Showing papers on "Hexane published in 2000"

Enhancement of the catalytic oxidation of hydrogen-lean chlorinated VOCs in the presence of hydrogen-supplying compounds

Abstract: The complete catalytic oxidation of trichloroethylene (TCE) over alumina-supported noble metal catalysts (Pt and Pd) and in the presence of hydrogen-rich compounds, i.e. water, hexane and toluene was evaluated. Experiments were performed at conditions of lean TCE concentration (around 1000 ppm) in air, between 250 and 550°C in a conventional fixed-bed reactor. Hexane and toluene were added to the feedstream in a concentration of around 1000 ppm and water concentration varied from 1000 to 15 000 ppm. TCE oxidation occurred faster in the presence of hexane and toluene over both catalysts. Over palladium catalysts, water did not alter catalytic activity, whereas over platinum catalysts water enhanced TCE oxidation at low temperatures ( 400°C). Selectivity to HCl was much improved by feeding water as a hydrogen-supplying reactant; 7500 ppm of water enhanced HCl outputs from 39.4 to 78.0% with Pd, and from 37.5 to 58.9% with Pt. Selectivities to C2Cl4, formed by chlorination of the feed, and Cl2 were greatly reduced. On the other hand water promoted complete oxidation of TCE to CO2, and thus reduced selectivity to CO. In the presence of hexane and toluene, formation of HCl was also enhanced. Hexane showed higher inhibition ability than toluene over both catalysts for the C2Cl4 and Cl2 formation. Unlike in the presence of water, selectivity to CO increased, as a consequence of partial oxidation of both hydrocarbons.

Surface Tensions, Refractive Indexes and Excess Molar Volumes of Hexane + 1-Alkanol Mixtures at 298.15 K

Abstract: Surface tensions and refractive indexes for binary mixtures of {hexane + ethanol, + 1-propanol, + 1-butanol, + 1-pentanol, + 1-hexanol, + 1-heptanol, and + 1-octanol} have been measured at 298.15 K. Surface tension deviations and changes of refractive index have been also calculated. Excess molar volumes of {hexane + ethanol, + 1-pentanol, and + 1-hexanol} mixtures have been determined at 298.15 K from density data and compared with literature.

Quality of wheat germ oil extracted by liquid and supercritical carbon dioxide

Abstract: The extraction of wheat germ oil by liquid and supercritical CO2 is described from the point of view of both operative method and pretreatment of raw material. The best conditions for wheat germ oil extraction are: pressure, 150 bar; temperature, 40°C; and solvent flow rate, 1.5 L/min at standard temperature and pressure. The yields and fatty acid compositions obtained are very similar to those resulting from the conventional extraction process using hexane as solvent (8.0 wt%), although a higher-quality oil is obtained by using CO2 as solvent (free fatty acids, 12.4%; tocopherol content, 416.7 mg tocopherol/g wheat germ oil). These factors lead to the conclusion that the extraction process using CO2 could be economically competitive with the conventional process, since it considerably simplifies the oil refinement stages and completely eliminates the solvent distillation stage, which are the most costly processing steps in terms of energy consumption.

Supersolubilization in Chlorinated Hydrocarbon Microemulsions: Solubilization Enhancement by Lipophilic and Hydrophilic Linkers

Abstract: In this paper, the effect of linker molecules on the solubilization capacity of an anionic surfactant system (sodium dihexyl sulfosuccinate) is studied. N-Alkyl alcohols are used as lipophilic linkers in middle-phase microemulsions of trichloroethylene, tetrachloroethylene, and hexane. The lipophilic linker effect increases the solubilization capacity of the anionic surfactant system. The solubilization parameter for both hydrocarbons and chlorinated hydrocarbon oil increases as a function of alcohol concentration. As the alkyl chain length of the alcohol linker molecule increases, the solubilization capacity increases. Moreover, the longer chain alcohol is more effective at linking oil molecules for hexane than for chlorinated hydrocarbon oils, indicating that the linker effect is more effective for higher equivilant alkane carbon number (EACN) oils. Sodium mono- and dimethylnaphthalenesulfonate is proposed as a hydrophilic linker to enhance the solubilization of lower EACN oils. The combination of lipop...

