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Solubility of Anthracene in Binary and Ternary Mixtures of Cyclohexanone, Ethyl Acetate, and Methanol at 298.2 K

Description: This article discusses the solubility of anthracene in binary and ternary mixtures of cyclohexanone, ethyl acetate, and methanol at 298.2 K.
Date: May 10, 2010
Creator: Jouyban, Abolghasem; Manzoori, Jamshid L.; Panahi-Azar, Vahid; Soleymani, Jafar; Fakhree, Mohammad Amin Abolghassemi; Shayanfar, Ali et al.
Partner: UNT College of Arts and Sciences

Solubility of Anthracene in Ternary Cyclohexane + Propanol + 2-Methyl-1-propanol and Cyclohexane + Butanol + 2-Methyl-1-propanol Mixtures

Description: Article on the solubility of anthracene in ternary cyclohexane + propanol + 2-methyl-1-propanol and cyclohexane + butane + 2-methyl-1-propanol mixtures.
Date: November 20, 2008
Creator: Proctor, Amy; Blake-Taylor, Brooke H. & Acree, William E. (William Eugene)
Partner: UNT College of Arts and Sciences

The Vacuum Ultraviolet Spectra of Cyclohexane, Cyclohexene, 1,4-Cyclohexadiene, Isotetralin, and Several Methyl Substituted Analogs

Description: A paucity of literature exists on the Independent System analysis of adjacent, parallel transition dipoles. Applying this theory and certain spectral information semiemperical calculations were made to predict absorption profiles and band intensities. To aid in the assignment of the 7*+7 absorption bands it was necessary to obtain the vacuum ultraviolet spectra of cyclohexane and cyclohexene. Because the spectra of these molecules contained sharp, atomic-like absorption bands a Rydberg series could be fitted to certain absorptions, thus the determination of their ionization potentials. Using Independent System analysis profiles and intensities of 7*+q-- absorption bands ins 'several methyl substituted 1,4- cyclohexadienes and isotetralin were predicted where general agreement was found with observed experimental spectra.
Date: December 1974
Creator: Tidwell, Edgar Rhea
Partner: UNT Libraries

Enhancement of Equilibrium Shift in Dehydrogenation Reactions Using a Novel Membrane Reactor Semi-Annual Report: October 1998-February 1999

Description: Using electroless deposition of palladium thin-films on a microporous ceramic substrate, we developed a hydrogen-selective palladium-ceramic composite membrane. The new membrane has significantly higher permeability and selectivity for hydrogen than many of the commercially available dense-metallic membrane. The hydrogen permeability of the new membrane increases with increasing temperature. These properties make it an ideal candidate for use in membrane reactors to study dehydrogenation reactions by equilibrium shift. To investigate the usefulness of the new membrane in membrane reactor-separator configuration, a model for studying dehydrogenation of cyclohexane by equilibrium in a membrane reactor is developed. Radial diffusion is considered to account for the concentration gradient in the radial direction due to permeation through the membrane. The model is investigated with and without the reaction. In the non-reaction case, a mixture of argon, benzene, cyclohexane, and hydrogen is used in the reaction side and argon is used in the separation side. In the case of dehydrogenation reaction, the feed stream to the reaction side contained hydrogen and argon while in the separation side argon is used as sweep gas. Equilibrium conversion for dehydrogenation of cyclohexane is 18.7%. Present study shows that 100% conversion can be achieved by equilibrium shift using Pd-Ceramic membrane reactor. For a feed containing cyclohexane and argon of 164X10{sup -6} and 1.0x10{sup -3} mol / s, 98% conversion is achieved.
Date: April 30, 1999
Creator: Ilias, Shamsuddin & King, Franklin G.
Partner: UNT Libraries Government Documents Department

Influence of Particle Size on Reaction Selectivity in Cyclohexene Hydrogenation and Dehydrogenation over Silica-Supported Monodisperse Pt Particles

