• Energy Research

Dans un système de pyrolyse comme dans un système de maturation naturelle de la matière organique, les différentes fractions du pyrolysat, qui constituent le milieu réactionnel, sont en contact intime sous l'effet de la pression développée dans le système. De façon à mettre en évidence les interactions entre ces différentes fractions et leur importance dans les réactions de maturation de la matière organique, cinq milieux réactionnels différents ont été reconstitués (1) une série de pyrolyse en milieu confiné classique du charbon de la Mahakam (280°C à 370°C - 24 h ; 700 bars) (2) une série EC où les hydrocarbures et les composés polaires sont prélevés à chaque étape de pyrolyse (étude du résidu solide au cours de la maturation) (3) une série EP ou le résidu solide et les composés polaires sont préservés dans le milieu tandis que les hydrocarbures sont prélevés (4, 5) l'influence d'un excès d'eau sur le comportement du résidu solide et de l'ensemble résidu solide-composés polaires est étudiée dans les séries ECO et EPO. Les résultats montrent l'importance des hydrocarbures dans les réactions de maturation du charbon. Ils jouent le role de phase mobile dans le milieu réactionnel et favorisent la mobilité des espèces, le transfert d'hydrogène et la plasticité du charbon. L’eau a aussi un rôle actif dans les processus de genèse des hydrocarbures mais sont rôle de source d'hydrogène dépend de la présence des composés polaires qui pourrait être les catalyseurs de la dissociation de l'eau Not available

Based on the isomer stability during their formation, PAH diagnostic ratios have been extensively used to determine PAH contamination origin. Nevertheless, it is known that these isomers do not present the same physicochemical properties and that reactions occurring during the transport from an atmospheric source induce changes in the diagnostic ratios. Yet, little is known about reactions occurring in soils contaminated by other sources such as coal tar and coal. Innovative batch experiments of abiotic oxidation and microbial incubations were performed to discriminate independently the influence of these two major processes occurring in soils on the diagnostic ratios of major PAH sources. Three samples were studied, a coking plant soil and two major PAH sources in this soil, namely coal and coal tar. The combustion signature of the coking plant soil showed the major influence of coal tar in the soil sample composition. Some of these ratios were drastically affected by oxidation and biodegradation processes inducing a change in the source signature. The coal tar signature changed to petrogenic source after oxidation with the anthracene/(anthracene+phenanthrene) ratio. According to this ratio, the initial petrogenic signature of the coal changed to a combustion signature after the biodegradation experiment.

Polluted soils of former coking plants are characterized by multiple organic contributions, e.g. coal tar, coal, coke, soot, and natural organic matter, that can either be sources of polycyclic aromatic hydrocarbons (PAHs) or act as sorption surfaces for pollutants. The contamination level is usually based on the quantification of 16 PAHs but it does not provide any information on PAH sources. We studied the aliphatic fractions of 25 soil samples from a former coking plant site by microscopy and gas chromatography-mass spectrometry (GC-MS). The microscopic investigation allowed to identify four main organic contributions: coal tar, coal, coke, and natural organic matter. These isolated sources were analyzed and considered as reference materials. Although the PAH distributions were very similar in the 25 contaminated soils, alkanes and hopanes distributions were representative from various contributions characterizing the relative enrichment in coal, coal tars, or natural organic matter. Two principal component analyses based on n-alkanes and hopanes showed that three molecular indices, the carbon preference index, the low molecular weight/high molecular weight n-alkanes ratio, and the 18α(H)-22,29,30-trisnorhopane/(18α(H)-22,29,30-trisnorhopane+17α(H)-22,29,30-trisnorhopane) ratio allow to classify polluted soils according to various organic contributions.

In contaminated soils, several natural processes (biodegradation, oxidation, etc.) can induce degradation of organic pollutants. The aim of this work was to evaluate the impact of an abiotic low-temperature oxidation on a coking plant soil and its main organic constituents (coal, coke, coal tar and road asphalts) in order to understand its long term evolution. This natural process was experimentally reproduced by oxidizing the soil and isolated organic matrices at 100 °C during 180 days. The samples were analyzed by total organic carbon measurements and elemental analyses, and the solvent-extractable organic matter was quantified by GC-MS (gas chromatography-mass spectrometry). Oxidation experiments on coal, coal tar and coking plant soil samples lead to the decrease in polycyclic aromatic hydrocarbon (PAH) concentrations correlated to an incorporation of oxygen evidenced by the production of oxygenated PAHs. The increasing amount of polar macromolecules and the decrease in solvent-extractable organic matter suggest a molecular growth through ether/ester cross-linking. The chemical environment of organic compounds and the presence of a reactive mineral fraction are important parameters that improve the efficiency of oxidation. This work reveals that abiotic low temperature oxidation, can strongly contribute to pollutant removal especially by a stabilization process and should be considered in the long term evolution of a soil.