Tracing the origins of polymethylene moieties in coal

Abstract

Many coals have been shown to contain long polymethylene segments (up to C 30 and longer) which crack to ethylene, propylene, butadiene and other low molecular weight hydrocarbons when the coals are pyrolyzed. The polymethylene content varies in different coals and can be 10% or more in low rank coals. Cannel coals may contain up to 20% polymethylene. Polymethylene moieties are either very low or absent in low-volatile bituminous coals and anthracite. A method of analysis for polymethylene in coals, based on liquefaction in a donor solvent followed by 1H NMR spectroscopy has been described. With this analysis, it has been shown that polymethylene moieties are present in higher concentrations in exinite macerals than in vitrinites or inertinites. Analysis of peats also show the presence of polymethylene components at levels similar to that found in coal. Analysis of various parts of present-day plants also shows the presence of polymethylene materials in concentrations varying significantly from one kind of plant to another. Within a given plant type, some parts of the plant appear to be richer in polymethylene than others. Spores and pollen are frequently especially rich in polymethylene, accounting for the corresponding high concentration in exinite macerals in coal. Samples of Texas Eocene lignites representing a depositional time interval of 15–20 million years and three distinctly different climatic and vegetational conditions were analyzed for polymethylene contents. The differences in polymethylene levels are consistent with differences in flora and support the idea that the original plants are the sources of polymethylene components in coal.