The behavior of aromatics substituted by a long aliphatic chain, such as are liable to be present in vacuum distillates used to replace naphtha during the supplying of steam cracking units, was examined in a micropilot plant at 800 °C in the presence of n-decane. The decomposition of dodecylbenzene, tetradecylphenanthrene, octadecylnaphthalene, and docosylbenzene, when available in sufficient quantity, led to a better assessment of the contribution to steam cracking of the different parts of this type of molecule. The simplified reaction mechanism of the thermal decomposition of dodecylbenzene leads to six principal

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In order to determine the behavior of cycloparaffins in steam cracking reactions, a study of the thermal decomposition of cyclohexane in the presence of n-decane has been carried out at ca. 810 °C by using the technique of plug flow reactor. Cyclohexane chiefly decomposes into ethylene, hydrogen, 1,3butadiene, and small amounts of cyclohexene. We propose a primary mechanism of the decomposition of cyclohexane initiated by n-decane. This mechanism leads to three main primary stoichiometries which account for the whole range of reaction products.

The Permian-Triassic Khuff Formation crops out in central Saudi Arabia along a N-S belt, some 1,200 km in length. It is 171.4 m (562.2 ft) thick in the type section and divided into five members; from oldest to youngest: Ash Shiqqah (formerly Unayzah member of the Khuff Formation), Huqayl, Duhaysan, Midhnab and Khartam. The base of the Khuff Formation is recognised as a regional unconformity (Pre-Khuff Unconformity), and the top of the formation is defined by the conformable contact with the overlying Sudair Shale. The Ash Shiqqah Member is tentatively dated as ?Middle Permian ?Capitanian (?Midian) based on the presence of the fusulinids Monodiexodina kattaensis and Reichelina sp. The Huqayl Member is tentatively dated as ?Late Permian ?Wuchiapingian (?Dzhulfian) based on an assemblage of smaller foraminifers dominated by Pseudomidiella cf. labensis, Earlandia? spp. and Neodiscus aff. qinglongensis. The Duhaysan Member is dated as Late Permian (Wuchiapingian-Changhsingian) based on Hemigordius baoqingensis, Graecodiscus cf. kotlyarae, “Dentalina” hoi, and Colaniella cf. minuta. The sMidhnab Member is dated as Changhsingian (Dorashamian) based on Paradagmarita sp. and “Glomospirella spirillinoides” and the disappearance of the genera Nankinella and Globivalvulina. Within the continental facies in the upper part of the Midhnab Member, incised channels facies yielded the Late Permian Midhnab Flora. The Lower Khartam Member is also dated as latest Permian (Dorashamian) based on the presence of several species of Paradagmarita and “Nodosaria” dzhulfensis in the lowest beds of the member, and the ostracods Paraparchites spp., Knoxiella spp. and Kloedenellitina sp. throughout the Lower Khartam Member. The Upper Khartam Member is assigned to an Early Triassic (‘Scythian’) age based on the occurrence of the characteristic annelid Spirorbis phlyctaena. The Khuff Formation, in central Saudi Arabian outcrops, consists of four regional depositional sequences (DS PKh, DS PKm, DS PKk and DS TrS), each containing a maximum flooding interval (MFI, with the same designation). The oldest sequence DS PKh (named after Permian-Khuff-Huqayl) consists of the Ash Shiqqah and overlying Huqayl members. The basal sequence boundary corresponds to the Pre-Khuff Unconformity (PKU) and represents the onset of the first Permian flooding event recorded in the outcrops of Saudi Arabia. The massive gypsum, gypsiferous claystone, and solution breccias in the Ash Shiqqah Member are correlated to the subsurface Khuff-D Anhydrite. The MFI PKh is positioned in the basal part of the Huqayl Member, and is followed by the regressive evaporitic palaeoenvironments of the Huqayl Member. The DS PKm (named after Permian-Khuff-Midhnab) starts with the subtidal to littoral deposits of the Duhaysan Member, over an erosive surface upon DS PKh; and ends with the regressive supratidal to continental deposits at the upper part of the Midhnab Member. The MFI PKm is located at the base of the Midhnab Member, where limestones yielded an abundant marine fauna including cephalopods and brachiopods. The terminal Permian DS PKk (Permian-Khuff-Khartam) corresponds to the Lower Khartam Member. The basal SB PKk is marked by a return to marine subtidal conditions after the continental break at the end of DS PKm. The MFI PKk is characterised by marine fauna including abundant Permian ostracods, bactritids, and locally cephalopods. The DS TrS (named after the Sudair Shale Formation) starts with the littoral, tidal to intertidal deposits of the Early Triassic Upper Khartam Member of the Khuff Formation, and ends with the closed basin, clayey to evaporitic rocks of the Early Triassic Sudair Shale.

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