Zeev Aizenshtat

Formation of immature asphalt from organic-rich carbonate rocks. I: Geochemical correlation

Abstract The formation of low-maturity asphaltic oils (immature asphalts) from carbonate source rocks was investigated. The Senonian bituminous rocks (SBR) in Israel are organic-rich carbonate rocks that were deposited in a high productivity environment, and they are part of a sedimentary sequence that also contains cherts and phosphorites. The SBR were studied in different basins, and the samples are from outcrops and three deep drillholes. The bitumen contents of the rocks are exceptionally high (up to 700 mg/g C org ), and immature asphalts are found to be associated with them. Geochemical analysis indicates that the bitumens are indigenous to the host SBR, and the associated asphalts are bitumens that have migrated a short distance with negligible chemical fractionation. The high heteroatom content of the kerogens (up to 30%) in the SBR is suggested as a possible cause of the generation of asphaltic oils in an early stage of maturation.

Biological markers in bitumens and pyrolyzates of Upper Cretaceous bituminous chalks from the Ghareb Formation (Israel)

Abstract The sterane and triterpane distributions of three bituminous chalks from the Upper Cretaceous Ghareb Formation (Israel) were investigated both in the original extractable bitumens and in extracts obtained after pyrolysis of whole rock and isolated kerogen samples at 450°C. Pyrolysis was performed in a closed system under hydrous (whole rock) and anhydrous conditions (isolated kerogens). The carbon number distributions of steranes and triterpanes differ significantly between original bitumen and pyrolyzates. Unlike the bitumens in which diasteranes were not detected, the anhydrous pyrolyzates contain small amounts of diasteranes. The presence of water during pyrolysis leads to an increase of sterane isomerization, the abundant formation of diasteranes and an increase of the 18α( H )- trisnorneohopane 17α( H )- trisnorhopane ratio. Sterane isomerization maturation parameters show a closer match between original bitumen and pyrolyzates after pyrolysis in a closed system when compared with an open system.

The distribution and isotopic composition of sulfur in organic-rich sedimentary rocks

Abstract Sulfur concentration in bituminous chalks of the Maastrichtian—Campanian Ghareb Formation is high (1.8–2.6%), its concentration and isotope composition were determined for the main S-bearing phases: pyrite, extractable bitumen and kerogen. Pyritic sulfur accounts for only 20–54% of total S content. Sulfur concentration in the bitumen and kerogen fractions are 8.9–16.4% and 6.5–12.1%, respectively. Two distinct types of isotope composition reflect different depositional environments and diagenetic processes; type-1 pyrite (−19.4 to −23.8‰) is much lighter than organically bonded S in the bitumen and kerogen (−4.2 and −8 to −10.7‰, respectively). Type 2, all sulfur compounds are heavier than type 1 and the difference between species smaller; pyritic sulfur (+6.1‰), bitumen and kerogen (+1.7 to +8.7 and +1.2 to +8.3‰, respectively). Sulfur-isotopic composition of the pyrite is as a rule the lightest species and indicates that bacterial activity is involved in pyrite formation. The heavier sulfur in organic compounds suggests a secondary enrichment, probably via a radical mechanism. The marked differences between the two types of isotope composition may be due to differences in the sulfate reduced, or to escape of light, reduced sulfur. Sulfur-enrichment experiments in kerogen showed that high degree of enrichment is associated with loss of oxygen; low-S kerogen is enriched more than high-S kerogen. Decrease in ESR N g -value is associated with secondary sulfur enrichment.

Investigations on the structural units of melanoidins

A series of sugar-amino acid derived melanoidins were synthesized and their chemical and physical properties were evaluated using spectral, chemical and thermal analyses. It is suggested that the melanoidin “back-bone” is probably a sugar-moiety polymer in which various nitrogen containing groups are grafted. Some resemblance between marine humics and synthetic melanoidins was found.

The formation of isoprenoid sulfur compounds during diagenesis: simulated sulfur incorporation and thermal transformation

Abstract The mechanism of natural sulfur incorporation into organic matter during early diagenesis was studied by simulation reactions carried out with three isoprenoid aldehydes under phase transfer catalysis (PTC) of ammonium polysulfide at ambient temperatures. The adehydes were phytenal ( 4 ), an α,β-unsaturated aldehyde formed by mild oxidation of phytol ( 3 ), citral ( 5 ), a monoterpene dienal, and 2H-dihydrocitronellal ( 6 ), a saturated monoterpene aldehyde. All three aldehydes gave polysulfide cross-linked macromolecules. The structures of the macromolecular substances were studied by the analysis of the products formed by MeLi/MeI depolymerization. The structures of these products are similar to the products formed by the same method from sulfur-rich macromolecular structures identified in immature sediments. Thermal decomposition experiments of the macromolecular products of the α,β-unsaturated aldehydes gave the corresponding isoprenoid thiophenes. The C 20 isoprenoid thiophenes formed from 4 are found in many natural immature sediments. A mechanism for the formation of these thiophenes is presented. These results give additional chemical support to the important role of inorganic polysulfide anions as molecular binders in nature. The results suggest that thermal processes that follow the incorporation of sulfur may play an important role in transforming the early formed sulfur-containing compounds into thermally stable structures. The results also provide a possible new pathway for phytol degradation in sulfide-rich environments and for the formation of C 20 isoprenoid thiophenes.

