Showing papers by "ExxonMobil published in 1998"

Condensation in Smooth Horizontal Tubes

Abstract: An experimental study of heat transfer and flow regimes during condensation of refrigerants in horizontal tubes was conducted. Measurements were made in smooth, round tubes with diameters ranging from 3.14 mm to 7.04 mm. The refrigerants tested were R-12, R-22, R-134a, and near-azeotropic blends of R-32/R-125 in 50 percent/50 percent and 60 percent/40 percent compositions. The study focused primarily on measurement and prediction of condensing heat transfer coefficients and the relationship between heat transfer coefficients and two-phase flow regimes. Flow regimes were observed visually at the inlet and outlet of the test condenser as the heat transfer data were collected. Stratified, wavy, wavy annular, annular, annular mist, and slug flows were observed. True mist flow without a stable wall film was not observed during condensation tests. The experimental results were compared with existing flow regime maps and some corrections are suggested. The heat transfer behavior was controlled by the prevailing flow regime. For the purpose of analyzing condensing heat transfer behavior, the various flow regimes were divided into two broad categories of gravity-dominated and shear-dominated flows. In the gravity dominated flow regime, the dominant heat transfer mode was laminar film condensation in the top of the tube. This regime was characterized by heat transfer coefficients that depended on the wall-to-refrigerant temperature difference but were nearly independent of mass flux. In the shear-dominated flow regime, forced-convective condensation was the dominant heat transfer mechanism. This regime was characterized by heat transfer coefficients that were independent of temperature difference but very dependent on mass flux and quality. Heat transfer correlations that were developed for each of these flow regimes successfully predicted data from the present study and from several other sources.

Two or four Neoproterozoic glaciations

Abstract: A thick Neoproterozoic carbonate and glaciogenic succession of the southern Congo craton has yielded δ 13 C and 87 Sr/ 86 Sr records through the later Cryogenian (ca. 750–600 Ma) and earlier part of the Terminal Proterozoic (ca. 600–570 Ma). Sizeable negative δ 13 C excursions (to less than–5‰) occur above each of two glacial intervals and the 87 Sr/ 86 Sr values of marine carbonates shift from ∼0.7072 to ∼0.7079 at the upper glacial level. These geochemical constraints provide a Marinoan (younger Varanger) age for the upper glacial interval, previously regarded as a second phase of the Sturtian glaciation. The δ 13 C record from the Congo craton is therefore incompatible with recent global δ 13 C syntheses that have identified four or more separate ice ages during the Neoproterozoic. A cladistic analysis of geologic and geochemical characters of 12 Neoproterozoic glacial deposits identifies two distinct groups that are found in a consistent stratigraphic order whenever two glacial units occur within a single succession. We use δ 13 C and 87 Sr/ 86 Sr records from the Congo craton and other key successions to test the null hypothesis that there were only two global glaciations (Sturtian and Marinoan) during the Neoproterozoic. Placing the GSSP (global stratotype section and point) for the base of the Terminal Proterozoic within or just above a cap carbonate of the younger (Marinoan) glaciogenic succession would confine all known Neoproterozoic glaciations to the Cryogenian. The rapid shift in marine 87 Sr/ 86 Sr to more radiogenic values during the Marinoan glaciation is opposite that predicted by the snowball Earth scenario which calls for continental runoff to cease during glaciation, resulting in a shift to less radiogenic values.

Hydroplaning of subaqueous debris flows

Abstract: We report laboratory experiments that demonstrate that the fronts of subaqueous debris flows can hydroplane on thin layers of water. The hydroplaning dramatically reduces the bed drag, thus increasing head velocity. These high velocities promote sediment suspension and turbidity-current formation. Hydroplaning causes the fronts of debris flows to accelerate away from their bodies to the point of completely detaching from the bodies, producing surging. Instigation of hydroplaning is controlled by the balance of gravity and inertia forces at the debris front and is suitably characterized by the densimetric Froude number. The laboratory flows constrain hydroplaning to cases where the calculated densimetric Froude number is greater than 0.4. The presence of a basal lubricating layer of water underneath hydroplaning debris flows and slides offers a possible explanation for the long run-out distances of many subaqueous flows and slides on very low slopes.

