Biomedical Engineering Reference
In-Depth Information
this method needs to be further refined to remove FFAs. Currently this technology would be
suitable for specialty oils due to the high cost of high-pressure equipment and low
throughputs.
Application of an electrostatic field through a non-conducting liquid such as oil facilitates
agglomeration of electrically charged bleaching earth on one electrode and oil leaves the
electrofilter completely clear (Transfeld, 1998). Finely ground bleaching earth is found to be
more effective than coarser bleaching earth in electrofiltration. Removal of finely ground
clay from oil is not feasible by the current filtration techniques but bleaching earth can be
removed as sludge by discontinuing the electric field in the bleacher. It has been reported
that this technology reduces the amount of bleaching clay used and power requirement for
filtration (Transfeld, 1998). Other advantages of this technique are: easier filter cleaning and
reduction of pre-coat filter area because of the formation of a highly porous filter cake by
the agglomerated bleaching clay. An electrofilter/agglomerator can be fitted in a conventional
bleaching unit.
Activation of bleaching clays with microwave treatment has been investigated (Boukerroui
and Ouali, 2002). Clay was impregnated with ammonium chloride then activated in a
microwave oven. Optimum conditions for activation were achieved at 3M ammonium
chloride concentration and 15 min heating time. Microwave activation improved chlorophyll
removal efficiency from the clay as compared to strong acid activation. This technique
presents two important advantages over the strong acid activation method: shorter activation
time and elimination of sulfuric acid, which is a toxic waste.
4.4.4 Deodorization
The presence of FFAs in oil correlates well with flavor and odor. The practical rule is that if
an oil has 0.1% FFA it will have an odor which could be eliminated by reducing the FFA
content to 0.01-0.03% (zero peroxide value) (Gavin, 1978). Deodorization is a steam
distillation process during which volatile and odoriferous compounds are stripped off with
steam. The objective of deodorization is to produce a bland and stable product by removing
FFAs, aldehydes, ketones, and peroxides from bleached oil. The amount of FFA removed
from the oil is inversely proportional to the system pressure and directly proportional to the
vapor pressure of the FFA and the sparge steam rate. Temperature plays a critical role during
deodorization. The rate at which odor compounds are removed could be tripled when
deodorization temperature increased from 178 to 205 °C. If the temperature is further raised
to 232°C, that rate can be expected to triple again. This means higher deodorization
temperature reduces processing time (Dudrow, 1983). However, high temperatures cause
development of undesirable polymers. Hence, optimization of time and temperature is
necessary for a given process. High vacuum is desirable for deodorization because it inhibits
oil hydrolysis. The volume of stripping steam needed in steam deodorizers is affected by
vacuum. For example, a deodorizer operating at 12 mm Hg pressure would require twice the
stripping steam of a unit operated at 6 mm Hg. Currently, 6 mm Hg vacuum is commonly
used for vegetable oil deodorizers. A relatively new approach is to use nitrogen instead of
steam for sparging. It has been demonstrated that this process improved oil quality.
A patent describes a continuous process for deodorizing oils with carbon dioxide at
150-250 °C and 100-250 Bars (Zosel, 1979). Impurities extracted with carbon dioxide are
removed by a solid adsorbent, such as activated charcoal, before the carbon dioxide is
recycled to the deodorizer column. The FFA content of soybean oil could be lowered from
0.4 to 0.02% by using this technology.
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