Chromatographic separation and characterization of coal-derived asphaltenes

Abstract

Coal-derived asphaltenes from five major demonstration processes in the United States (Synthoil, HRI H-Coal, FMC-COED, PAMCO SRC, and Catalytic Inc. SRC) have been separated by a simple, rapid chromatographic procedure, on silica gel, into a limited number of acid/neutral and basic fractions which contain high concentrations of major functional groups. Analytical, molecular weight, and nuclear magnetic resonance methods have been used to deduce features of the microstructures of these asphaltenes. They usually have number-average MWs in the 400–550 range, and are made up of cata-systems of small ring number (3–5), with 30–50% of the available aromatic edge atoms occupied by substituents, and joined by naphthenic, methylenic or etheric bridges. Chemical and instrumental methods were used to determine qualitatively and quantitatively the composition of the functional groups OH, NH, and N. The fraction of O as OH ranges from 0.59 to 0.83, and of N as NH from 0.53 to 0.74. The macrostructure of asphaltene crystallites was studied by X-ray diffraction methods and average dimensions deduced from an assumed model. The nature of the association between asphaltene molecules was studied by electron spin resonance; if charge-transfer interactions are present, they appear not to be significant as binding forces between the asphaltene molecules or nuclei.