Patent GB-579766-A (GB)
Title: Aromatization process
IPC: C07C5/367
Filed: 1943-08-18
Abstract: Aromatic hydrocarbons are produced by subjecting hydroaromatic naphthenes or hydrocarbon fractions containing them and boiling in the gasoline boiling range to catalytic dehydrogenation in a substantially continuous manner in the presence of at least 3 mols. of hydrogen per mol. of hydrocarbon feed, a molecular excess with respect to hydroaromatic naphthenes of an added olefin, and with a catalyst comprising a sulphide of a metal of the iron group and tungsten sulphide under conditions chosen within the following limits to give dehydrogenation of said naphthenes and hydrogenation of said olefin: temperature 425-525 DEG  C., pressure 5-75 atm., and liquid hourly space velocity 0.3-5.  Naphthenic fractions containing hydroaromatic naphthenes, either narrow boiling, e.g. 205-230 DEG F., or boiling up to 400-450 DEG  F. may be treated to increase their octane number or relatively pure hydroaromatics or narrow fractions containing them may be converted to the corresponding aromatic hydrocarbons.  Thus, toluene is obtained from a 200-250 DEG  F. fraction of straight-run gasoline, benzene from a 165-185 DEG  F. fraction, and xylene from a 245-270 DEG  F.  Such substantially saturated fractions are treated in the presence of added olefins, preferably normally liquid olefins of branched chain character, which may be added as cracked or reformed gasolines or their fractions which are desirably highly unsaturated, or as olefin polymers such as butene dimers. Olefinic fractions with an appreciable aromatic content are useful and, where pure aromatics are sought, containing olefins separable therefrom by fractionation.  The concentration of olefins is usually below 3 mols. per mol. of hydroaromatic naphthene. The molar ratio may be adjusted between 1.8 and 2.8 : 1 so that there is neither a net consumption nor production of hydrogen.  If the reacted olefins and hydroaromatic naphthenes are in a mol. ratio of about 1.8 : 1, the endothermic heat of dehydrogenation balances the exothermic heat of hydrogenation.  The catalyst contains iron, cobalt and/or nickel sulphide mixed with tungsten sulphide, generally in a mol. ratio of about 0.4-2.5 : 1.  A preferred catalyst contains nickel and tungsten sulphides in a mol. ratio of about 2 : 1.  It may be prepared by dry mixing nickel carbonate and tungstic acid, treating with hot hydrogen sulphide and pelleting.  Preferably, tungstic acid is dissolved in aqueous ammonia and treated with hydrogen sulphide under pressure at above about 35 DEG  C. to give ammonium thiotungstate, a nickel salt solution added, and then sulphuric acid to a pH of 1-2.  The precipitated sulphides are dried, heated to about 250-450 DEG  C. in a stream of hydrogen with or without hydrogen sulphide, and pelleted.  Such a catalyst can be regenerated in situ at the reaction temperature with sulphur dioxide. The molar ratio of hydrogen to hydrocarbons may be up to 30 : 1, but is usually 3-12 : 1.  After starting, hydrogen is usually produced in the process and continuously recycled, sufficient being withdrawn, and, if desired, returned after removal of diluent hydrocarbons, to maintain the hydrogen content above 80 per cent.  The hydrogen sulphide usually present activates the catalyst.  Although the catalyst may be circulated as a powder, it is generally used in a fixed bed, for example in a converter of the adiabatic type.  In some cases, the olefin may be added at successive points along the length of the reaction zone.  The process may be combined with cracking, reforming, isomerization and other processes.  Thus, a naphthenic petroleum may be fractionated to give a light and heavy naphtha, the latter cracked, a light naphtha separated and this processed with the straight naphtha, or a heavy naphtha is cracked, the light cracked naphtha subjected to iso-forming and then processed with a straight naphthenic naphtha.  A blend of straight naphthenic distillate and an olefinic distillate may be processed as described, aromatics separated and the remainder isomerized.  The olefins may be produced in a naphthenic fraction by light cracking, the recycled hydrogen-containing gas being used to cool the cracked product to the aromatization temperature. Examples describe the treatment of various blends of naphthenic fractions, including methyl cyclohexane fractions, with olefinic fractions or olefin polymers such as butene dimers.