Gel permeation chromatographic studies of polynuclear aromatic hydrocarbon materials

Abstract

Information on the molecular size or weight distribution of pyrogenous raw materials that are complex mixtures of aromatic hydrocarbons has been difficult to obtain. The relatively new technique of gel permeation chromatography (GPC), augmented by the excellent apparatus made available by Waters Associates, offers the opportunity to measure routinely such distribution curves. For years we studied the composition, properties, and thermal reaction mechanisms of complex polynuclear aromatic mixtures such as coal tars, pitches, and heavy petroleum residues. A great deal of work has also been done on pure compounds, with the result that we have accumulated a large number of high‐purity reference aromatic and heterocyclic compounds. We recently determined the elution behavior of more than a hundred polycyclic compounds and also fractionated a variety of thermally produced aromatic residues, using a Model 200 Waters Gel Permeation Chromatograph. Our results with model compounds in tetrahydrofuran solutions indicate that GPC separations occur, not as a function of a single parameter, but as a complex function of molecular size, shape, and polarity. The simplicity of operation and reproducibility of the GPC method will make it extremely useful both as a means of studying the composition of thermal residual products and as a routine screening technique.