Isoparaffinic lube basestock compositions

Abstract: A liquid hydrocarbon composition, containing paraffinic hydrocarbon components in which the extent of branching, as measured by the percentage of methyl hydrogens (BI), and the proximity of branching, as measured by the percentage of recurring methylene carbons which are four or more carbons removed from an end group or branch (CH2⊃4), are such that: (a) BI - 0.5(CH2⊃4)⊃15; and (b) BI + 0.85(CH2⊃4)∫45 as measured over said liquid hydrocarbon composition as a whole.

Autoprogressive training of neural network constitutive models

Abstract: A new method, termed autoprogressive training, for training neural networks to learn complex stress–strain behaviour of materials using global load–deflection response measured in a structural test is described. The richness of the constitutive information that is generally implicitly contained in the results of structural tests may in many cases make it possible to train a neural network material model from only a small number of such tests, thus overcoming one of the perceived limitations of a neural network approach to modelling of material behaviour; namely, that a voluminous amount of material test data is required. The method uses the partially-trained neural network in a central way in an iterative non-linear finite element analysis of the test specimen in order to extract approximate, but gradually improving, stress–strain information with which to train the neural network. An example is presented in which a simple neural network constitutive model of a T300/976 graphite/epoxy unidirectional lamina is trained, using the load–deflection response recorded during a destructive compressive test of a [(±45)6]S laminated structural plate containing an open hole. The results of a subsequent forward analysis are also presented, in which the trained material model is used to simulate the response of a compressively loaded [(±30)6]S structural laminate containing an open hole. Avenues for further improvement of the neural network model are also suggested. The proposed autoprogressive algorithm appears to have wide application in the general area of Non-Destructive Evaluation (NDE) and damage detection. Most NDE experiments can be viewed as structural tests and the proposed methodology can be used to determine certain damage indices, similar to the way in which constitutive models are determined. © 1998 John Wiley & Sons, Ltd.

Biological hydrogen production: not so elementary.

Abstract: Many organisms metabolize hydrogen gas by means of an enzyme called hydrogenase. The nature of the catalytic sites in the hydrogenases has long been a subject of conjecture and debate. In their Perspective, Adams and Stiefel discuss results reported in the same issue by Peters et al. in which x-ray crystallography was used to provide the first structural glimpse of the iron-only hydrogenase from the hydrogen-producing, anaerobic bacterium Clostridium pasteurianum. With this information, it is hoped that the properties of the hydrogenase enzyme can now be understood and possibly mimicked for chemical processing applications.

Photooxidation of crude oils

Abstract: Photooxidation is a potentially significant process in the degradation of crude oil spilled at sea. Moreover, a fundamental understanding of the effect of photochemical degradation on crude oil is a prerequisite for providing an accurate description of the recent history and potential fate of oil spilled in a marine environment. In this report we examine the effect of ultraviolet illumination on crude oil using a variety of techniques including gas chromatography/mass spectroscopy and X-ray absorption spectroscopy. The saturated compounds are resistant, but the aromatic compounds are particularly sensitive to photooxidation. Greater size and increasing alkyl substitution increase the sensitivity of aromatic compounds to photochemical oxidation. The photooxidized products appear in the resin and polar fractions as determined by thin-layer chroma tography. Thus, the effect of photooxidation is distinctly different from that of biodegradation, where larger and more substituted compounds are more resistant to...

