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The BTX aromatics can be extracted from catalytic reformate or from pyrolysis gasoline by many different methods. Most of those methods, but not all, involve the use of a solvent either for liquid-liquid extraction or extractive distillation .
The process, which is catalyzed by platinum supported by aluminium oxide, is exemplified in the conversion methylcyclohexane (a naphthene) into toluene (an aromatic). [2] Dehydrocyclization converts paraffins (acyclic hydrocarbons) into aromatics. [3] A related aromatization process includes dehydroisomerization of methylcyclopentane to benzene:
Xylenes are produced mainly as part of the BTX aromatics (benzene, toluene, and xylenes) extracted from the product of catalytic reforming known as reformate. Several million tons are produced annually. [3] In 2011, a global consortium began construction of one of the world's largest xylene plants in Singapore. [5]
The production of p-xylene is industrially significant, with annual demand estimated at 37 million tons in 2014, and still on the increase. [12] [13] p-Xylene is produced by catalytic reforming of petroleum naphtha as part of the BTX aromatics (benzene, toluene and the xylene isomers) extracted from the catalytic reformate.
The table just below lists some fairly typical straight-run heavy naphtha feedstocks, available for catalytic reforming, derived from various crude oils. It can be seen that they differ significantly in their content of paraffins, naphthenes and aromatics:
Pyrolysis gasoline or pygas is a naphtha-range product with high aromatics content. [1] It is a by-product of high temperature naphtha cracking during ethylene and propylene production, a high octane number mixture that contains aromatics from the aromatization reactions, olefins, and paraffins ranging from C5s to C12s.
Transalkylation is employed in the commercial production of aromatics beyond the usual BTX feedstocks. For example, 4- tert -butylphenol is produced in part via two transalkylation reactions. [ 7 ] In one example, tert -butylphenyl ether is isomerized to the phenol:
Aromatics includes benzene, toluene and xylenes, as a whole referred to as BTX and primarily obtained from petroleum refineries by extraction from the reformate produced in catalytic reformers using naphtha obtained from petroleum refineries. Alternatively, BTX can be produced by aromatization of alkanes.