Showing papers by "ExxonMobil published in 1994"

Facile Catalyst Separation Without Water: Fluorous Biphase Hydroformylation of Olefins

Abstract: A novel concept for performing stoichiometric and catalytic chemical transformations has been developed that is based on the limited miscibility of partially or fully fluorinated compounds with nonfluorinated compounds. A fluorous biphase system (FBS) consists of a fluorous phase containing a dissolved reagent or catalyst and another phase, which could be any common organic or nonorganic solvent with limited or no solubility in the fluorous phase. The fluorous phase is defined as the fluorocarbon (mostly perfluorinated alkanes, ethers, and tertiary amines)-rich phase of a biphase system. An FBS compatible reagent or catalyst contains enough fluorous moieties that it will be soluble only or preferentially in the fluorous phase. The most effective fluorous moieties are linear or branched perfluoroalkyl chains with high carbon number; they may also contain heteroatoms. The chemical transformation may occur either in the fluorous phase or at the interface of the two phases. The application of FBS has been demonstrated for the extraction of rhodium from toluene and for the hydroformylation of olefins. The ability to separate a catalyst or a reagent from the products completely at mild conditions could lead to industrial application of homogeneous catalysts or reagents and to the development of more environmentally benign processes.

Effectiveness of bioremediation for the Exxon Valdez oil spill

Abstract: The effectiveness of bioremediation for oil spills has been difficult to establish on dynamic, heterogeneous marine shorelines A new interpretative technique used following the 1989 Exxon Valdez spill in Alaska shows that fertilizer applications significantly increased rates of oil biodegradation Biodegradation rates depended mainly on the concentration of nitrogen within the shoreline, the oil loading, and the extent to which natural biodegradation had already taken place The results suggest ways to improve the effectiveness of bioremediation measures in the future

Reduction of frictional forces between solid surfaces bearing polymer brushes

Abstract: THE use of lubricants to reduce friction and wear between rubbing surfaces has been documented since antiquity1–3. Recent approaches have focused on boundary lubrication by surfactant-like species coating the surfaces, whereby the friction between them is replaced by the weaker forces required for shear of adhesive contacts between the surfactant layers3,4. An alternative approach is to tether polymer chains to the surfaces by one end which, when swollen by a solvent, then act as molecular ‘brushes’ that may facilitate sliding. The normal forces between sliding brush-bearing surfaces have been previously investigated5,6, but the lateral forces, which are the most important from the point of view of lubrication, are harder to measure. Here we report the measurement of lateral forces in such a system. We find a striking reduction in the effective friction coefficients μb between the surfaces to below our detection limit (μb < 0.001), for contact pressures of around 1 MPa and sliding velocities from zero to 450 nm s−1. We believe that this effect is due to the long-ranged repulsion, of entropic origin, between the brushes, which acts to keep the surfaces apart while maintaining a relatively fluid layer at the interface between them.

A photoluminescence study of poly(phenylene vinylene) derivatives: The effect of intrinsic persistence length

Abstract: We report the results of light scattering, absorption, excitation, and emission spectroscopy of three polyphenylene vinylene (PPV) derivatives; poly[2‐methoxy, 5‐(2’‐ethyl‐hexyloxy‐p‐phenylene‐ vinylene] (MEH‐PPV), poly[2‐butoxy, 5‐(2’‐ethyl‐hexyloxy‐p‐phenylene‐vinylene] (BEH‐PPV), and poly[2‐dicholestanoxy‐p‐phenylene‐vinylene] (BCHA‐PPV) in solution with p‐xylene. We find that increasing the size of the solubilizing side chains increases the intrinsic persistence length of the polyphenylene vinylene backbone and that this change in stiffness has dramatic effects on the photoluminescence of polyphenylene vinylene. We have determined the luminescence quantum efficiencies of the polyphenylene vinylene derivatives relative to a known standard, Rhodamine 6G, and find that the photoluminescence can be greatly enhanced by increasing the intrinsic stiffness of the polymer backbone. The stiffest polymer, poly[2‐dicholestanoxy‐p‐phenylene‐vinylene] (BCHA‐PPV), has a quantum efficiency of 0.66±0.05. The quantum e...

Entropically driven surface phase separation in binary colloidal mixtures.

