Gel permeation chromatography, spectroscopy measurements, densimetric analysis, mass spectrometry and spark source mass spectrometry were used to study maltenes fractions and asphaltenes components of a soft bitumen.
Results from spectroscopy and mass spectrometry measurements indicated that the bitumen was less aromatic in character than indicated by densimetric analysis.
The degree of conjugation in fractions was observed to increase as the molecular weights of fractions increased.
Bitumen, which can vary in composition according to its source, is a viscous high-boiling mixture containing aliphatic and aromatic hydrocarbons1T2 and small amounts of organic acids3, bases and heterocyclic compounds'.
Information on its composition has been largely obtained from the study of fractions which represented a small proportion of the parent bitumeniY2, and from analyses on highboiling petroleum fractions and shale oils4-'.
A limited number of analytical techniques have been applied'~8-" in order to characterize bitumen and its fractions.
The present work investigated, by application of a wide range of physical methods, the composition of a bitumen material and of five of its fractions, each of which contained more than 10% of the parent material.
EXPERIMENTAL
Reagents and materials
Bitumen, 200 penetration'? straight reducedi from Tia Juana (Venezuela) crude petroleum, was supplied by the Esso Petroleum Company Research Centre, Abingdon, Berkshire.
Solvents used for its fractionation were of reagent grade.
Alumina type H, 100-200 mesh BS (Laporte Industries, Widnes, Lancashire), was heated for 2 h at 450ยฐC before-use for the column chromatography of the maltenes.
The tetrahydrofuran, used after distillation for the gel permeation chromatography experiments, contained 1% of 2,6ditert. butyl-p-cresol as a stabilizer. Carbon disulphide was distilled over phosphorus pentoxide, and cyclohexane, and the carbon disulphide used for spectroscopy, were stored over phosphorus pentoxide.
Elemental analyses
Carbon, hydrogen and nitrogen were determined in a Perkin-Elmer Model 240 elemental analyser. Sulphur was determined by the oxygen flask combustion method14.