Longer N-alkanes Research Articles

Biodegradation of Petroleum Sludge by Methylobacterium sp. Strain ZASH.

A bacterium was isolated from sludge-contaminated soil in a petroleum refinery and tested for its ability to degrade aliphatic hydrocarbon compounds present in petroleum sludge. The isolate was grown on minimal salt media agar supplemented with 1% (w/v) petroleum sludge. The isolate was tentatively identified as Methylobacterium s p. s t rain ZASH based on the partial 16s rDNA molecular phylogeny. The bacterium grew optimally between the temperatures of 30°C and 35°C, pH 7 and 7.5, 0.5% and 1.5% (v/v) Tween 80 as the surfactant, and between 1% and 2% (w/v) peptone as the nitrogen source. The constants derived from the Haldane equation were μmax = 0.039 hr-1, Ks = 0.385% (w/v) total petroleum hydrocarbons (TPH) or 3,850 mg/L TPH, and Ki =1.12% (w/v) TPH or 11,200 mg/L. The maximum biodegradation rate exhibited by this strain was 19 mg/L/hr at an initial TPH concentration of 10,000 mg/L. Gas chromatography analysis revealed that after 15 days the strain was able to degrade all aliphatic n-alkanes investigated with different efficiencies. Shorter n-alkanes were generally degraded more rapidly than longer n-alkanes with 90% removal for C-12 compared to only 30% removal for C-36. The addition of sawdust did not improve bacterial degradation of petroleum hydrocarbons, but it assisted in the removal of remaining undegraded hydrocarbons through adsorption.

C14–22 n-Alkanes in Soil from the Freetown Layered Intrusion, Sierra Leone: Products of Pt Catalytic Breakdown of Natural Longer Chain n-Alkanes?

Soil above a platinum-group element (PGE)-bearing horizon within the Freetown Layered Intrusion, Sierra Leone, contains anomalous concentrations of n-alkanes (CnH2n+2) in the range C14 to C22 not readily attributable to an algal or lacustrine origin. Longer chain n-alkanes (C23 to C31) in the soil were derived from the breakdown of leaf litter beneath the closed canopy humid tropical forest. Spontaneous breakdown of the longer chain n-alkanes to form C14–22 n-alkanes without biogenic or abiogenic catalysts is unlikely as the n-alkanes are stable. In the Freetown soil, the catalytic properties of the PGE (Pt in particular) may lower the temperature at which oxidation of the longer chain n-alkanes can occur. Reaction between these n-alkanes and Pt species, such as Pt2+(H2O)2(OH)2 and Pt4+(H2O)2(OH)4 can bend and twist the alkanes, and significantly lower the Heat of Formation. Microbial catalysis is a possibility. Since a direct organic geochemical source of the lighter n-alkanes has not yet been identified, this paper explores the theoretical potential for abiogenic Pt species catalysis as a mechanism of breakdown of the longer n-alkanes to form C14–22 alkanes. This novel mechanism could offer additional evidence for the presence of the PGE in solution, as predicted by soil geochemistry.

Sensitive detection of <i>n</i>-alkanes using a mixed ionization mode proton-transfer-reaction mass spectrometer

Abstract. Proton-transfer-reaction mass spectrometry (PTR-MS) is a technique that is widely used to detect volatile organic compounds (VOCs) with proton affinities higher than water. However, n-alkanes generally have a lower proton affinity than water and therefore proton transfer (PT) by reaction with H3O+ is not an effective mechanism for their detection. In this study, we developed a method using a conventional PTR-MS to detect n-alkanes by optimizing ion source and drift tube conditions to vary the relative amounts of different primary ions (H3O+, O2+, NO+) in the reaction chamber (drift tube). There are very few studies on O2+ detection of alkanes and the mixed mode has never been proposed before. We determined the optimum conditions and the resulting reaction mechanisms, allowing detection of n-alkanes from n-pentane to n-tridecane. These compounds are mostly emitted by evaporative/combustion process from fossil fuel use. The charge transfer (CT) mechanism observed with O2+ was the main reaction channel for n-heptane and longer n-alkanes, while for n-pentane and n-hexane the main reaction channel was hydride abstraction (HA). Maximum sensitivities were obtained at low E ∕ N ratios (83 Td), low water flow (2 sccm) and high O2+ ∕ NO+ ratios (Uso = 180 V). Isotopic 13C contribution was taken into account by subtracting fractions of the preceding 12C ion signal based on the number of carbon atoms and the natural abundance of 13C (i.e., 5.6 % for n-pentane and 14.5 % for n-tridecane). After accounting for isotopic distributions, we found that PT cannot be observed for n-alkanes smaller than n-decane. Instead, protonated water clusters of n-alkanes (M ⋅ H3O+) species were observed with higher abundance using lower O2+ and higher water cluster fractions. M ⋅ H3O+ species are probably the source for the M + H+ species observed from n-decane to n-tridecane. Normalized sensitivities to O2+ or to the sum of O2++ NO+ were determined to be a good metric with which to compare sensitivities for n-alkane detection between experiments. Double hydride abstraction was observed from the reaction with O2+. Sensitivity to CT increased with carbon chain length from n-pentane to n-dodecane, sensitivity to HA increased from n-heptane to n-dodecane and sensitivity to PT increased from n-decane to n-tridecane. Sensitivity to CT exponentially decreased with molecular ionization energy, which is inversely related to the carbon chain length. We introduce a calibrated fragmentation algorithm as a method to determine the concentrations of n-alkanes and demonstrate its effectiveness using a custom n-alkane mixture and a much more complex oil example representing perhaps the most difficult mixture available for application of the method. We define optimum conditions for using the mixed ionization mode to measure n-alkanes in conventional PTR-MS instruments regardless of whether they are equipped with switchable reagent ion (SRI) capabilities.

