&kromatic hydrocarbons have been lcnoivn to be byproducts of cracking processes; from a study of the mechanism of their formation by cracking, it was hoped to develop a method for their industrial production from petroleum or petroleum fractions. The present four papers show that the high temperature aromatization of hydrocarbons proceeds largely through degradation to small unsaturated units, outstanding among them butadiene, and through subsequent "diene reactions" leading to hydroaromatic hydrocarbons which are eventually dehydrogenated to the aromatics. For naphthenic charging atocks, direct thermal dehydrogenation represents a second source of aromatic hydrocarbons.A process is described which converts a nonaromatic (or only partly aromatic) charging stock intoliquidand gaseous products. The gases are predominantly unsaturated (ethyl-HE cyclization of paraffinic hydrocarbons into aromatics, T discovered over a decade ago (10, 21, 24-27) has been described (16, 68, 36, 36, 39) as a three-step process: dehydrogenation of the paraffin hydrocarbon t o a corresponding olefin, cycloisomerization of this olefin to a hexahydrobenzene, and simultaneous removal of the supernumerary hydrogen atoms from the latter to form the aromatic hydrocarbon. This process is catalyzed by various oxides which are used either in the pure state or supported on carriers such as alumina.This reaction mechanism, however, cannot account for the formation of aromatics by thermal cracking in empty or packed tubes (9, 31). Two alternative mechanisms have been proposed. Both suggest that in the first stage of the reaction the starting material undergoes considerable breakdown, followed by resynthesis. Groll (9) assumes that the intermediate is acetylene or, rather, a diradical form of that hydrocarbon, whereas other workers (1.2, 30, 47) believe this intermediate is butadiene. The latter is known to combine with other unsaturated hydrocarbons-for example, with ethylene to form cyclohexene (19), or with a second butadiene molecule to form vinylcyclohexene (2). This reaction is an extension of the classical Diels-Alder synthesis.The present paper describes the second type of aromatization The distinction between them is that in the first type the starting material and the end product have the same number of carbon atoms. In the present work any hydrocarbonaceous starting material will result in the complete series of aromatics, from benzene to the most complicated polycyclic system (53, 46, 46, 46).Under the following conditions a pure, or almost pure, aromatic liquid product can be obtained from a given petroleum fraction or other hydrocarbonaceous raw material: temperature, 630 ' to 680" C.; pressure, 1 to 3 atmospheres; space velocity, 0.05 to 0.5 (litera of liquid charging stock per liter catalyst volume per ene, propylene, butylene, isobu tylene, and some butadiene), and the liquid product is more than 90%, and up to 98%, of aromatic nature and largely free of sulfur and nitrogen, even in cases in which the charging stock contained organic...