Heterogeneous Reaction of NO2 on Hexane Soot: A Knudsen Cell and FT-IR Study

Abstract: In this study, the reaction of NO2 on freshly prepared hexane soot has been studied using a Knudsen cell reactor and FT-IR spectroscopy. Initial uptake coefficients were determined using gas-diffus...

Evaporation rates of structured and non-structured liquid mixtures

Abstract: We have used a gravimetric technique to measure the rate of evaporation of a volatile liquid in mixtures with a second, involatile component under conditions of controlled gas flow. A range of non-structured and structured mixtures were investigated in order to examine whether the rate limiting step for evaporation may switch from vapour diffusion across the stagnant gas layer above the liquid to mass transfer within the liquid mixture. Evaporation rates of pentane and hexane from mixtures with squalane (involatile) show excellent agreement with rates calculated on the basis that vapour diffusion across a stagnant gas layer is rate limiting and that mass transfer within the liquid mixture is fast. Hexane gelled by the addition of silica particles is found to evaporate at a rate very similar to that for un-gelled hexane because the equilibrium vapour pressure of hexane is unaffected by silica particle addition. Water evaporation rates from mixtures with the non-ionic surfactant n-dodecyl hexaoxyethylene glycol ether (C12E6) were found to be up to 10 times slower than calculated vapour space diffusion controlled rates owing to the slow development of concentration gradients within these highly structured liquid mixtures.

Influence of Pt concentration on tungsten oxide-promoted zirconia during n-hexane isomerization

Abstract: The effect of platinum concentration on tungsten oxide-promoted zirconia over the catalytic activity for n -hexane isomerization was studied. Catalysts were prepared by impregnation of tungsten oxide-promoted zirconia reaching up to 1.50% platinum, followed by calcination at 500°C. The n -hexane reaction was studied at 200°C, 5.9 bar, WHSV 4 and H 2 : n -hexane (molar) ratio 7. It was found that catalytic activity and stability increase for platinum concentrations above 0.05% because of higher hydrogen availability at the surface, measured as a function of the methylcyclopentane/C 6 isomers ratio. Further increments in platinum concentration do not produce important modifications in catalytic activity or hydrogen availability. Mechanical mixtures of Pt/SiO 2 and tungsten oxide-promoted zirconia present a lower conversion than platinum over tungsten oxide-promoted zirconia due to the larger distance between the acid and metallic functions.

Evidence of different reaction mechanisms during the cracking of n-hexane on H-USY zeolite

Abstract: Experimental data were collected for n -hexane cracking on acidic ultrastable Y (H-USY) zeolite at 673 K which clearly document a change from monomolecular cracking to bimolecular/oligomeric cracking as the reactant partial pressure and contact time (or conversion) increased. Under conditions of low pressure (

Permeation of hexane isomers through an MFI membrane

Abstract: The pervaporation tests for n-hexane, 2-methylpentane (2-MP), and 2,3-dimethylbutane (2,3-DMB) were performed using an MFI-type zeolitic membrane at 303 K. In the unary systems, those fluxes followed the order n-hexane ≫ monobranched hexane (2-MP), > dibranched hexane (2,3-DMB). The ideal selectivities of n-hexane/2-MP and n-hexane/2,3-DMB were 37 and 50, respectively. n-Hexane preferentially permeated in the measurements of a binary mixture of n-hexane/2-MP and n-hexane/2,3-DMB. The feed composition dependence in separating n-hexane/2,3-DMB binary mixtures was studied. The separation factor for the 50/50 n-hexane/2,3-DMB mixture exceeded 120, which was much greater than 54 in the 50/50 n-hexane/2-MP system. When the feed concentration of n-hexane was 10 mol %, the separation factor α(n-hexane/2,3-DMB) at the steady state was as high as 270. n-Hexane effectively inhibited the permeation of 2,3-DMB, even when the concentration of n-hexane was very small.

