Showing papers by "ExxonMobil published in 1997"

Parameter-free theory for stress relaxation in star polymer melts

Abstract: We present a theory of stress relaxation in star polymer melts with no adjustable parameters beyond those measurable in linear melts. We incorporate the effect of higher Rouse modes on star arm retraction and the Colby−Rubinstein scaling of entanglement length within “dynamic dilution”. Our results for G‘‘(ω) compare well with experimental data, with excellent agreement in shape and within a factor of 2 in time and modulus scales.

Surface freezing in chain molecules: Normal alkanes

Abstract: A rare surface freezing phenomenon is observed in molten normal alkanes, using x-ray and surface tension measurements. An ordered monolayer forms on the surface of the liquid alkane at temperatures up to 3 \ifmmode^\circ\else\textdegree\fi{}C above the bulk freezing temperature ${\mathrm{T}}_{\mathrm{f}}$. The structure of the monolayer was studied in detail for a wide range of molecular lengths and temperatures. The single layer formed persists down to ${\mathrm{T}}_{\mathrm{f}}$. The rare surface phase exists only for carbon numbers of 16\ensuremath{\leqslant}n\ensuremath{\leqslant}50. The molecules in the layer are hexagonally packed and show three distinct ordered phases: two rotator phases, with molecules oriented vertically (16\ensuremath{\leqslant}n\ensuremath{\leqslant}30) and tilted towards nearest neighbors (3044) and one crystalline phase with molecules tilted towards next-nearest neighbors (n\ensuremath{\geqslant}44). The temperature dependence of the surface tension and the range of existence vs carbon number are satisfactorily accounted for within a simple theory based on surface energy considerations.

Osmotic pressure and viscoelastic shear moduli of concentrated emulsions

Abstract: We present an experimental study of the frequency \ensuremath{\omega} dependence and volume fraction \ensuremath{\varphi} dependence of the complex shear modulus ${G}^{*}(\ensuremath{\omega},\ensuremath{\varphi})$ of monodisperse emulsions which have been concentrated by an osmotic pressure \ensuremath{\Pi}. At a given \ensuremath{\varphi}, the elastic storage modulus ${G}^{\ensuremath{'}}(\ensuremath{\omega})=\mathrm{Re}[{G}^{*}(\ensuremath{\omega})]$ exhibits a low-frequency plateau ${G}_{p}^{\ensuremath{'}},$ dominating the dissipative loss modulus ${G}^{\ensuremath{'}\ensuremath{'}}(\ensuremath{\omega})=\mathrm{Im}[{G}^{*}(\ensuremath{\omega})]$ which exhibits a minimum. Above a critical packing fraction ${\ensuremath{\varphi}}_{c},$ we find that both \ensuremath{\Pi}(\ensuremath{\varphi}) and ${G}_{p}^{\ensuremath{'}}(\ensuremath{\varphi})$ increase quasilinearly, scaling as $(\ensuremath{\varphi}\ensuremath{-}{\ensuremath{\varphi}}_{c}{)}^{\ensuremath{\mu}},$ where ${\ensuremath{\varphi}}_{c}\ensuremath{\approx}{\ensuremath{\varphi}}_{c}^{\mathrm{rcp}},$ the volume fraction of a random close packing of spheres, and \ensuremath{\mu} is an exponent close to unity. To explain this result, we develop a model of disordered droplets which interact through an effective repulsive anharmonic potential, based on results obtained for a compressed droplet. A simulation based on this model yields a calculated static shear modulus $G$ and osmotic pressure \ensuremath{\Pi} that are in excellent agreement with the experimental values of ${G}_{p}^{\ensuremath{'}}$ and \ensuremath{\Pi}.

