ExxonMobil

About: ExxonMobil is a company organization based out in Irving, Texas, United States. It is known for research contribution in the topics: Catalysis & Polymer. The organization has 16969 authors who have published 23758 publications receiving 535713 citations. The organization is also known as: Exxon Mobil Corporation & Exxon Mobil Corp..

Enrichment, resolution, and identification of nickel porphyrins in petroleum asphaltene by cyclograph separation and atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass spectrometry.

Abstract: We report here the first high resolution mass spectrometric evidence of nickel porphyrins in petroleum. A petroleum asphaltene sample is fractionated by a silica-gel cyclograph. Nickel content is enriched by ∼3 fold in one of the cyclograph fractions. The fraction is subsequently analyzed by atmospheric pressure photoionization (APPI) Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) with an average mass resolving power of over 500 K (M/ΔMfwhm). Similar to vanadyl porphyrins, monocylcoalkano-type (presumed to be deocophylerythro-etioporphyrin DPEP) Ni porphyrins are found to be the most abundant family followed by etio, bicycloalkano-type, and rhodo-monocylcoalkano-type Ni porphyrins. A Z number ranging from −28 to −44 and a carbon number ranging from 26 to 41 were observed. A significant amount of nickel and vanadyl geoporphyrins are in more condensed tetrapyrrolic cores than just chlorophyll-derived DPEP- and etioporphyrins. Ni has a higher etio/DPEP ratio and rhodo-etio/rhodo-DPEP ...

Effect of tides on mouth bar morphology and hydrodynamics

Abstract: [1] Mouth bars are morphological units important for deltas, estuaries, or rivers debouching into the sea. Several processes affect the formation of these deposits. This paper focuses on the role of tides on shaping mouth bars, presenting both hydrodynamic and morphodynamic results. The effect of tides is analyzed in two end-member configurations: a river with a small tidal discharge compared to the fluvial discharge (fluvial dominated) and a river with a very large tidal discharge (tidal dominated). Mouth bar formation is analyzed using the coupled hydrodynamic and morphodynamic model Delft3D. The presence of tides influences the hydrodynamics of the jet exiting the river mouth and causes an increase in the averaged jet spreading. At low tide the lower water depth in the basin promotes a drawdown water profile in the river and an accelerated flow near the mouth. The resulting velocity field is characterized by residual currents affecting growth and final shape of the mouth bar. Simulations indicate that mouth deposits are characterized by the presence of two channels for negligible tidal discharge, whereas three principal channels are present in the tidal-dominated case, with a central channel typical of tidal inlets. On the basis of our numerical analyses, we present a robust criterion for the occurrence of mouth deposits with three channels. Trifurcations form when the tidal discharge is large with respect to the fluvial one and the tidal amplitude is small compared to the water depth. Finally, predicted mouth bar morphologies are compared with good agreement to river mouths in the Gulf of Mexico, USA.

The Molybdenum Site of Sulfite Oxidase: A Comparison of Wild-Type and the Cysteine 207 to Serine Mutant Using X-ray Absorption Spectroscopy

Abstract: X-ray absorption spectroscopy at the molybdenum and sulfur K-edges has been used to probe the active site of wild-type and cysteine 207 → serine mutant human sulfite oxidases. We compare the active site structures in the Mo(VI) oxidation states: the wild-type enzyme possesses two MoO ligands at 1.71 A and three Mo−S ligands at 2.41 A. The mutant molybdenum site is a novel trioxo site with MoO bond lengths of 1.74 A, with two Mo−S ligands at 2.47 A. We conclude that cysteine 207 is a ligand of molybdenum in wild-type human sulfite oxidase, and that, in the mutant, the Mo is ligated to an extra oxo group rather than the hydroxyl of the substituent serine 207.

Catalytic conversion with improved catalyst

Abstract: A process is provided for converting feedstock hydrocarbon compounds over a catalyst composition which comprises clay and a zeolite component, at least one of which has been treated with a phosphorus-containing compound, for example, ammonium dihydrogen phosphate or phosphoric acid, and which is spray dried at a low pH, preferably lower than about 3. An embodiment of the present invention comprises an improved catalytic cracking process to produce high octane gasoline and increased lower olefins, especially propylene and butylene.

Thermodynamics of isotopic polymer mixtures: Significance of local structural symmetry

Abstract: The dependence on composition (Φ) and degree of polymerization (N) of the effective segment–segment interaction parameter, χ=− 1/2 ∂2Γ/∂Φ2, has been determined for mixtures of perdeuterated and normal (protonated) poly(vinylethylene) and poly(ethylethylene) by small angle neutron scattering (SANS), where Γ represents the excess free energy of mixing. Owing to the small reduction in length and polarizability of carbon–hydrogen bonds with deuterium substitution, isotopic polymer mixtures are characterized by small positive χ parameters. However, deuterium substitution does not significantly influence the local structural symmetry (i.e., the liquid structure or reduced thermodynamic properties) of polymer isotopes, consistent with the assumptions of Flory–Huggins (FH) lattice theory. Nevertheless, we find that χ depends significantly on both Φ and N, contrary to the predictions of FH theory. A general theory, which corrects FH theory for monomer concentration fluctuations, is shown to closely account for these experimental results. In understanding the previous experimental investigations of χ for mixing chemically different species, the monomer concentration fluctuations discussed here must be addressed in addition to the effects due to local structural asymmetry.