Lecithin Inverse Microemulsions for the Pulmonary Delivery of Polar Compounds Utilizing Dimethylether and Propane as Propellants

Abstract: Lecithin inverse microemulsions were investigated as a means of pulmonary drug delivery, utilizing dimethylethyleneglycol (DMEG) and hexane as models for dimethyl ether (DME) and propane, respectively. Addition of lecithin to the model propellant mixtures increased the solubility of water in a nonlinear, solvent-dependent manner. The concentration of water necessary to fully hydrate cobalt(II) decreased as the solvent composition was varied from DMEG to hexane. Water proton chemical shift increased in the presence of lecithin, with the largest increases in high hexane content samples. Equilibrium dialysis and component diffusion rate determination (by pulsed-field gradient [PFG]-NMR) indicated the quantity of water associated with the dispersed phase. Collectively, these methods demonstrated that a greater fraction of water was associated with the microemulsion-dispersed phase as the solvent was varied from DMEG to hexane. Iodine solubilization indicated microemulsion formation (operational critical micelle concentration [cmc], 10 moles water per mole lecithin) at approximately 10(-4)-10(-5) molal lecithin. NMR data (trimethylammonium proton chemical shift, water, and lecithin T1) were consistent with microemulsion formation. Water-soluble compounds dissolved in lecithin inverse microemulsions in a lecithin- and water-dependent manner. Experiments with DME/lecithin demonstrated microemulsion characteristics similar to those in the model propellant. DME/lecithin metered-dose inhalers (MDIs) produced a particle size and a fine particle fraction (36% by twin impinger method) suitable for pulmonary drug delivery.

Thermodynamic Properties of n-Alkoxyethanols + Organic Solvent Mixtures. XIV. Liquid−Liquid Equilibria of Systems Containing 2-(2-Ethoxyethoxy)ethanol and Selected Alkanes

Abstract: Liquid−liquid equilibria (LLEs) data are reported for 2-(2-ethoxyethoxy)ethanol + hexane, heptane, octane, decane, dodecane, and hexadecane mixtures between 274.5 K and the upper critical solution temperatures (UCSTs). The coexistence curves were determined visually. They have a rather horizontal top, and their symmetry depends on the size of the alkane. For systems with dodecane or hexadecane, they are skewed to the region of higher mole fractions of 2-(2-ethoxyethoxy)ethanol. An opposite behavior is observed when hexane or heptane is involved. The (x1, T) data were fitted to the equation T = Tc + k|y − yc|m, where y = αx1/[1 + x1(α − 1)] and yc = αx1c/[1 + x1c(α − 1)]. Tc and x1C are the coordinates of the critical points fitted together with k, m, and α. Results are briefly discussed on the basis of the existence of inter- and intramolecular H-bonds as well as of dipole interactions, which occur in solutions containing hydroxyethers.

Influence of sulfation and structure of zirconia on catalytic isomerization of n‐hexane

Abstract: Two series of sulfated zirconia have been prepared by immersing amorphous or crystalline zirconia in an H2SO4 solution (0.25–2.5 M). They were compared with a commercial sulfated zirconium hydroxide. Activation temperature was varied between 300 and 725°C. Sulfate density varied so that the mean surface area of an individual sulfate ranged from 0.14 to 0.54 nm2. Three limiting sulfate states are evidenced and characterized by TPR‐MS. Catalysts are tested for isomerization of n‐hexane at 150°C and 3 MPa. Factors influencing the activity are discussed. The data show that a highly active and selective catalyst for producing hexane isomers requires tetragonal zirconia with a sulfate occupancy of about 0.40 nm2. Preparation parameters must therefore be adapted to match these constraints.

Comparison of solvents for determination of monoterpenes in wine using liquid-liquid extraction

Abstract: The extraction capacity of seven solvents for volatile compounds in a model aqueous alcohol system was investigated. The five major terpenes usually found in grapes and wines (linalool, α-terpineol, citronellol, nerol and geraniol) were studied in a model wine. Liquid-liquid extraction with dichloromethane, diethyl ether, freon-11, ether-pentane (1∶1), ether-hexane (1∶1), pentane and hexane as extracting solvents are compared. Dichloromethane and diethyl etherpentane (1∶1,v/v) were the best solvents for a quantitation of these aromatic compounds.