Multiple timescales for neutralization of fossil fuel CO2

Abstract: The long term abiological sinks for anthropogenic CO2 will be dissolution in the oceans and chemical neutralization by reaction with carbonates and basic igneous rocks. We use a detailed ocean/sediment carbon cycle model to simulate the response of the carbonate cycle in the ocean to a range of anthropogenic CO2 release scenarios. CaCO3 will play only a secondary role in buffering the CO2 concentration of the atmosphere because CaCO3 reaction uptake capacity and kinetics are limited by the dynamics of the ocean carbon cycle. Dissolution into ocean water sequesters 70–80% of the CO2 release on a time scale of several hundred years. Chemical neutralization of CO2 by reaction with CaCO3 on the sea floor accounts for another 9–15% decrease in the atmospheric concentration on a time scale of 5.5–6.8 kyr. Reaction with CaCO3 on land accounts for another 3–8%, with a time scale of 8.2 kyr. The final equilibrium with CaCO3 leaves 7.5–8% of the CO2 release remaining in the atmosphere. The carbonate chemistry of the oceans in contact with CaCO3 will act to buffer atmospheric CO2 at this higher concentration until the entire fossil fuel CO2 release is consumed by weathering of basic igneous rocks on a time scale of 200 kyr.

Long-range correlations in sedimentation

Abstract: Using particle image velocimetry we have measured the sedimentation dynamics of non-Brownian colloidal spheres over a wide range of low concentrations ( $\ensuremath{\varphi}\ensuremath{\le}0.05$) and sample cell sizes $W$. Fluctuations in the settling velocity show universal large-scale finite-range correlations, in the form of swirls, which depend simply on volume fraction and particle radius and follow $〈\ensuremath{\delta}{V}_{z}(0)\ensuremath{\delta}{V}_{z}(z){〉}^{1/2}\ensuremath{\simeq}{2.0V}_{\mathrm{sed}}{\ensuremath{\varphi}}^{1/3}\mathrm{exp}(\ensuremath{-}z/2\ensuremath{\xi})$, where $\ensuremath{\xi}\ensuremath{\simeq}20a{\ensuremath{\varphi}}^{\ensuremath{-}1/3}$. In turn, the predicted divergence of the velocity variance with increasing cell size $W$ is cut off in a universal way as $W$ exceeds the swirl size and is well represented by $〈\ensuremath{\delta}{V}_{z}^{2}(0){〉}^{1/2}{\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2.0V}_{\mathrm{sed}}{\ensuremath{\varphi}}^{1/3}[1\ensuremath{-}\mathrm{exp}(\ensuremath{-}W/60a{\ensuremath{\varphi}}^{\ensuremath{-}1/3})]$.

Diffusing-wave-spectroscopy measurements of viscoelasticity of complex fluids

Abstract: We present a new use of dynamic light scattering that permits the determination of the viscoelastic behavior of a complex fluid. By describing the motion of a scattering particle in a viscoelastic medium in terms of a generalized Langevin equation with a memory function, we relate the time evolution of its mean-square displacement to the frequency-dependent storage and loss moduli of the medium. The utility of this technique is illustrated through the application of diffusing-wave spectroscopy to probe the viscoelastic behavior of two complex fluids. The properties of a concentrated suspension of colloidal particles interacting as hard spheres are shown to be strongly influenced by the incipient colloidal glass transition, which leads to an extended range of frequencies over which they behave like an elastic solid. Similar elasticity is observed in a compressed emulsion, resulting in this case from the additional interfacial energy of the deformed droplets. In both cases diffusing-wave spectroscopy is used to measure the frequency dependence of the storage and loss moduli, and these results are compared with those from mechanical measurements. Besides providing a purely optical method for measuring mechanical properties, this technique provides new insight into the origin of the viscoelastic behavior.

