IMPORTANCE OF THE REACTING MEDIUM IN ARTIFICIAL MATURATION OF A COAL BY CONFINED PYROLYSIS .1. HYDROCARBONS AND POLAR COMPOUNDS

The reactivity of coal during confined pyrolysis strongly depends on the reacting medium and on the nature of the coexisting phases. Thus, understanding the mechanisms of organic matter maturation also requires consideration of the role of each fraction of the pyrolysate in the reaction mechanisms. Although the pyrolysis of individual fractions (asphaltenes, crude oils,...) has been extensively investigated, the importance of the interactions between the different components of the pyrolysate has been poorly considered. Successive pyrolysis-extraction experiments with the selective removal of the generated fractions (gas + polars + hydrocarbons or gas and hydrocarbons only) allow the behavior of solid and solid + polar compounds during pyrolysis to be compared. Loss of aliphatic chains in the effluents and in the solid residue, extensive condensation of the solid residue, and condensation of polar compounds when they are preserved in the reacting medium clearly indicate that the absence of hydrocarbons in the reacting medium induces a deleterious effect on the solid residue and on the behavior of the polar compounds. These results suggest that hydrocarbons play a major role as a solvating fluid that promotes hydrogen transfer reactions and thus influences the conversion of organic matter and polar compounds. Therefore, maturity indices and stability parameters may be more sensitive to the nature of the reacting medium than to the time-temperature conditions.