Description: The role of particle size during the hydrogenation/dehydrogenation of cyclohexene (10 Torr C{sub 6}H{sub 10}, 200-600 Torr H{sub 2}, and 273-650 K) was studied over a series of monodisperse Pt/SBA-15 catalysts. The conversion of cyclohexene in the presence of excess H{sub 2} (H{sub 2}:C{sub 6}H{sub 10} ratio = 20-60) is characterized by three regimes: hydrogenation of cyclohexene to cyclohexane at low temperature (< 423 K), an intermediate temperature range in which both hydrogenation and dehydrogenation occur; and a high temperature regime in which the dehydrogenation of cyclohexene dominates (> 573 K). The rate of both reactions demonstrated maxima with temperature, regardless of Pt particle size. For the hydrogenation of cyclohexene, a non-Arrhenius temperature dependence (apparent negative activation energy) was observed. Hydrogenation is structure insensitive at low temperatures, and apparently structure sensitive in the non-Arrhenius regime; the origin of the particle-size dependent reactivity with temperature is attributed to a change in the coverage of reactive hydrogen. Small particles were more active for dehydrogenation and had lower apparent activation energies than large particles. The selectivity can be controlled by changing the particle size, which is attributed to the structure sensitivity of both reactions in the temperature regime where hydrogenation and dehydrogenation are catalyzed simultaneously.
Date: July 11, 2008
Creator: Rioux, R. M.; Hsu, B. B.; Grass, M. E.; Song, H. & Somorjai, Gabor A.
Partner: UNT Libraries Government Documents Department

Heavy Oil Process Monitor: Automated On-Column Asphaltene Precipitation and Re-Dissolution

Description: An automated separation technique was developed that provides a new approach to measuring the distribution profiles of the most polar, or asphaltenic components of an oil, using a continuous flow system to precipitate and re-dissolve asphaltenes from the oil. Methods of analysis based on this new technique were explored. One method based on the new technique involves precipitation of a portion of residua sample in heptane on a polytetrafluoroethylene-packed (PTFE) column. The precipitated material is re-dissolved in three steps using solvents of increasing polarity: cyclohexane, toluene, and methylene chloride. The amount of asphaltenes that dissolve in cyclohexane is a useful diagnostic of the thermal history of oil, and its proximity to coke formation. For example, about 40 % (w/w) of the heptane asphaltenes from unpyrolyzed residua dissolves in cyclohexane. As pyrolysis progresses, this number decrease to below 15% as coke and toluene insoluble pre-coke materials appear. Currently, the procedure for the isolation of heptane asphaltenes and the determination of the amount of asphaltenes soluble in cyclohexane spans three days. The automated procedure takes one hour. Another method uses a single solvent, methylene chloride, to re-dissolve the material that precipitates on heptane on the PTFE-packed column. The area of this second peak can be used to calculate a value which correlates with gravimetric asphaltene content. Currently the gravimetric procedure to determine asphaltenes takes about 24 hours. The automated procedure takes 30 minutes. Results for four series of original and pyrolyzed residua were compared with data from the gravimetric methods. Methods based on the new on-column precipitation and re-dissolution technique provide significantly more detail about the polar constituent's oils than the gravimetric determination of asphaltenes.
Date: March 31, 2007
Creator: Schabron, John F.; Rovani, Joseph F. & Sanderson, Mark
Partner: UNT Libraries Government Documents Department

Evaluating open-path FTIR spectrometer data using different quantification methods, libraries, and background spectra obtained under varying environmental conditions

Description: Studies were performed to evaluate the accuracy of open-path Fourier Transform Infrared (OP-FTIR) spectrometers using a 35 foot outdoor exposure chamber in Pittsboro, North Carolina. Results obtained with the OP-FTIR spectrometer were compared to results obtained with a reference method (a gas chromatograph equipped with a flame ionization detector, GC-FID). Concentration results were evaluated in terms of the mathematical methods and spectral libraries used for quantification. In addition, the research investigated the effect on quantification of using different backgrounds obtained at various times during the day. The chemicals used in this study were toluene, cyclohexane, and methanol; and these were evaluated over the concentration range of 5-30 ppm.
Date: December 31, 1995
Creator: Tomasko, M.S.
Partner: UNT Libraries Government Documents Department

Characterization of fullerenes and fullerene derivatives by small-angle neutron scattering and transmission measurements

Description: Small-angle neutron scattering (SANS) has been shown to be an appropriate technique for the structural characterization of fullerenes (1) in solvents with strong SANS contrast (e.g. CS{sub 2}) and we have extended initial studies of C{sub 60} (1) to include C{sub 70} and C{sub 84} moieties. Deuterated solvents (e.g. toluene-d{sub 8}) have a high scattering length density (SLD), which is close to that of C{sub 60}, so there is virtually no SANS contrast with the solvent. Hence, these particles are practically {open_quotes}invisible{close_quotes} in such media, though the negative scattering length of hydrogen means that SLD of H{sup 1}-containing materials is much lower, so they have strong contrast with toluene-d{sub 8}. Thus, SANS makes it possible to study the size and shapes of modified buckyballs and this paper describes the first results on cyclohexane-substituted fullerenes.
Date: January 1, 1997
Creator: Melnichenko, Y.B.; Wignall, G.D. & Affholter, K.A.
Partner: UNT Libraries Government Documents Department