Rate-Based Construction of Kinetic Models for Complex Systems

Abstract: A general-purpose rate-based algorithm for the construction of chemical kinetic models for systems with hundreds or thousands of reacting species is presented. The algorithm comprehensively works out the details of the chemistry implied by given reaction rate estimation rules, identifies the species and reactions that are numerically significant, and solves the resulting system of differential equations to compute the concentrations of the significant species as a function of time. A key innovation is a definition and numerical test for the “completeness” of the kinetic scheme. This approach obviates the need to arbitrarily neglect certain species and reactions in order to keep reaction schemes small enough to be manageable and allows chemical kinetic modelers to focus on the chemistry rather than on the computational details. Examples of hydrocarbon pyrolysis and combustion applications are presented, where the computer evaluates the importance of nearly 100 000 reactions in the process of identifying the few hundred species that are kinetically significant. The new algorithm, given reliable rate estimation rules, provides a framework for systematically constructing kinetic schemes including all of the numerically significant species, even for systems involving so many reactions that they could not be handled manually.

Copolymerization of 1,2-Epoxycyclohexane and Carbon Dioxide Using Carbon Dioxide as Both Reactant and Solvent

Abstract: The copolymerization of 1,2-epoxycyclohexane (cyclohexene oxide, CHO) and carbon dioxide was performed using no other solvent than carbon dioxide itself. A CO2-soluble, ZnO-based catalyst was synthesized and used to catalyze the polymerization. Polymerizations were conducted at different temperatures, pressures, and mole fractions of CHO giving rise to polymer yields as high as 69% with catalyst activities as high as 400 g of polymer/g of Zn. The best results were obtained at temperatures of 100−110 °C and at mole fractions of CHO above XCHO = 0.15. This polymer was >90% polycarbonate with weight average molecular weights (Mw) ranging from 50 000 to 180 000.

A principal-component and least-squares method for allocating polycyclic aromatic hydrocarbons in sediment to multiple sources

Abstract: A method was developed to allocate polycyclic aromatic hydrocarbons (PAHs) in sediment samples to the PAH sources from which they came. The method uses principal-component analysis to identify possible sources and a least-squares model to find the source mix that gives the best fit of 36 PAH analytes in each sample. The method identified 18 possible PAH sources in a large set of field data collected in Prince William Sound, Alaska, USA, after the 1989 Exxon Valdez oil spill, including diesel oil, diesel soot, spilled crude oil in various weathering states, natural background, creosote, and combustion products from human activities and forest fires. Spill oil was generally found to be a small increment of the natural background in subtidal sediments, whereas combustion products were often the predominant sources for subtidal PAHs near sites of past or present human activity. The method appears to be applicable to other situations, including other spills.

A relational database system containing a multidimensional hierarchical model of interrelated subject categories with recognition capabilities

Abstract: The present invention is a database and a method of producing that database which can be used to determine the meaning of scientific or technical documents, such as patents and/or technical or scientific publications and/or abstracts of these patents or publications, and to assign the technical documents to one or more scientific or technical categories within a multidimensional hierarchical model which reflects the business, scientific or technical interests of a business, scientific or technical entity or specialty.

Small Angle Neutron Scattering Investigations of Melt Miscibility and Phase Segregation in Blends of Linear and Branched Polyethylenes as a Function of the Branch Content

Abstract: We have performed a series of small angle neutron scattering (SANS) experiments on blends of linear and branched polyethylenes to investigate the level of branching that is required to phase separate the system. These results confirm that the mixtures are homogenous for all compositions when the branch content is low (i.e., 2. In each case, the resolution of conventional SANS pinhole cameras (Qmin ∼ 10-3 A-1) is adequate to determine the state of mixing, even for systems with large domains.

Structural Rearrangement of Strained Coals

Abstract: Native coals are strained and glassy. When coals are swollen, this strain is relieved as the coal structure rearranges to a lower free energy and more highly noncovalently associated state. Four coals ranging in carbon content from 77% C to 84% C were warmed in the weak swelling solvent chlorobenzene at 132 °C for 2 weeks and samples were withdrawn at intervals. After evaporation of the chlorobenzene, the pyridine extractability of the treated coals had decreased, sometimes by a factor of 2. The pyridine swelling of Pittsburgh No. 8 coal was sharply reduced. The extractability and swelling decreases with time demonstrate that changes in coal structure occurred with the rearranged coal being more associated. This increased association is not due to hydrogen bond formation because pyridine is known to break most if not all of the hydrogen bonds which occur in coals. The rearranged Pittsburgh No. 8 coal was studied by differential scanning calorimetry. Over the 2 week chlorobenzene reflux period, the heat ca...

