Most ethyl is manufactured by the alkylation of benzene with ethylene. Small amounts are still obtained in several countries from superfractionation of C₈ aromatics cuts.

Two commercial processes for the ethylation of benzene have developed alongside one another:
1. Liquid-phase ethylation with Friedel-Crafts catalysts such as AlCl₃, BF₃, FeCl₃, ZrCl₄, SnCl₄, H₃PO₄, or alkaline earth phosphates (e.g., BASF, CdF Chimie (now Orkern), Dow, Monsanto, or UCC process).
2. Gas-phase ethylation with H₃PO₄ carrier catalysts or Al silicates (e.g. Koppers, Phillips, and UOP process) or with zeolites (new Mobil-Badger or ABB Lummus Crest/UOP process), or with BF₃/γ-Al₂O₃ (UOP process).

To 1:

The alkylation of benzene with ethylene is carried out at 85-95 °C and slight pressure (1-7 bar):

A 0.6:1 mixture of ethylene and benzene is fed continuously into the bottom of an alkylation column, while the catalyst, generally AlCl₃, is introduced periodically at the head of the column. At the same time, a little ethyl chloride is added a as Dromoter; under the reaction conditions, it reacts with benzene to form ethyl-benzene. The coproduct HCl acts as a cocatalyst for AlCl₃. The actual catalytically active system is formed from AlCl₃ and ethylbenzene as the particularly strong addition product HAlCl₄^.nC₆H₅C₂H₅. The gradual decrease in catalytic activity can be counteracted by partially removing the catalyst and replacing it with fresh catalyst. About 1 kg AlCl₃ is required per 100 kg ethylbenzene.

The selectivity is enhanced by limiting the benzene conversion to approximately 52-55% and having a high benzene/ethylene ratio, since only an ethylene deficiency prevents further alkylation to diethyl- and polyethylbenzenes. Higher ethylbenzenes are recycled to the reaction where they displace the alkylation equilibrium towards ethylbenzene and yield additional monoethyl product by transalkylation with benzene. Multiethylated benzenes can also be dealkylated in a special reaction with AlCl₃ at 200°C before being recycled to the reaction. In this way, an ethylbenzene selectivity of 94-96% (based on C₆H₆) and of 96-97% (based on C₂H₄) can be attained.

The reaction mixture, consisting of about 45% benzene, 37% ethylbenzene, 15% diethylbenzenes, 2% polyethylbenzenes, and 1% tarry residues, is separated into its components in a four-column distillation unit.

A more recent variation of benzene ethylation in the presence of AlCl₃ was developed by Monsanto-Lummus. Using a lower AlCl₃  concentration than the classical processes, it is possible to conduct the alkylation in a single-phase system at temperatures of 140-200°C and 3-10 bar with a high selectivity to ethyl-benzene (ca. 99%). The AlCl₃  consumption decreases to 0.25 kg per 1000 kg ethylbenzene. An important prerequisite is, however, the controlled introduction of ethylene in amounts such that it is never present in excess. This very economical process is operated in several plants throughout the world with a total capacity of about 3.1×10⁶ tonnes per year.

The necessity, in the AlCl₃-catalyzed liquid-phase ethylation of benzene, of ensuring that numerous parts of the plant are corrosion resistant, of separating the suspended or dissolved catalyst by aqueous and alkaline washes, and of drying the benzene to be recycled led to the development of gas-phase alkylations on solid catalysts. However, in a new development from CdF Chimie-Technip (now Orkem) already in use in several plants, the customary washing of the reaction product to remove the catalyst and the subsequent neutralization can be replaced by anhydrous treatment of the alkylation mixture with gaseous ammonia.

To 2:

The gas-phase ethylation of benzene has been particularly successful in the USA. Benzene is reacted with ethylene at about 300°C and 40-65 bar over acidic catalysts such as Al₂O₃^.SiO₂ (Koppers) or H₃PO₄/SiO₂ (UOP). To avoid further alkylation at the high reaction temperature of the gas-phase process, the mole ratio of ethylene to benzene must be adjusted to 0.2:1. The catalysts used are not capable of dealkylating recycled oligoethylbenzenes.

In the Mobil-Badger process for the ethylation of benzene, the catalyst is a crystalline aluminium silicate in the form of a modified zeolite (ZSM5). It is used at 435-450°C and 14-28 bar. The catalyst is also suitable for transalkylations. However, it must be regenerated after 2-4 weeks of operation, so the reactor section in the plant must be in duplicate. At an 85% conversion, ethylbenzene selectivities of 98% (based on C₆H₆) and 99% (based on C₂H₄) can be reached. The first 500000 tonne-per-year plant was brought on-line by American Hoechst (now Huntsman) in 1980. Since then 21 plants have been licensed worldwide to produce more than 6.5×10⁶ tonnes annually. Production capacity of individual plants can reach 800000 tonnes per year. In a similar Mobil process using an H₃PO₄/ Mg²⁺-modified ZSM5 zeolite, a shape-selective ethylation (up to 99%) of toluene top-ethyltoluene can be done at, e. g., 425 °C and 7 bar. In 1982, MobiVHoechst started up a 16000 tonne-per-year plant in the USA. n-Ethyltoluene is dehydrogenated to give p-methylstyrene, a monomer and comonomer analogous to styrene, but with special advantages including higher thermal stability (higher glass temperature).

In a new process developed by Mobil for the ethylation of benzene or toluene on modified ZSM5 zeolites, an aqueous ethanol solution can also be used directly without the need for expensive extraction or distillation.

Another zeolite-catalyzed benzene ethylation using a fixed-bed, liquid-phase technology has been operated by ABB Lummus Crest/UOP in a 220000 tonne-per-year plant in Japan since 1990. Since then, other plants have been started up or are being planned.