Methylbenzenes (Toluene and Xylenes)

 Methylbenzenes occur in small quantities in naphtha and higher boiling fractions of petroleum. Those presently of commercial importance are toluene, o-xylene, p-xylene, and to a much lesser extent m-xylene.

  The primary sources of toluene and xylenes are reformates from catalytic reforming units, gasoline from catcracking, and pyrolysis gasoline from steam reforming of naphtha and gas oils. As mentioned earlier, solvent extraction is used to separate these aromatics from the reformate mixture. Only a small amount of the total toluene and xylenes available from these sources is separated and used to produce petrochemicals.

  Toluene and xylenes have chemical characteristics similar to benzene, but these characteristics are modified by the presence of the methyl substituents. Although such modification activates the ring, toluene and xylenes have less chemicals produced from them than from benzene. Currently, the largest single use of toluene is to convert it to benzene. para-Xylene is mainly used to produce terephthalic acid for polyesters. o-Xylene is mainly used to produce phthalic anhydride for plasticizers. In 1997, the U.S. produced approximately 7.8 billion pounds of pxylene and only one billion pounds of o-xylene.

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