Handbook of Solvents - George Wypych - ChemTech - Ventech!

14.10 Food industry 941
ronmental regulations, a short term option to commercial hexane appears to be
hydrocarbons with significantly reduced n-hexane content.
14.10.4.1 Hydrocarbon solvents
Extraction of oils has largely relied on mechanical or heat rendering process for centuries. 50
Increased demand of productivity to separate oils from oilseeds has been the principal factor
driving the changes of oilseed processing from the ancient hydraulic press to a continuous
screw press or expeller in early 1900’s. 51,52 This operation still left more than 4-5% residual
oil in the pressed cake. 51 More complete recovery of oil can only be effectively accomplished
by solvent extraction. 53,54
Solvent extraction of oils had an early beginning. Deiss in France received a patent to
extract fat from bone and wool with carbon bisulfide in 1855. 53 A year later, Deiss received
additional patents covering the extraction of oil bearing seeds. Large scale solvent extraction
already was established in Europe in 1870. 55 The earliest extractors were unagitated
single-unit batch extractors of small capacity and not very efficient. 56,57 These extractors
were gradually modified by the addition of agitation. They were organized in a battery of
ten batch extractors which can be operated in a countercurrent principle. Extractors of this
type operated in European plants during the last three decades of the 19th century. 57
Further development in solvent extraction technology was relatively slow until early
twentieth century. Solvent extraction spread from Europe to various parts of the world including
the United States and South America. 57 The first extraction plant in the United
States was used to recover grease from garbage, bones, cracklings, and other packing-house
wastes and to recover residual oil from castor pomace. 57 Wesson 58 reported his efforts applying
solvent extraction to recover cottonseed oil from 1889 till the close of World War I.
During the 1930’s solvent extraction was introduced in the United States for the recovery of
oil from soybeans and the German equipment of the continuous type was used almost exclusively.
57-61 Just prior to World War II the installation of continuous solvent extraction equipment
was greatly accelerated and throughout the period of the War new plants were erected
in an effort to keep pace with the constantly increasing production of soybeans. All of the
later installations have been of American manufacture and in a number of cases of American
design. 57-61
Solvents used in the early effort to extract grease and oils were diverse. Besides carbon
bisulfide used by Deiss, 53 chlorinated hydrocarbons, benzene, and alcohols were all being
tried. Extracting oil from corn and cottonseed with both aviation gasoline and petroleum
distillate was performed in the United States in 1915 and 1917 respectively. 62 The hydrocarbon
paraffins became the preferred solvents for oilseed extraction during 1930’s through
the process of elimination. 63-71 Due to the prominent defects of early solvent extraction: dark
crude oil, strong solvent odor in meal and high cost associated with solvent loss, low boiling
hydrocarbons such as propane and butane were recommended as oil extraction media. 72 The
flammability of hydrocarbons also prompted much research in 1940’s using chlorinated hydrocarbons
as the extraction solvents 73,75 before its meal was found unsafe as feed. 75-77 For
the purpose of improved protein and oil quality 75,78 and of processing safety and
biorenewable solvents, 75,79,80 both ethanol and isopropanol were investigated as the oil extracting
solvents. While these alcohols offer various advantages in product quality and process
safety and are renewable, they are still not economically feasible to replace
hydrocarbons as oilseed extraction solvents. 81 Hexane rich solvent became popular for the
oilseed industry, 54,57,82,83 because it is the most efficient solvent, extracts minimum non-oil