Rapid microprecipitation method for determining insolubles in asphalts,pitches and petroleum residua

A novel rapid microprecipitation method using an ultrasonic bath for determining n-heptane, toluene and trichloroethylene insolubles in asphalts, pitches and petroleum residua has been developed. The method is applicable to all solid and semi-solid petroleum residua (pitches) and asphalts containing little or no mineral matter. The procedure uses non-sophisticated equipment and only takes ≈ 30 min per determination. The method was applied to 10 pitches and asphalt samples. Results are compared with those obtained from the standard ASTM procedures. Repeatability of the method is also presented with ASTM D 2042-76.     

Mechanistic Studies on the Coupled Reaction of n-Hexane and Ethanol Over HZSM-5 Zeolite Catalyst

The coupled reaction of n-hexane and ethanol over HZSM-5 zeolite has been, for the first time, investigated with a pulse-reaction system. The catalytic reaction results showed an improvement of the initial conversion activity of n-hexane when ethanol was introduced as co-reactant. The FT-IR analysis revealed that the ethanol molecules adsorbed on Brønsted acidic sites were immediately transformed into surface ethoxy groups, which were active species for converting n-hexane and improving the initial conversion activity of n-hexane by a bimolecular hydride transfer mode. Also, the catalytic tests suggested that alkenes resulting from the transformation of ethanol could not enhance the initial conversion of n-hexane compared to active ethoxy groups at the shortest contact time. A mechanism involving the ethoxy groups was proposed to understand the coupled reaction of ethanol and n-hexane.     

Synthesis of carbon nanotubes on Ni/carbon-fiber catalysts under mild conditions

Methane, n-hexane, benzene, and cyclopentadiene were decomposed at a relatively mild temperature (773 K) over a Ni catalyst supported on either vapor grown carbon fibers (VGCF) or graphitized carbon fibers (GCF). Transmission electron microscopy showed that the morphology of the fibers changed according to hydrocarbon and particle size. Decomposition of methane and n-hexane produced fishbone-type fibers. The fibers from n-hexane sometimes showed intermittent hollow structures but the diameters of the fibers were widely distributed. Decomposition of benzene and cyclopentadiene mainly produced winding type carbon nanotubes of relatively uniform diameters (10-20 nm). Bidirectional fishbone-type fibers (fibers growing outward from a central catalyst particle) were also observed as a by-product. Small Ni particles (10-20 nm) with stretched tails were present on the tips of tubular fibers, some of which frequently changed growth direction. The varying tubular morphologies can be ascribed to liquid-like Ni particles resulting from the freezing point depression due to a fast dissolution of carbons during decomposition of benzene or cyclopentadiene. The formation of bidirectional fibers was also observed in the decomposition of n-hexane. Relatively large well-faceted Ni particles (diameter 50-110 nm) grew bidirectional fibers.     

Investigation of stabilization of α-Fe particles in pores of silica SBA-15 in a hexane atmosphere

The present paper is devoted to the investigation of the possibility to stabilize the metallic state of iron nanoparticles (10–14 nm) in pores of a mesoporous silica SBA-15, using adsorption of n-hexane from a gas phase at room temperature. By means of the method of Moessbauer spectroscopy and measurements of ferromagnetic properties (measurements of magnetization), it is shown that the sample treated with n-hexane in the gas phase preserves its chemical composition and ferromagnetic properties after a month of storage in air.     

The liquid—liquid equilibrium for activity coefficient determination

A method based on liquid—liquid equilibrium is proposed for the determination of activity coefficients. The reliability of this procedure is tested on the systems cyclohexane—benzene, cyclohexane—toluene, n-hexane—benzene, n-heptane—toluene.     

Dehydrocyclization of n-hexane on a bifunctional catalyst

Dehydrocyclization of n-hexane was investigated in the temperature range 400–500 °C, pressure range 3–20 atm, and at space velocities 10–150 (g feed/g cat × hr) on a commercial $\text{Pt}\text{Al}{}_2\text{O}{}_3$ catalyst in a fixed bed reactor. From product distributions of the individual conversions of n-hexane, 1-hexene, 2-methylpentane, 2-methyl-1-pentene, 1,5-hexadiene, and methylcyclopentane at the same reaction conditions and from experiments with variation of residence time at constant temperature and pressure, a reaction mechanism for the dehydrocyclization of n-hexane is proposed, in which at least four different reaction paths for the aromatization are possible: 5- and 6-membered ring closure and cyclization of cis-2-hexene and 1,5-hexadiene.     

