1982 Volume 1982 Issue 4 Pages 644-649
Nitrogen type analyses of asphaltenes of Khafji atmospheric residuum and its hydrotreated products were carried out by the USBM-API 60 methods. Although highly polar materials remained on ion-exchange resins after the usual elution procedure, most of them were reco vered by using chloroform as an elution solvent. The yield of each fractionated asphltene did not accurately show the distribution of nitrogen compounds because of the following reasons: ( 1 ) association of asphaltene molecules prohibited the functional groups from interaction with the resins, ( 2 ) multifunctional compounds were included in a considerable amount, and ( 3 ) some elution solvents were possibly incorporated into the separated fractions. In quali tative analysis of pyridine by ir spectroscopy inherent were some inaccuracies due to the presence of skeletal vibration bands of condensed aromatic rings in the asphaltene. No marked difference, however, was found in the degree of removal of the following three types of nitrogen compounds: pyrroles, amides, and pyridines. Separation of the asphaltenes by GPC showed that, in the hydrotreatment, preferential decomposition of their lower molecular weight fractions took place leading to the significant decrease in their nitrogen contents. These fin dings would suggest that the rate of diffusion of large asphaltene molecules into the catalyst pores became rate determing, resulting in the equivocal difference among the reactivities of nitrogen compounds.
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