Increasing Alkane Chain Length Research Articles

Effect of gas type on properties of anionic surfactant foam system

The foam drainage technique is considered to be a promising measure for solving the problem of liquid accumulation in natural gas wells and gathering pipelines. However, differences in gases can greatly affect the performance of surfactant foam, thus limiting the application of this technology. To elucidate the mechanism of natural gas components influencing foam properties, the interfacial properties of hydrocarbon gas-surfactant-water system were analyzed thermodynamically and kinetically by combining molecular dynamics simulations and foaming experiments. The results show that with the increasing alkane chain length, the foaming volume and half-life of the foam are gradually rising, while the gas–liquid interfacial tension is decreasing, which is consistent with the results of molecular dynamics simulations. Compared with air, hydrocarbon gases are more beneficial for foam generation and stabilization. The interfacial adsorption of alkane molecules and the interaction between alkanes and surfactants are the main factors affecting the interfacial tension and film stability of different systems.

Effect of line tension on domain formation of fluorinated compounds at alkane/water interface

Condensed domain formation of fluorinated compounds (alcohol and ester) in adsorbed films at alkane/water interfaces was investigated by interfacial tensiometry, X-ray reflectometry, and BAM observation. The results obtained are explained by the effects of contact energy and dipole-dipole interaction, which are competitive contributions to the line tension acting at the domain boundary. Estimation of the two contributions indicated that the former is more dominant than the latter for the domain formation. In the adsorbed films of fluorinated alcohol, F8H2OH, at alkane/water interfaces, the domain formation was suppressed with increasing alkane chain length due to an increase in contact energy. The mixing of hybrid alcohol with fluorocarbon and hydrocarbon chains of the same carbon number, F6H6OH, in adsorbed film reduces contact energy. This stabilizes the dispersion of many domains with small size. On the other hand, when F8H2OH molecules are mixed with a cationic surfactant, C12TAB, in the adsorbed film, an attractive dipole-ion interaction between the hydrophilic groups relaxes the repulsive dipole-dipole interaction between F8H2OH molecules, resulting in the formation of domains with smooth boundary and large size. Furthermore, fluorinated ester, FC12Me molecules form flower shaped domains with intricate boundary mainly due to a larger dipole moment of FC12Me than F8H2OH.

Lithium recovery by solvent extraction from simulated shale gas produced water – Impact of organic compounds

Shale gas produced water has a large number of inorganic compounds, originating from the shale layer and the fracturing fluid. Especially, the Marcellus shale gas produced water contains a relatively high concentration of lithium, one of the important metals in various industries; as a result, there have been several studies on recovering lithium from the produced water. However, the fluid also includes organic compounds, but their probable inhibitory effect on the recovery of profitable metal has not been thoroughly examined. In this study, solvent extraction was implemented to recover lithium from the produced water, containing different types and concentrations of alkanes in two consecutive stages. The first and second stage involved the removal of the divalent ions in the produced water, as well as the extraction of Li+ ions, respectively. During the extraction process, there was an inhibitory influence of organic compounds, with their effects on the Li recovery efficiency predominantly observed in the first stage vs. the second stage. Final lithium recovery efficiency after two extraction stages decreased with increasing alkane chain length and increasing concentrations of n-hexane.

Stabilization of foam using hydrophobic SiO2 nanoparticles and mixed anionic surfactant systems in the presence of oil

The use of nanoparticles has been intensively investigated to improve foam flooding in oil production. Because nanoparticles have larger adhesion energy at the air-water interface than the surfactant, they help to prevent a gas diffusion between bubbles that leads to foam film rupture. In this study, the detail investigation on the behavior of mixed-surfactant foam stabilized by silica nanoparticles (SiO2-NPs) was conducted. The binary surfactant systems of an internal olefin sulfonate (IOS) and sodium polyethylene glycol monohexadecyl ether sulfate (C32H66Na2O5S) were selected. The impact of alkane oil with varying carbon chain length (i.e. hexane, octane, dodecane, and hexadecane) was investigated. The findings from a similar system of foam in deionized water (DI) and brine solution also presented for comparison. For SiO2-NPs foam/brine system in the presence of oil, the foam stability increased to a maximum with respect to certainly added nanoparticles (10 ppm), and the additional surfactant is required to maintain the foam stability when the alkane chain length increases. The foam stability parameter indicated by spreading (S) and entering (E) coefficients shows that the SiO2-NPs foam systems with the shorter-tail surfactant (mixed C15-18 IOS) had lower the coefficient values compared to the longer-tail one (mixed C19-23 IOS), suggesting that the structure of surfactant influents on foam stability. The findings from this study bring an understanding of the SiO2-NPs foam/alkane oil behavior in the brine solution, which helps to select the appropriate system for improving foam flooding in EOR applications.

