The influence of impregnation by hydrocarbons on coal structure during its thermal evolution

Abstract

The present work analyses the changes in the chemical structure of a perhydrous coal during its thermal evolution at different temperatures in an open-medium pyrolysis system. The results obtained were compared with those described for non-perhydrous coals in order to establish the effect of the substances assimilated by the coal structure (hydrocarbon/oil-like substances) on the thermal evolution of the coal. The transformation ratio at each stage of thermal treatment was determined and the chemical-structural characterisation of the resultant products was performed. Changes in textural and microtextural properties associated with structural modifications during the evolution were also tested. The results obtained show that this perhydrous coal develops a specific evolution pathway different from that followed by non-perhydrous coals with a normal H/C ratio. The substances assimilated by the perhydrous coal cannot be easily and totally released from its structure so that they can be only partially removed after thermal treatment. Thus, the treatment debilitates the interactions between the substances and the coal matrix in addition to weakening and cracking the matrix during the thermal process. The increase in temperature also leads to the conversion of some of the heavy assimilated substances into lighter compounds. However, the assimilated substances are present even at high temperatures of the thermal process, providing hydrogen which has the effect of stabilising the radicals originated during the pyrolysis and improving the fluidity properties in the reacting medium

Thermal maturity of the Upper Triassic–Middle Jurassic Shemshak Group (Alborz Range, Northern Iran) based on organic petrography, geochemistry and basin modelling: implications for source rock evaluation and petroleum exploration

“…In the studied coals, micrinite ( fluorescence, probably due to either higher hydrogen content or different precursor material which shows suppressed reflectance (VRr=0.9%) (Perrussel et al, 1999;Iglesias et al, 2001).…”

Coalbed methane producibility from the Mannville coals in Alberta, Canada: A comparison of two areas

“…Since many of the vitrinite macerals in the Upper Medicine River Seam fluoresce, vitrinite reflectance values are likely suppressed, as has been demonstrated for the Mannville coals . Suppression has been attributed to: (1) the impregnation of the vitrinitic matrix by bitumen generated under severe bacterial activity; and (2) the incorporation into the vitrinite structure of lipids derived from bacteria cell walls themselves ( [Veld and Fermont, 1990], [Rathbone and Davis, 1993], , [Suarez-Ruiz et al, 1994], [Perrussel et al, 1999] and [Iglesias et al, 2001]). …”

Chemical-structural changes during the thermal treatment of hydrogen-rich vitrinites caused by the presence of terpene-type resin

“…Thus, natural evolution can be considered as a peculiar kind of pyrolysis which normally occurs at low temperatures (<200 8C) over millions of years. For this reason, different pyrolysis experiments were used to obtain valuable information about the phenomena that occur during natural evolution [3][4][5][6][7][8][9].…”

“…Pyrolysis 77 (2006) [177][178][179][180][181][182][183][184][185][186][187][188][189][190][191] Whereas vitrinites are generally gas-prone materials, perhydrous vitrinites have the potential to generate liquid products [10]. Upon Gray-King pyrolysis they yield much more oil than non-perhydrous vitrinites [11] and they show a very high petroleum potential and low thermostability [12][13][14][15]. Thermogravimetric studies on hydrogen-rich vitrinites [14,16] have shown that their thermal behaviour is similar to that of type I kerogens.…”

“…They can show a higher contribution of aliphatic structures over condensed aromatic ones but also a very significant amount of aromatic rings of a low degree of condensation with a preponderance of para-substitution [15,26,27]. Thus, the study of the degradation products points to para-alkyl substituted phenols as the major structural units for these vitrinites [11,15]. From these findings, the presence of aromatic units of a low size and a low degree of substitution cannot be discarded when trying to explain the perhydrous character in vitrinites and its implication for the properties and behaviour of these materials.…”