Mixed transition metal catalyst systems for olefin polymerization

Abstract: The invention encompasses a mixed transition metal olefin polymerization catalyst system suitable for the polymerization of olefin monomers comprising one late transition metal catalyst system and at least one different catalyst system selected from the group consisting of late transition metal catalyst systems, transition metal metallocene catalyst systems or Ziegler-Natta catalyst systems. Preferred embodiments include at least one late transition metal catalyst system comprising a Group 9, 10, or 11 metal complex stabilized by a bidentate ligand structure and at least one transition metal metallocene catalyst system comprising a Group 4 metal complex stabilized by at least one ancillary cyclopentadienyl ligand. The polymerization process for olefin monomers comprises contacting one or more olefins with these catalyst systems under polymerization conditions.

Selective para-xylene production by toluene methylation

Abstract: There is provided a process for the selective production of para-xylene which comprises reacting toluene with methanol in the presence of a catalyst comprising a porous crystalline material having a Diffusion Parameter for 2,2 dimethylbutane of about 0.1-15 sec-1 when measured at a temperature of 120 °C and a 2,2 dimethylbutane pressure of 60 torr (8kPa). The porous crystalline material is preferably a medium-pore zeolite, particularly ZSM-5, which has been severely steamed at a temperature of at least 950 °C. The porous crystalline material is preferably combined with at least one oxide modifier, preferably including phosphorus, to control reduction of the micropore volume of the material during the steaming step.

Remarks Concerning the Relation between Rotator Phases of Bulk n-Alkanes and Those of Langmuir Monolayers of Alkyl-Chain Surfactants on Water

Abstract: Substantial advances have recently been made in characterizing the structures and phase diagrams of Langmuir monolayers of alkyl-chain surfactants on water. These allow detailed comparisons to be made with the bulk phases formed by n-alkanes, in particular, the rotator phases. It is shown that the untilted Langmuir phases denoted CS, S, and LS, correspond to the herringbone-crystal, distorted rotator without long-range herringbone order (RI) and hexagonal rotator (RII), respectively. The quantitative behavior of the distortion and area/molecule in the Langmuir monolayers, their derivatives and jumps at the transitions are shown to correspond more closely to the behavior of n-alkane mixtures where the interlayer interaction is weakened than to that of the pure n-alkanes. It is shown that the tilted phases can be associated with the same three categories regarding distortion and herringbone order that characterize the untilted phases, if the distortion is measured perpendicular to the chain-axis. An “anomal...

Conversion of fisher-tropsch waxes to lubricants by countercurrent processing

Abstract: A process for converting Fischer-Tropsch wax streams to lubricants by reacting said stream with a dewaxing catalyst in a reaction zone where the stream flows countercurrent to upflowing hydrogen-containing treat gas.

Thermoplastic olefin compositions

Abstract: The invention relates to novel Thermoplastic Olefin compositions comprising polypropylene, and ethylene-alpha olefin elastomer and a compatibilizer comprising an ethylene-propylene copolymer having a propylene content of greater than 80 weight percent. The ethylene-propylene copolymer compatibilizer imparts a greater degree of compatibility between the polypropylene and elastomer phases yielding improved physical properties.