Confinement Effect on Molecular Conformation of Alkanes in Water-Filled Cavitands: A Combined Quantum/Classical Density Functional Theory Study.

The depletion force exerted on an alkane molecule from surrounding solvent may greatly alter its conformation. Such a behavior is closely related to the selective molecular recognition, molecular sensors, self-assembly, and so on. Herein, we report a multiscale theoretical study on the conformational change of a single alkane molecule confined in water-filled cavitands, in which the quantum and classical density functional theories (DFTs) are combined to determine the grand potential of alkane-water system. Specifically, the intrinsic free energy of the alkane molecule is tackled by quantum DFT, while the solvent effect arising from the solvent density inhomogeneity in confined space is addressed by classical DFT. By varying the alkane chain length, pore size, and wettability of inner pore surface, we find that pore confinement and hydrophilic inner surface facilitate the alkane conformational change from extended state to helical state, which becomes more significant as the alkane chain length increases. Our findings, which are in line with previous experimental observations, provide not only the microscopic mechanism but also theoretical guidance for elaborately manipulating molecular conformation at the nanoscale.

Molecular dynamics simulation of the folding of single alkane chains with different lengths on single-walled carbon nanotubes and graphene.

Chain folding is an important step during polymer crystallization. In order to study the effects of the surface on chain folding, molecular dynamics simulations of the folding of different alkane chains on three kinds of single-walled carbon nanotubes (SWCNTs) and graphene were performed. The folding behaviors of the single alkane chains on these surfaces were found to be different from their folding behaviors in vacuum. The end-to-end distances of the chains were calculated to explore the chain folding. An increasing tendency to fold into two or more stems with increasing alkane chain length was observed. This result indicates that the occurrence and the stability of chain folding are related to the surface curvature, the diameter of the SWCNT, and surface texture. In addition, the angle between the direction of the alkane chain segment and the direction of the surface texture was measured on different surfaces.

Influence of External Forces during Supercooling on Dispersion Stability during Melt Emulsification

AbstractA special high‐pressure homogenization process – simultaneous homogenization and mixing (SHM) – was applied to produce hexadecane (C16H34), octadecane (C18H38), eicosane (C20H42), and docosane (C22H46) in water dispersions. Additionally, a high‐shear stress zone (HSSZ) was connected to the SHM unit to investigate the influence of external forces during supercooling on dispersion stability. The HSSZ did not affect the droplet disruption efficiency but induced aggregation behavior of the dispersed phase with increasing alkane chain length and dispersed‐phase content. High‐shear treatment during crystallization led to a change in particle shape, which was more favorable to aggregation.

Guest Controlled Nonmonotonic Deep Cavity Cavitand Assembly State Switching.

Octa-acid (OA) and tetra-endo-methyl octa-acid (TEMOA) are water-soluble, deep-cavity cavitands with nanometer-sized nonpolar pockets that readily bind complementary guests, such as n-alkanes. Experimentally, OA exhibits a progression of 1:1 to 2:2 to 2:1 host/guest complexes (X:Y where X is the number of hosts and Y is the number of guests) with increasing alkane chain length from methane to tetradecane. Differing from OA only by the addition of four methyl groups ringing the portal of the pocket, TEMOA exhibits a nonmonotonic progression of assembly states from 1:1 to 2:2 to 1:1 to 2:1 with increasing guest length. Here we present a systematic molecular simulation study to parse the molecular and thermodynamic determinants that distinguish the succession of assembly stoichiometries observed for these similar hosts. Potentials of mean force between hosts and guests, determined via umbrella sampling, are used to characterize association free energies. These free energies are subsequently used in a reaction network model to predict the equilibrium distributions of assemblies. Our models accurately reproduce the experimentally observed trends, showing that TEMOA's endo-methyl units constrict the opening of the binding pocket, limiting the conformations available to bound guests and disrupting the balance between monomeric complexes and dimeric capsules. The success of our simulations demonstrate their utility at interpreting the impact of even simple chemical modifications on supramolecular assembly and highlight their potential to aid bottom-up design.

