Handbook of Solvents - George Wypych - ChemTech - Ventech!

14.10 Food industry 945
Figure 14.10.3. Schematic of bench-scale dynamic percolation extractor.
A more recent study by Wan
et al. 85 using a laboratory scale
dynamic percolation type of extractor
(Figure 14.10.3) operated
at the following conditions such
as, temperature (5 o C below the
boiling point of each solvent) and
miscella flow rate (9 gal/min/ft 2 ),
similar to those applied in the oil
mill practice. Commercial grade
hexane, heptane, isohexane,
neohexane, cyclohexane, and
cyclopentane were used to extract
cottonseed flakes which had 5.8%
moisture and 31.4% oil. When
these solvents were tested near
their boiling points, hexane apparently
extracted cottonseed oil
at a higher initial rate, > 94% oil
extracted after 2 minutes, than all
other solvents. Both heptane and
hexane were able to extract more
oil at the end of 10 minutes of extraction.
Isohexane demonstrated
to have adequate initial extraction
rate (80% oil extracted after 2
minutes) and extraction capacity
(93% oil extracted after 10 min-
utes of extraction) but is noticeably less effective than hexane. Similar to findings by
Ayers and Dooley, 84 results from the study by Wan et al. 85 also demonstrates that
neohexane, cyclohexane and cyclopentane performed distinctly less efficiently than hexane,
heptane and isohexane. Conkerton et.al. 98 tested commercial heptane versus hexane in
a Soxtec extractor. Under this extraction condition, heptane actually extracted more oil than
hexane from ground cottonseed kernel passed through a 20 mesh screen. The oil and meal
quality were not appreciably affected by the higher temperature extraction of heptane.
Plant scale results: Although hydrocarbon solvents have been used for oilseed extraction
since the 1930’s, very little in plant operating data are available. During the spring of
1994, Wan et al. 7 conducted plant trials with commercial heptane and isohexane at a 300
tons/day cottonseed crushing plant which routinely used hexane as the extraction solvent.
Test results indicated that heptane performed well as an extraction solvent. However, it required
extra energy and time to recover and consequently reduced the throughput rate of
cottonseed being processed. Isohexane on the other hand was termed as an “easier” solvent
by the plant engineers than hexane to operate. The plant also experienced a 40% steam savings
and better than 20% throughput increase when it was operating with isohexane. 7 This
encouraging result prompted a second plant trial with commercial isohexane. 45 The second
plant trial was carried out at a cottonseed oil mill with a relatively new extraction and