Coke characteristics in relation to the colloidal matter of petroleum for thermal processes

The purpose of this work is to research the characteristics of the production of coke in thermal and hydrothermal cracking from residual oils and their deasphalted oils using ethyl acetate, because it allows the elimination of both resins and asphaltenes (colloidal matter) from the parent oil in only one step. This improves the deasphalted oil as coke precursors and basic nitrogen compounds present in the resin fraction are practically eliminated. A 104 ml batch autoclave reactor with a cooling system was used for the thermal and hydrothermal cracking experiments. This reactor can withstand temperatures of up to 500°C, pressures of 500 bar and a rocking velocity of 1 Hz. The influence of the temperature was investigated at 400, 425 and 450°C and at 0, 20, 40, 80, 120 min. In these experiments, four types of oils were studied: Kuwait and Laguna residua and their deasphalted oils. Kinetic measurements of thermal cracking show a faster cracking for deasphalted oils. The yield of product oil boiling under 200°C is higher for the deasphalted oil compared with the original feeds. Coke formation shows an opposite trend. Asphaltenes' formation decreases with time and temperature due to this latter trend. Molecular weight, sulphur and metals content as well as gas formation are the lowest at 68 bar hydrogen (20'C). Therefore, all the experiments were carried out at this pressure. The H/C values for the products of the thermal cracking of untreated oils are higher than those corresponding to product oils from thermal hydrocracking. The opposite effect is observed with deasphalted oil. That behaviour indicates that without the colloidal matter, hydrogen is used more for conversion reactions or that in presence of such a matter it first reacts with the colloids. Contribution to coke aromaticity from asphaltenes and resins is lower than that from the aromatics in the original oil- As resins contribute little to coking this indicates that asphaltenes are formed of small polynuclear aromatics. Coke aromaticity from thermal hydrocracking is higher than that from thermal cracking, because only components with strong tendency to form coke do so. Studies employing hot stage microscopy confirm the above analysis. So, the formation of coke in H2 occurs later than that at the same conditions in argon. Besides that, the deasphalted oils, higher in aromatics produce more anisotropic coke and more rapidly than the oils containing asphaltenes and resins, which in turn produce more isotropic coke. © 1994, Taylor & Francis Group, LLC. All rights reserved.