In the
petroleum refining
An oil refinery or petroleum refinery is an industrial process plant where petroleum (crude oil) is transformed and refined into useful products such as gasoline (petrol), diesel fuel, asphalt base, fuel oils, heating oil, kerosene, liquefi ...
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 so ...
industries, the initialism BTX refers to mixtures of
benzene
Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms ...
,
toluene
Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon. It is a colorless, water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group (CH3) a ...
, and the three
xylene isomers, all of which are
aromatic hydrocarbon
Aromatic compounds, also known as "mono- and polycyclic aromatic hydrocarbons", are organic compounds containing one or more aromatic rings. The parent member of aromatic compounds is benzene. The word "aromatic" originates from the past groupin ...
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
Ethylbenzene is an organic compound with the formula . It is a highly flammable, colorless liquid with an odor similar to that of gasoline. This monocyclic aromatic hydrocarbon is important in the petrochemical industry as an reaction intermedia ...
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 (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
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 refinery naphthas distilled from crude oil (typically having low octane ratings) into high-octane liquid products called reformates, which are premium blending stocks for high-oc ...
of
naphtha
Naphtha ( or ) is a flammable liquid hydrocarbon mixture.
Mixtures labelled ''naphtha'' have been produced from natural gas condensates, petroleum distillates, and the distillation of coal tar and peat. In different industries and regions ' ...
in a
petroleum refinery
An oil refinery or petroleum refinery is an industrial process plant where petroleum (crude oil) is transformed and refined into useful products such as gasoline (petrol), diesel fuel, asphalt base, fuel oils, heating oil, kerosene, liquefie ...
.
[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 hydrophobic, and their odors are usually weak or ...
s with 6 to 12 carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon mak ...
atom
Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons.
Every solid, liquid, gas, ...
s and typically produces a ''reformate'' product containing C6 to C8 aromatics (benzene, toluene, xylenes) as well as paraffin Paraffin may refer to:
Substances
* Paraffin wax, a white or colorless soft solid that is used as a lubricant and for other applications
* Liquid paraffin (drug), a very highly refined mineral oil used in cosmetics and for medical purposes
* Alkan ...
s 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 gasoline or Pygas is a naphtha-range product with high aromatics content. It is a by-product of high temperature naphtha cracking during ethylene and propylene production. Also, it is a high octane number mixture that contains aromati ...
'', ''pyrolysis gas
Pyrolysis gasoline or Pygas is a naphtha-range product with high aromatics content. It is a by-product of high temperature naphtha cracking during ethylene and propylene production. Also, it is a high octane number mixture that contains aromati ...
'' or ''pygas
Pyrolysis gasoline or Pygas is a naphtha-range product with high aromatics content. It is a by-product of high temperature naphtha cracking during ethylene and propylene production. Also, it is a high octane number mixture that contains aromati ...
''. The pyrolysis gasoline typically consists of C6 to C8 aromatics, heavier aromatics containing 9 to 12 carbon atoms, and non-aromatic cyclic hydrocarbon
A cyclic compound (or ring compound) is a term for a compound in the field of chemistry in which one or more series of atoms in the compound is connected to form a ring. Rings may vary in size from three to many atoms, and include examples where ...
s (naphthenes
In organic chemistry, the cycloalkanes (also called naphthenes, but distinct from naphthalene) are the monocyclic saturated hydrocarbons. In other words, a cycloalkane consists only of hydrogen and carbon atoms arranged in a structure containing ...
) 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 (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
either for liquid-liquid extraction or extractive distillation
Extractive distillation is defined as distillation in the presence of a miscible, high-boiling, relatively non-volatile component, the solvent, that forms no azeotrope with the other components in the mixture. The method is used for mixtures h ...
. Many different solvents are suitable, including sulfolane (C4H8O2S), furfural (C5H4O2), tetraethylene glycol
Polyethylene glycol (PEG; ) is a polyether compound derived from petroleum with many applications, from industrial manufacturing to medicine. PEG is also known as polyethylene oxide (PEO) or polyoxyethylene (POE), depending on its molecular we ...
(C8H18O5), dimethylsulfoxide
Dimethyl sulfoxide (DMSO) is an organosulfur compound with the formula ( CH3)2. This colorless liquid is the sulfoxide most widely used commercially. It is an important polar aprotic solvent that dissolves both polar and nonpolar compounds and ...
(C2H6OS), and N-methyl-2-pyrrolidone
''N''-Methyl-2-pyrrolidone (NMP) is an organic compound consisting of a 5-membered lactam. It is a colorless liquid, although impure samples can appear yellow. It is miscible with water and with most common organic solvents. It also belongs to t ...
(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