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   Updated: 5 Mar 2018



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Xylene (from Greek ξύλο, xylo, "wood"), xylol or dimethylbenzene is an aromatic hydrocarbon mixture consisting of a benzene ring with two methyl groups at various substituted positions. The three isomers of xylene have the molecular formula C8H10, also representated by the semi-structural formula C6H4(CH3)2. Xylene is a major petrochemical produced by catalytic reforming and also by coal carbonisation in the manufacture of coke fuel. It represents about 0.5–1% of crude oil (depending on the source), and is found in small quantities in gasoline and aeroplane fuels. Xylenes are mainly produced as part of the BTX aromatics (benzene, toluene and xylenes) extracted from the product of catalytic reforming known as "reformate". The mixture is a slightly greasy, colorless liquid commonly encountered as a solvent. Xylene was named in 1851, having been discovered as a constituent of wood tar. Several million tons are produced annually. In 2011, a global consortium began construction of one of the world’s largest xylene plants in Singapore.

Xylene exists in three isomeric forms. The isomers can be distinguished by the designations ortho- (o-), meta- (m-), and para- (p-), which specify to which carbon atoms (of the benzene ring), the two methyl groups are attached. By counting the carbon atoms around the ring starting from one of the ring carbons bonded to a methyl group, and counting towards the second methyl group, the o-isomer has the IUPAC name of 1,2-dimethylbenzene, the m-isomer is 1,3-dimethylbenzene, and the p-isomer is 1,4-dimethylbenzene. Of the three isomers, the p-isomer is the most industrially sought after after since it can be oxidized to terephthalic acid.

Industrial production
Xylenes are produced by the methylation> of toluene and benzene. Commercial or laboratory grade xylene produced usually contains about 40-65% of m-xylene and up to 20% each of o-xylene, p-xylene and ethylbenzene. The ratio of isomers can be shifted to favor the highly valued p-xylene via the patented UOP-Isomar process0ff">[7] or by transalkylationof xylene with itself or trimethylbenzene. These conversions are catalyzed by zealots.

The chemical and physical properties of xylene differ according to the respective isomers. The melting point ranges from −47.87 °C (−54.17 °F) (m-xylene) to 13.26 °C (55.87 °F) (p-xylene). The boiling point for each isomer is around 140 °C (284 °F). The density of each isomer is around 0.87 g/mL (7.26 lb/U.S. gallon or 8.72 lb/imp gallon) and thus is less dense than water. Xylene in air can be smelled at concentrations as low as 0.08 to 3.7 ppm (parts of xylene per million parts of air) and can be tasted in water at 0.53 to 1.8 ppm

ATEX Gas detectors are available for 2 explosion classes as follows:

Zone 1 is available with or without display

Gas detectors for ATEX Zone 1 are located in a flameproof enclosure, EEx d

The shell is such that ignition and combustion within the shell of a potential explosive gas mixture is not propagated to the explosive mixture outside the enclosure and the enclosure can thus endure the resulting explosion pressure without damage.

In Zone 1 one can expect an explosive atmosphere to occur during normal operation but the presence of it is relatively short.

The equipment shall not be a source of ignition in normal operation or when an error occurs.

Gas detectors for ATEX Zone 2 are of the design Non-sparking EEx nA

EEx nA is a non-sparking piece of equipment.

In Zone 2, you need not count with an explosive atmosphere to occur during normal operation, and if it should occur, which is probably rare of duration.

The equipment shall not be a source of ignition during normal operation.

Information on LEL och explosion hazard



EEx-d ATEX Protection Class






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EEx-n ATEX Protection Class






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