Analytical Methods for Characterizing High-Mass Complex Polydisperse Hydrocarbon Mixtures: An Overview

By attempting to define the principal chemical features and the complete ranges of molecular mass of the heavy ends of coal and petroleum derived liquids, this review aims to facilitate process development for improved utilization of heavy fractions (coal and biomass tars and pitches, petroleum asphaltenes and resids). Historically much heavy petroleum derived material has been used as cheap fuel or simply thrown away. With the rising cash-value of the “bottom of the barrel,” greater emphasis on the detailed chemistry of these materials has become an imperative. This paper reviews analytical techniques used for estimating molecular mass distributions and structural features of complex polydispersed hydrocarbons, with masses above those identifiable by gas-chromatography (or GC-MS). The features of the least soluble – and usually large molecular mass - materials in complex mixtures are not generally observable by examination prior to the fractionation of (i.e. “whole”) complex samples. This has been observed even in cases where the “heavy” fraction accounts for about 50% of the total sample. The major approach reviewed covers the combined use of UV-fluorescence spectroscopy, size exclusion chromatography, mass spectroscopy and NMR-spectroscopy. This is preceded by a description and critical review of useful sample fractionation methods found in the literature.JRC.F.2-Cleaner energ