Abstract: We investigate the phase diagram of mixtures of charge stabilized polystyrene spheres of two different sizes in the hard-sphere limit. We observe bulk phase separation into two disordered phases and find a new ordered phase located on the cell walls. The ordered phase occurs at volume fractions as low as 0.2, much less than the value of 0.49 for hard-sphere freezing in monodisperse suspensions, and is qualitatively explained with simple geometric arguments.

Neutron reflectivity study of the density profile of a model end-grafted polymer brush: Influence of solvent quality

Abstract: Neutron reflectivity measurements are made on a chemically end-grafted polymer brush swollen over a range of temperatures above and below the theta point. Good agreement between the brush profiles and recent self-consistent field calculations and numerical simulations is obtained for temperatures in the vicinity of the theta point and in a good solvent. The expansion of the main body of the brush resembles a swelling gel, while the brush tail expands similarly to a polymer in solution.

Fundamental Studies of Transition-Metal Sulfide Catalytic Materials

Abstract: Publisher Summary This chapter reviews the current understanding of the relation between the properties of the transition-metal sulfide (TMS) and how they catalyze hydrotreating reactions. The TMS are unique class of catalysts that are able to perform numerous hydrogenation and hydrogenolysis reactions in the presence of sulfur. In fact, they require sulfur for activity maintenance. The catalytic activity and selectivity of the TMS arises from the electronic and structural properties of the sulfides themselves. Support effects are secondary, improving sulfide dispersion and reducing metal cost in commercial catalysts. Fundamental effects can only be elucidated by studying TMS catalysts in their fully sulfided and catalytically stabilized states. Studies are often simplified by studying the unsupported TMS, which in the past have been commercial catalysts with extraordinarily stable catalytic activity. The study of supported catalysts can also be useful if the experiments are carefully designed and the results are compared consistently with those from unsupported systems.

Electronic and nuclear chemical reactivity

Abstract: The local softness and the Fukui function emerge from density functional theory as measures of local electronic reactivity. We obtain here an exact linear integral relation between the Fukui functions of insulators or molecules and the probability density of the frontier orbitals of Kohn–Sham theory. The same linear map holds between the local softness and the local Kohn–Sham density of states at the Fermi level for metals. The kernel in those relations is the inverse of the transpose of the potential response function (PRF) of Kohn–Sham theory. The PRF has the form of the static Hartree dielectric function with an exchange and correlation interaction added to the bare Coulomb interaction. The exact static dielectric function also has the Hartree form, but with a renormalized polarization propagator. The map is norm preserving for systems with energy gaps such as insulators and molecules and norm reducing or screening for systems with a finite density of states above the ground state such as normal metals...

Process for preparing short chain alkyl aromatic compounds

Abstract: A process for producing alkyl aromatic compounds which comprises contacting at least one aromatic compound with at least one alkylating agent or transalkylating agent possessing at least one aliphatic group having from 1 to 5 carbon atoms under alkylation or transalkylation reaction conditions and in the presence of an alkylation or transalkylation catalyst, to provide an alkylated aromatic product possessing at least one alkyl group derived from said alkylating agent or transalkylating agent, said catalyst comprising a binder-free molecular sieve having an X-ray diffraction pattern that includes the lines set forth in Table A

A review of pseudospectral methods for solving partial differential equations

Abstract: Finite Difference (FD) methods approximate derivatives of a function by local arguments (such as du(x) / dx ≈ (u(x + h) − u(x − h))/2h, where h is a small grid spacing) – these methods are typically designed to be exact for polynomials of low orders. This approach is very reasonable: since the derivative is a local property of a function, it makes little sense (and is costly) to invoke many function values far away from the point of interest.

Polymerization catalysts, their production and use

Abstract: The invention generally relates to a catalyst, particularly a metallocene catalyst and catalyst system useful in the polymerization of olefins into a polymer product. The polymer product has a broad molecular weight distribution, a high molecular weight and a narrow composition distribution and is easily processable.

Suppression of Rupture in Thin, Nonwetting Liquid Films

Abstract: Stabilization against the rupture and breakup of thin, nonwetting liquid films spread on surfaces is generally sought by modification of equilibrium interfacial properties. A mechanism for suppressing rupture in such films that uses surface-attached polymers togetherwithfree chains in the bulk of the film is reported. Films of an oligostyrene liquid, which rupture within several minutes when spread on a silicon wafer, may be stabilized for many months by a polystyrene brush attached to the substrate, together with some free polystyrene in the liquid. The effect may arise from entanglements of the free chains with the immobilized brush.

