André Amblès

Free and esterified aliphatic carboxylic acids in humin and humic acids from a peat sample as revealed by pyrolysis with tetramethylammonium hydroxide or tetraethylammonium acetate

Abstract The combination of TMAH thermochemolysis and TEAAc treatment makes it possible to discriminate between the different forms of mono- and dicarboxylic acids present in the structure of humin and humic acids, that is, “free” uncombined acids, methyl or ethyl esters present as tightly trapped molecules within the matrix, or acids chemically linked to the matrix by ester groups. The results confirm that ester groups are involved in the structure of humin and humic acids. The cross-linking of moieties originating from microbial metabolism or inherited from higher plants is partly ensured by these chemical groups. On the other hand, significant amounts of fatty monocarboxylic acids and linear dicarboxylic acids are present as free acids in the humin of the studied sample. Humin contains also fatty acid methyl esters. Free, uncombined α,ω-dicarboxylic acids were only found in humin.

Stability and maturity of a green waste and biowaste compost assessed on the basis of a molecular study using spectroscopy, thermal analysis, thermodesorption and thermochemolysis.

The organic matter (OM) of a green waste and bio waste compost was characterised over 8months and the observed evolution was correlated with physico-chemical parameters (temperature, pH, carbon content, C/N ratio). Thermochemolysis and thermodesorption were used to monitor bacterial activity (stability) whereas diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) and thermodifferential analysis (TDA) permitted to determine the degree of OM humification (maturity). DRIFT spectroscopy and TDA provide two indicators of maturity since, with these two techniques, the signals associated with the biodegradable organic matter decrease relatively to the signals associated with refractory organic matter. This increase in R(TG) and R(IR) ratios between aromatic to aliphatic signals constitutes a proof for OM complexification. It correlates with humic acids/fulvic acids ratio known to be a maturity index. Pyrolysates are mainly constituted of lignin moieties, terpenoids, nitrogen containing compounds, carbohydrates (furanosic moiety), mono- and diacids (as methyl esters), and methoxyesters. The R(branched/linear) ratio between branched to linear acids traduces the evolution of the bacterial activity during composting. Moreover the R(di/mono) ratio between aliphatic mono to diacids correlates with the latter showing that diacids can occur from the biological oxidation of monoacids. These two ratios determined by thermochemolysis are useful to monitor the stability of compost. VOC, observed by thermodesorption are mainly constituted of terpenes, light acids, aldehydes and ketone. An unexpected result was obtained since the amount of phytol increases relatively to the isoprenoid ketone considered to originate from the latter.

CHANGES IN THE KETONE PORTION OF LIPIDIC COMPONENTS DURING THE DECOMPOSITION OF PLANT DEBRIS IN A HYDROMORPHIC FOREST-PODZOL

The ketonic part of soil lipids was studied in a hydromorphic forest-podzol. The undecomposed forest litter layer (L) and the fragmented mycelium-invaded litter layer (F), and the soil A1 horizon were sampled and analyzed for total lipid and total ketone contents. Total ketones were separated into methylketones and triterpenic ketones. Extractable ketones were not observed in the L layer, but were determined in the F layer of the soil litter. From the F litter layer to the soil A1 horizon, the portions of the two types of ketones, mainly the methylketones, decreased sharply. These last components, which are not primarily plant substances, originated essentially from the β-oxidation of n-alkanes, and the amount of transformation of n-alkanes into methylketones was in inverse ratio to their carbon number. Triterpenic ketones were the dominant part of soil ketones, and all their identified components were of plant origin. An important decrease of the amount of triterpenic ketones was observed from litter to soil, but their decomposition processes were not clearly determined.

Ester- and ether bond cleavage in immature kerogens

Abstract Quaternary ammonium salt Aliquat 336 and 18-Crown-6 enhance hydrolysis of Timahdit-M kerogen when used as a phase transfer catalyst. The yield of hydrolysis products was higher with Aliquat than with 18-Crown-6, but the identified products were found in lower concentration, the difference being soluble heavy parts from kerogen which cannot be analyzed directly. Both reactions afforded series of aliphatic mono- and dicarboxylic acids, alkylsuccinic acids and alkanols, but differences in distributions were observed. The range of monocarboxylic acids was shorter with Aliquat than with 18-C-6, C14C18 compared to C12C32, but palmitic and stearic acids were dominant in the two cases. C10 and C12 alkyl succinic acids were identified in Aliquat products. Aromatic acids were the major hydrolysis products (59%) with crown ether; only one aromatic acid was found with Aliquat. Hydrocarbons and tertiary amines were obtained from both reactions, they were obviously present in the kerogen as trapped molecules. Many tertiary amines arising from the decomposition of the reagent were obtained with Aliquat. The results give evidence of an important reticulation involving ester groups in the Timahdit-M kerogen. Series of n-, iso- and anteisoalkanes were obtained through HI/LAD treatment of Irati and Aleksinac kerogens, originating probably from glycerol-ether lipids. C27C34 α,β-hopanes were also found to be linked to kerogen (Irati) by ether bonds. Reaction with CF3CO2H (Irati) afforded seven series of branched alkenes, indicating that branched saturated alkyl chains were bound to aromatic moieties of kerogen by ether groups. Acetates of cholesterol and 24-ethylcholesterol were identified in the BF3-Et2O/Ac2O products. Esters of fatty acids (max C16, C18) were also identified. Only alkanes were produced on AII3 reaction. Each reaction afforded the same series of n-alkanes. This would reflect modifications in the kerogen matrix during these various treatments, resulting in the release of tightly trapped molecules.

