The variations in chemical structures of the neutral oils from hydrogenated various coals were examined by means of HPLC-MS method.
Coal hydrogenation reactions were performed using an autoclave at 400°C, 100kg/cm2 initial hydrogen pressure with Adkins catalyst for 60 minutes of reaction time. Then neutral oils, free of the acidic and the basic portions, were separated into 5 compound classes, which were Fr-P (alkanes), Fr-M (monoaromatics), Fr-D (diaromatics), Fr-T (polyaromatics), Fr-PP (hetero compounds), using HPLC equipped with a Zorbax BP-NH₂ column.
The compound type analyses of each compound class were performed using electron impact mass spectroscopy (EI-MS) or field ionization mass spectroscopy (FI-MS). Based on the separation behaviour of HPLC and the type analyses according to Z number by MS, a neutral oil was characterized in terms of the distribution of the numbers of aromatic rings, naphthenic rings and carbons of alkyl groups attached to these rings. The variations in chemical structures of the neutral oils with C% of coal were discussed in terms of these chemical structural factors.
Content of compound types with a larger number of aromatic rings or naphthenic rings increase with increase in the C% of coal. The modes of the changes in the average carbon number of alkyl side chain for each compound type with C% of coal were classified into three groups. These are monotonously increasing or decreasing with increase in the C % of coal, or have the minimum values at about C75%.
The changes in average molecular weight of each compound class have the minimum values at about C 75%. This result is explained according to the chemical structural factors which were, above mentioned, the numbers of aromatic rings, naphthenic rings and carbons of alkyl side chain.