Preparation of sulfated zirconia catalysts with improved control of sulfur content II. Effect of sulfur content on physical properties and catalytic activity

Abstract: The sulfur content of sulfated zirconia can be varied by changing the quantity of sulfuric acid used for impregnation in the controlled impregnation method, in which a pre-set quantity of sulfuric acid is added and evaporated without filtration or decanting. The material is then dried and calcined (in this work, for 5 h at 610°C). The sulfur content of the calcined material increases with the increase in the quantity of sulfuric acid, but the ratio of sulfate retained after calcination to sulfate impregnated decreases at first and then increases. The surface area gradually increases with the quantity of the acid up to 3 ml of acid per gram of zirconium hydroxide (2.5% S in SZ after calcination), then decreases abruptly. The crystal structure of the sulfated zirconia is also affected by the sulfur content. XRD data show that the sulfated zirconia with a low or medium sulfur content crystallizes only in the tetragonal form, whereas at higher sulfur content a minor fraction of monoclinic zirconia begins to be seen, in addition to the major tetragonal form. XPS data indicate that at the higher sulfate loading part of the sulfate is present in the bulk phase, rather than on the surface. Thus, the increase in sulfur uptake, decrease in surface area and change in crystallinity appear related to sulfate migration inside the particles. The catalytic activity for the isomerization of methylcyclopentane at 65°C shows a maximum for a sulfur content around 3%. It appears that the optimum catalyst should contain the maximum amount of sulfate near the surface, but not necessarily on the surface, and crystallize in the tetragonal form.

A process for blending potentially incompatible petroleum oils

Abstract: A method for blending two or more petroleum feedstreams, N, at least one of which includes the solute asphaltenes so that said asphaltenes remain a solute.

Polymers derived from olefins useful as lubricant and fuel oil additives, processes for preparation of such polymers and additives and use thereof

Abstract: Polymers (including copolymers) derived from one or more olefins, such including ethylene and C3-C20 α-olefins such as propylene and 1-butene, which polymers have (a) an average ethylene sequence length, ESL, of from about 1.0 to less than about 3.0; (b) an average of at least 5 branches per 100 carbon atoms of the polymer chains comprising the polymer; (c) at least about 50 % of said branches being methyl and/or ethyl branches; (d) at least about 30 % of said polymer chains terminated with a vinyl or vinylene group; (e) a number average molecular weight, Mn, or from about 300 to about 15,000 when the polymer is intended for dispersant or wax crystal modifier uses and up to about 500,000 where intended for viscosity modifier uses; and (f) substantial solubility in hydrocarbon and/or synthetic base oil. The polymers are produced using late-transition-metal catalyst systems and, preferably, inexpensive, highly dilute refinery or steam cracker feed streams that have undergone only limited clean-up steps. Fuel and lubricating oil additives, particularly dispersants, wax crystal modifiers and flow improvers, are produced. Where functionalization and derivatization of these polymers is required for such additives it is facilitated by the olefinic structures available in the polymer chains.

Crystal-growth studies of natural gas clathrate hydrates using a pressurized optical cell

Abstract: The crystal-growth behavior of structure I (sl), structure II (sll), and structure H (sH) clathrate hydrates has been studied using a specially designed, pressurized optical cell, Single crystals of each hydrate type, methane sl, methane-propane (95%-5%) sll, and methane-methylcyclopentane sH, were grown in equilibrium with aqueous liquid + vapor ::':: liquid hydrocarbon, Each structure type exhibits characteristic crystal morphology, which suggests that crystal habit in natural settings, such as sea-floor outcrops, may allow visual identification of hydrate types. In addition, the relative growth rates for different Miller planes for each crystal type were determined. The relative growth-rate schemes and resulting crystal morphology of each structure can be related to the unit-cell density distribution of the small cages in each structure, Four-phase P- T equilibrium data for methanemethylcyclopentane sH data were also measured using optical methods. Evaluation of these and previously published phase-equilibrium data for all three known hydrate structures strongly suggests that hydrate assemblages of coexisting sll and sH should be common in natural settings.

