Mixed xylenes are produced by high severity catalytic reforming of naphtha, from which the C8 stream contains ortho-, meta- and para -xylenes, and ethyl benzene. Xylenes are also obtained from the pyrolysis gasoline stream in a naphtha steam cracker and by toluene disproportionation.
Conventional PX technology is based on the isomerisation of mixed xylenes. High purity product can be obtained using crystallisation or selective adsorptive separation, such as UOP's Parex and IFP's Eluxyl processes.
Toluene disproportionation offers an alternative route with the latest catalysts able to produce a PX-rich stream, but this route co-produces benzene. Processes have also been developed using a zeolite catalyst for the alkylation of toluene with methanol to produce PX without the benzene coproduct.
The UOP/BP Cyclar process, where propane and butane are converted to PX and benzene, was commercialised in Saudi Arabia in 1999.
Paraxylene
Price Reports
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Paraxylene
Uses and Outlook
Paraxylene (PX) is the largest volume isomer of the mixed xylenes. Around 98% of PX is consumed in the polyester chain, mainly in the production of fibre, film and polyethylene terephthalate (PET), via one of two intermediates – purified terephthalic acid (PTA) or dimethyl terephthalate (DMT). A small amount of PX is used as a solvent and to produce di-paraxylene and herbicides.
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