Premium synthetic lubricant base stock having at least 95% non-cyclic isoparaffins

Abstract: A premium synthetic lubricating oil base stock having a high VI and low pour point is made by hydroisomerizing a Fischer-Tropsch synthesized waxy, paraffinic feed wax and then dewaxing the hydroisomerate to form a 650-750° F.+ dewaxate. The waxy feed has an initial boiling point in the range of about 650-750° F., from which it continuously boils up to at least 1050° F. and has a T90−T10 temperature difference of at least 350° F. The feed is preferably hydroisomerized without any pretreatment, other than optional fractionation. The 650-750° F.+ dewaxate is fractionated into two or more base stocks of different viscosity.

Molecular Engineering in Homogeneous Catalysis: One-Phase Catalysis Coupled with Biphase Catalyst Separation. The Fluorous-Soluble HRh(CO){P[CH2CH2(CF2)5CF3]3}3 Hydroformylation System

Abstract: The hydroformylation of decene-1 was studied in the presence of the fluorous-soluble P[CH2CH2(CF2)5CF3]3 modified rhodium catalyst at 100 °C and 1.1 MPa of CO/H2 (1:1) in a 50/50 vol % toluene/C6F11CF3 solvent mixture, which forms a homogeneous liquid phase at and above 100 °C. P[CH2CH2(CF2)5CF3]3 was selected on the basis of a semiempirical calculation of the electronic properties of P[(CH2)x(CF2)yCF3]3 (x = 0, y = 2, 4 and x = 0−5, y = 2) and prepared by the reaction of PH3 with CH2CH(CF2)5CF3. The solution structure of HRh(CO){P[CH2CH2(CF2)5CF3]3}3 (1) in C6F11CF3 is similar to that of HRh(CO)(PPh3)3 (2) in toluene and HRh(CO){P(m-C6H4SO3Na)3}3 (3) in water. High-pressure NMR of 1 under 2.1−8.3 MPa of CO/H2 (1:1) revealed that 1 is in equilibrium with HRh(CO)2{P[CH2CH2(CF2)5CF3]3}2 (4). Kinetic studies show that the reaction is first order in both rhodium and decene-1. While the reaction is inhibited by P[CH2CH2(CF2)5CF3]3, the normal/iso (n/i) ratio of the aldehyde increases with increasing phosphine ...

Thermoplastic polymer blends of isotactic polypropylene and alpha-olefin/propylene copolymers

Abstract: Improved thermoplastic polymer blend compositions comprising an isotactic polypropylene component and an alpha-olefin and propylene copolymer component, said copolymer comprising crystallizable alpha-olefin sequences. In a preferred embodiment, improved thermoplastic polymer blends are provided comprising from about 35% to about 85% isotactic polypropylene and from about 30% to about 70% of an ethylene and propylene copolymer, wherein said copolymer comprises isotactically crystallizable propylene sequences and is predominately propylene. The resultant blends manifest unexpected compatibility characteristics, increased tensile strength, and improved process characteristics, e.g., a single melting point.

Anaerobic Biodegradation of Long-Chain n-Alkanes under Sulfate-Reducing Conditions

Abstract: The ability of anaerobic microorganisms to degrade a wide variety of crude oil components was investigated using chronically hydrocarbon-contaminated marine sediments as the source of inoculum. When sulfate reduction was the predominant electron-accepting process, gas chromatographic analysis revealed almost complete n-alkane removal (C15−C34) from a weathered oil within 201 d of incubation. No alteration of the oil was detected in sterile control incubations or when nitrate served as an alternate electron acceptor. The amount of sulfate reduced in the oil-amended nonsterile incubations was more than enough to account for the complete mineralization of the n-alkane fraction of the oil; no loss of this anion was observed in sterile control incubations. The mineralization of the alkanes was confirmed using 14C-14,15-octacosane (C28H58), with 97% of the radioactivity recovered as 14CO2. These findings extend the range of hydrocarbons known to be amenable to anaerobic biodegradation. Moreover, the rapid and e...

