dehydrocyclisatie

Dehydrocyclization (British spelling dehydrocyclisation) is a chemical reaction in organic chemistry in which a molecule containing a linear or branched hydrocarbon chain undergoes intramolecular cyclization accompanied by removal of hydrogen, producing a cyclic product. The resulting compound is typically a cycloalkene or, upon further dehydrogenation, an aromatic hydrocarbon. The reaction is endothermic and is favored at high temperatures and in the presence of appropriate catalysts.

Mechanistically, dehydrocyclization proceeds by formation of a cyclized intermediate, such as a cycloalkyl species, followed by dehydrogenation steps that restore unsaturation and often lead to aromatization. In practice, many dehydrocyclizations occur in petrochemical processing as part of catalytic reforming and related upgrading of paraffinic feeds. The process can convert linear hydrocarbons or partially unsaturated precursors into more condensed, aromatic-rich products.

Catalysts used to promote dehydrocyclization include acidic solid catalysts such as zeolites (for example ZSM-5, Beta) and metal-containing systems (such as Pt, Ni, or other noble metals supported on alumina or silica). These catalysts facilitate the cyclization step by providing acid- or surface-activated sites and promote dehydrogenation on metal sites. Operating conditions typically involve elevated temperatures (roughly 450–550 °C or higher) and hydrogen controls that balance dehydrogenation rate and coke formation; reactor design often emphasizes the removal of deposited carbon.

Applications include the production of aromatics (benzene, toluene, xylenes) from aliphatic feeds, as part of catalytic reforming and related refinery processes. Safety and performance depend on feed composition, catalyst lifetime, and coke management.