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{{Image|BTX.png|right|350px|Structural diagrams of the BTX aromatic hydrocarbons.}}
In the [[Petroleum refining processes|petroleum]] and [[Petrochemicals|petrochemical]] industries, the acronym '''BTX''' refers to mixtures of the [[hydrocarbons|aromatic hydrocarbons]] [[benzene]], [[toluene]], and the three [[Xylenes|xylene isomers]]. 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.<ref name=Chem-Systems-2010>[http://www.chemsystems.com/about/cs/news/items/PPE%20PCMD%20Aromatics%202011.cfm The Future of Benzene and Para-Xylene after Unprecedented Growth In 2010]. From a ChemSystems report in 2011.</ref>
Toluene is also a valuable petrochemical for use as a solvent and intermediate in chemical manufacturing processes and as a high octane gasoline component.<ref name=BTX-Chain>[http://www1.eere.energy.gov/manufacturing/industries_technologies/chemicals/pdfs/profile_chap4.pdf The BTX Chain: Benzene, Toluene, Xylene]. Chapter 4 of the DOE's Office of Energy Efficiency and Renewable Energy (EERE) report entitled [http://www1.eere.energy.gov/manufacturing/industries_technologies/chemicals/pdfs/profile_full.pdf "Energy and Environmental Profile of the U.S. Chemical Industry" of May 2000.]</ref><ref name=Siemans>[http://www.industry.usa.siemens.com/automation/us/en/process-instrumentation-and-analytics/process-analytics/pa-case-studies/Documents/CS_AROMATICS_EN.pdf Use of Process Analytics in Aromatics (BTX and phenol) production plants]. Case Study, August 2008. (scroll down to "Aromatics" section.</ref><ref name=Chem-Systems>[http://www.chemsystems.com/about/cs/news/items/PERP%200607_6_BenzeneToluene.cfm Benzene/Toluene]. Introduction to a ChemSystems report, 2009.</ref><ref name=TrecanniEncyclopedia>[http://www.treccani.it/export/sites/default/Portale/sito/altre_aree/Tecnologia_e_Scienze_applicate/enciclopedia/inglese/inglese_vol_2/591-614_ING3.pdf 10.6 Aromatics], Online Italian [http://www.treccani.it/export/sites/default/Portale/sito/altre_aree/Tecnologia_e_Scienze_applicate/enciclopedia/inglese/inglese_vol_2/idro_vol_2_I-XXXVI_eng.pdf <i>Encyclopedia of Hydrocarbons</i>], Istituto della Enciclopedia Italiana, Volume II, 2006, pages 603-605.</ref>
==Properties of the BTX hydrocarbons==
The table below lists some of the properties of the BTX aromatic hydrocarbons, all of which are liquids at typical room conditions:
{|class=wikitable align=
|+Properties<ref name=CRC-Hdbk>{{cite book|author=Robert C. Weast (Editor)|title=Handbook of Chemistry and Physics|edition=56th Edition|publisher=CRC Press|year=1975|id=ISBN 0-87819-455-X}}</ref>
!&nbsp;!!benzene!!toluene!!ethylbenzene!!''p'' - xylene!!''m'' - xylene!!''o'' - xylene
|- align=center
|[[Molecule#Empirical_formula|Molecular formula]]||C<sub>6</sub>H<sub>6</sub>||C<sub>7</sub>H<sub>8</sub>||C<sub>8</sub>H<sub>10</sub>||C<sub>8</sub>H<sub>10</sub>||C<sub>8</sub>H<sub>10</sub>||C<sub>8</sub>H<sub>10</sub>
|- align=center
|[[Molecular mass]], g&thinsp;'''&middot;'''&thinsp;mol<sup> –1</sup>||78.12||92.15||106.17||106.17||106.17||106.17
|- align=center
|[[Boiling point]], &deg;C||80.1||110.6||136.2||138.4||139.1||144.4
|-align=center
|[[Melting point]], &deg;C||5.5||–&thinsp;95.0||–&thinsp;95.0||13.3||–&thinsp;47.9||–&thinsp;25.2
