n-Hexane (normal hexane) is a colourless, volatile liquid.
Commercial hexane is mainly a mixture of hexane isomers and related
6-carbon compounds, and has an n-hexane content varying between 20
and 80%. Gas chromatography coupled with flame ionization
detection or mass spectroscopy is a suitable technique for the
measurement of n-hexane. Occupational exposure limits range from
100 - 1800 mg/m3 (time-weighted average, TWA) and 400 - 1500 mg/m3
(ceiling value, CLV) in various countries.
n-Hexane can be isolated from natural gas and crude oil. It is
used in food processing, including the extraction of vegetable oil,
and as a solvent in various products and processes.
Once emitted into the environment, n-hexane exists
predominantly in the vapour phase. In the atmosphere its half-life
is estimated to be approximately 2 days, based on its reactivity
with the OH radical alone. Reported LC50 values for aquatic
organisms are few and variable and have been conducted under
inappropriate conditions; an assessment of the toxic effects of
n-hexane in this environment is, therefore, not possible. Low
water solubility and high volatility make exposure of aquatic
organisms unlikely except from uncontrolled discharge into surface
waters.
In mammals, n-hexane is absorbed rapidly through the lungs and
is distributed widely in the adult body, as well as to fetal
tissue. Dermal absorption is limited. n-Hexane is metabolized
oxidatively to a number of compounds, including 2,5-hexanedione,
which is thought to be the ultimate neurotoxic agent. Particularly
high levels of n-hexane and 2,5-hexanedione can occur in the
sciatic nerve of rats. Most n-hexane is excreted unchanged in
exhaled air; some is excreted as metabolites in exhaled air and
urine.
n-Hexane is of low acute toxicity for adult rats by oral
administration or inhalation. Oral LD50 values of 15 - 30 g/kg
have been recorded, and an inhalation LC50 value of 271 040 mg/m3
(77 000 ppm) has been reported for a 1-h exposure. At high vapour
concentrations, animals show ataxia, seizures, and signs of central
nervous system depression.
Testicular lesions and neurotoxicity appear to be the principal
effects of repeated n-hexane exposure in rats. Severe testicular
lesions have resulted from inhalation exposure to n-hexane and oral
exposure to 2,5-hexanedione. Effects have been attributed to
disruption of the cytoskeleton of Sertoli cells. There are
secondary effects on post-spermatogonial germ cells, which
disappear from affected tubules. Testicular effects were
reversible after a single exposure for 24 h to 17 600 mg/m3 (5000
ppm) but irreversible after a 2-week exposure to the same
concentration for 16 h/day, 6 days/week. 2,5-Hexanedione at 1% in
drinking-water produced similar reversible testicular lesions after
2 to 3 weeks of dosing and irreversible effects (within 17 weeks)
after 5 weeks of dosing.
The neurotoxic effect is characterized clinically by hindlimb
weakness, which can progress to paralysis. Axonal swellings
develop in the central and peripheral nervous systems; more severe
lesions (axonal degeneration and loss) can occur, particularly in
the longest, largest-diameter nerves. In essentially continuous
6-month inhalation studies, peripheral and central nervous system
lesions were present at doses of 1760 mg/m3 (500 ppm) or more, but
no clinical or pathological effects were noted at 440 mg/m3 (125
ppm). Only limited recovery of amplitude of the fifth brainstem
auditory-evoked response (believed to reflect central nervous
system activity) and tail nerve action potential was recorded 15 -
22 weeks after cessation of continuous exposure to a vapour
concentration of 3520 mg/m3 (1000 ppm), 5 days/week, for 11 weeks.
Discontinuous exposure of rats to 3168 mg/m3 (900 ppm) for 72 weeks
did not cause any apparent peripheral or central nervous system
lesions, but there was some evidence of electrophysiological
effects on peripheral nerves.
n-Hexane-induced neurotoxicity can be enhanced by combined
exposure to methyl ethyl ketone, methyl isobutyl ketone, and lead
acetate, and decreased by co-exposure to toluene. Toluene and
n-hexane also have a synergistic effect in the disturbance of
dopamine levels.
