Molecular-Level Structural Insight into Clarified Oil by Nuclear Magnetic Resonance (NMR) Spectroscopy: Estimation of Hydrocarbon Types and Average Structural Parameters

摘要

A direct and easy-to-grasp methodology based on the combination of quantitative H-1 and C-13 nuclear magnetic resonance (NMR) has been developed for the estimation of total aromatics, saturates, and several important structural parameters, such as aromaticity, average number of aromatic rings per molecule, average number of aromatic carbon atoms per molecule, average molecular weight, degree of aromatic substitution, degree of aromatic condensation, nature of condensation, and substitution to aromatic ring, etc. for clarified oil (CLO) from Indian oil refineries. These parameters, along with HPLC analysis data for di- to penta-ring aromatics, provide a molecular-level understanding of this potentially valuable feedstock, which can thus be correlated with process parameters for needle coke production from CLO. The method exploits the concept of group molecular weight (GMWt) and uses three empirical equations governing the nature of aromatic condensation. The various types of CLO that originated from Indian oil refineries have been classified into three major classes, by virtue of their differential nature and composition. Two-dimensional (2D) HSQC NMR has been extensively studied for accurate assignment of different classes of protons in H-1 NMR spectra of CLOs. The method was validated by SARA analysis using TLC-FID (IP-469) (R-2 = 0.9698) and by open column chromatography (ASTM D-2549) (R-2 = 0.9887) for hydrocarbon types.