Alkylation

Abstract

AbstractThe alkylation described in this article is the substitution of a hydrogen atom bonded to the carbon atom of a paraffin or aromatic ring by an alkyl group. The alkylations of nitrogen, oxygen, and sulfur are described in separate articles. Significant technological development has been made in the area of alkylation in recent years. Environmental concerns associated with mineral acid catalysts have encouraged process changes and the development of solid‐bed alkylation processes. The application of heterogeneous catalysts, especially zeolite catalysts, has led to new alkylation technologies. More new technologies are expected to be commercialized as research efforts to develop environmentally acceptable, economical technologies continue. Paraffin alkylation refers to the addition reaction of an isoparaffin and an olefin. The desired product is a higher molecular weight paraffin that exhibits a greater degree of branching than either of the reactants. The principal industrial application of paraffin alkylation is in the production of premium quality fuels for spark‐ignition engines. Future gasoline specifications will continue to favor the clean‐burning characteristics and the low emissions typical of alkylate. Catalytic alkylation of paraffins is the basis of all processes in commercial use. The catalysts used are strong liquid acids, either sulfuric acid (H2SO4) or hydrofluoric acid (HF). Although other isoparaffins can be alkylated, isobutane is the only paraffin commonly used as a commercial feedstock. Butylenes are the primary olefin feedstock of alkylation and produce a product high in trimethylpentanes. Propylene alkylation produces a product rich in dimethylpentane and has a research octane in the range of 89–92. Amylenes (C‐5 monoolefins) produce alkylates with a research octane in the range of 90–93. Most of the industrially important alkyl aromatics used for petrochemical intermediates are produced by alkylating benzene with monoolefins, eg, ethylene, propylene, and olefins with 10–18 carbons. Among industrial applications, ethylbenzene, primarily produced by the alkylation of benzene with ethylene, is used as an intermediate for the manufacture of styrene monomer. Cumene demand has risen at an average rate of 2–3%(year since 1970. Cymene can be produced by alkylation of toluene with propylene. The synthetic detergent industry has become one of the largest chemical process industries. The most recent advance in detergent alkylation is the development of a solid catalyst system. The main application of xylene isomers, primarilyp‐ ando‐xylenes, is in the manufacture of plasticizers and polyester fibers and resins. The alkylation of polynuclear aromatics with olefins and olefin‐producing reagents is effected by acid catalysts. Improvements in aromatic alkylation technology are expected to continue into the future. A new alkylation process called Alkymax was introduced by UOP in 1990. The alkylate formed has a high octane value and can typically boost the octane of the gasoline pool by 0.5 RON. Other alkylations are the alkylation of phenol, derivatives of which are used as raw materials for the production of resins, herbicides, insecticides, and other chemicals, and alkylation of aromatic amines and pyridines. Commercially important aromatic amines are aniline, toluidine, phenylenediamines, and toluenediamines. In industrial applications, specialized procedures are required to ensure the safe handling of the materials described. Replacing these materials with solid acid catalysts will become more important in the future. The solid acid catalysts themselves present a disposal problem that favors the regenerable catalysts or recycling procedures.