Scanning tunneling microscopy studies of organic monolayers adsorbed on the rhodium(111) crystal surface

Description: Scanning Tunneling Microscopy studies were carried out on ordered overlayers on the (111) surface of rhodium. These adsorbates include carbon monoxide (CO), cyclohexane, cyclohexene, 1,4-cyclohexadiene, para-xylene, and meta-xylene. Coadsorbate systems included: CO with ethylidyne, CO with para- and meta-xylene, and para-xylene with meta-xylene. In the case of CO, the structure of the low coverage (2x2) overlayer has been observed. The symmetry of the unit cell in this layer suggests that the CO is adsorbed in the 3-fold hollow sites. There were also two higher coverage surface structures with ({radical}7x{radical}7) unit cells. One of these is composed of trimers of CO and has three CO molecules in each unit cell. The other structure has an additional CO molecule, making a total of four. This extra CO sits on a top site.
Date: August 1, 1999
Creator: Cernota, Paul D.
Partner: UNT Libraries Government Documents Department

Radical cations in radiation chemistry of liquid hydrocarbons

Description: The state of knowledge concerning radical cations in liquid alkanes is discussed with particular emphasis on those which exhibit high mobility. Uncertainty has existed in the interpretation of previous results with respect to the nature and reactivity of high mobility ions, especially for cyclohexane. Recent time-resolved studies on pulse radiolysis/transient absorption, photoconductivity, and magnetic resonance in these systems have led us to propose new mechanisms for the high mobility ions. In decalins, scavenging of these ions by solutes is a pseudo-first-order reaction. In cyclohexane, the behavior is more complex and is indicative of the involvement of two species. This bimodality is rationalized in terms of a dynamic equilibrium between two conformers of the solvent radical cation. Several experimental tests supporting these views include a recent study on two-color laser photoionization in cyclohexane.
Date: July 1, 1996
Creator: Trifunac, A.D.; Sauer, M.C., Jr.; Shkrob, I.A. & Werst, D.W.
Partner: UNT Libraries Government Documents Department

The intermolecular vibrational dynamics of substituted benzene and cyclohexane liquids, studied by femtosecond OHD-RIKES

Description: By using the femtosecond optical-heterodyne detected, Raman-induced Kerr effect spectroscopy (OHD-RIKES), we have studied the intermolecular dynamics of toluene, benzyl alcohol, benzonitrile, cyclohexane, and methylcyclohexane in both the time and frequency domains.
Date: June 1, 1995
Creator: Castner, E.W. Jr. & Chang, Yong Joon
Partner: UNT Libraries Government Documents Department

Enhancement of Equilibrium Shift in Dehydrogenation Reactions Using a Novel Membrane Reactor Semi-Annual Report: September 1999-February 2000

Description: In our previous report we reported technical difficulties encountered in the fabrication of tubular membrane reactor using our Pd-ceramic composite membranes. Although the membrane is highly selective to hydrogen but in test runs we observed leakage of hydrogen from the end-seals and metallic fittings. This was a serious problem. An attempt to improve the seal by tightening was not helpful but resulted in cracks and breakage of the ceramic tube. To test the equilibrium conversion and equilibrium shift effect on dehydrogenation of cyclohexane to benzene and hydrogen in membrane reactor, we used Pd-ceramic discs in our diffusion cell as reactor packed with Pt-catalyst pellets. Test results show that by manipulating the feed (cyclohexane) flow rate and sweep gas flow rate (permeate side) we can have over 55% conversion as opposed to 18.7% equilibrium conversion under identical conditions. This demonstrates the usefulness of the new membrane in H{sub 2} separation and also in membrane-reactor configurations for equilibrium limited decomposition and dehydrogenation reactions.
Date: March 9, 2000
Creator: Ilias, Shamsuddin & King, Franklin G.
Partner: UNT Libraries Government Documents Department

Enhancement of Equilibrium Shift in Dehydrogenation Reactions Using a Novel Membrane Reactor Semi-Annual Report: March-September 1998

Description: Electroless deposition of palladium thin-films on a surface of microporous ceramic substrate has been used to develop a new class of perm-selective inorganic membrane. In the last report, we presented a numerical method to analyze the stability in single-stage gas permeation. In this reporting period, we present our modeling work on dehydrogenation of cyclohexane in Pd-Ceramic membrane reactor. A model for studying dehydrogenation of cyclohexane in a membrane reactor is developed. Radial diffusion is considered to account for the concentration gradient in radial direction due permeation through the membrane. The model equations are derived for systems with reaction and without reaction. In the non-reaction case, a mixture of argon, benzene, cyclohexane, and hydrogen is used in the reaction side and argon is used as sweep gas in the separation side. Currently, we are working on the details of numerical solution of the model equations.
Date: December 16, 1998
Creator: Ilias, Shamsuddin & King, Franklin G.
Partner: UNT Libraries Government Documents Department


