Continuous-flow systems, with closed extraction

In the simplest case, the feed solution consists of a solvent A containing a consolute component C, which is brought into contact with a second solvent B. Eor efficient contact there must be a large interfacial area across which component C can transfer until equiHbrium is reached or closely approached. On the laboratory scale this can be achieved in a few minutes simply by hand agitation of the two Hquid phases in a stoppered flask or separatory fuimel. Under continuous flow conditions it is usually necessary to use mechanical agitation to promote coalescence of the phases. After sufficient time and agitation, the system approaches equiHbrium which can be expressed in terms of the extraction factor S for component C ... 

After the desired extraction temperature is reached about 80 g of sample, with particle size of 16-20 mesh-size, is charged into the extraction vessel, supported by two 260 mesh wire disks. The system is immediately closed and the solvent is continuously fed into the vessel by a high pressure pump (TSP, constaMetric 3200 P/F). The pressure is controlled by a micrometering valve from where the solvent and the extract are withdrawn into a glass collector. The experiments were accomplished in 195 min. (unless otherwise stated), isothermally, at constant pressure and using a solvent flow of approximately 3 cmVmin in all... 

An Sl E system can be operated in one of two ways. In the dynamic extraction mode, the valve between the extraction cell and the restrictor remains open so that the sample is continually supplied with fresh supercritical fluid and the extracted material flows into the collection vessel where depressuriz-ation occurs. In the static extraction mode, the valve between the extraction cell and the restrictor is closed and the extraction cell is pressurized under static conditions. After a suitable period, (he exit valve is opened and the cell contents arc iransferred through the rcsiricior by a dynamic flow of fluid from the pump. The dynamic mode is more widciv used than the static mode. 

---