Aromatic Ring Index (ARI): A Characterization Factor for Nonpolar Hydrocarbons from Molecular Weight and Refractive Index

Abstract

Crude oils consist of tens of thousands of components belonging to various hydrocarbon families, including n-alkanes, cyclo-alkanes, and aromatics. Because the experimental determination of the composition and molecular structure of each component is an infeasible task, it is common to use characterization factors that describe the nature of the pseudo fractions based on their bulk thermophysical properties. In this work, a new characterization factor, called the aromatic ring index (ARI), is developed based on measurements of molecular weight and refractive index. Unlike other popular characterization factors (e.g., Watson's K w ), ARI can clearly distinguish between various hydrocarbon families. Additionally, and most importantly, ARI can provide a quantitative measure of the aromaticity of the hydrocarbon of interest as it provides a rough indication of the number of aromatic rings contained within the molecular structure. Applications of the new ARI concept to well-defined mixtures of hydrocarbons as well as true boiling point (TBP) distillation data of bitumen and heavy oils indicate that ARI shows reasonable trends consistent with the current understanding of the nature of petroleum fractions. Additionally, the concept of ARI can be used to explain some of the apparent discrepancies in the reported results from popular characterization methodologies for asphaltenic systems. Unlike other measures of aromaticity, ARI shows a clear monotonic trend in the aromaticity of the saturates-aromaticsresins-asphaltenes fractions with asphaltenes as most aromatic, which is consistent with the current understanding of asphaltenes.

Empirical Models to Characterize the Structural and Physiochemical Properties of Vacuum Gas Oils with Different Saturate Contents

“…where, n D20 = refractive index at 20 • C [26,27]. The methods discussed in this section describe the complex mixture, which is the VGO, in terms of average structural features of the molecules, that is, groups of carbon and/or hydrogen types, in contrast to the compound group.…”

“…The aromatic ring index developed by Abutiqiya et al [26,27] was confirmed to properly predict the actual aromatic ring numbers of individual hydrocarbons and fluid catalytic cracking slurry oils characterized by NMR.…”

“…In the case of missing data for the molecular weight or refractive index T 50% , Equation ( 30) can be used to estimate the refractive index and the molecular weight reported by the correlations reported in [23,56,57]. The characterization of petroleum fractions by empirical models, which relate the oil bulk physicochemical properties to the content of important structural parameters, has been developed for the last 70 years (from 1951 [41] with the n-d-M method to 2021 with ARI [27]. They have proved their usefulness in predicting VGO reactivity and product selectivity in the processes of catalytic and thermal cracking [5,7,17,47,48] and in the modeling of the most complex petroleum compounds-the asphaltenes [27].…”

“…The characterization of petroleum fractions by empirical models, which relate the oil bulk physicochemical properties to the content of important structural parameters, has been developed for the last 70 years (from 1951 [41] with the n-d-M method to 2021 with ARI [27]. They have proved their usefulness in predicting VGO reactivity and product selectivity in the processes of catalytic and thermal cracking [5,7,17,47,48] and in the modeling of the most complex petroleum compounds-the asphaltenes [27]. Over the years improvement in the predictions of the content of the VGO characterizing parameters has been registered [19,21].…”

“…Considering that in Resources 2021, 10, 71 2 of 20 both FCC and thermal cracking the reactivity of the vacuum gas oils increases with the saturate content enhancement and aromatic carbon content reduction, the information about these vacuum gas oil characteristics is of paramount importance for optimizing their performance [17]. Different empirical models for predicting important vacuum gas oil characteristics have been developed and published in the open literature [18][19][20][21][22][23][24][25][26][27][28]. To the best of our knowledge, these empirical models have not been evaluated to predict the content of saturates of vacuum gas oils in the whole range of possible variation (between 0 and 100%).…”