Mixtures of benzene, toluene, and the three xylene isomers
In the petroleum refining and petrochemical industries, the initialism BTX refers to mixtures of benzene, toluene, and the three xylene isomers, all of which are aromatic hydrocarbons. The xylene isomers are distinguished by the designations ortho– (or o–), meta– (or m–), and para– (or p–) as indicated in the adjacent diagram. If ethylbenzene is included, the mixture is sometimes referred to as BTEX.
The BTX aromatics are very important petrochemical materials. Global consumption of benzene, estimated at more than 40,000,000 tons in 2010, showed an unprecedented growth of more than 3,000,000 tons from the level seen in 2009. Likewise, the para-xylene consumption showed unprecedented growth in 2010, growing by 2,800,000 tons, a full ten percent growth from 2009.[1]
Benzene, toluene, and xylenes can be made by various processes. However, most BTX production is based on the recovery of aromatics derived from the catalytic reforming of naphtha in a petroleum refinery.[4][7]
Catalytic reforming usually utilizes a feedstock naphtha that contains non-aromatic hydrocarbons with 6 to 12 carbonatoms and typically produces a reformate product containing C6 to C8 aromatics (benzene, toluene, xylenes) as well as paraffins and heavier aromatics containing 9 to 12 carbon atoms.
Another process for producing BTX aromatics involves the steam cracking of hydrocarbons which typically produces a cracked naphtha product commonly referred to as pyrolysis gasoline, pyrolysis gas or pygas. The pyrolysis gasoline typically consists of C6 to C8 aromatics, heavier aromatics containing 9 to 12 carbon atoms, and non-aromatic cyclic hydrocarbons (naphthenes) containing 6 or more carbon atoms.[4][7]
The adjacent table compares the BTX content of pyrolysis gasoline produced at standard cracking severity or at medium cracking severity with the BTX content of catalytic reformate produced by either a continuous catalytic regenerative (CCR) reformer or by a semi-regenerative catalytic reformer. About 70 percent of the global production of benzene is by extraction from either reformate or pyrolysis gasoline.[4]
Below is a schematic flow diagram of one method, involving extractive distillation, for extraction of the BTX aromatics from a catalytic reformate:[2]
Petrochemicals produced from BTX
There are a very large number of petrochemicals produced from the BTX aromatics. The following diagram shows the chains leading from the BTX components to some of the petrochemicals that can be produced from those components:[2]
Catalysis– Process of increasing the rate of a chemical reaction
Pyrolysis– Thermal decomposition of materials at elevated temperatures, often in an inert atmosphere
External links
J.H. Gary and G.E. Handwerk (1984). Petroleum Refining Technology and Economics (3rded.). Marcel Dekker, Inc. ISBN0-8247-9157-6. (see Chapter 15 available here[permanent dead link]).
Donald L. Burdick and William L. Leffler. Petrochemicals in Nontechnical Language (3rded.). PennWell Publishing. ISBN0-87814-798-5. Available at Google Books.
This article uses material from the Wikipedia article BTX_(chemistry), and is written by contributors.
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