Density, Viscosity, Speed of Sound, Bulk Modulus, Surface Tension, and Flash Point of Binary Mixtures of Butylbenzene + Linear Alkanes (n-Decane, n-Dodecane, n-Tetradecane, n-Hexadecane, or n-Heptadecane) at 0.1 MPa

This work reports physical property measurements of binary mixtures of butylbenzene with n-decane, n-dodecane, n-tetradecane, n-hexadecane, or n-heptadecane. Densities and viscosities were measured at temperatures from (293.15 to 373.15) K, and speeds of sound were measured at temperatures from (293.15 to 333.15) K, except for those of n-heptadecane, which were measured starting at 303.15 K. Densities increased with increasing mole fraction of butylbenzene. Excess molar volumes were positive and increased with increasing alkane chain length, except for those of heptadecane which were similar to those of n-hexadecane. Analysis of excess molar volumes using the Prigogine–Flory–Patterson model showed that the interaction term contributed more to excess molar volume than the free volume or P* term. As the mole fraction of butylbenzene increased, speeds of sound increased for n-decane and n-dodecane mixtures but decreased for other alkane mixtures to values below those of both pure components before increasing...

Effects of Chain Length on the Mechanism and Rates of Metal-Catalyzed Hydrogenolysis ofn-Alkanes

C–C cleavage in C2–C10 n-alkanes involves quasi-equilibrated C–H activation steps to form dehydrogenated intermediates on surfaces saturated with H atoms. These reactions are inhibited by H2 to similar extents for C–C bonds of similar substitution in all acyclic and cyclic alkanes and, thus, show similar kinetic dependences on H2 pressure. Yet, turnover rates depend sensitively on chain length because of differences in activation enthalpies (ΔH⧧) and entropies (ΔS⧧) whose mechanistic origins remain unclear. Density functional theory (DFT) estimates of ΔH⧧ and ΔG⧧ for C–C cleavage via >150 plausible elementary steps for propane and n-butane reactants on Ir show that hydrogenolysis occurs via α,β-bound RC*–C*R′⧧ transition states (R = H, CxH2x+1) in which two H atoms are removed from each C*. Calculated ΔH⧧ values decrease with increasing alkane chain length (C2–C8), consistent with experiment, because attractive van der Waals interactions with surfaces preferentially stabilize larger transition states. A c...

Phase Behavior of Nitrate Based Ionic Liquids with Thiophene and Alkanes

In this study, the extraction of thiophene from alkane compounds (hexane, heptane, and octane) was investigated by using 1-butyl 3- methylimidazolium nitrate ([Bmim][NO3]) and 1-methyl 3-octylimidazolium nitrate ([Omim][NO3]). Liquid–liquid equilibrium (LLE) data for ternary systems of ionic liquid + thiophene + alkane were reported at atmospheric pressure and 298.15 K. The calculated selectivity and solute distribution coefficient values from the experimental data demonstrate that the selectivities increase with increasing alkane chain length while the solute distribution coefficients decrease. Moreover, the selectivity values for the systems containing [Bmim][NO3] are higher than those containing [Omim][NO3]. This implies that [Bmim][NO3] is a more suitable solvent than [Omim][NO3] for desulfurization of alkane. The nonrandom two-liquid (NRTL) and universal quasi-chemical (UNIQUAC) models were used to correlate the experimental data. The results show both models can correlate the experimental data with ...

Adaptation of the Hydrocarbonoclastic Bacterium Alcanivorax borkumensis SK2 to Alkanes and Toxic Organic Compounds: a Physiological and Transcriptomic Approach

The marine hydrocarbonoclastic bacterium Alcanivorax borkumensis is able to degrade mixtures of n-alkanes as they occur in marine oil spills. However, investigations of growth behavior and physiology of these bacteria when cultivated with n-alkanes of different chain lengths (C6 to C30) as the substrates are still lacking. Growth rates increased with increasing alkane chain length up to a maximum between C12 and C19, with no evident difference between even- and odd-numbered chain lengths, before decreasing with chain lengths greater than C19. Surface hydrophobicity of alkane-grown cells, assessed by determination of the water contact angles, showed a similar pattern, with maximum values associated with growth rates on alkanes with chain lengths between C11 and C19 and significantly lower values for cells grown on pyruvate. A. borkumensis was found to incorporate and modify the fatty acid intermediates generated by the corresponding n-alkane degradation pathway. Cells grown on distinct n-alkanes proved that A. borkumensis is able to not only incorporate but also modify fatty acid intermediates derived from the alkane degradation pathway. Comparing cells grown on pyruvate with those cultivated on hexadecane in terms of their tolerance toward two groups of toxic organic compounds, chlorophenols and alkanols, representing intensely studied organic compounds, revealed similar tolerances toward chlorophenols, whereas the toxicities of different n-alkanols were significantly reduced when hexadecane was used as a carbon source. As one adaptive mechanism of A. borkumensis to these toxic organic solvents, the activity of cis-trans isomerization of unsaturated fatty acids was proven. These findings could be verified by a detailed transcriptomic comparison between cultures grown on hexadecane and pyruvate and including solvent stress caused by the addition of 1-octanol as the most toxic intermediate of n-alkane degradation.