Use of correlational data to examine the effects of risk perceptions on precautionary behavior

Abstract: The idea that perceptions of high personal risk lead people to adopt precautionary behavior (the “motivational hypothesis”) is mainly tested with correlational data. A review of studies from selective journals reveals a high proportion with methodological and conceptual problems that make them invalid as tests of this hypthesis. Three problems arc emphasized: (1) the misinterpretation of correlations from cross-sectional studies as testing the motivational hypothesis when they actually indicate the accuracy of risk perceptions; (2) the failure to control for prior behavior in prospective studies; and (3) the we of prospective studies in situations of little behavior change. Path models are used to help explain these problems. Recommendations for selecting research designs and for calculating the least problematic correlations are given, along with warnings about the many assumptions needed to interpret even these correlations. Summary Overall, 27 of the 61 cross-sectional analyses listed in Table...

Nickel molybdotungstate hydrotreating catalysts

Abstract: A hydrodenitrogenation catalyst is prepared by decomposing a nickel (ammonium) molybdotungstate precursor and sulfiding, either pre-use or in situ, the decomposition product.

Strong segregation theory of bicontinuous phases in block copolymers

Abstract: We compute phase diagrams for A n B m starblock copolymers in the strong-segregation regime as a function of volume fraction o, including bicontinuous phases related to minimal surfaces (G, D, and P surfaces) as candidate structures. We present the details of a general method to compute free energies in the strong segregation limit and demonstrate that the gyroid G phase is the most nearly stable among the bicontinuous phases considered. We explore some effects of conformational asymmetry on the topology of the phase diagram.

Preparation of high activity catalysts; the catalysts and their use

Abstract: A process for the preparation of a catalyst useful for conducting carbon monoxide hydrogenation reactions, especially a Fischer-Tropsch catalyst, use of the catalyst for conducting such reactions, especially Fischer-Tropsch reactions, and the composition produced by said process. In the preparation of the catalyst, a solution of a multi-functional carboxylic acid having from about 3 to 6 total carbon atoms, preferably about 4 to 5 total carbon atoms, is employed to impregnate and disperse a compound or salt of rhenium and a compound or salt of a catalytic metal, or metals, e.g., copper or an Iron Group metal such as iron, cobalt, or nickel onto a refractory inorganic oxide support, e.g., titania. The rhenium, which need be present only in small amount permits full and complete reduction of the catalytic metal, or metals, dispersed by the acid. Higher catalyst activities with lower rhenium loadings are thus achieved than in previous preparations where higher concentrations of rhenium were required to both effectively disperse, and reduce the catalytic metal, or metals, during the preparation. Surprisingly, as little as about 1/10 of the rhenium is required to accomplish the reduction promotion where the dispersion is effected with the acid.

Ultra-high strength ausaged steels with excellent cryogenic temperature toughness

Abstract: An ultra-high strength, weldable, low alloy steel with excellent cryogenic temperature toughness in the base plate and in the heat affected zone (HAZ) when welded, having a tensile strength greater than about 830 MPa (120 ksi) and a microstructure comprising (i) predominantly fine-grained lower bainite, fine-grained lath martensite, fine granular bainite (FGB), or mixtures thereof, and (ii) up to about 10 vol % retained austenite, is prepared by heating a steel slab comprising iron and specified weight percentages of some or all of the additives carbon, manganese, nickel, nitrogen, copper, chromium, molybdenum, silicon, niobium, vanadium, titanium, aluminum, and boron; reducing the slab to form plate in one or more passes in a temperature range in which austenite recrystallizes; finish rolling the plate in one or more passes in a temperature range below the austenite recrystallization temperature and above the Ar3 transformation temperature; quenching the finish rolled plate to a suitable Quench Stop Temperature (QST); stopping the quenching; and either, for a period of time, holding the plate substantially isothermally at the QST or slow-cooling the plate before air cooling, or simply air cooling the plate to ambient temperature.