Observation of a Reversible Thermotropic Order–Order Transition in a Diblock Copolymer

Abstract: The authors report the observation of a reversible thermotropic transition between the lamellar and cylindrical morphologies in a polystyrene-poly(ethene-co-butene) diblock copolymer. The nature of the intermediate structures which form as the transition progresses has been examined using two-dimensional small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Results show that the transformation from the lamellar to the cylindrical morphology proceeds in two steps. Initially, fluctuations along the interface joining the components of the copolymer grow in amplitude until the lamella transforms into a sheet of eventually spaced cylinders; cylinders which form in adjacent lamellae are usually in poor register with one another. This intermediate structure subsequently anneals into the hexagonal packing of cylinders characteristic of the cylindrical morphology. The reverse transition from cylinders to lamellae proceeds without producing any intermediate signature detectable by SAXS.

Distillate fuel production from fischer-tropsch wax

Abstract: Distillate fuels with excellent cold flow properties are produced from waxy Fischer-Tropsch products by separating the product into a heavier and a lighter fraction, isomerizing the heavier fraction, hydrotreating and isomerizing the lighter fraction, and recovering products in jet and diesel fuel ranges.

Practical considerations in the application of simulated annealing to stochastic simulation

Abstract: Realizations generated by conditional simulation techniques must honor as much data as possible to be reliable numerical models of the attribute under study. The application of optimization methods such as simulated annealing to stochastic simulation has the potential to honor more data than conventional geostatistical simulation techniques. The essential feature of this approach is the formulation of stochastic imaging as an optimization problem with some specified objective function. The data to be honored by the stochastic images are coded as components in a global objective function. This paper describes the basic algorithm and then addresses a number of practical questions: (1) what are the criteria for adding a component to the global objective function? (2) what perturbation mechanism should be employed in the annealing simulation? (3) when should the temperature be lowered in the annealing procedure? (4) how are edge/border nodes handled? (5) how are local conditioning data handled? and (6) how are multiple components weighted in the global objective function?

Diffuse-transmission spectroscopy: A structural probe of opaque colloidal mixtures

Abstract: The wavelength-dependent diffuse transmission through a monodisperse colloidal suspension is shown to provide wave-vector-dependent information about the colloid structure factor. Experiments demonstrate that the spectral fingerprint can be used to distinguish quantitatively samples of different particle sizes, different concentrations, and different interparticle interactions.

The X-ray Surface Forces Apparatus: Structure of a Thin Smectic Liquid Crystal Film Under Confinement

Abstract: An x-ray surface forces apparatus for simultaneously measuring forces and structures of confined complex fluids under static and flow conditions is described. This apparatus, combined with an intense synchrotron x-ray source, allows investigation of molecular orientations within a thin liquid crystal film confined between two shearing mica surfaces 3900 angstroms apart. The layer-forming smectic liquid crystal 8CB (4-cyano-4'-octylbiphenyl) adopted a series of distinct planar layer orientations, including the bulk flow-forbidden b orientation.

A phase of liposomes with entangled tubular vesicles

Abstract: An equilibrium phase belonging to the family of bilayer liposomes in ternary mixtures of dimyristoylphosphatidylcholine (DMPC), water, and geraniol (a biological alcohol derived from oil-soluble vitamins that acts as a cosurfactant) has been identified. Electron and optical microscopy reveal the phase, labeled Ltv, to be composed of highly entangled tubular vesicles. In situ x-ray diffraction confirms that the tubule walls are multilamellar with the lipids in the chain-melted state. Macroscopic observations show that the Ltv phase coexists with the well-known L4 phase of spherical vesicles and a bulk L alpha phase. However, the defining characteristic of the Ltv phase is the Weissenberg rod climbing effect under shear, which results from its polymer-like entangled microstructure.

Inelastic neutron scattering from the spin ladder compound (VO)2P2O7.

Abstract: We present results from an inelastic neutron scattering experiment on the candidate Heisenberg spin ladder vanadyl pyrophosphate, (VO)[sub 2]P[sub 2]O[sub 7]. We find evidence for a spin-wave excitation gap of [ital E][sub gap]=3.7[plus minus]0.2 meV, at a band minimum near [ital Q]=0.8 A[sup [minus]1]. This is consistent with expectations for triplet spin waves in (VO)[sub 2]P[sub 2]O[sub 7] in the spin-ladder model, and represents the first confirmation in nature of a Heisenberg antiferromagnetic spin ladder.