A topological approach to mass barotropic phenomena in asymmetric mixtures

Mass density inversion, a phenomenon also known as mass barotropy, corresponds to a singular behavior that directly affects the relative position of phases in heterogeneous mixtures when exposed to gravitational fields. In this contribution we introduce a topological description of the mass density inversions observed in asymmetric binary mixtures, a case that is appropriately exemplified by the evolution of the barotropy experimentally observed in carbon dioxide + hydrocarbon mixtures. From this basic example, necessary and sufficient conditions are deduced for exhibiting mass density inversions in direct relation with the global phase behavior of the mixture. Finally, the global phase diagram (GPD) predicted by the PC-SAFT equation is used for describing barotropic ranges in mixtures composed by carbon dioxide and hydrocarbons of increasing chain length, together with the specific effects that transitional mechanisms induce on the phenomenon. In excellent agreement with the available experimental data, results show that mass barotropy is present over ranges essentially involving Type III and IV systems. In addition, since the phenomenon is shown to appear also in Type II systems, it is concluded that mathematical double point (MDP) transitions do not necessarily control barotropic behavior. Finally, the occurrence of double critical end points satisfying the conditions of mass barotropy unequivocally explains the shift of barotropic points along the branch(es) of the liquid–liquid–gas line, as the alkane's chain length increases.

Thermal Decomposition Kinetics of Some Di‐ and Triorganotin(IV) Carboxylates Derived from para‐Nitrophenylethanoic Acid

AbstractThermogravimetric (TG) investigations of organotin(IV) carboxylates with the general formula RmSnL4−m (where R=CH3, C2H5, n‐C4H9, C6H5, cyclo‐C6H11, n‐C8H17, m=2, 3, and L=para‐nitrophenylethanoate anion) have been performed. Derivative thermogravimetry (DTG) and differential thermal analysis (DTA) techniques, Horowitz‐Metzger method and the fundamental thermodynamic relations are used to evaluate the thermokinetic parameters of each thermal degradation pattern. Results reveal that the thermal stability is functional to SnC and SnO bonds. In the case of R2SnL2, activation energy, reaction order and pre‐exponential factor associated with the bulk degradation processes increase as the alkane chain length increases. Hence, Oct2SnL2 is thermally more stable than Bu2SnL2, which in turn is more resistant to thermal dissociation than Et2SnL2. The same phenomenon is not observed for R3SnL compounds because their degradation is highly irregular. Furthermore, R2SnL2 has larger values of kinetic parameters than those of corresponding triorganotin(IV) para‐nitrophenylethanotes. Thermodynamic parameters of these compounds also reinforce the above facts.

The influence of alkane chain length on the skin irritation potential of 1,2-alkanediols

Several studies have reported that 1,2-alkanediols show increasing anti-microbial activity as their alkane chain length increases. However, there are no reports on the influence of alkane chain length on the skin irritation potential of 1,2-alkanediols. To investigate the influence of alkane chain length on the skin irritation potential of 1,2-alkanediols. The objective and subjective (sensory) skin irritation potentials of five 1,2-alkanediols - 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2-octanediol and 1,2-decanediol - were evaluated. We also estimated percutaneous absorption by measuring in vitro skin penetration using a Franz diffusion cell system. Like anti-microbial activity, sensory irritation potential increased as alkane chain length increased, most likely due to increasing membrane interference and/or intrinsic toxicity of 1,2-alkanediols. 1,2-Hexanediol showed the lowest objective skin irritation potential, which increased when the alkane chain length decreased or increased. Furthermore, percutaneous absorption negatively correlated with the alkane chain length of 1,2-alkanediols. These results show that a lower skin absorption potential is not indicative of a low skin irritation potential. Our results suggest that the factors and processes involved in skin irritation potential are complex and that skin irritation potential is influenced by intrinsic toxicity and the potential for penetration or integration in the lipid bilayer.