Effect of n-Butane and propane on performance and emission characteristics of an SI engine operated with DME-blended LPG fuel

In this study, a spark ignition engine operated with DME-blended LPG fuel was studied experimentally. In particular, the effect of n-Butane and propane on performance, emissions characteristics (including hydrocarbon, CO, and NOx), and the combustion stability of an SI engine fuelled with DME-blended LPG fuel were examined. Four kinds of test fuel with different blend ratios of n-Butane, propane, and DME were used. The percentage of DME in the fuel blend was 20% by mass.The results showed that stable engine operation was possible for a wide range of engine loads with propane containing LPG/DME-blended fuel rather than n-Butane containing LPG/DME-blended fuel since the octane number of propane is higher than that of n-Butane. Also, engine power output, break specific fuel consumption (BSFC), and combustion stability when operating with propane containing DME-blended fuel were comparable to those values in case of pure LPG fuel operation. Engine power output was decreased and BSFC was increased with n-Butane containing DME-blended fuel due to the lower energy density of DME. To examine the effect of n-Butane and propane on emissions and fuel economy in an actual vehicle, a vehicle was tested during an FTP-75 cycle. Through the emission and fuel economy test in the FTP-75 cycle, we conclude that the differences in emission level and fuel economy were not significant according to the blend of n-Butane, propane, and DME.Considering the experimental results from the engine bench and the actual vehicle, the 20% content of DME-blended fuel, regardless of LPG type, can be used as an alternative fuel for LPG.     

Optimization of enzymatic pretreatment for n-hexane extraction of oil from Silybum marianum seeds using response surface methodology

An investigation on enzymatic pretreatment for n-hexane extraction of oil from the Silybum marianum seeds was conducted. The optimum combination of extraction parameters was obtained with the response surface methodology (RSM) at a four-variable and five-level central composite design (CCD). The optimum parameters of enzymatic pretreatment were as follows: enzyme concentration of 2.0% (w/w), temperature of 42.8 °C, reaction time of 5.6 h, and pH of 4.8. After enzymatic pretreatment, the oil was extracted by n-hexane for 1.5 h, and the oil yield on a dry basis was 45.70%, which well matched with the predicted value (45.86%). The results of the effects of the enzymatic pretreatment for n-hexane extraction of oil from the aspects of oil yield, microstructure and the fatty acid compositions showed that the enzymatic pretreatment had not affected on the fatty acid compositions, but could cause structure breakage of the S. marianum seeds and accelerate releasing extra oil, which increased the oil yield by 10.46% compared with n-hexane extraction for 1.5 h without enzymatic pretreatment, and confirmed the efficacy of enzymatic pretreatment for n-hexane extraction of oil from the S. marianum seeds.     

Isomerization of light alkanes catalyzed by ionic liquids: An analysis of process parameters

The effect of process parameters on the catalytic properties of the chloroaluminate ion liquid has been investigated for n-hexane isomerization. The n-hexane conversion and isomerizate yield increase with an increasing temperature, contact time, and catalyst-to-substrate ratio, while the liquid-isoalkane selectivity of the catalyst decreases.     

Simple group contribution theory for adsorption of alkanes in nanoporous carbons

This paper develops a simplified form of the group-contribution theory of Russell and LeVan (Chem. Eng. Sci. 51 (1996) 4025) for the prediction of adsorption equilibria of n-alkanes on activated carbon. Molecules are separated into elements or groups, and adsorbate group-adsorbent interactions are the determining factor for adsorption equilibrium. The adsorbent surface is considered to be heterogeneous with a single dimensionless energy distribution. Model parameters are determined for pure-component adsorption of methane, ethane, n-butane, and n-hexane on BPL activated carbon at multiple temperatures. The resulting parameters are then used to predict adsorption equilibrium of propane and n-octane at multiple temperatures and mixtures of methane and n-hexane and ethane and n-hexane. The model gives a more accurate prediction of mixture adsorption than the ideal adsorbed solution theory. The model is also used to describe methane, propane, and n-pentane adsorption on BAX activated carbon (Ind. Eng. Chem. Res. 40 (2001) 338) and methane, ethane, and propane on Columbia Grade L carbon (Ind. Eng. Chem. 42 (1950) 1315) at multiple temperatures. The model is shown to describe adsorption equilibria of alkanes on all three activated carbons with good accuracy and can also be used as a predictive tool for components on which no experimental data are available.     

