Bulk and molecular composition variations of gold-tube pyrolysates from severely biodegraded Athabasca bitumen

Gold-tube pyrolysis experiments were performed on two Athabasca oil sand bitumens at 300℃to 525℃with 2℃/h rate and 25℃step under 50 MPa.Pyrolysis temperature of 425℃is critical for weight loss of bulk bitumen and hydrocarbon generation and destruction.Polar compounds are the main source of saturated and aromatic hydrocarbon,gas and coke fractions.Molecular compositions in pyrolyzates vary systematically with increasing pyrolysis temperatures.High molecular weight n-alkanes(C26^+) are gradually destructed during pyrolysis due to thermal cracking.Moderate molecular weight n-alkanes(C21-C25)show the highest thermal stability in designed pyrolysis temperatures.The loss of low molecular weight n-alkanes(C20^-)might be caused by volatilization during pyrolysis,which may alter commonly used molecular parameters such as∑n-C20^-/∑n-C21^+,Pr/n-C17 and Ph/n-C18.Aromatic hydrocarbons were generated from 300 to 425℃,then condensation and dealkylation have been initiated at 425℃as evidenced by decreased summed alkylnaphthalenes to alkylphenanthrenes ratios and increased unsubstituted aromatics to substituted homologs ratios in higher temperatures.The occurrence of anthracene and benz[a]anthracene in pyrolysates indicates pyrogenic origin,while fluoranthene shows unexpected behaviors during pyrolysis.Ratios derived from them are not always reliable for pyrogenic source input diagnosis in environmental samples.

A novel redox indicator based on relative abundances of C_(31) and C_(32) homohopanes in the Eocene lacustrine Dongying Depression, East China

A suite of oils and bitumens from the Eocene Shahejie Formation(Es) in Dongying Depression was geochemically characterized to illustrate impact of source input and redox conditions on distributions of pentacyclic terpanes. The Es_(4) developed under highly reducing, sulfidic hypersaline conditions, while Es_(3) formed under dysoxic, brackish to freshwater conditions. Oils derived from Es_(4) are enriched in C_(32) homohopanes(C_(32) H), while those from Es_(3) are prominently enriched in C_(31) homohopanes(C_(31) H). The C_(32) H/C_(31) H ratio shows positive correlation with homohopane index(HHI), gammacerane index, and negative correlation with pristane/phytane ratio, and can be used to evaluate oxic/anoxic conditions during deposition. High C32 H/C_(31) H ratio(> 0.8) is an important characteristic of oils derived from anoxic environments, while low values(< 0.8) indicate dysoxic conditions and extremely low values(< 0.4)indicate strong oxic conditions. The C_(32) H/C_(31) H ratio can be applied for deposition condition diagnosis because carboxyl group of C_(32) hopanoic acids might be reduced to C_(32) homohopanes under anoxic conditions, and oxidized to C_(31) homohopane under oxic conditions. Advantages to use C_(32) H/C_(31) H ratio as redox condition proxy compared to the HHI and gammacerane indexes are wider valid maturity range,less sensitive to biodegradation influence and better differentiating reducing from oxic environments.

One-step thermal oxidation synthesis of large-area Mn_(3)O_(4)nanoflakes at low temperature in air atmosphere

Single-crystalline Mn_(3)O_(4)nanoflakes were grown on manganese sheets by one-step thermal oxidation process at 360-500℃in ambient atmosphere.The samples were characterized by scanning electron microscope(SEM),X-ray diffraction(XRD),Raman and transmission electron microscope(TEM).The nanoflakes with a size of 15-20 nm in thickness,~60 nm in width,and~210 nm in length are obtained at 360℃for 24 h.A surface diffusion mechanism is proposed to explain the growth of manganese oxide nanostructures via thermal oxidation,which includes two steps:manganese oxide(MnO/Mn_(3)O_(4))layers form firstly,and then Mn_(3)O_(4)nanostructures grow above the upper metal oxide layer to form multi-layered structures,MnO/Mn_(3)O_(4)/Mn_(3)O_(4)-nanoflakes.The nucleation and growth of Mn_(3)O_(4)nanostructures are related to the surface energy and different growth rates along different crystal directions,which are controlled by the diffusion of the metal and gas molecule.