Severe microscopic lesions were noted in skin when n-hexane
was applied dermally under occlusive conditions for short periods.
Prolonged exposure to an n-hexane vapour concentration of 10 560
mg/m3 (3000 ppm) can cause conjunctival irritation in rats and
marked ocular irritation in rabbits. No skin sensitization data
are available from animal studies.
Chromosomal damage (polyploidy in one study, structural
aberrations in a second study) has been reported in both in vitro
and in vivo studies. No increase in point mutation frequency or
effects in tests for DNA damage has been noted.
There has been one carcinogenicity study with n-hexane (skin
painting on mice), which provided no evidence of carcinogenicity.
The reproductive toxicity of n-hexane has not been studied
adequately. There was no substantial evidence of embryotoxicity or
teratogenicity in rats following inhalation, though concentrations
were relatively low, or in mice after oral dosing. Postnatal
development of rats was transiently delayed when dams were exposed
to an n-hexane vapour concentration of 3520 mg/m3 (1000 ppm).
Very little information is available on the acute toxicity of
n-hexane to humans. Most studies have involved occupational
exposure to solvent mixtures. The available data suggest that
n-hexane has low acute toxicity. Signs of central nervous system
depression, such as drowsiness, vertigo, and giddiness, have been
reported after exposure to a commercial hexane level of 3520 to
17 600 mg/m3 (1000 - 5000 ppm) for 10 - 60 min.
n-Hexane is a mild irritant causing transient erythema when in
contact with human skin for short periods. More severe effects
(erythema and blistering) were documented after occlusive skin
contact for 5 h with commercial grade hexane. There have been no
case reports of sensitization of skin in exposed workers, and no
skin sensitization was noted in a maximization test with n-hexane.
On repeated exposure, n-hexane is neurotoxic, inducing a type
of sensorimotor peripheral neuropathy. Many studies on the
prevalence of n-hexane-induced neurotoxicity have been published;
however, adequate exposure data are often lacking. Exposure to
n-hexane concentrations in air varying from 106 - 8800 mg/m3
(30 - 2500 ppm) has been associated with neuropathy. Cases of
marked peripheral neuropathy were reported among Japanese sandal
workers and Taiwanese press proofers exposed to n-hexane levels of
approximately 176 and 352 mg/m3 (50 and 100 ppm), respectively, for
periods exceeding 8 h per day. In many cases exposure measurements
were recent and probably did not accurately reflect previous
exposures causing neuropathy.
Several cross-sectional studies have independently reported
mild subclinical effects (for example, electrophysiological
changes in peripheral nerves) in workers exposed to 70 - 352 mg/m3
(20 - 100 ppm). However, no clear cases of clinically overt
peripheral neuropathy were identified in any of these studies at
exposure levels of less than 352 mg/m3 (100 ppm).
The effects of n-hexane on the central nervous system have been
investigated only in a few studies. Changes in somatosensory
evoked potentials recorded from workers exposed to n-hexane were
suggested to result from a central nerve conduction block. Altered
visual evoked potentials and EEG traces have also been noted.
These results suggest that n-hexane may produce central nervous
system dysfunction, but the available data provide no information
on related exposure levels.
Identity
Common synonyms: Hexyl hydride, hexane, Skellysolve
B Chemical structure:
H H H H H H
| | | | | |
| | | | | |
H---C---C---C---C---C---C---H
| | | | | |
| | | | | |
H H H H H H
Chemical formula: C6H14
CAS registry number: 110-54-3
Relative molecular mass: 86.177
Physical and chemical properties
Some physical and chemical properties of various grades of
n-hexane are given in Table 1.
