Handbook of Solvents - George Wypych - ChemTech - Ventech!

942 Phillip J. Wakelyn, Peter J. Wan
material and is easy to separate from the crude oil and marc. 63 A thorough comparison of
various hydrocarbon solvents for cottonseed oil extraction on a lab scale basis was reported
by Ayers and Dooley in 1948. 84 A more recent study by Wan et al. 85 used a laboratory scale
dynamic percolation extractor which operates at the conditions similar to those applied in
the oil mill practice. Plant trials of isohexane and heptane solvents versus hexane in a 300
tons/day cottonseed factory revealed some interesting findings. 7
14.10.4.1.1 Nomenclature, structure, composition and properties of
hydrocarbons
Petroleum and natural gas are the most abundant and affordable sources of hydrocarbon.
Sometimes naphtha is used to describe the low boiling liquid petroleum and liquid products
of natural gas with a boiling range from 15.6 o C (60 o F) to 221 o C (430 o F). This large group of
compounds can be structurally classified as aliphatic and aromatic. Aliphatic hydrocarbons
include saturated alkanes (paraffins), unsaturated alkenes (olefins) and alkynes
(acetylenes), and cycloparaffins (naphthenes). Paraffins can be linear such as n-butane,
n-pentane, and n-hexane, and branched such as isobutane, isopentane, isohexane, etc. Example
of olefins is ethylene; of cycloparaffins, cyclopentane and cyclohexane; and of an aromatic,
benzene. 8,86,87 These compounds are derived from natural gas and petroleum oils
which normally contain thousands of hydrocarbons with molecular weight ranging from
methane to about 50,000 - 100,000 Daltons. Upon refining, the crude petroleum is divided
into hydrocarbon gases (methane, ethane, propane and butane), light distillates (naphthas
and refined oils), intermediate distillates (gas oil and absorber oil), heavy distillates (technical
oils, paraffin wax and lubricating oils), residues (petroleum grease, residual fuel oil still
wax, asphalts and coke), and refinery sludges (acid coke, sulphonic acid, heavy fuel oils and
sulfuric acid). 88 Historically, various fractions of petroleum naphthas, pentane and hexane
from the light naphthas, aviation gasoline and benzol from the intermediate naphthas, and
aromatic hydrocarbon, benzene, have been tested for oil extraction. 62-71
14.10.4.1.2 Performance of selected hydrocarbon solvents
Factors affecting extraction: There is little theoretical basis to be followed for the extraction
of oilseeds. 66,89-91 The study of the extraction of oilseeds is complicated by the fact that the
total extractible material is variable in quantity and composition. 66,89 Composition of the
early extracted material is nearly pure triglycerides. As the extraction progresses, increasing
amount of non-glyceride material will be extracted. 66,89 IT is believed that the majority of
the oil from oilseed flakes is easily and readily extracted. 66,90 While the thickness of flakes
affects extraction rate, the concentration of miscella below 20% does not greatly increase
the amount of time to reduce the residual oil in flakes to 1%. 89 Good 91 summarized much of
the early effort in soybean extraction: (1) The first oil extracted is superior in quality to the
last small fraction; (2) While other solvents have been used in the past, hexane has become
the primary solvent due to a combination of properties; (3) Flake thickness is the most important
factor in achieving good extraction results; (4) Higher extractor temperatures up to
nearly the boiling point, improve extraction results; (5) Moisture control is important
throughout the extraction process; (6) Heat treatment affects the total extractibles; and (7)
The soaking theory of extraction indicates that weak miscellas are very effective in helping
to achieve good extraction results.
Particle size which relates to the surface area available for extraction and is obviously
one of the most important factors for extraction study. Coats and Wingard 92 noticed that par-