Dynamic similarity 284 Supercritical Fluid Cleaning

Dynamic similarity is achieved when the forces retarding or accelerating the movement of mass within the system are correspondingly similar. These are the forces that define the dynamics of fluid systems in motion. In a supercritical fluids cleaning system, the forces of pressure, inertia, viscosity, and interfacial interactions are important for scaleup when it is desirable to predict either pressure drops or power consumption. For most cleaning systems, however, dynamic similarity is usually only of importance as an indirect means of establishing kinematic similarity. 

Supercritical fluid extraction (SFE) with solid-phase trapping has been used for the extraction of DBDE and PBBs together with PCBs and chlorinated benzenes from sediment samples, with CO2 as the supercritical fluid. ° Before the extraction, the sediment sample can be mixed with copper powder and sodium sulphate for the removal of moisture and sulphur. Usually, the extraction combines static and dynamic extraction. The time required for the extraction ranges from 40 to 60 min, the extraction temperature is around 120°C and the pressure 374 bar. Compared with Soxhlet extraction, SFE gives similar yields, but the extracts are generally much cleaner and it might not be necessary to clean the extracts before GC analysis. 

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