Synthetic jet fuel and process for its production

Abstract: Clean distillate useful as a jet fuel or jet blending stock is produced from Fischer-Tropsch wax by separating wax into heavier and lighter fractions; further separating the lighter fraction and hydroisomerizing the heavier fraction and that portion of the light fraction above about 475 °F. The isomerized product is blended with the untreated portion of the lighter fraction to produce high quality, clean, jet fuel.

Propylene polymers incorporating macromers

Abstract: A polyolefin composition is provided which consists essentially of isotactic polypropylene and, optionally, one or more comonomers, wherein the total comonomer content of the polyolefin composition is from 0 to 20 mole percent, and further, wherein the weight average branching index g' for the lower molecular weight region of the polyolefin composition is less than 0.93. Additionally, a process is provided for producing a polyolefin composition comprising: a) contacting in solution, at a temperature from about 90 °C to about 120 °C, propylene monomers with a catalyst composition comprising a first chiral, stereorigid transition metal catalyst compound capable of producing isotactic polypropylene; b) copolymerizing the product of a) with propylene and, optionally, one or more copolymerizable monomers, in a polymerization reactor under suitable polypropylene polymerization conditions using a second chiral, stereorigid transition metal catalyst capable of producing isotactic polypropylene; and c) recovering a branched olefin polymer.

Supercooling, Nucleation, Rotator Phases, and Surface Crystallization of n-Alkane Melts

Abstract: We demonstrate the relation between supercooling of n-alkane melts and the appearance or nonappearance of rotator phases. Supercooling occurs for the shorter, even chain lengths. The lack of supercooling in most n-alkane melts is discussed in terms of surface crystallization. We argue that melt crystallization of the nonrotator triclinic crystal phase is likely mediated by surface-crystallization-induced nucleation of a metastable rotator phase.

Vinyl-containing stereospecific polypropylene macromers

Abstract: Stereospecific polypropylene macromers having a high percentage of vinyl terminal bonds and a method for preparing them are provided. The stereospecific polypropylene macromers have number average molecular weights (Mn) of about 2,000 Daltons to about 50,000 Daltons, and the total number of vinyl groups per 1000 carbon atoms is greater than or equal to 7000 Mn. The method for preparing the macromers involves: a) contacting, in solution, at a temperature from about 90 °C to about 120 °C, two or more propylene monomers with a catalyst composition comprising a chiral, stereorigid transition metal catalyst compound; and b) recovering stereospecific polypropylene chains having number average molecular weights of about 2,000 Daltons to about 50,000 Daltons and significant vinyl unsaturation.

Manufacturing method for the production of polyalphaolefin based synthetic greases

Abstract: A method is disclosed for improving the thickener yield in soap thickened polyalphaolefin base oil greases comprising the steps of (a) producing a simple or complex soap thickener in a quantity of a first PAO of viscosity lower than that of the base oil component in the final grease composition to produce a thickened PAO and (b) adding to the thickened PAO a quantity of a second PAO of viscosity higher than that desired of the base oil component in the final grease composition sufficient to produce a final grease product having the desired base oil viscosity.

Dynamics of Lightly Sulfonated Polystyrene Ionomers

Abstract: The tracer diffusion coefficients of both ion-containing polymer chains and their associated counterions were measured in lightly sulfonated ionomers as a function of temperature, ion content, and chain length. The data are shown to be in good agreement with relaxation times derived from viscoelastic measurements at high temperatures. The results are interpreted in terms of a reptation model, modified to account for the additional constraints on individual chain motion imposed by the associating ion pairs. {copyright} {ital 1998} {ital The American Physical Society}

