Hydrocarbon generation potential of some Hungarian low-rank coals

Abstract

Several Hungarian lignite and brown coal samples were studied by coal petrographical, palynological and organic geochemical methods. Three of these were chosen for a series of pyrolysis experiments. Thermal treatment was carried out on two H-rich Eocene brown coals (kerogen: Type II) and a H-poor Miocene lignite (kerogen Type III) between 200 and 500°C. The products of experiments (insoluble residue, chloroform soluble bitumen and volatilized bitumen) were investigated. During diagenesis the hydrocarbon potential of lignite decreased by 75% and that of the coals diminished approximately 50%. The zone of the catagenesis was reached at 350°C by lignite and at 375°C by coals. The coal-2 is somewhat more resistant to thermal degradation than coal-1. Various hydrocarbon classes (alkanes, alkenes, phyllocladanes, isoprenoids) were measured in non-aromatic hydrocarbon fractions. Volatile bitumens contained much more unsaturated hydrocarbons than the bitumens extracted after pyrolysis. Prist-1-ene and prist-2-ene were measurable only in the volatile yields. 16α(H)-phyllocladane was present among the products and its generation stability and isomerization were also studied. The ratios between different hydrocarbon products were found variable in the case of different samples as a function of increasing temperature and time (e.g. n-alkenes to n-alkanes).