Helmholtz energies from equations of state and their relative deviations

Extension of the hard-sphere equations of state to non spherical hard-body systems represents a formidable task. For an equation of state that is applicable to liquid and vapor states (and explicit for pressures), the corresponding characteristic function is the residual energy. The equations of state of Carnahan Starling, Boublik and R J Sadus are used to derive an expression for residual Helmholtz energies. Relative deviations of residual Helmholtz energies for these equations of state have been reviewed. The deviations of compressibility factor against packing fraction have been plotted for these equations of state. The agreement of these plots is found to be good for lower n-alkanes but not for longer n-alkanes. Thus it becomes obvious that the compressibility factor depends considerably on the shape of the studied molecules.

Alkyl Groups Fold to Fit within a Water-Soluble Cavitand

We report here a widened, deep cavitand host that binds hydrophobic and amphiphilic guests in D2O. Small alkanes (C6 to C11) are bound in compressed conformations and tumble rapidly within the space. Longer n-alkanes (C13 to C14), n-alcohols, and α,ω-diols are taken up in folded conformations. The guests' termini are exposed to solvent while atoms near the alkane's center are buried and protected. The cavitand acts as a concave template that pushes terminal atoms of the guest closer together. The unexpected binding modes are interpreted in terms of the size and shape of the space accessible in the new cavitand.

A Perturbed-Chain SAFT Equation of State Applied to Mixtures of Short- and Long-Chainn-Alkanes

A simplified hard-chain dimer theory is employed with perturbed-chain statistical associating fluid theory (PC-SAFT) in calculating the vapor pressures and saturated liquid volumes of pure n-alkanes from methane to n-eicosane. Compared to the original PC-SAFT, the developed model is in better agreement with the experimental vapor pressures and saturated liquid volumes of n-alkanes along the vapor–liquid coexistence curve and the critical properties from n-butane toward longer n-alkanes. Predicting the vapor–liquid equilibria (VLE) of binary mixtures containing methane and a long-chain n-alkane, the new model describes the mixtures more accurately than PC-SAFT. With no binary interaction parameter, the model adequately describes the experimental VLE data, in particular, near the critical points. In the prediction of the VLE of mixtures containing ethane, propane, n-hexane, and a long-chain n-alkane, the differences between the two models become less appreciable.

Self‐Assembled Capsules of Unprecedented Shapes

Self‐Assembled Capsules of Unprecedented Shapes

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 d 010, 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.

Effect of chain-length of n-alkane on solvent-induced crystallization and solvent exchange phenomenon in syndiotactic polystyrene

The effect of molecular size and the vapor pressure of a series of n-alkanes as a solvent on solvent-induced crystallization of amorphous sPS and also the solvent exchange phenomenon in the δ form of syndiotactic polystyrene (sPS) were investigated by means of FT-IR spectroscopy and X-ray diffraction. The crystallization of amorphous sPS was found to be very much influenced by the molecular size and the vapor pressure of the n-alkanes used. At room temperature, n-alkanes with six and seven carbon atoms crystallize the sPS into the δ form, whereas the longer n-alkanes did not induce the crystallization of the amorphous sPS. By increasing the crystallization temperature to 50 °C, the vapor pressure of n-alkanes increases and as a result n-alkanes with eight to ten carbon atoms crystallize the amorphous sPS into the γ form unlike the cases of n-hexane and n-heptane. On further increasing the chain-length of n-alkanes to n-tridecane and n-hexadecane, no crystallization of amorphous sPS was observed even at 50 °C. By keeping the crystallization behavior in mind, we used these n-alkanes to exchange the existing solvent in the δ form of sPS/chloroform complex. n-Alkanes with six and seven carbon atoms easily replace the chloroform enclosed in the crystal lattice at room temperature and the d 010 lattice spacing was found to increase according to the molecular size of the solvent used in the exchange process. n-Alkanes with eight to ten carbon atoms could also replace the chloroform enclosed in the crystal lattice at room temperature. But in this case the d 010 lattice spacing was found to be similar or lower than that of the δ form of sPS/chloroform complex and a new reflection was observed 2 θ = 6.6°, indicating the formation of the ɛ form. On the other hand, longer n-alkanes (C13 and C16) did not intrude into the cavities of the δ form at room temperature. By increasing the solvent exchange temperature to 50 °C, the longer n-alkanes (C13 and C16) also replaced the existing chloroform in the δ form and structure transformed to the ɛ form. In this way, we found that the crystallization and solvent exchange process of sPS using n-alkanes is quite complicated and depends strongly on the chain-length of n-alkane molecule.

