Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev

5 DECOCTION AND HOT CONTINUOUS EXTRACTION TECHNIQUES
FRESH SOLVENT
SOLID UNDERFLOW
EXTRACTION
STAGE
OVERFLOW SOLUTION
SOLID FEED
Figure 1: Single-stage solid-liquid extraction
The single-stage system represents the complete operation
of contacting the solid feed and fresh solvent. This is rarely encountered
in industrial practice because of the low recovery of solute obtained and
relatively dilute solution produced. Effi ciency of extraction is somewhat improved
by dividing the solvent into a number of smaller portions and then
carrying out multiple successive extractions instead of only one contact of
the entire amount of solvent with the solid.
FRESH SOLVENT
EXTRACTION
STAGE 1
SOLID UNDERFLOW
EXTRACTION
STAGE 2
EXTRACTION
STAGE n
OVERFLOW SOLUTION
SOLID FEED
Figure 2: Multistage counter-current solid-liquid extraction
In the continuous counter-current multistage system shown in
Figure 2, the underfl ow and overfl ow streams fl ow counter-current to each
other. This system allows high recovery of solute with a highly concentrated
product because the concentrated solution leaves the system after contact
with fresh solid.
FRESH SOLVENT
SOLID FEED
EXTRACTION
STAGE 1
FRESH SOLVENT
EXTRACTION
STAGE 2
OVERFLOW SOLUTION OVERFLOW SOLUTION OVERFLOW SOLUTION
FRESH SOLVENT
EXTRACTION
STAGE n
SOLID UNDERFLOW
Figure 3: Multistage co-current solid-liquid extraction
In the multistage co-current (parallel) system shown in Figure
3, fresh solvent and solid feeds are contacted in the fi rst stage. Underfl ow
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