Extraction processes static columns

Supercritical fluid extraction (SFE) can be coupled to SFC using a series of switching valves and either a loop or an accumulator trap interface [79,172,174,187-192]. The loop interface is used with a closed-loop static extractor, sometimes equipped with a recirculating pump. The fluid from the extraction cell passes continuously through the injection valve loop and back to the extraction cell. Injection of an aliquot of the extract onto a packed column is made by periodically switching the loop so that it is in-line with the flow of mobile phase to the separation column. This approach is used to determine fundamental parameters of the extraction process more so than for analysis. 

The extract is collected by depressurization on a column packed with a solid sorbent, in a vessel containing the appropriate solvent, in a collection device connected to a chromatograph, or on combined solid phase-solvent traps [92]. For extraction of volatile compounds, such solvents as acetone, CH2CI2, methanol, or liquid nitrogen are used. Silica gel columns are the most popular way of trapping solids. In this case, the selectivity of the process can be improved by selective elution of the sorbent [88, 92]. SFE can be conducted in a static mode in which sample and solvent are mixed and kept for a user-specified time at a constant pressure and temperature, or in a dynamic mode where the solvent flows through the sample in a continuous manner [56]. The extracted analytes can be collected into an off-line device or transferred to an on-line chromatographic system for direct analysis. 

A. Frank Seibert, Ph.D., P.E. Technical Manager, Separations Research Program, The University of Texas at Austin Member, American Institute of Chemical Engineers (Liquid-Liquid ITispersion Fundamentals, Process Fundamentals and Basic Calculation Methods, Hydrodynamics of Column Extractors, Static Extraction Columns, Process Control Considerations, Membrane-Based Processes)... 

The processing equipment used to conduct solvent extraction of metals is the same as that used in conventional liquid-liquid extraction.1 1 The most common choices have been mixer-settlers, columns with agitated internals, and static mixers. Some advantages and disadvantages of several classes of equipment are summarized in Table 8.5-1. Many of the practical aspects of equipment selection are diicussed by Pratt and Hanson5 and by Ritcey and Ashbrook. ... 

---