Three different modes of continuous countercurrent extractors
have been investigated: spray column, sieve tray column, and
packed column. Lahiere and Fair [28] studied the mass transfer performance
for the system 2-propanol/water/SC-CO2 in spray, tray,
and packed columns. Mass transfer efficiencies of packed columns
were found to be higher than those of the tray or spray columns.
This is due to the increased residence time for coexisting phases,
small backmixing effects, and higher specific area for mass transfer.
In addition, the throughput capacity of packed columns is higher
compared to spray or tray columns. Siebert and Moosberg [27]
investigated the mass transfer performance of spray, sieve tray, and
packed columns for the system isopropanol/water/SC-CO2. They
concluded that packed columns provided the best mass transfer
performance. Tiegs [24] investigated the influence of Raschig rings,
spirals, and structured packing’s on the mass transfer efficiencies
of packed columns. Structured packing provided the best mass
transfer efficiency. Czech [23] investigated the mass transfer performance
of packed columns with different structured packing’s
as follows: wire mesh packing (Sulzer CY), mixer packing (Sulzer
SMV), and wire mesh packing with collector–distributor units. The
best results were obtained by Sulzer CY with collector–distributor
units.