Mutual solubilities of hydrocarbons and water: III. 1-hexene; 1-octene; C10C12 hydrocarbons

Abstract: This article completes the analysis of high-temperature mutual solubilities of hydrocarbons and water. Part I (Tsonopoulos and Wilson, 1983) presented benzene, cyclohexane, and n-hexane, while Part II (Heidman et al., 1985) extended the investigation to ethylbenzene, ethylcyclohexane, and n-octane. Part III presents experimental data up to the three-phase critical end point for C6, C8, and C10 1-alkenes, n-decane, n-butylcyclohexane, m-diethylbenzene, p-diisopropylbenzene, cis-decalin, tetralin, 1-methylnaphthalene, and 1-ethylnaphthalene. The thermodynamic analysis of Henry's constants for hydrocarbons in water is extended to the critical temperature of water, while the solubility and volatility of water in hydrocarbons are successfully correlated with several modifications of the Redlich-Kwong equation of state.

Stochastic analysis of seafloor morphology on the flank of the Southeast Indian Ridge: The influence of ridge morphology on the formation of abyssal hills

Abstract: In this study we estimate the statistical properties of abyssal hill morphology adjacent to the Southeast Indian Ridge in a region where the axial morphology changes from axial high to axial valley without a corresponding change in spreading rate. We explore the influence of axial morphology on abyssal hills and place these results within the context of response to spreading rate. Two cruises aboard the R/V Melville collected Sea Beam 2000 multibeam data along the Southeast Indian Ridge, providing continuous multibeam coverage of the axis from ∼89°W to ∼118°W, and ∼100% coverage within four survey regions extending out to ∼45 km (∼1.2 Ma) from the axis [Sempere et al., 1997; Cochran et al., 1997]. We apply the statistical modeling method of Goff and Jordan [1988] to gridded data from the four survey areas, examining in particular estimates of abyssal hill rms height, characteristic width and length, aspect ratio, and skewness. Two analyses are performed: (1) comparison of the along-axis variation in abyssal hill characteristics to ridge segmentation, and (2) a calculation of population statistics within axial high, intermediate, and axial valley data populations of this study, and comparison of these results to population statistics derived from studies adjacent to the Mid-Atlantic Ridge and East Pacific Rise. We find that abyssal hills generated along axial high mid-ocean ridges are very different from those generated along axial valley mid-ocean ridges, not only with respect to size and shape, but also in their response to such factors as spreading rate and segmentation.

Rapid injection process and apparatus for producing synthesis gas (law 560)

Abstract: A novel injector/reactor apparatus and an efficient process for the partial oxidation of light hydrocarbon gases, such as methane, to convert such gases to useful synthesis gas for recovery and/or subsequent hydrocarbon synthesis. Sources of a light hydrocarbon gas, such as methane, and oxygen or an oxygen-containing gas are preheated and pressurized and injected through an injector means at high velocity into admixture with each other in the desired relating proportions, at a plurality of mixing nozzles which are open to the partial oxidation zone of a reactor and are uniformly-spaced over the face of the injector means, to form a gaseous premix having a pressure drop through the injector. The gaseous premix is injected in a time period which is less than 5 milliseconds, preferably at a velocity between about 25 to 1000 feet/second, into a partial oxidation reaction zone so that the gaseous premix reacts therein, to reduce the amounts of CO 2 , H 2 O and heat produced by the partial oxidation reaction and form, cool and recover a useful syngas.

On-line control of a chemical process plant

Abstract: A process plant for the manufacture of halobutyl rubber is provided with online monitoring and control of the process parameters to control the properties of the product. It incorporates an in situ measurement system that does not require the removal of any sample material from the process. It uses a Fourier Transform Near Infrared (FTNIR) spectrometer, fiber-optic cables, a viscometer for measuring solution viscosity and a Resistance Temperature Device (RTD) for temperature measurement. An online real-time analyzer system using a Constrained Principal Spectral Analysis program predicts the property of the polymer product and provides the process control system with analysis of the data using derived relationships between the physical properties of the polymer and these spectral measurements and the measured values of fluid viscosity and temperature. Differences between the predicted and desired property of the product are used to control process parameters. The method can be used for a variety of chemical process plants.