Page 401 - Biosystems Engineering

378 Cha pte r T h i r tee n

1100 1.0% charred
sawdust
1000 0.7% charred
Annual oil loss (MT/year) 800 0.5% charred
900
sawdust

700
sawdust
600
500

400
300
12 13 14 15 16 17
% of oil retention on charred sawdust
FIGURE 13.3 Graphical representation of oil retention (i.e., annual oil loss) during
the bleaching process of edible oil using charred sawdust as an adsorbent.
where N is Avogadro’s constant (6.023 × 10 ), and h is Planck’s con-
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stant (6.626 × 10 –31 JS).
The negative value of ΔS indicates there is less disorder, that is,
the crude oil contains more colorant and impurities before the bleach-
ing process, and these are decreased during the adsorption process
because disorder is directly proportional to entropy.
Generally, loss of oil in the bleaching process results from oil lost
to the filter cake and oil lost to the changes in the free fatty acid con-
tent. From David D. Brooks’s statistical data we observe that for
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bleaching edible oil in different refinery industries, oil loss varies
from 24 to 30 percent. A refinery running at 0.6 percent adsorbent
with a production rate of 1000 tons per day has a 28 percent oil loss of
613 tons. In our system with 1 percent charred sawdust, oil loss is
only 17 percent (Fig. 13.3), which is very economical for bleaching
edible oil.
Vacuum bleaching, batch or continuous, is somewhat more
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effective than atmospheric bleaching. It can use less earth, emphasize
quantity not quality, operate at lower top temperatures, and mini-
mize oxidation by reducing exposure to air and providing an oppor-
tunity to cool the oil before returning it to atmospheric conditions.
Although vacuum bleaching practices are preferred, atmospheric
bleaching can and does produce high-quality bleached oils. Some
refiners prefer batch vacuum or atmospheric bleaching because it
provides absolute control, whereas continuous bleaching gives an
average treatment because it is not a plug–flow system.

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Deodorization Zosel described the deodorization of edible oil with
CO at a temperature between 50 and 55°C and pressures of 10 to 25 MPa
2