Process for the production of plasticizer and polyol esters

Abstract: A process for the catalytic or non-catalytic esterification of acids or anhydrides with a mono-alcohol or a polyhydroxy compound which comprises the steps of adding the reagents to a reaction vessel to form a reaction mixture, and heating the reaction mixture and maintaining a pressure sufficient to obtain boiling of the reaction mixture thereby causing esterification and removing water as vapor while continuously mixing the reaction mixture in the reactor vessel such that at least about 2.5 to about 20 volumes of reaction mixture are internally recirculated per minute, whereby the rate of conversion is enhanced.

Permeability determination from NMR relaxation measurements for fluids in porous media

Abstract: The present invention is a method to rapidly determine the fluid-flow permeability of porous media with nuclear magnetic resonance (NMR). The method can be applied to measurements of permeability in fluid-saturated earth formations using NMR logging tools.

Temperature-programmed oxidation technique: kinetics of coke-O2 reaction on supported metal catalysts

Abstract: Coke oxidation rates on supported metal catalysts were studied by temperature-programmed oxidation (TPO). The TPO data were successfully modeled with a linear combination of power-law kinetic expressions. The validity and limitations of the model, for carbon oxidation on metal containing catalysts, were analyzed in detail. The influence of heating rate, coke concentration, coke particle size and number, catalyst mass and oxygen concentration on TPO spectra predicted by the model agreed well with experimental results. Coke particle size and morphology have a great influence on a TPO spectrum. Even though this simplified form of kinetic expression does not explicitly account for all the physical phenomena in a coke-burn process, it considers some of the most important factors: the effect of carbon surface area and the promotional effect of supported metals on coke-burn kinetics. Deconvolution of a complex TPO spectrum by the above model provides kinetic parameters which can be used to predict TPO spectra of partial-coke-burn experiments. Difficulties in the predictive capability of this model arrive if other factors such as large variations in coke morphology and coke particle size exist and there is no information relating them to a particular feature in the TPO spectrum. However, the model can adequately account for these variations, if their characteristics and extent are known, e.g., they may be determined by electron microscopy.

Membrane process for increasing conversion of catalytic cracking or thermal cracking units (law011)

Abstract: The yield and quality of products secured from cracking units is increased by the process of subjecting the product stream secured from such cracking unit to a selective aromatics removal process and recycling the recovered aromatics lean (saturates rich) stream to the cracking unit whereby such saturates rich stream is subjected to increased conversion to higher value desired products.

Supported zeolite membranes with controlled crystal width and preferred orientation grown on a growth enhancing layer

Abstract: The present invention is directed toward a new zeolite membrane which exhibits a columnar cross-sectional morphology and preferred crystallographic orientation comprising a porous substrate having coated thereon a mesoporous growth enhancing layer and a layer of columnar zeolite crystals on said mesoporous growth enhancing layer, and wherein said mesoporous growth enhancing layer comprises nanocrystalline or colloidal sized zeolites, nanocrystalline or colloidal zeolite and metal oxide, or nanocrystalline or colloidal zeolite and colloidal metal, or nanocrystalline or colloidal zeolite, colloidal metal and metal oxide, and wherein said mesoporous growth enhancing layer has interstices of about 20 to about 2000 Å, and wherein said columnar zeolite layer is a polycrystalline layer wherein 99.9% of said columnar zeolite crystals have at least one point between adjacent crystals that is ≦20 Å. The invention is further directed to a process of producing a zeolite membrane exhibiting a columnar crystallographic orientation.

The Science of Rubber Compounding

Abstract: This chapter reviews both the types and the properties of elastomers, compounding with a range of filler or reinforcement systems such as carbon black, and enhancement of filler performance by novel use of compounding ingredients such as silane coupling agents. Other issues such as antioxidant systems and vulcanization systems are also discussed.

Ethylene copolymers having narrow composition distribution, their production and use

Abstract: This disclosure concerns copolymers of ethylene and at least one C4-C12 monomer, and also concerns the production and application of these copolymers. These copolymers may be produced using supported metallocene catalysts in a gas phase polymerization process. These copolymers can be produced to have composition distributions intermediate those of polyethylene resins derived from Ziegler-Natta catalysts and those of single site catalysts. The polyethylene resins of the disclosure are particularly useful in producing films and in certain other applications.