GPC Separation and Molecular Wcight Distribution of Benzene Soluble Components from Coal Derivatives

Abstract

Fundamental studies on the separation of coal derivatives by means of gel permeation chromatography (GPC) are reported on (1) the chromatographic conditions for preparative GPC separation for structural analyses of coal and (2) basic experiments to odtain the molecular weight distributtion from analytical GPC elution curves using the chloroform soluble qart (γ-part) of pyridine extract from Akabira coal. On the basis of this informaton, the distributions of molecularweight of oil and asphaltene obtained from hydrogenolysis of Akabira coal are investigated by GPC analyses and their variation with reaction temperature is discussed.The petroleum soluble portion (γ1-part) and the insoluble portion (γ2-4-part) from the γ-part were selected as the sample for the discussion of the optimum conditions for GPC separation, such as pore size of gel and elution solvent. From the experimental results, it is obvious that separation by preparative GPC is achieved, odtaining fractions of considerably narrow molecular weight distribution. This contributed remarkably to the resolution of thechemical structure of coal. The relationship detween the elution volume (Ve) of the analytical GPC and average molecular weight (M) estimated by vapor pressure osmometry is fairly good for the fractionation products from preparative GPC (Fig. 9, 10). The M-Ve correlation lines of the 1- and the 2-4-parts were straight lines of different slope. Therefore it was assumed that the difference was due to a difference in structural type on the components. Consequently, these γ relationships of log M-Ve can be applied to the estimation of the molecular weight distribution from analytical GPC chromatograms as the correlation lines of high-molecular and low-molecular weight components respectively for the coal derived liquids.Oil and asphaltene in hydrogenolysis products werealso separated into fraction on the basis of molecular weight by preparative GPC and each fraction was correlated by elution counts of analytical GPC and average molecular weight. The results of these relationships were in fairly good agreement with correlation lines of log M-Ve odtained from the γ1 and the γ2-4 componets respectively (Fig. 13, 14). From the elution curves of analytical GPC for oil and asphaltene of varying reaction temperature, it is recognized that the distribution of molecular wight for asphaltene shifts gradually in the direction of a lower molecular weight distribution as the reaction temperature increases. On the other hand, the distribution of moleclar weight of oil changes only slightly and tends to converge to the constant distribution of low molecular weight components.