Polar lipid fraction in soil: a kerogen-like matter

Lipid extracts from two acidic hydromorphic soils contained simple lipids and a slightly soluble fraction (named polar fraction or complex lipids). Ether- and ester-bond cleavage and KMnO4 oxidation of the polar fraction was followed by GC-MS analyses of the released compounds. In contrast to n-alkanols and α,ω-diacids, normal monoacids were found to be the same as in simple lipids. It is concluded that the polar fraction of the soil corresponds to highly aliphatic macromolecules with a polyethylene-like structure, in which some simple lipids may be incorporated to form a protokerogen.

Supercritical fluid extraction of Moroccan (Timahdit) oil shale with water

Timahdit oil shale was subjected to supercritical water extraction. The results reveal significant difference in oil yields and composition when compared with those obtained from conventional pyrolysis. In addition, the effect of temperature and residence time on the supercritical water extraction of oil was investigated in a set of three experiments. The results revealed that the yield and the fraction of paraffins and aromatics increase while the percentage of asphaltenes decreases as the temperature is increased from 380 to 400°C. The residence time was found to affect the yield and the fraction of asphaltenes and polar compounds.

Relationship between kerogens of various structural types and the products of their multistep oxidative degradation

Abstract Three shale samples were investigated: Green River shale (type I kerogen), Toarcian shale, Paris Basin (type II), and Mannville shale, Canada (type III). Identical experimental conditions were used for all three samples. The degradations were complete in 25, 27 and 13 steps. Very high total yields of oxidation products were obtained, 76.38, 72.29 and 81.89%, respectively. Detailed GC-MS analyses of ether-soluble acids, as well as soluble products of further controlled permanganate degradation of precipitated acids, served as basis for approximate quantitative estimation of the share of various types of oxidation products, and for a corresponding comparison of kerogens. Substantial differences in the compositions and nature of oxidation products have been revealed: from typical saturated aliphatic mono- and dicarboxylic acids as the main (over 90%) oxidation product of type I kerogen, to typical aromatic mono-, di- and tricarboxylic acids as the major (over 90%) oxidation product of type III kerogen. Preliminary investigation of the acids from aqueous solutions remaining after the usual isolation of oxidation products with ether, suggested slight modifications of the image on the nature of various types of kerogens based on examination of ether-soluble acids only.

Characterization of kerogen from Timahdit shale (Y-layer) based on multistage alkaline permanganate degradation

Abstract A 15-step alkaline permanganate degradation of the kerogen from Moroccan Timahdit Oil Shale (Y-layer) was carried out. Oxidation products were obtained in a good yield (64 wt% based on initial kerogen). Detailed g.c. and g.c.-m.s. analyses of ether- and water-soluble acids and products of further controlled permanganate degradation of precipitated acids served as a basis for the quantitative estimation of the contributions of various types of products and for comparison with other kerogens. Taking into account the dominant aliphatic (44.2%) and aromatic (34.8%) nature of the acidic oxidation products, the existence of an aliphatic cross-linked nucleus mixed with cross-linked aromatic units in the Timahdit-Y shale kerogen is postulated. These findings were corroborated by FT-i.r. and 13C CP-MAS n.m.r. analyses. Saturated hydrocarbons were also found in the oxidation products; they were probable trapped in the kerogen matrix.

n-Alkane oxidation in soil. Formation of internal monoalkenes

Abstract The biodegradation of pure eicosane (nC20) in rendzina soil samples was studied in a laboratory experiment at 20°C. After 8 weeks, 25% of eicosane was mineralized. Terminal oxidation led to C20:0 acid, with eicosan-1-ol as probable intermediate. An interesting dehydrogenation process occurred, leading to eicos-9-ene which was oxidized into eicos-9-enoic and eicos-11-enoic acids. This process was also observed with C19 and C22 hydrocarbons. Hydrolysis of the complex lipid fraction demonstrated the incorporation of eicosane-derived molecules in this fraction.

Characterisation and differentiation of kerogens by pyrolytic and chemical degradation techniques

Abstract The structural characterization of a set of kerogen concentrates belonging to the three well differentiated conventional main types (I, II, III) has been undertaken by pyrolysis–gas chromatography–mass spectrometry (Py–GC/MS) both in the absence and presence of tetramethylammonium hydroxide (TMAH). The results obtained have been compared to the structural features as discerned by chemical degradative methods (KMnO 4 or RuO 4 oxidation, hydrolysis with phase transfer catalyst and transalkylation reactions) and solid state 13 C-NMR spectroscopy. The compounds released upon conventional pyrolysis were mainly saturated and olefinic hydrocarbons for the type I and II kerogen samples, whereas aromatic compounds were predominant in the kerogen of type III, in agreement with KMnO 4 oxidation data and the NMR spectra. Pyrolysis/TMAH released relatively high amounts of saturated and unsaturated unbranched mono- and dicarboxylic acids (as their methyl esters) from all the samples, as well as minor amounts of aromatic acids (as their methyl esters), which indicates that considerable amounts of functionalized compounds are bound to the macromolecular structure via ester or ether linkages. Overall, Py/TMAH and chemical degradations give complementary results concerning the chemical nature of the released fatty acid series identified.