Hexane elimination from soybean oil by continuous packed tower processing with supercritical CO2

Abstract: Hexane elimination is the most energy-consuming step in the industrial extraction of soybean oil. It utilizes three sets of equipment: two evaporation stages in series followed by a stripper at a pressure of about 0.07 bar. The final hexane residue in the oil is about 1000 ppm. We propose an alternative to the present process for hexane elimination, based on the extraction of the soybean oil/hexane mixture with supercritical CO2 in a continuous countercurrent packed tower. In this work, we tested a soybean oil/hexane mixture feed containing 10% by weight of hexane. Various pressures and temperatures of the column were tested to reduce hexane residue in the oil. The extraction process was demonstrated to be very effective for hexane separation. Indeed, at the bottom of the column we recovered soybean oil containing quantities of hexane as low as 20 ppm when we operated at 120 bar, 40°C. The effect of process parameters is also discussed.

Vapor−Liquid Equilibria for the Hexane + Tetracosane and Hexane + Hexatriacontane Systems at Elevated Temperatures and Pressures

Abstract: Vapor and liquid equilibrium compositions have been measured for the hexane + tetracosane and hexane + hexatriacontane systems at temperatures from 473.0 K to 622.9 K and pressures from 6.2 bar to 64.5 bar. A continuous-flow apparatus was used so that the low wax concentrations in the vapor phase could be accurately measured. Mixture critical pressures and compositions were also measured. The effects of chain length, branching, and substituent groups on the phase behavior of binary systems containing hexane + a long-chain alkane are summarized in the form of a pressure versus temperature projection. A practical application of this work is the separation of Fischer-Tropsch waxes from reactor catalyst via supercritical extraction. The proposed process uses near or supercritical solvents such as pentane and hexane for extraction and recovery of the waxes, which consist of paraffins, olefins, and alcohols up to C{sub 200} in size.

An attempt to bridge the pressure and material gap with a disperse model catalyst for low-temperature alkane reforming

Abstract: Pt black was exposed to n>-hexane/H2 mixtures between 483 and 663 K followed by O2 and H2 treatments at 603 K. XP and UP spectra were measured without exposing the samples to air. 20–30% carbon accumulated after hydrocarbon exposures. O2 removed most carbon. The surface C content increased after a subsequent contact with H2, C 1s showing more “atomic carbon” as opposed to graphite after n-hexane exposure. Anisotropic recrystallization of Pt black favoring (220) and (311) lattice planes occurred under hydrogen-rich conditions. Both findings were attributed to a H2-induced solid-state rearrangement; H atoms penetrating into the crystal lattice, force subsurface carbon and oxygen atoms to the surface and a concomitant restructuring would occur. Thus another “hydrogen effect” has been recognized, leading to structures favorable for skeletal reactions of alkanes.

Excess Molar Enthalpies of Propyl Propanoate + Hexane + Benzene at 298.15 K and 308.15 K

Abstract: Excess molar enthalpies of the ternary system {x1 propyl propanoate + x2 hexane + (1 − x1 − x2) benzene} and of their binary mixtures {x1 propyl propanoate + x2 hexane}, {x1 propyl propanoate + x2 benzene}, and {x1 hexane + x2 benzene} have been determined at 298.15 K and 308.15 K and atmospheric pressure, over the whole composition range. The excess molar enthalpies were measured using a Calvet microcalorimeter. The experimental values were compared with the results obtained with empirical expressions for estimating ternary properties from binary data.

Heterogeneity of the Glass Fiber Surface from Inverse Gas Chromatography

Abstract: The chromatographic peak profiles of hexane and butanol on a column packed with E-glass fibers show that the surface of the fiber is homogeneous for hexane and heterogeneous for butanol. The distri...