|}
==Production of BTX hydrocarbons==
{| border="0" width="375" align="right"
|
{|class=wikitable align="right"
|+BTX content of Pyrolysis Gasoline and Reformate<ref name=Chem-Systems/>
!rowspan=2|&nbsp;!!colspan=2|Pyrolysis!!colspan=2|Reformate
|-
!Standard<br />severity!!Medium <br />severity!!CCR!!SR
|-
|BTX content, wt % ||align=center|58||align=center|42||align=center|51||align=center|42
|-
|Benzene, wt % of BTX||align=center|48||align=center|44||align=center|17||align=center|14
|-
|Toluene, wt % of BTX||align=center|33||align=center|31||align=center|39||align=center|39
|-
|Xylenes, wt % of BTX||align=center|19||align=center|25||align=center|44||align=center|47
|-
|colspan=5|<span style="font-size:90%;">CCR = Continuous catalytic regenerative reformer<br />SR = Semi-regenerative catalytic reformer</span>
|}
|}
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 [[Petroleum naphtha|naphtha]] in a [[Petroleum refining processes|petroleum refinery]].<ref name=Chem-Systems/><ref name=IEA-Book>International Energy Agency (2006).[http://books.google.com/books?id=s0spIzYtrCAC&pg=PA414&lpg=PA414&dq=Benzene+toluene+xylene+production&source=bl&ots=ttMkz7Hl5x&sig=_01oioDJ3HXTVmXXnpA8bPdzf94&hl=en&sa=X&ei=wYFjT4uVIJCFsALapc2cCw&ved=0CIUBEOgBMAw4UA#v=onepage&q=Benzene%20toluene%20xylene%20production&f=false <i>Energy Technology Perspectives</i>]. 1st Edition. Organisation for Economic Co-operation and Development (OECD). Page 414. ISBN 08070-1556-3.</ref>
Catalytic reforming usually utilizes a feedstock naphtha that contains non-aromatic hydrocarbons with 6 to 11 or 12 [[carbon]] [[atom]]s and typically produces a '''''reformate''''' product containing C<sub>6</sub> to C<sub>8</sub> aromatics (benzene, toluene, xylenes) as well as [[Hydrocarbons|paraffins]] and heavier aromatics containing 9 to 11 or 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 C<sub>6</sub> to C<sub>8</sub> aromatics, heavier aromatics containing 9 to 11 or 12 carbon atoms, and non-aromatic cyclic hydrocarbons (naphthenes) containing 6 or more carbon atoms.<ref name=Chem-Systems/><ref name=IEA-Book/>
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 a 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.<ref name=Chem-Systems/>
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]]. Many different solvents are suitable, including [[sulfolane]] (C<sub>4</sub>H<sub>8</sub>O<sub>2</sub>S), [[furfural]] (C<sub>5</sub>H<sub>4</sub>O<sub>2</sub>), [[tetraethylene glycol]] (C<sub>8</sub>H<sub>18</sub>O<sub>5</sub>), [[dimethylsulfoxide]] (C<sub>2</sub>H<sub>6</sub>OS), and [[N-methyl-2-pyrrolidone]] (C<sub>5</sub>H<sub>9</sub>NO).
Below is a schematic flow diagram of one method, involving extractive distillation, for extraction of the BTX aromatics from a catalytic reformate:<ref name=BTX-Chain/>
{{Image|BTX-ReformateExtraction.png|center|535px|Schematic flow diagram for the extraction of BTX aromatics from a catalytic reformate.}}
==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:<ref name=BTX-Chain/>
{{Image|BTX Derivatives.png|center|680px|Diagram of the chain of petrochemicals derived from the BTX aromatics.}}
==References==
<references/>

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