Estimation of Average Molecular Structural Parameters of Heavy Hydrocarbons Using Infrared Spectroscopy

Heavy hydrocarbons, such as coal tars and petroleum residues are inexpensive raw materials for the manufacture of carbon fiber. Average molecular structural analysis is a useful technique to derive average structural models of these heavy hydrocarbons. These models are conventionally determined based on elemental composition, average molecular weight, and nuclear magnetic resonance (NMR) spectroscopy. However, laboratory preparations sometimes fail to provide sufficient sample quantities for NMR analysis, and some samples may not dissolve in solvents. We have developed an alternative approach for estimation of the average molecular structural parameters of heavy hydrocarbons using infrared (IR) spectroscopy which requires only small sample quantities (1-2 mg) and can accommodate insoluble materials. The equations that predict the parameters, i.e., the carbon aromaticity, molar ratios of terminal methyl groups to aromatic carbon, molar ratios of methyl groups to the sum of the methyl and methylene groups, and oxygen contents of ketones and carboxylic acids, were determined using IR spectra and hydrogen-to-carbon atomic ratios of various samples such as coal, asphaltene, and/or model compounds.

Automated summary

Infrared spectroscopy can be used to estimate the average molecular structural parameters of heavy hydrocarbons, providing an alternative to conventional methods that require larger sample quantities and solubility.