Table 1. Physical and chemical properties of n-hexanea
Boiling point (°C) 68.74b
Melting point (°C) -95.35b
Relative density (20 °C/4 °C) 0.66
Vapour pressure (25 °C) 20 kPa (150 mmHg)
Vapour density 2.97
Autoignition temperature (°C) 225
Explosive limit in air (% by volume) 1.1-7.5
Flash point (°C) -21.7
Closed-cup flash point (°C)c -30.56
Solubility in water (mg/litre at 25 °C) 9.5
Log n-octanol/water partition coefficient
(log Pow at 25 °C) 3.6
Refractive index (20 °C) 1.37
Colour, Saybolt +39
a From: Mellan (1977)and IRPTC (1990).
b From: Clayton & Clayton (1981).
c From: ACGIH (1986).
n-Hexane is colourless, highly volatile (NIOSH, 1977a), and
flammable (Dale & Drehman, 1980; ACGIH, 1986). It is poorly
soluble in water but is soluble in most organic solvents including
ethanol and ether (McAuliffe, 1963; NIOSH, 1977a; ACGIH, 1986).
Purified n-hexane contains 95 - 99.5% n-hexane, together with
small amounts of other hexane isomers as impurities (Mellan, 1977;
Baker & Rickert, 1981; Sandmeyer, 1981). Traces of benzene (0.05%)
have been detected (Baker & Rickert, 1981). Commercial hexane is a
mixture of hexane isomers ( n-hexane, 2-methylpentane,
3-methylpentane, 2,3-dimethylbutane), cyclohexane, methyl
cyclopentane and small amounts of pentane and heptane isomers,
acetone, methyl ethyl ketone, dichloromethane, and
trichloroethylene (Perbellini et al., 1981a,b,c; ACGIH, 1986). The
n-hexane content of commercial hexane (Table 2) can vary between
20% and 80% (ACGIH, 1986).
Table 2. Composition (% by weight) of different
grades of n-hexanea
Research Pure Technical
grade grade grade
n-Hexane 99.98 99.5 95-97.7
2-Methylpentane trace trace trace
3-Methylpentane 0.02 0.1 0.2
Methylcyclopentane trace 0.4 2.1
a From: Mellan (1977).
Pure n-hexane contains approximately 0.0005% of non-volatile
material (Mellan, 1977), whereas commercial hexane may contain up
to 0.04% (Patty & Yant, 1929; Vicedo et al., 1985). In commercial
hexane, a number of phthalate esters (including dimethyl, diethyl,
di- n-butyl, di-isobutyl, dihexyl, and diethylhexyl), adipate
esters (dibutyl and dioctyl), and organophosphorus compounds (e.g.,
triphenyl phosphate) have been identified and total about 0.3% of
the distillation residue (Vicedo et al., 1985).
Commercial hexane (containing about 30% n-hexane) has a
slightly disagreeable odour, perceptible at 282 mg/m3 (80 ppm)
(intermittent exposure) or 528 mg/m3 (150 ppm) (continuous
exposure) (Patty & Yant, 1929). An odour threshold of 211 mg/m3
(60 ppm) for hexane (purity not stated) has also been reported
(Laffort & Dravnieks, 1973).
-
Petroleum Ether, 61-76 °C
-
n-Hexane, 70%, CAS No. 110-54-3
-
n-Hexane, 80%, CAS No. 110-54-3
-
n-Hexane 90%, CAS No. 110-54-3
-
Isohexane, 99%, CAS No.107-83-5
-
n-Hexane, 60%, CAS No. 110-54-3, in ISO Tanks
-
n-Hexane, 60%, CAS No. 110-54-3, in Drums
-
n-Hexane, 99%, CAS No. 110-54-3, in ISO Tanks
-
n-Hexane, 99%, CAS No. 110-54-3, in Drums
Normal hexane (n-hexane) is both an anthropogenic and naturally occurring chemical. n-Hexane is a minor constituent of crude oil and natural gas. Its inclusion in a variety of petroleum products is a consequence of refining operations that separate hydrocarbons within specific ranges of boiling points for such uses as heating oils or automotive fuels. It may also be a metabolic byproduct from certain types of fungi (Ahearn et al.1996). Such sources of natural releases are discussed in Chapter 5. In commercial products prepared from the distillation of petroleum, n-hexane has many uses as a special-purpose solvent
and oil extractant. In a highly purified form, n-hexane is used in chemical laboratories as an extractant for a wide range of hydrocarbons and nonpolar organic compounds.
