Linear alkyl benzene
Encyclopedia
Linear alkylbenzene is a family of organic compound
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

s with the formula C6H5CnH2n+1. Typically, n lies between 10 and 16, although generally supplied as a tighter cut, such as C12-C15, C12-C13 and C10-C13, for detergent use. The CnH2n+1 chain is unbranched. They are sometimes called LAB's. They are mainly produced as intermediate in the production of surfactant
Surfactant
Surfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid...

s, for use in detergent
Detergent
A detergent is a surfactant or a mixture of surfactants with "cleaning properties in dilute solutions." In common usage, "detergent" refers to alkylbenzenesulfonates, a family of compounds that are similar to soap but are less affected by hard water...

. Since the 1960s resulted in LAB emerging as the dominant precursor of biodegradable detergents.

Production

Hydrotreated kerosene
Kerosene
Kerosene, sometimes spelled kerosine in scientific and industrial usage, also known as paraffin or paraffin oil in the United Kingdom, Hong Kong, Ireland and South Africa, is a combustible hydrocarbon liquid. The name is derived from Greek keros...

 is a typical feedstock for high purity linear paraffins, which are subsequently dehydrogenated to linear olefins:
CnH2n+2 → CnH2n + H2

Alternatively, ethylene can be oligomerized (partially polymerized) to produce linear alkenes. The resulting linear mono-olefins react with benzene
Benzene
Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....

 in the presence of a catalyst to produce the LABs. Hydrogen fluoride
Hydrogen fluoride
Hydrogen fluoride is a chemical compound with the formula HF. This colorless gas is the principal industrial source of fluorine, often in the aqueous form as hydrofluoric acid, and thus is the precursor to many important compounds including pharmaceuticals and polymers . HF is widely used in the...

 (HF) and aluminum chloride (AlCl3) are the two major catalysts for the alkylation of benzene with linear mono-olefins. The HF-based process is commercially dominant; however, the risk of releasing HF (a poisonous substance) into the environment became a concern particularly after the Clean Air Act
Clean Air Act
A Clean Air Act is one of a number of pieces of legislation relating to the reduction of airborne contaminants, smog and air pollution in general. The use by governments to enforce clean air standards has contributed to an improvement in human health and longer life spans...

 Amendment. In 1995, a solid catalyst system (the DETAL process) became available. The process eliminates catalyst neutralization and HF disposal. Consequently, most LAB plants built since then have utilized this process.

Production details

Given the large scale applications of LAB-derived detergents, a variety routes have been developed to produce linear alkylbenzenes:
  • The HF/n-paraffins process involving dehydrogenation of n-paraffins to olefins, and subsequent reaction with benzene using hydrogen fluoride as catalyst. This process accounts for the majority of the installed LAB production in the world. It includes a PACOL Stage where n-paraffins are converted to mono-olefins (typically internal mono-olefins), a DEFINE Unit whose primary function is to convert residual diolefins to mono-olefins, a PEP Unit which is essentially an aromatic removal unit - introduced before the alkylation step to improve LAB yield and quality, an alkylation step where mono-olefins, both internal and alpha olefins, are reacted with benzene to produce LAB in the presence of HF catalyst.
  • The DETAL process involving dehydrogenation of n-paraffins to olefins, and subsequent reaction with benzene using a fixed bead catalyst. This is newer technology and has several of the stages depicted in the HF/n-paraffins process, but it is principally different in the benzene alkylation step, during which a solid-state catalyst is employed. There is a developing transalkylation
    Transalkylation
    Transalkylation is a chemical reaction of transfer of an alkyl group from one organic compound to another. Zeolite catalysts are often used. The reaction is widely used in the petrochemical industry to manufacture p-xylene, styrene, and other aromatic compounds....

     (TA) stage to the Detal process wherein any higher alkylated benzenes (HAB) are contacted with additional benzene over a transalkylation catalyst.
  • The Friedel-Crafts alkylation process involves chlorination of n-paraffins to monochloroparaffins followed by alkylation of benzene using aluminum chloride (AlCl3) catalyst. This method is one of the oldest commercial routes to LABs.


Each process generates LAB products with distinct features. Important product characteristics include the bromine index, sulfonatability, amount of 2-phenyl isomers (2-phenylalkane), the tetralin content, amount of non-alkylbenzene components, and the linearity of the product.

The production of n-paraffins often occurs as part of an integrated LAB plant where the producers start from kerosene as raw material. The UOP
UOP LLC
UOP LLC, formerly known as Universal Oil Products, is a multi-national company developing and delivering technology to the petroleum refining, gas processing, petrochemical production, and major manufacturing industries....

 process for producing normal paraffin includes a kerosene prefractionation unit, a hydrotreating unit and a Molex unit. The ExxonMobil Chemical technology includes a recovery process and can produce LAB grade n-paraffins from most medium to low sulfur kerosene without the use of a hydrotreater stage upstream. A desulfurization process is needed to reduce the sulfur content of some n-paraffins.

Applications of LABs

Linear alkylbenzene is sulfonated to produce linear alkylbenzene sulfonate (LAS), a biodegradable surfactant
Surfactant
Surfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid...

. LAS replaced branched dodecylbenzene sulfonates, which were phased out because they biodegrade more slowly.

Niche uses

LAB is currently used as a liquid scintillator
Scintillator
A scintillator is a special material, which exhibits scintillation—the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, i.e., reemit the absorbed energy in the form of light...

 in neutrino detectors (SNO+
SNO+
SNO+ is an underground physics experiment under construction that makes use of the equipment already installed underground for the former Sudbury Neutrino Observatory experiment at SNOLAB...

 for example
) due to of its good optical transparency (~20 m), its high light yield, its low amount of radioactive impurities, and its high flash point
Flash point
The flash point of a volatile material is the lowest temperature at which it can vaporize to form an ignitable mixture in air. Measuring a flash point requires an ignition source...

 (140 °C) which makes safe handling easier. The material performs well in deep underwater environments. One study suggested LAB as a suitable material to be employed in a Secret Neutrino Interactions Finder (SNIF), a type of antineutrino detector designed to detect the presence of nuclear reactors at distances of between 100 and 500 km.

Environmental considerations

LAB has been subject to concern about its effect on the environment and human health. European Council Regulation (EC) 1488/94 led to it being extensively evaluated. The life-cycle analysis considered the emissions and resulting environmental and human exposures. Following the exposure assessment, the environmental risk characterization for each protection target in the aquatic, terrestrial and soil compartment was determined. For human health the scenarios for occupational exposure, consumer exposure and human exposure indirectly via the environment have been examined and the possible risks identified.

The report concludes that there are no concerns for the environment or human health. There is no need for further testing or risk reduction measures beyond those currently practiced. LAB was therefore de-classified and was removed from Annex 1 in the 28th ATP (Directive 2001/59).

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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