Synthesis of a hexagonal modification of C60 using cryoextraction

Samples of the hexagonal close-packed phase (h.c.p.) of fullerite C₆₀ with a low (less then 7%) content of more stable face-centered cubic (f.c.c.) phase were synthesized using cryoextraction with n-hexane. X-Ray diffraction analysis and thermogravimetry were applied for characterization of the samples. The role of n-hexane in the formation of the h.c.p. structure is discussed.     

Ni-ZSM-5 catalysts: Detailed characterization of metal sites for proper catalyst design

Nickel was introduced in ZSM-5 zeolite by two different methods: dry impregnation and ionic exchange. Different loadings of metal, ranging from 0.4 to 6 wt% were explored. These materials were thoroughly characterized by EXAFS, TPR, acidity measurements by H/D isotope exchange and ethane hydrogenolysis. Regardless of the metal introduction method, at 0.4 wt% Ni, the Ni-ZSM-5 catalysts present only nickel located inside the zeolite channels as compensation cations. In contrast, an increase to 1 wt% nickel (via impregnation) led to its presence both inside and outside the channels.The catalytic activity of these Ni-ZSM-5 zeolites was tested in n-hexane cracking. Depending on the way the metal was introduced, it was possible to modify the n-hexane cracking activity and the selectivity toward light alkenes. Hence, a proper design of metal and acid sites could be achieved.     

Three-liquid-phase salting-out extraction of effective components from waste liquor of processing sea cucumber

A three-liquid-phase (TLP) salting-out extraction system composed of n-hexane/ethanol/sodium carbonate/water was investigated to extract oils, saponins, proteins and polysaccharides simultaneously from waste liquor of processing sea cucumber. The effects of the ratio of ethanol to sodium carbonate, n-hexane concentration and extraction time were investigated. The results showed that 86.7% of oils were distributed in the top n-hexane phase, 82.9% of saponins in the middle ethanol phase, 93.2% of proteins and 92.9% of polysaccharides in the interface between the middle and the bottom salt phase when the system composed of 28% (w/w) n-hexane/11.52% (w/w) ethanol/8.64% (w/w) sodium carbonate was used at 37 °C for 0.5 h. When the system was progressively enlarged from 30 g to 25 kg, the yield of polysaccharides, proteins, oils and saponins was decreased only by 1.0%, 2.8%, 1.0% and 2.6%, respectively. The recycle of salt and solvents in three-liquid-phase system was also studied, and the results showed that the recovery of n-hexane, ethanol and salt were 81.4%, 80.8% and 72.0%, respectively. Recycling materials for the extraction, the yield for proteins and oils decreased by 2.0% and 5.4%, respectively, comparing with the pure system.     

Conventional and in situ transesterification of castor seed oil for biodiesel production

In the present study, biodiesel production from Ricinus communis L. red and BRS-149 nordestina varieties seed oil is reported. Reactions were made through conventional and in situ processes using ethanol and evaluating the addition of n-hexane as co-solvent. The content of ethyl esters was quantified by ¹H NMR. The highest conversions were obtained from crude oil (conventional reaction) after pre-esterification, using ethanol and a molar ratio of alcohol to oil of 60; furthermore, the addition of n-hexane was not significant on yield. Under these conditions, best conversion was around 95% for both varieties.     

Surface chemistry and contrast-modified SAXS in polymer-based activated carbons

The adsorption of non-polar and polar molecules, n-hexane and water, on activated carbons, functionalized by oxidation with concentrated nitric acid, is investigated by small angle X-ray scattering. A relative mass density function p(q) is introduced in order to trace the filling characteristics of these probe molecules in the pore structure. Inspection of p(q) shows that while the pores affected by the applied relative pressure are completely filled by n-hexane, pore filling by water is only partial, even in the most oxidized carbon. The differences between the solid-liquid contact areas of these two molecules adsorbed from the vapour phase on the various carbons illustrate the influence of surface chemistry and molecular polarity on the contrast-modified SAXS response.     

Kinetics of the low-temperature isomerization of <Emphasis Type="Italic">n</Emphasis>-hexane on the NIP-3A catalyst in an isothermal flow reactor

Low-temperature n-hexane isomerization kinetics was studied in an isothermal fixed-bed flow reactor on the chlorinated platinum-alumina catalyst NIP-3A under conditions of the coexistence of liquid and vapor phases. Optimum n-hexane isomerization conditions have been determined. Kinetic equations for the process are suggested.     

