Linear alkylbenzene

Production

Hydrotreated kerosene is a typical feedstock for high purity linear paraffins (n-paraffins), which are subsequently dehydrogenated to linear olefins:

C_nH_2n+2 → C_nH_2n + H₂

Alternatively, ethylene can be oligomerized (partially polymerized) to produce linear alkenes. The resulting linear mono-olefins react with benzene in the presence of a catalyst to produce the LABs. Hydrogen fluoride (HF) and aluminium 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 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 (paraffin conversion to olefins) 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 bed 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 (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 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.

Farabi Petrochemicals, Nirma are one of the manufacturers commercially produce LAB in large scale.