Handbook of Solvents - George Wypych - ChemTech - Ventech!

940 Phillip J. Wakelyn, Peter J. Wan
clude neutral clay, acid activated clay, and activated carbon. The choice of adsorbent will
depend on a balance between activity of the adsorbent, oil retention loss, and adsorbent cost.
The process is generally carried out via batch or continuous bleaching. Adsorbent is
mixed with the refined oil creating a slurry that is agitated to enhance contact between the
oil and the adsorbent. This is generally carried out under a vacuum at 90-95ºC (194-203ºF)
for 15-30 minutes. Vacuum bleaching offers the advantages of an oil with improved oxidative
and flavor stability. Finally the adsorbent is filtered from the oil using pressure leaf filters
precoated with diatomaceous earth. Spent clay is steamed for efficient oil recovery.
Deodorization: Deodorization, which removes the volatile compounds along with residual
FFA, is a critical step in ensuring the purity of any vegetable oil and improves flavor,
odor, color, and oxidative stability. Many of the volatile compounds removed are formed by
the auto-oxidation of fat, which produces aldehydes, ketones, alcohols, and hydrocarbons
that are associated with undesirable flavors and odors. The process also is effective in removing
any remaining pesticide residues or metabolites that may be in the oil.
Deodorization, which can be conducted as a batch operation in smaller plants or as a
continuous or semicontinuous process by larger deodorizing facilities, consists of a steam
distillation process in which the oil is heated to 230ºC (446ºF) under a vacuum of 2-10 mm
Hg. Steam is sparged through the oil to carry away the volatiles and provide agitation. The
odor and flavor compounds, which are more volatile than the triglycerides, are preferentially
removed. After deodorization and during the cooling stage, 0.005-0.01% citric acid is
generally added to chelate trace metals, which can promote oxidation. Deodorized oils preferably
are stored in an inert atmosphere of nitrogen to prevent oxidation. Tocopherols and
sterols are also partially removed in the deodorization process. Tocopherols can be recovered
from the deodorizer distillate in a separate operation.
14.10.4 REVIEW OF SOLVENTS STUDIED FOR EXTRACTION EFFICIENCY
Research on solvents for extraction has been carried out for more than 150 years and has intensified
since the first patent was issued to Deiss of France in 1855. 1,3,48 In the early effort of
selecting an extraction solvent, the availability, operation safety, extraction efficiency,
product quality and cost were the major concerns. In recent decades, toxicity, bio-renewability,
environmental friendliness have been added to the solvent selection criteria. Among
the solvents tested, a majority of the candidate solvents were excluded on the ground of toxicity
and safety. Only a handful of solvents are used to any degree. These are acetone, alcohol,
hexanes, heptane, and water. 1,4-7,49 Water is used in rendering of fat from animal tissues
and fish and in coconut processing, 49 alcohol for spice and flavorants extraction, 5,49 acetone
for lecithin separation and purification. 4 For commodity oils derived from vegetable
sources, only hydrocarbon solvents have been used since 1930’s. Acetone was used by an
Italian cottonseed oil mill during the 1970’s. 4 Aqueous acetone and acetone-hexane-water
azeotrope were studied by the scientists at the Southern Regional Research Center of Agricultural
Research Service, USDA during the 1960’s and 1970’s. 4 The effort was stopped
due to the cost of retrofit required, the difficulties in managing the mixture of solvents with
the presence of water and product quality concerns - a strong undesirable odor associated
with the acetone extracted meals. 4 Ethanol and isopropanol were studied in the 1980’s as a
potential replacement of hexane for oil extraction. Both were proven technically feasible
but economically unacceptable. 5,6 n-Hexane is listed as a HAP under the CAA 14,15 (See Section
14.10.2.2.1 CAA) and there are other regulatory requirements. As a way to meet envi-