Xylene flammability limits

The aerobic oxidation of o-xylene to phthalic acid or anhydride at elevated temperatures is industrially important, and the flammability limits and explosion parameters at 350°C under a range of pressures have been redetermined. 

Fire Hazards - Flash Point (deg. F) 84 CC (solution) Flammable Limits in Air (%) 1.1 - 6.4 Fire Extinguishing Agents Foam, dry chemical, or carbon dioxide Fire Extinguishing Agents Not To Be Used Water may be ineffective fecial Hazards of Combustion Products Toxic vapors are generated when heated Behavior in Fire Solution in xylene may produce corrosive products when heated Ignition Temperature (deg. F) 986 (solution) Electrical Hazard Not pertinent Burning Rate 5.8 mm/min. 

Flammable permanent gases and vapours have well-defined flammability limits in air, usually in the range l-35 5F v/v" "2. Many hydrocarbons such as toluene and xylene can also bum in atmospheres such as chlorine. ... 

The lower flammability limit of o-xylene in air is 1 mole%, and the upper flammability limit is 6 mole%. For safety reasons, it is necessary that process conditions not be within these limits. It is also necessary that the o-xylene content of the reactor never exceed 10 mole%, because if that limit is exceeded, the catalyst no longer operates at the desired selectivity, and the reaction could become ojgrgen starved, forming significant amounts of CO and other undesired by-products. 

The xylene isomers are flammable Hquids and should be stored in approved closed containers with appropriate labels and away from heat and open flames. Limits for transportation by air are 5 L on passenger planes and 60 L on cargo planes. 

Flammable or Explosive Limits — the upper and lower vapor eoneentrations at whieh a mixture will bum or explode. The lower explosive limit of p-xylene is 1.1 pereent by volume in air, whereas the upper explosive limit is 7.0 percent in air. A mixture of p-xylene vapor and air having a coneentration of <1.1 pereent in air is too lean in p-xylene vapor to bum. Conversely, a mixture containing more than 7.0 percent is too rieh in p-xylene to bum. By subtraetion (7.0 - 1.1), p-.xylene is said to have a flammable range of 5.9. Materials having low explosive limits and wide flammable ranges are extremely dangerous. 

They are sensitive to all flammable gases, and they give approximately the same response to the presence of the lower explosive limit (LEL) concentrations of all the common hydrocarbon gases and vapors. However it should be remembered that gas detectors do not respond equally to different combustible gases. The milli-volt signal output of a typical catalytic detector for hexane or xylene is roughly one half the signal output for methane. 

The xylenes are flammable and are shipped under the same regulations and using the same methods as benzene and toluene rank cars, trucks, barges, and tankers. Pipeline movements are limited. Toxicological problems dictate handling in closed systems like benzene and toluene. 

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. 

METHYL PARATHION (298-00-0) CgHjoNOjPS Combustible solid or a flammable hydrocarbon solvent solution (commercial product). Forms explosive mixture with air [explosion limits in air (vol %) 1.0 to 7.0 (xylene) 0.7 to 7.0 (light aromatic solvent naphtha) flash point 78°F/26°C 115°F/46°C oc autoignition tenp 498°F/928°C (in xylene) 830 to 870°F/443 to 466°C (light aromatic solvent naphtha) ... 

---