Hydrocarbon degradation by Dietzia sp. A14101 isolated from an oil reservoir model column

The hydrocarbon-degrading strain Dietzia sp. A14101 was isolated from an oil reservoir model column inoculated with oil-field bacteria. The column was continuously injected with nitrate (0.5 mM) from the start of water flooding, which lead to a gradual development of nitrate reduction in the column. Strain A14101 was able to utilize a range of aliphatic hydrocarbons as sole carbon and energy source during aerobic growth. Whole oil gas chromatography analysis of the crude oil phase from aerobic pure cultures showed that strain A14101 utilized the near complete range of aliphatic components and aromatic components toluene and xylene. Longer n-alkanes >/=C(17) were utilized simultaneously with the shorter C(10) and C(15). After 120 days aerobic incubation, the whole oil gas chromatography profile of the crude oil phase was similar to that of heavily biodegraded oils. Anaerobic degradation of hydrocarbons with nitrate was not observed. Nitrate reduction was, however, observed during anaerobic growth on propionate, which suggests that strain A14101 grows on fatty acids in the column rather than on hydrocarbons.

Modeling the Phase Behavior of H2S + n-Alkane Binary Mixtures Using the SAFT-VR+D Approach

A statistical associating fluid theory for potential of variable range has been recently developed to model dipolar fluids (SAFT-VR+D) [Zhao and McCabe, J. Chem. Phys. 2006, 125, 104504]. The SAFT-VR+D equation explicitly accounts for dipolar interactions and their effect on the thermodynamics and structure of a fluid by using the generalized mean spherical approximation (GMSA) to describe a reference fluid of dipolar square-well segments. In this work, we apply the SAFT-VR+D approach to real mixtures of dipolar fluids. In particular, we examine the high-pressure phase diagram of hydrogen sulfide+n-alkane binary mixtures. Hydrogen sulfide is modeled as an associating spherical molecule with four off-center sites to mimic hydrogen bonding and an embedded dipole moment (micro) to describe the polarity of H2S. The n-alkane molecules are modeled as spherical segments tangentially bonded together to form chains of length m, as in the original SAFT-VR approach. By using simple Lorentz-Berthelot combining rules, the theoretical predictions from the SAFT-VR+D equation are found to be in excellent overall agreement with experimental data. In particular, the theory is able to accurately describe the different types of phase behavior observed for these mixtures as the molecular weight of the alkane is varied: type III phase behavior, according to the scheme of classification by Scott and Konynenburg, for the H2S+methane system, type IIA (with the presence of azeotropy) for the H2S+ethane and+propane mixtures; and type I phase behavior for mixtures of H2S and longer n-alkanes up to n-decane. The theory is also able to predict in a qualitative manner the solubility of hydrogen sulfide in heavy n-alkanes.

Test liquids for quantitative MRI measurements of self-diffusion coefficient in vivo.

A range of liquids suitable as quality control test objects for measuring the accuracy of clinical MRI diffusion sequences (both apparent diffusion coefficient and tensor) has been identified and characterized. The self-diffusion coefficients for 15 liquids (3 cyclic alkanes: cyclohexane to cyclooctane, 9 n-alkanes: n-octane to n-hexadecane, and 3 n-alcohols: ethanol to 1-propanol were measured at 15-30 degrees C using an NMR spectrometer. Values at 22 degrees C range from 0.36 to 2.2 10(-9) m(2)s(-1). Typical 95% confidence limits are +/-2%. Temperature coefficients are 1.7-3.2% degrees C. T1 and T2 values at 1.5 T and proton density are given. n-tridecane has a diffusion coefficient close to that of normal white matter. The longer n-alkanes may be useful T2 standards. Measurements from a spin-echo MRI sequence agreed to within 2%.