Description: North Slope of Alaska has huge oil deposits in heavy oil reservoirs such as Ugnu, West Sak and Shrader Bluff etc. The viscosity of the last two reservoir oils vary from {approx}30 cp to {approx}3000 cp and the amount in the range of 10-20 billion barrels. High oil viscosity and low formation strength impose problems to high recovery and well productivity. Water-alternate-gas injection processes can be effective for the lower viscosity end of these deposits in West Sak and Shrader Bluff. Several gas streams are available in the North Slope containing NGL and CO{sub 2} (a greenhouse gas). The goal of this research is to develop tools to find optimum solvent, injection schedule and well-architecture for a WAG process in North Slope shallow sand viscous oil reservoirs. Coreflood, quarter 5-spot study, compositional simulation, wettability, relative permeability study and streamline-based simulation were conducted in this project. 1D compositional simulation results agree reasonably well with those of the slim tube experiments. Injection of CO{sub 2}-NGL is preferable over that of PBG-NGL. MME is sensitive to pressure (in the range of 1300-1800 psi) for the injection of PBG-NGL, but not for CO{sub 2}-NGL. Three hydrocarbon phases form in this pressure range. As the mean thickness of the adsorbed organic layer on minerals increases, the oil-water contact angle increases. The adsorbed organic films left behind after extraction of oil by common aromatic solvents used in core studies, such as toluene and decalin, are thinner than those left behind by non-aromatic solvents, such as cyclohexane. The force of adhesion for minerals aged with just the asphaltene fraction is similar to that of the whole oil implying that asphaltenes are responsible for the mixed-wettability in this reservoir. A new relative permeability model for a four-phase, mixed-wet system has been proposed. A streamline module is developed which ...
Date: December 1, 2004
Creator: Mohanty, Kishore K.
Partner: UNT Libraries Government Documents Department

Variation of solvent scattering-length density small-angle neutron scattering as a means of determining structure of composite materials

Description: As part of our work on the, structure of composite materials we have been exploring the use of small-angle neutron scattering using the method of contrast variation to dissect the component form, structure and distribution. This approach has resulted in a new look at very old problem reinforcement of elastomers by carbon black. Using this approach we studied an experimental high surface area (HSA) carbon black and a gel of ``HSA-bound`` rubber in cyclohexane/deuterocyclohexane mixtures. HSA in cyclohexane is found to be short rodlike particle aggregates. The aggregates have a shell-core structure with a high density graphitic outer shell and an inner core of lower density amorphous carbon. The core is continuous throughout the carbon black aggregate, making the aggregate a stiff, integral unit. Contrast variation of swollen composite gels shows that there are two length scales in the gel structure. Above 10 {Angstrom}, scattering from carbon black predominates, and below 10 {Angstrom} the scattering is from both carbon black and the elastomer. The HSA in the composite is completely embedded in polyisoprene. An estimate of the carbon black structure factor shows strong exclusion of neighboring aggregates, probably from excluded volume effects. The surface structure of the carbon black is unaltered by the interactions with elastomer and appears smooth over length scales above about 10 {Angstrom}. These results show that contrast variation can provide information on composite structure that is not available by other means. This information relates to the reinforcement mechanism of elastomers by carbon blacks.
Date: December 31, 1994
Creator: Hjelm, R. P.; Wampler, W. & Gerspacher, M.
Partner: UNT Libraries Government Documents Department

High-Pressure Catalytic Reactions of C6 Hydrocarbons on PlatinumSingle-Crystals and nanoparticles: A Sum Frequency Generation VibrationalSpectroscopic and Kinetic Study