Virtually all n-hexane is obtained from petroleum mixtures through controlled fractional distillation and other refinery-based processes (Speight 1991). n-Hexane can also be synthesized from sugar cane wastes
using special catalysts (SUCRON 1996). This type of synthesis is relatively new and the volume produced is still very limited. The presence of many types of hydrocarbon impurities in many commercial grades of n-hexane, combined with the intentional denaturing of n-hexane preparations to discourage substance abuse, make it difficult to establish odor thresholds for many products containing n-hexane.
Hexane in Solvent extraction method. Hexane in its pure form is a colorless liquid , and its boiling point is between 50℃ – 70℃ all of which work in favor for oil extraction. To begin the process of solvent extraction, oil seeds (soybean, rapeseed etc.) are removed of impurities and dried to reduce moisture content.
Hexane is the solvent that is widely utilized in the process of herbal medicine and bioactive components production and oil industry. Hexane is one of the most commonly used solvents not only in the edible oil industry but also in the process of herbal medicine and bioactive components production.
Edible oils and fats can be produced either by solvent or mechanical extraction of oilseeds. Hexane is one of the most commonly used solvents in the edible oil industry.
Is soybean oil hexane free?
Whole soybeans (edamame) are always a hexane-free and healthy option. Expeller-pressing and cold-pressing are physical methods to extract oils that do not involve solvents, so soy and other vegetable oils produced in this manner are also hexane-free.
Is hexane toxic to humans?
Hexane has a long record of use without as much irritation of human skin or the immediate or severe toxicity of many competitive solvents. It does not mix with water, allowing fairly simple processes to keep it in the system while water passes through the extraction process as moisture in the seed, meal, oil or air.
USE
n-Hexane is used mainly as an edible-oil extractant for a variety of seed crops such as soybeans, cottonseed, rape seed (canola), flax (linseed), mustard seed, peanuts, safflower seed, and corn germ, which are then processed into foods for humans or livestock. While other petroleum-derived solvents (e.g., pentane) or other organic solvents (e.g.,
chloroform, methanol, ethanol, or ammonia-alcohol mixtures) are currently being studied or are used for certain processes, n-hexane has been widely used since the early part of this century, especially with
soybeans, cottonseed, and linseed (Conkerton et al.1995). Part of n-hexane’s appeal relates to aesthetic properties such as preserving the colors of the original plant materials. Different extractant mixtures can also have significant effects on the levels of materials that can cause bitter tastes (e.g., tannins) and on the degree to which certain flatulence-causing sugars are removed. While other solvents could be used in the initial oil extraction phases, several decades of experience in combining the oil-extraction steps with other procedures to preserve desirable colors and eliminate unwanted tastes or other undesirable food properties have worked to maintain a heavy reliance on n-hexane for edible-oil extraction (Lawson 1995). In the
1970s it was estimated that soybean oil extraction alone accounted for approximately 30% of all uses of n-hexane in the United States (HSDB 1996).