Effect of thermal history on free volume and transport properties of high molar mass polyethylene

The desorption of n-hexane from high molar mass polyethylene at 298 K has been studied. The polymer was given different thermal treatments to obtain differences in crystallinity, morphology and composition of the non-crystalline fraction. Crystal contents determined by Raman spectroscopy were always lower than those determined by density measurements. The systems with high crystallinity showed in relative terms a low content of interfacial component. The n-hexane solubilities of the samples were strictly proportional to the volume fraction of penetrable polymer (liquid-like and interfacial components) and the solubility was low in comparison with that of branched polyethylene of the same crystallinity. The Cohen-Turnbull-Fujita free volume theory was numerically capable of describing the desorption process in the polyethylenes studied. One of the methods used assumed that all three non-crystalline components—liquid-like, interfacial liquid-like and interfacial crystal core components—are penetrable by n-hexane and this method yielded data for the geometrical impedance factor and the fractional free volume with physically realistic trends, but the changes in the geometrical impedance factor was not in quantitative agreement with the Fricke model applied to the morphological data. This lack of numerical agreement is tentatively due to the fact that the assessment of crystal shape by transmission electron microscopy of stained sections systematically underestimates the crystal widths, particularly for the low-crystallinity samples with curved and ‘twisting’ crystal lamellae.     

Development and Scale-up of Aqueous Surfactant-Assisted Extraction of Canola Oil for Use as Biodiesel Feedstock

Aqueous surfactant-assisted extraction (ASE) has been proposed as an alternative to n-hexane for extraction of vegetable oil; however, the use of inexpensive surfactants such as sodium dodecyl sulfate (SDS) and the effect of ASE on the quality of biodiesel from the oil are not well understood. Therefore, the effects on total oil extraction efficiency of surfactant concentration, extraction time, oilseed to liquid ratio and other parameters were evaluated using ASE with ground canola and SDS in aqueous solution. The highest total oil extraction efficiency was 80 %, and was achieved using 0.02 M SDS at 20 °C, solid–liquid ratio 1:10 (g:mL), 1,000 rpm stirring speed and 45 min contact time. Applying triple extraction with three stages reduced the amount of SDS solution needed by 50 %. The ASE method was scaled up to extract 300 g of ground canola using the best combination of extraction conditions as described above. The extracted oil from the scale-up of the ASE method passed the recommendation for biodiesel feedstock quality with respect to water content, acid value and phosphorous content. Water content, kinematic viscosity, acid value and oxidative stability index of ASE biodiesel were within the ASTM D6751 biodiesel standards.     

Structural characterization of the δ-clathrate forms of syndiotactic polystyrene with n-alkanes

The δ-clathrate forms of syndiotactic polystyrene (s-PS) containing a homologous series of guests characterized by an increasing molecular volume (n-alkanes ranging from n-pentane to n-dodecane) have been investigated. The present analysis allows concluding that the volume of the guest plays a crucial role in the choice of the type of δ-clathrate that can be obtained. As a matter of fact, longer n-alkanes, such as n-octane, n-nonane or n-decane, turned out to give rise triclinic δ-clathrates presenting a guest/monomeric-unit ratio of 1/8, while δ-clathrates containing shorter alkanes, like n-hexane or n-heptane, instead, present a monoclinic or a triclinic structure with a guest/monomeric-unit ratio of 1/4. These results confirm the validity of a simple criterion to predict the type of s-PS δ-clathrate with a certain guest on the basis of the experimental d₀₁₀, as described in Macromolecules 2010, 43, 8549-8558. Moreover, our analysis confirms previous solid state ¹³C NMR and Raman spectroscopy data, indicating that shorter n-alkanes molecules, like n-hexane, are hosted in the cavities with an all-trans conformation while longer alkanes, like n-nonane, present bent conformations. The effect of n-alkanes molecules on the crystallization of s-PS amorphous samples has been investigated too.     

Precipitation, fractionation and characterization of asphaltenes from heavy and light crude oils

Asphaltenes of Maya and Isthmus crude oils were precipitated, fractionated and characterized in this work. Isolation of asphaltenes was performed by following the ASTM D3279 method, which uses n-heptane for solvent precipitation. Asphaltenes were separated into three fractions by Soxhlet extraction with a binary solvent system of toluene and n-heptane. C, H, O, N, S, and Ni and V contents were determined in asphaltenes and in their fractions by elemental analysis and atomic absorption, respectively. VPO aggregate weight and NMR measurements were also performed in all samples. Important differences in properties of unfractionated asphaltenes and asphaltenes fractions were observed. Some of these differences were attributed to impurities in the unfractionated asphaltenes.