Description: Catalytic reactions of cyclohexene, benzene, n-hexane, 2-methylpentane, 3-methylpentane, and 1-hexene on platinum catalysts were monitored in situ via sum frequency generation (SFG) vibrational spectroscopy and gas chromatography (GC). SFG is a surface specific vibrational spectroscopic tool capable of monitoring submonolayer coverages under reaction conditions without gas-phase interference. SFG was used to identify the surface intermediates present during catalytic processes on Pt(111) and Pt(100) single-crystals and on cubic and cuboctahedra Pt nanoparticles in the Torr pressure regime and at high temperatures (300K-450K). At low pressures (<10{sup -6} Torr), cyclohexene hydrogenated and dehydrogenates to form cyclohexyl (C{sub 6}H{sub 11}) and {pi}-allyl C{sub 6}H{sub 9}, respectively, on Pt(100). Increasing pressures to 1.5 Torr form cyclohexyl, {pi}-allyl C{sub 6}H{sub 9}, and 1,4-cyclohexadiene, illustrating the necessity to investigate catalytic reactions at high-pressures. Simultaneously, GC was used to acquire turnover rates that were correlated to reactive intermediates observed spectroscopically. Benzene hydrogenation on Pt(111) and Pt(100) illustrated structure sensitivity via both vibrational spectroscopy and kinetics. Both cyclohexane and cyclohexene were produced on Pt(111), while only cyclohexane was formed on Pt(100). Additionally, {pi}-allyl c-C{sub 6}H{sub 9} was found only on Pt(100), indicating that cyclohexene rapidly dehydrogenates on the (100) surface. The structure insensitive production of cyclohexane was found to exhibit a compensation effect and was analyzed using the selective energy transfer (SET) model. The SET model suggests that the Pt-H system donates energy to the E{sub 2u} mode of free benzene, which leads to catalysis. Linear C{sub 6} (n-hexane, 2-methylpentane, 3-methylpentane, and 1-hexene) hydrocarbons were also investigated in the presence and absence of excess hydrogen on Pt(100). Based on spectroscopic signatures, mechanisms for catalytic isomerization and dehydrocyclization of n-hexane were identified. The structure sensitivity of benzene hydrogenation on shape controlled platinum nanoparticles was also studied. The nanoparticles showed similar selectivities to those found for Pt(111) and Pt(100) single-crystals. ...
Date: December 19, 2007
Creator: Bratlie, Kaitlin
Partner: UNT Libraries Government Documents Department

Detailed Chemical Kinetic Modeling of Cyclohexane Oxidation

Description: A detailed chemical kinetic mechanism has been developed and used to study the oxidation of cyclohexane at both low and high temperatures. Reaction rate constant rules are developed for the low temperature combustion of cyclohexane. These rules can be used for in chemical kinetic mechanisms for other cycloalkanes. Since cyclohexane produces only one type of cyclohexyl radical, much of the low temperature chemistry of cyclohexane is described in terms of one potential energy diagram showing the reaction of cyclohexyl radical + O{sub 2} through five, six and seven membered ring transition states. The direct elimination of cyclohexene and HO{sub 2} from RO{sub 2} is included in the treatment using a modified rate constant of Cavallotti et al. Published and unpublished data from the Lille rapid compression machine, as well as jet-stirred reactor data are used to validate the mechanism. The effect of heat loss is included in the simulations, an improvement on previous studies on cyclohexane. Calculations indicated that the production of 1,2-epoxycyclohexane observed in the experiments can not be simulated based on the current understanding of low temperature chemistry. Possible 'alternative' H-atom isomerizations leading to different products from the parent O{sub 2}QOOH radical were included in the low temperature chemical kinetic mechanism and were found to play a significant role.
Date: November 10, 2006
Creator: Silke, E J; Pitz, W J; Westbrook, C K & Ribaucour, M
Partner: UNT Libraries Government Documents Department


Description: About 37-50% (w/w) of the heptane asphaltenes from unpyrolyzed residua dissolve in cyclohexane. As pyrolysis progresses, this number decrease to below 15% as coke and toluene insoluble pre-coke materials appear. This solubility measurement can be used after coke begins to form, unlike the flocculation titration, which cannot be applied to multi-phase systems. Currently, the procedure for the isolation of heptane asphaltenes and the determination of the amount of asphaltenes soluble in cyclohexane spans three days. A more rapid method to measure asphaltene solubility was explored using a novel on-column asphaltene precipitation and re-dissolution technique. This was automated using high performance liquid chromatography (HPLC) equipment with a step gradient sequence using the solvents: heptane, cyclohexane, toluene:methanol (98:2). Results for four series of original and pyrolyzed residua were compared with data from the gravimetric method. The measurement time was reduced from three days to forty minutes. The separation was expanded further with the use of four solvents: heptane, cyclohexane, toluene, and cyclohexanone or methylene chloride. This provides a fourth peak which represents the most polar components, in the oil.
Date: June 1, 2006
Creator: Schabron, John F.; Jr, Joseph F. Rovani & Sanderson, Mark
Partner: UNT Libraries Government Documents Department