Hexane, flash-point

Properties of the principal hydrocarbons found in commercial hexane are shown in Table 9. The flash point of / -hexane is —21.7 °C and the autoignition temperature is 225°C. The explosive limits of hexane vapor in air are 1.1—7.5%. Above 2°C the equiUbrium mixture of hexane and air above the Hquid is too rich to fall within these limits (42). 

Compounds with low flash points (below room temperature). Examples are acetaldehyde, acetone, acetonitrile, benzene, carbon disulfide, cyclohexane, diethyl ether, ethyl acetate and -hexane. 

The flash point of condenstate is generally taken as that of hexane, where precise measurements have not been taken. Hexane has the lowest flash point of any material in the constitution of condensate. In atmospheric burning smoke production normally occurs. 

Samples from the same study averaged over a typical 8-hour workshift for the area around the backhoe showed average levels of 3.06 mg/m3 (1.10 ppmv). Even higher levels (perhaps in excess of 10,000 ppmv) are possible around large spills of -hexane at such elevated concentrations, as with many components of gasoline-type hydrocarbons, there could be considerable danger from explosions, which are possible when the -hexane levels exceed approximately 1.2% of the volume of air (Merck 1989). Since 0.1% by volume is equivalent to 1,000 ppmv, this flash-point level for -hexane would be at a level of 12,000 ppmv or higher. 

Ignitability-flammability. A liquid that has a flash point of less than 60°C (140°F) is considered ignitable. Some examples are benzene, hexane, heptane, benzene, pentane, petroleum ether (low boiling), toluene, and xylene(s). 

Benzene s molecular formula is C6H6, but it does not behave like hexane, hexene, or any of their isomers. One would expect it to be similar to these other six-carbon hydrocarbons in its properties. Table 4 provides a comparison between benzene, hexane and 1-hexene. The table shows that there are major differences between benzene and the straight-chain hydrocarbons of die same carbon content. Hexene s ignition temperature is very near to hexane s. The flash point difference is not great, however, there are significant differences in melting points. The explanation for these differences is structure which in the case of benzene is a cyclical form with alternating double bonds. 

Allyl alcohol (2-propen-l-ol, CH2=CHCH2OH, boiling point 96.9°, density 0.8520, flash point 25°C) is the simplest unsaturated alcohol and is a colorless corrosive liquid with a pungent odor. The vapor can cause severe irritation and injury to eyes, nose, throat, and lungs. Allyl alcohol is miscible with water and miscible with many polar organic solvents and aromatic hydrocarbons, but is not miscible with //-hexane. It forms an azeotropic mixture with water and a ternary azeotropic mixture with water and organic solvents. 

Flash Point-Pensky-Martens Closed Cup for Fats and Oils (Cc 9b-55) determines the temperature at which an oil sample will flash when a test flame is applied. This technique sometimes is used to estimate levels of residual hexane and to ensure the safety of workers handling the oil. Some refineries use gas chromatography methods instead. 

If desired, one could replace CCI4 with hexane (a mixture of several isomers), since hexane is not very toxic and has an exposure limit of 100 ppm vapor in the air. However, hexane is more volatile, and the distribution constant for I2 is different in different hexane isomers, leading to problems with the data analysis. Perhaps a better alternative is p-xylene. Although less toxic this solvent is however more flammable than CCI4, with a flash point of 17°C. Finally, we note that it is also possible to determine I2 concentrations spectrophotometrically, which eliminates the titrations. 

A flammable chemical substance is a solid, liquid, vapor, or gas that ignites easily and burns rapidly in air. Many of the flammable chemicals used in laboratories are flammable liquids and organic solvents. The vapors of these chemical substances form ignitable mixtures with air. Based on the flash points of these chemicals, classifications are made. The flash point of a chemical substance is defined as the lowest temperature at which a fuel-air mixture present above the surface of a liquid will ignite, if an ignition source is present. The common flammable chemical substances include, but are not restricted to, acetone, benzene, cyclohexane, ethanol, ethyl acetate, ethyl ether, gasoline, hexane, isopropyl alcohol, methanol, propanol, tetrahydro-furan and toluene, and xylene. 

Detwiler and Markley (76) found that the smoke point varied considerably with the degree of refining, especially the removal of free fatty acids, and also with the mode of oil extraction. Yen et al. (118) found a smoke point of 191°C, which was raised several degrees by the addition of phenolic antioxidants. The flash point of soybean oil, the temperature at which vapors coming from the oil will catch fire from an ignition source, were reported as 304°C (117), 326-331°C (76), 174°C (69), 318°C (70), and 320°C (119). The low value reported by Ali et al. (69) was obtained by using a Pensky-Martens closed tester and ASTM method 093-90. The flash points of hexane-soybean oil mixtures were determined and correlated with headspace gas chromatography data (120). 

N,N DIMETHYLAMINO-C YCLO-HEXANE (98-94-2) CgH N Highly flammable liquid. Forms explosive mixture with air (flash point 108°F/42°C). An organic base. Reacts with oxidizers acids (reaction may be exothermic). Contact with strong reducing agents, including metal hydrides, nitrides, sulfides, alkali metals, and metal alkyls, may form flammable hydrogen gas. Incoirqjatible with acrylates, alcohols. 

DI-/1-PROPYLALUMINUM HYDRIDE, 15% solution in hydrocarbons (2036-15-9) See also above entry. Forms explosive mixture in air [flash point (based on hexane)-14°F/-26°C]. Once solvent has evaporated, this substance is pyrophoric. Flow or agitation of substance may generate electrostatic charges due to low conductivity ground all equipment containing this material. 

HEXANAL or 1-HEXANAL (66-25-1) CjHjjO Highly flammable liquid. Forms explosive mixture with air (flash point... 

HEXANE or -HEXANE (110-54-3) C H,4 Highly flammable liquid extremely low ignition temperature makes it very dangerous. Forms explosive mixture with air [explosion limits in air (vol %) 1.1 to 7.5 flash point -7°F/-22°C autoignition temp 437°F/225°C Fire Rating 3]. Violent reaction with strong oxidizers bromine, chlorine, fluorine, chromic acid, sodium peroxide. Contact with dinitrogen tetraoxide may explode at 82°F/28°C. Incompatible... 

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