Assignment of Compound Type (Z value) and Aromatic Oil Composition by LC, GPC and Mass Spectrometric Technique

Abstract

Hexane soluble part (oil) from Akabira coal-derived liquid was separated into 5 fractions of compound type using dual packed silica-alumina gel liquid chromatography (Fig.2). Neutral aromatic fractions, Fr-M, D, and T, which included aromatic compound with increasing aromatic ring number in that order, were further separated into 5 or 6 subfractions according to molecular size using GPC (Fig.3).
From the low voltage-low resolution mass spectrum of each fractions, the nominal Z values of respective ion peaks were decided directly by selecting m/z with each interval of 14 mass number. From the molecular weight distributions of nominal Z series (Fig.5), the true Z values were assigned as follows: ( 1 ) By LC separation, Fr-M, D and T were obtained, consisting mainly of monocyclic, dicyclic, and tri and/or tetracyclic aromatic hydrocarbons. ( 2 ) On bi-modal molecular weight distribution of the same nominal Z series, higher m/z distribution mode has 14 smaller Z number than the lower mode. ( 3 ) The minimum m/z of molecular weight distribution mode is the same or larger than the molecular weight of the corresponding aromatic-naphthenic parent ring system (Table 4).
The series of compound type with true Z values decided by the above methods were characterized by M_w-V_e (GPC) correlation (Fig.6). Components of the oil were shown as compound types and alkyl side chain carbon number distribution (Table 5). Aromatic compound type are distributed from Z=-12 to Z=-42, and showing a maximum at Z=-14. Alkyl side chain carbons range from 0 to 20, and having a maximum at 4 carbon atoms. t Chemical Structure of Coal-derived Liquids. I.