The selective removal of nitrogen-containing compounds from oil and oil fractions is of interest because of the potential deleterious impact of such compounds on products and processes. Problems caused by nitrogen-containing compounds include gum formation, acid catalyst inhibition and deactivation, acid−base pair-related corrosion, and metal complexation. A brief overview of the classes of nitrogen compounds found in oil is provided. The review of processes to remove nitrogen from oil emphasizes studies that investigated denitrogenation of industrial feedstocks, such as refinery fractions, heavy oils, and bitumens. The main topics covered are hydrotreating, liquid−liquid phase partitioning, solvent deasphalting, adsorption, chemical conversion followed by separation, and microbial conversion. Chemical conversion processes include oxidative denitrogenation, N-alkylation, complexation with metal salts, and conversion in high-temperature water. There are many processes for denitrogenation by separation of the nitrogen-rich products from oil without removing the nitrogen group from the nitrogencontaining compounds. As a consequence, most of these processes are viable mainly for removal of nitrogen from low-nitrogencontent oils, typically with <0.1 wt % N. At present, hydrodenitrogenation appears to be the only industrially viable process for nitrogen removal from oils with high nitrogen content.

The reactivity and reactions of asphaltenes were explored over the temperature range 100−250°C following reports of reactivity and meaningful free radical content in asphaltenes. This study employed industrial pentane precipitated asphaltenes from Athabasca oilsands bitumen. The presence of free radicals in the asphaltenes feed was confirmed. On heating the asphaltenes to 150°C, the aromatic hydrogen content increased relative to the feed by a factor 1.12. It was also found that on heating the asphaltenes to 150°C the n-heptane insoluble fraction increased from 67% to 75%. Almost no gas phase products were produced. The observed changes were ascribed to hydrogen transfer reactions and addition products formed by combination reactions. Direct evidence of hydrogen transfer reactions taking place in the asphaltenes was obtained through the use of the model systems, α-methylstyrene and cumene, as well as anthracene and 9,10-dihydroanthracene. The extent of hydrogen transfer was of the order 1.8 mg H/g asphaltenes in 1 h at 250°C. Asphaltenes also caused dimerization of model compounds, providing indirect evidence that free radical combination reactions took place in the asphaltenes. Interpretation relying on thermodynamic arguments combined with experimental results indicated that at 250°C the reactive species in asphaltenes were incapable of abstracting hydrogen by hydrogen transfer that had bond strengths (based on homolytic bond dissociation energy) exceeding around 353 kJ mol −1 . Using similar arguments, it was deduced that the ratio of reactive species in asphaltenes capable of abstracting hydrogen with bond strengths in the range around 315−353 kJ mol −1 , compared to transferable hydrogen in asphaltenes with a bond strength less than 315 kJ mol −1 was about 2:1.

No abstract

The formation of new heavier material during thermal processing has long been known, and under typical visbreaking conditions, vacuum conversion of deasphalted oil is described using a first-order kinetic reaction. Using the equivalent residence time (ERT) assumption, the residence time and reaction temperature are interchangeable variables to achieve the same conversion, where conversion is defined as the decrease of the vacuum residue through its conversion to lighter boiling fractions. With the combination of these observations about the visbreaking process, the following research question was raised: would process conditions that, in principle, lead to the same conversion also lead to the same asphaltenes content in the final product? The answer to this question was evaluated in this work, where vacuum residue deasphalted oil was submitted to visbreaking. Isoconversion conditions were obtained by the ERT concept. As expected, an increase in n-pentaneinsoluble material was obtained at all process conditions studied. The kinetics of asphaltenes formation was different to the kinetics of vacuum residue conversion because the amount of asphaltenes formed were different at the same conversion and vice versa. Subsequent analysis of the new n-pentane-insoluble material revealed that asphaltenes were participating in hydrogen transfer reactions. The amount of hydrogen transferred during conversion at 438 °C were around 20 mg of H/g of asphaltenes in the product. Free radicals were formed as a consequence of hydrogen transfer reactions, and their recombination resulted in the formation of heavier material, which was reflected in an increase in n-pentane-insoluble material during visbreaking. Further investigation revealed that the free radicals remained reactive upon storage, which resulted in a 9 wt % increase in asphaltenes after 210 days of storage under nitrogen. Results also showed that isoconversion was not achieved as predicted by the ERT definition and the differences between predicted and experimental values are discussed on the basis of the assumptions to calculate ERT.

No abstract