Monomethyl-Branching of Long n-Alkanes in the Range from Decane to Tetracosane on Pt/H-ZSM-22 Bifunctional Catalyst

Single long n-alkanes in the range n-C10–n-C24 were hydroisomerized at 233° C in a fixed-bed down-flow vapor phase reactor loaded with Pt/H-ZSM-22 catalyst. The conversion was varied by varying the contact time. Up to ca. 60% conversion, the n-alkane molecules undergo almost exclusively a single methyl branching. In this conversion range, the distribution of positional methyl-branched isomers remains constant. The distributions of the positional methyl-branched isomerization products obtained with n-C12 and longer n-alkanes are typically bimodal. The first maximum in the methylalkane product distribution occurs at the 2-methyl-branched isomer. There is a minimum in the distribution at the 4-methylbranched isomer. The second maximum is broad and occurs at methyl positions at C5–C11, depending on the carbon number. These peculiar product distributions can be explained by the different pore mouth and key lock modes of physisorption of these long n-alkanes in pore openings of the zeolite. The physisorption enthalpies and entropies were estimated from molecular models of the positional methyluncosane isomers and a giant cluster of ZSM-22 framework having 1300 oxygen atoms. The physisorption energies are very large and dominate the reaction coordinate. The branching is always formed in that part of the chain that is residing in a pore mouth. In one favorable adsorption mode, designated as the pore mouth, the n-alkane penetrates partially into one pore opening only. The pore mouth mode favors branching at C2 and is less favorable at more central positions along the carbon chain. In the second favorable adsorption mode, designated as the key lock type, the two ends of the hydrocarbon chain penetrate each into a different pore opening. This mode favors more central branching of the chain. The contribution of the key lock mode increases with increasing carbon number.

Isothermal Sections of Ternary Mixtures: n-docosane + n-tricosane + n-tetracosane

The crystallographic long c parameter of the binary and ternary β′1, β′2, β″1, intermediate solid solutions (n-C22H46 + n-C23H48 + n-C24H50) is approximately equal to the average c parameter of mixture equivalent orthorhombic pure n-alkanes: this finding shows that the longer n-alkane chain is not straight in unit cell of the mixture, but flexible near the chain end, as earlier observed from spectroscopy analyses by other authors. Four ternary isothermal sections were determined at 305 K, 308 K, 311 K and 313 K from binary diagram data and differential scanning calorimetry and X-ray diffraction analyses of thirty ternary mixtures: the ternary intermediate solid solutions undergo the same first-order solid-solid equilibrium transitions as those of binary alloys with the observation of β(Fmmm)-RI and α(R3m)-RII Rotator states below the solidus point.

Thermodynamic properties for binary liquid mixtures of 1-chlorobutane+n-alkanes

Isothermal compressibilities KΥ and isobaric thermal expansion coefficients αp have been measured at 25 and 45°C for pure components and the following binary mixtures: 1-chlorobutane+normal alkanes (n-Cn) where n=6, 8, 10, 12, 14 and 16. With these results and other thermodynamic data from literature the next mixing quantities have also been reported: (∂V E/∂T)P, − (∂V)E/∂P)T, K S v , ∂H E/∂P)T, Δ(αpγVT and ΔCv. The obtained results have been compared at 25°C with the calculated values by using the Prigogine-Flory-Patterson theory of liquid mixtures. The theory predicts the excess volume VE and ∂V E/∂P)T values rather well, the C P E quite poorly, while for ∂V E/∂T)P and ∂V E/∂P)T it is only predicted the trend with the chain length of the n-alkane. The last two quantities show deviations between theoretical and experimental, slightly higher in systems with longer n-alkanes than for shorter ones. Our conclusion is that a nonrigid linear molecule, like 1-chlorobutane, has a low ability as a breaker of the pure n-Cn orientation correlations, in between that which we found for toluene and p-xylene and much smaller than for cyclohexane or benzene.

New possibilities of applications of the Barker quasi-lattice theory. Prediction of gE and hE of binary systems whose one component is formed by n-alkanes

For binary systems of the type an arbitrary component + n-alkane we derived relations, on the basis of the Barker theory and on the basis of the group contribution concept, for predicting gE and hE from one system to another when the n-alkane length is changed. To carry out the prediction it is not necessary to evaluate any adjustable parameters. The developed method was tested using a large number of different systems covering alcohols, amines, ketones, esters, chlorinated derivatives of hydrocarbons, aromatic hydrocarbons and n-alkanes from n-pentane to n-hexadecane. The results of predictions are in very good agreement with experimental data in the cases, when the n-alkanes involved are not longer than n-decane. Systematic regular deviations in hE in the cases, when at least one of n-alkanes involved is longer, can be explained by the presence of orientation effects in the pure longer n-alkanes. The correction suggested by us for these effects improves considerably results obtained. The developed method appears to be suitable for the systematic prediction of excess quantities of systems of the given type and represents an effective test of the Barker theory.