Polyoxometalates as Reduction Catalysts: Deoxygenation and Hydrogenation of Carbonyl Compounds

Excellent deoxygenation of ketones and aldehydes is achieved with Keggin-type polyoxometalates in the presence of hydrogen (see Equation (1) for an example). The mixed addenda phosphovanadomolybdate [PV(2)Mo(10)O(4)](5-) was found to be the best catalyst. X-ray diffraction and IR studies suggest that the polyoxometalates are structurally stable under the strongly reducing conditions.

Preferential catalytic hydrogenation of aromatic compounds versus ketones with a palladium substituted polyoxometalate as pre-catalyst

A palladium-substituted polyoxometalate having a Keggin structure, supported on γ-alumina or active carbon, was used as a catalyst precursor for catalytic hydrogenation. The catalyst system enabled fast hydrogenation of arenes at 30 bar H2 and 230 °C. Most interesting was the finding that arenes could be selectively reduced in the presence of distal ketone groups under similar conditions, 30 bar H2 and 200 °C. For example, 1-phenyl-2-propanone yielded 1-cyclohexyl-2-propanone with no reduction of the ketone moiety. Additionally, aromatic compounds with vicinal (conjugated) ketone moieties underwent complete hydrogenation to saturated hydrocarbons and catalytic McMurry coupling was observed for aliphatic aldehydes.

Thermal behavior of brominated and polybrominated compounds. I: closed vessel conditions

Abstract Israel is one of the leading manufacturers of organic brominated compounds, hence the very intensive manufacturing of such compounds creates both, hazardous industrial refuge and large amounts of brominated byproducts. Environmentally the storage of these huge amounts of materials may lead to major hazards: (a) water reservoirs contamination; (b) land contamination. It is suggested to incinerate the accumulated and presently produced organic wastes by the existing organic hazardous wastes incineration plants, one should take into account the fact that polybrominated compounds are fire retardants! The thermal behavior of the CBr bond was scantly investigated up-to-date. In the present work and those to follow we report on our examinations of various brominated organics pyrolysis experiments e.g. bromohexane (BH) bromocyclohexane (BCH), bromonaphthalene, 4,4′-isopropylidene bis(2,6-dibromophenol) measurements were carried out only for the solid and polybrominated compounds whereas time and temperature experiments were conducted under closed vessel conditions (quartz ampoules). The analyses of the pyro-products were initially monitored by gas, extractables and solids using both selective detectors (FID, ECD), GC and GC/MS (for gases and liquids). Experiments were conducted between 400 and 1000°C, and pyrolysis exposure times from 10 s to 1 h. We present the results obtained for single compound and hydrogen donor mixed with compound. The conclusions drawn as presented in the concluding remarks are: (1) most of the released bromine is in HBr form and probably the reason for retardation; (2) At 1000°C the organic products are low molecular weight gases and char; (3) The amounts of dibenzodioxins and dibenzofurans are minute and thermally unstable; (4) the aliphatic brominated compounds are thermally less stable than the aromatics; (5) Under oxygen conditions the formation of large amounts of HBr is acting as retardant even in the presence of excess hydrogen donors; (6) the presence of hydrogen donors is conducive to the formation of HBr, increase of rate and quantity.

Carbon-13 cross polarized magic-angle samples spinning nuclear magnetic resonance of melanoidins

Abstract Melanoidins synthesized from amino-acids and sugars in various ratios and humic substances from Hula Basin (Israel) have been investigated by 13 C-CP/MAS NMR spectroscopy. Most spectra indicated a significant similarity between melanoidins and humics. It is suggested that the Maillard reaction plays a more significant role in the formation of humic substances than the “traditional” theory based on a lignin source. Several heterocyclic and heteroaromatic moieties (mainly furanoid, hydroxy-alkyl-furanone and hydroxy-alkyl-cyclopentenone) have been considered as major “building blocks” of humic substances and melanoidins. Aromaticities calculated from NMR spectral data of SM (“sugar” enriched melanoidins) and AAM (amino acid enriched melanoidins) coincide remarkably with the aromaticities of terrestrial and marine humics, respectively.

Formation of immature asphalt from organic-rich carbonate rocks. II: Correlation of maturation indicators

The present study focuses on some discrepancies among maturation indicators of the Senonian bituminous rocks (SBR) in Israel. These rocks are mainly carbonates that were deposited under reducing conditions and contain heteroatom-rich organic matter that has been severely reworked by bacteria. In two cases, heavy asphaltic oils are associated with the SBR and a genetic relation between them has been established. Whereas the time-temperature index (TTI < 3) and vitrinite reflectance (R0 = 0.3−0.4%) indicate early stage maturation, the bitumen content (up to 700 mg g Corg−1) and the asphaltic oils imply an oil generation zone in the SBR. Other indicators such as isomerization of hopanes and steranes and CPI values indicate even higher maturation levels. The discrepancies between these maturation indicators are explained by the different kinetic parameters of the maturation processes in the various constituents of the organic matter.