n-Hexane has other major uses as a special-purpose solvent and cleaning agent (degreaser) in such industries as textile manufacture, shoe and leather making, and furniture manufacturing (Jorgensen and Chor 1981). It is used in the printing industry as a cleaner and as a component of some inks (EPA 1996c; Wadden et al.1995). Facilities that use rotogravure printers (facilities that produce catalogues, magazines, “glossy” newspaper inserts, or telephone directories) or similar rotogravure or flexographic technologies (for labels, gift wrap, metal foils, flexible packaging materials, and some floor coverings) also use n-hexane (EPA 1996c). While not used in most glues or epoxy cements (Rastogi 1993), n-hexane is the solvent used
in “rubber” cement (also known as gum adhesive) widely used in schools and libraries and by artists (McCann 1992). Various glues, adhesives, and leather-dressing preparations, especially those used in assembling shoes, may contain n-hexane (Cardona et al.1993; Periago et al.1993; Takeuchi et al.1993).
In bookbinding and leather working, n-hexane, often mixed with other hydrocarbon solvents, is used as a carrier for cedar oil, beeswax, or lanolin dressings (Jorgensen and Chor 1981; Roberts and Etherington 1996). n-Hexane is used in some typeover correction (“white-out”) fluids (Ong et al.1993). It has been used in many types of non-mercury thermometers, especially for thermometers used in low temperature ranges (EPA 19948). It has been used as a denaturing agent in some alcohol preparations (HSDB 1996).
New roofing materials using rubber or plastic films and membranes held together by adhesives, sealants, or hardening agents may contain n-hexane (Herbert et al.1995). It may be used as a carrier or aerosol (propellant) agent in some perfumes (Bouhamra 1995; Jorgensen and Chor 1981). It is used in the pharmaceutical industry to help shape pills and tablets, which are then dried to vent off the n-hexane before packaging (Jorgensen and Chor 1981). In the petrochemical industry, lighter alkane fractions including n-hexane may be used as feedstocks in the manufacture of polyethylene or polypropylene (Jorgensen and Chor 1981). In canning operations, the ends of tin cans are held in place with adhesives that commonly contain n-hexane (Bachmann et al.1993). The balls used in several sports (e.g., baseball) have cores wrapped with strings or yarns, which are often held in place with adhesives containing n-hexane (Huang et al.1991). In the manufacture of truck and automobile tires, n-hexane is a solvent in mixtures (called “thinners”) used to adjust the viscosity of the rubber while it is being polymerized and formed into tires (Jorgensen and Chor 1981; Van Ert et al.1980). n-Hexane is apparently in the adhesives for certain types
of tapes, bandages, and dressings used in hospitals (Jorgensen and Chor 198I). Adhesives, cleaners, or lacquers containing n-hexane are also used to prepare the veneers used in making many types of furniture or ornamental boxes (Graham et al.1995).
Pure n-hexane is widely used in laboratories as an extractant for nonpolar compounds and in calibrating instruments for analyses of volatile organic compounds (VOC) or total petroleum hydrocarbons (TPH) (Kanatharana et al.1993). Since such analyses may require very high levels of purity, laboratories sometimes carry out their own fractional distillation or other pretreatment-purification procedures to remove petroleum hydrocarbon impurities found in commercially available grades of n-hexane
(Kanatharana et al.1993). Request a quote or for more information about testing for n-hexane, please email us at: info@junyuanpetroleumgroup.com.
Finally, n-hexane may be a component of many types of commercial preparations or in mixtures produced in small batches on-site such as paint thinners, general-purpose solvents, degreasing agents, or cleaners.
For instance, until the 1970s naphtha, a mixture with a high n-hexane content, was widely used as a dry cleaning agent. Since the early 1900s construction workers, metal workers, janitors, furniture workers, motor-vehicle mechanics, and print-shop workers have used these general-purpose mixtures. Such mixtures have also been used extensively for home repair and hobby projects. These mixtures have wide variations in their compositions but often contain up to 20% n-hexane even when the main components are other petroleum alkane fractions (e.g., kerosene), aromatic hydrocarbons (e.g., toluene), chlorinated hydrocarbon solvents, or other organic liquids (Farmer 1996; Veulemans et al.1987).