In the
petroleum refining and
petrochemical
Petrochemicals (sometimes abbreviated as petchems) are the chemical products obtained from petroleum by refining. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable s ...
industries, the initialism BTX refers to mixtures of
benzene
Benzene is an Organic compound, organic chemical compound with the Chemical formula#Molecular formula, molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar hexagonal Ring (chemistry), ring with one hyd ...
,
toluene
Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon with the chemical formula , often abbreviated as , where Ph stands for the phenyl group. It is a colorless, water
Water is an inorganic compound with the c ...
, and the three
xylene isomers, all of which are
aromatic hydrocarbon
Aromatic compounds or arenes are organic compounds "with a chemistry typified by benzene" and "cyclically conjugated."
The word "aromatic" originates from the past grouping of molecules based on odor, before their general chemical properties were ...
s. 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.
[The Future of Benzene and Para-Xylene after Unprecedented Growth In 2010]
. From a ChemSystems report in 2011.
Toluene is also a valuable petrochemical for use as a
solvent
A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...
and intermediate in
chemical manufacturing processes and as a
high octane gasoline component.
[The BTX Chain: Benzene, Toluene, Xylene]
Chapter 4 of the DOE's Office of Energy Efficiency and Renewable Energy (EERE) report entitle
"Energy and Environmental Profile of the U.S. Chemical Industry" of May 2000.
[Use of Process Analytics in Aromatics (BTX and phenol) production plants]
Case Study, August 2008. (scroll down to "Aromatics" section.[Benzene/Toluene]
. Introduction to a ChemSystems report, 2009.[10.6 Aromatics]
Online Italia
''Encyclopedia of Hydrocarbons''
Istituto della Enciclopedia Italiana, Volume II, 2006, pages 603-605.
Properties of BTX hydrocarbons
The table below lists some of the properties of the BTX aromatic hydrocarbons, all of which are liquids at typical room conditions:
Production of BTX hydrocarbons
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
Catalytic reforming is a chemical process used to convert petroleum naphtha, naphthas from crude oil into liquid products called reformates, which are premium "blending stocks" for high-octane gasoline. The process converts low-octane linear hydr ...
of
naphtha
Naphtha (, recorded as less common or nonstandard in all dictionaries: ) is a flammable liquid hydrocarbon mixture. Generally, it is a fraction of crude oil, but it can also be produced from natural-gas condensates, petroleum distillates, and ...
in a
petroleum refinery.
[International Energy Agency (2006]
''Energy Technology Perspectives''
1st Edition. Organisation for Economic Co-operation and Development (OECD). Page 414. .
Catalytic reforming usually utilizes a feedstock naphtha that contains non-aromatic hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and Hydrophobe, hydrophobic; their odor is usually fain ...
s with 6 to 12 carbon
Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...
atom
Atoms are the basic particles of the chemical elements. An atom consists of a atomic nucleus, nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished fr ...
s 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.[
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.][
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
A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...
either for liquid-liquid extraction or extractive distillation. Many different solvents are suitable, including sulfolane
Sulfolane (also tetramethylene sulfone, IUPAC nomenclature, systematic name: 1λ6-thiolane-1,1-dione) is an organosulfur compound, formally a cyclic sulfone, with the formula . It is a colorless liquid commonly used in the chemical industry as a s ...
(C4H8O2S), furfural (C5H4O2), tetraethylene glycol (C8H18O5), dimethylsulfoxide (C2H6OS), and N-methyl-2-pyrrolidone (C5H9NO).
Below is a schematic flow diagram of one method, involving extractive distillation, for extraction of the 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:[
]
See also
*
*
*
External links
* (see Chapter 15 availabl
here
.
* Available a
Google Books
Benzene Supply Trends and Proposed Method For Enhanced Recovery
David Netzer. Presented to 2005 World Petrochemical Conference, March 2005, Houston, Texas, U.S.A.
James A. Johnson, Feb. 12, 2009.
''Para'' – xylene Production
From the website of GTC Technology, Houston, Texas.
References
{{Reflist
Chemical mixtures
Petroleum technology
Alkylbenzenes