. This mass transfer rate is quite important in particle formation process using CO2 as solvent or antisolvent. In antisolvent processes mass transfer rate will influence on the size and morphology of the particles. Higher mass transfer rate is related to smaller particle size. Anyway, mass transfer of supercritical antisolvent process depends on the one hand on the situation of phase equilibrium diagram of operating conditions and on the other hand on the hydrodynamics of the process. The hydrodynamics of the process is controlled by flow rates of CO2 and solution and by the nozzle that forms the spray. This spray reduces the boundary between CO2 and microdroplets of solution, improving the mass transfer of the process. Heat transfer in supercritical antisolvent process influences directly on the mixing step in non-isothermal process. If the solution is colder than bulk CO2, the mixing time that is less interesting for crystal production will increase. However, in the opposite situation, a warmer solvent immersed in colder CO2 accelerates the mixing process. Thus, high supersaturation ratio can be achieved, so smaller particles are precipitated.

In rapid expansion of supercritical solution, mass transfer happens in solubilization chamber and in nozzle and expansion chamber. Saturation of the solution which is governed by solubility of solute in supercritical fluid will decide the place where to start the precipitation. This location could be into the nozzle or after in the expansion chamber. Heat transfer happens at the exit of the nozzle due to the drastic change of pressure by Joule effect. Nozzle should be thermostatized to prevent freezing and clogging.