Surface freezing in chain molecules. ii. neat and hydrated alcohols

Abstract: Surface freezing is studied in dry and hydrated normal-alcohol melts by x-ray scattering and surface tensiometry. A single crystalline bilayer forms at the surface, for even carbon numbers only, at temperatures up to 1{degree}C (dry) or 2{degree}C (wet) above the bulk freezing, and persists without change down to bulk freezing. The packing is hexagonal, with untilted molecules for short chains and tilted molecules for long chains. The lattices of the upper and lower monolayers are shifted along the next-nearest-neighbor direction. Hydration is found to swell the bilayer by {approximately}2.5 {Angstrom} due to water intercalation into the bilayer, at a molecular water:alcohol ratio of {approximately}1:2. It also increases the transition temperatures, and the temperature and chain-length ranges for which surface crystallization is observed. These effects are accounted for quantitatively by considering the surprising {ital increase} in hydration upon freezing, and taking into account the Gibbs-rule-predicted water depletion at the surface in the liquid surface phase. {copyright} {ital 1998} {ital The American Physical Society}

Elastomeric propylene polymers

Abstract: A thermoplastic elastomer is provided comprising a branched olefin polymer having crystalline sidechains and an amorphous backbone wherein at least 90 mole percent of the sidechains are isotactic or syndiotactic polypropylene and at least 80 mole percent of the backbone is atactic polypropylene. Additionally, a process is provided for producing a thermoplastic elastomer composition comprising: a) contacting, in solution, at a temperature from 90 °C to 120 °C propylene monomers with a catalyst composition comprising a chiral, stereorigid transition metal catalyst compound capable of producing isotactic or syndiotactic polypropylene; b) copolymerizing the product of a) with propylene and, optionally, one or more copolymerizable monomers, in a polymerization reactor using an achiral transition metal catalyst capable of producing atactic polypropylene; and c) recovering a branched olefin polymer.

Process for separating a multi-component gas stream containing at least one freezable component

Abstract: This invention relates generally to a separation process in which a multi-component feed stream (401) is introduced into a separation system (490) that operates under solids forming conditions for at least one of the feed stream components. The freezable component, although typically CO2, H2S or another acid gas, can be any component that has the potential for forming solids in the separation system (490). The multi-component feed stream is introduced into a separation system (490), at least a portion of which operates under solids forming conditions for at least one component of the feed stream. A overhead vapor stream (406) is withdrawn and compressed to a higher pressure stream (408). At least a portion of the compressed stream is cooled and then expanded to a lower pressure to further cool the compressed stream. At least a portion (409) of the expanded stream is returned to the separation system (490), thereby providing refrigeration to the separation system (490).

Polymeric supported catalysts for olefin polymerization

Abstract: The described invention provides a low fouling, high particle density polymerization process and an olefin polymerization cocatalyst activator composition comprising a cross-linked polymer bead having a surface area of from about 1 to 20 m2/g to which are bound a plurality of non-coordinating anions, where the polymeric support comprises ligands covalently bound to the central metal or metalloid atoms of said anions, and an effective number of cationic species to achieve a balanced charge. The invention also provides an olefin polymerization catalyst compositions comprising the reaction product of a) the foregoing cocatalyst activator, and b) an organometallic transition metal compound having ancillary ligands, at least one labile ligand capable of abstraction by protonation and at least one labile ligand into which an olefinic monomer can insert for polymerization. In a preferred embodiment, the polymeric support has a surface area of ≤ 10 m2/g and is particularly suitable for use with high activity organometallic, transition metal catalyst compounds.

Material Reuse Modeling: A Case Study of Water Reuse in an Industrial Park

Abstract: Summary The techniques of water distribution modeling, a well-developed subject, have been applied to water management in an industrial park-the Bayport chemical manufacturing complex in Houston, Texas in the United States. Linear and other mathematical programming approaches were used to evaluate water reuse opportunities for a variety of scenarios, including redesigning the industrial water use network, adding a facility to the network, limiting the total water available to the network, and varying the price of water rhe results of the modeling demonstrate that a number of economical water reuse opportunities may exist for this network of facilities. More generally, the types of mathematical models developed for water reuse may find application in reuse modeling for other materials.