Thermodynamic study of the mixtures (butylbenzene + an alkane or + an alkyl ethanoate): experimental and values

This article shows the experimental data of mixing properties for a set of nine binary mixtures formed by an aromatic hydrocarbon, butylbenzene, with several alkanes (C7 to C12) and several alkyl ethanoates (methyl to butyl). The excess enthalpies, , were measured at T = 298.15 K for all systems, while the excess volumes, , were obtained for the same set of systems but at two temperatures of 298.15 and 318.15 K. All systems studied presented endothermic effects with the excess enthalpy increasing regularly as the alkane chain-length increases, however in the mixtures with ethanoates the endothermicity decreases with the increase of the ester molecular weight. In this case are positive for all systems except for those mixtures containing heptane or octane, which present < 0. In both sets of mixtures the temperature effect on is analysed. All experimental values are correlated with a suitable equation. Lastly, the UNIFAC model is applied to all the mixtures to estimate the considering two versions, being necessary to recalculate the interaction parameters corresponding to methyl/aromatic and carboxylate/aromatic in the version of Dang and Tassios (Ind. Eng. Chem. Des. Dev., 25, 22, 1986). The estimation for the elected mixtures is acceptable.

Excess Thermodynamics of Mixtures Involving Xenon and Light Linear Alkanes by Computer Simulation

Excess molar enthalpies and excess molar volumes as a function of composition for liquid mixtures of xenon + ethane (at 161.40 K), xenon + propane (at 161.40 K) and xenon + n-butane (at 182.34 K) have been obtained by Monte Carlo computer simulations and compared with available experimental data. Simulation conditions were chosen to closely match those of the corresponding experimental results. The TraPPE-UA force field was selected among other force fields to model all the alkanes studied, whereas the one-center Lennard-Jones potential from Bohn et al. was used for xenon. The calculated H(m)(E) and V(m)(E) for all systems are negative, increasing in magnitude as the alkane chain length increases. The results for these systems were compared with experimental data and with other theoretical calculations using the SAFT approach. An excellent agreement between simulation and experimental results was found for xenon + ethane system, whereas for the remaining two systems, some deviations that become progressively more significant as the alkane chain length increases were observed.

Molecular simulation of temperature-programmed desorption

We use accelerated molecular dynamics to probe the thermal desorption of n-alkanes from the Au(111) and C(0001) surfaces. Studying an alkane series ranging from CH4 to C16H34, we find that the desorption prefactor increases with increasing chain length for the short chains until a certain chain length is reached when it becomes essentially constant and independent of chain length. We can understand the dependence of the preexponential factor on alkane chain length in terms of conformational changes within the alkane molecules. For the shorter molecules, the desorption temperatures probed in experimental temperature-programmed desorption studies lie below those for which torsional motion is activated. Thus, the short alkanes can be treated as rigid rods, and the loss in translational and rotational entropy upon adsorption leads to a preexponential factor that increases with increasing chain length. As the alkane chain length increases, the binding energy and the experimental desorption temperatures also increase. Thus, torsional motion is activated to an extent that increases with increasing chain length. This torsional activation increases the entropy of adsorption and counteracts the entropy decrease due to a loss of translation and rotation. This leads to a virtually constant prefactor for sufficiently long chains. Our findings are consistent with experimental data for the thermal desorption of alkanes from the Au(111), Pt(111), MgO(100) and C(0001) surfaces.

Surface vibrational structure at alkane liquid/vapor interfaces

Broadband vibrational sum frequency spectroscopy (VSFS) has been used to examine the surface structure of alkane liquid/vapor interfaces. The alkanes range in length from n-nonane (C(9)H(20)) to n-heptadecane (C(17)H(36)), and all liquids except heptadecane are studied at temperatures well above their bulk (and surface) freezing temperatures. Intensities of vibrational bands in the CH stretching region acquired under different polarization conditions show systematic, chain length dependent changes. Data provide clear evidence of methyl group segregation at the liquid/vapor interface, but two different models of alkane chain structure can predict chain length dependent changes in band intensities. Each model leads to a different interpretation of the extent to which different chain segments contribute to the anisotropic interfacial region. One model postulates that changes in vibrational band intensities arise solely from a reduced surface coverage of methyl groups as alkane chain length increases. The additional methylene groups at the surface must be randomly distributed and make no net contribution to the observed VSF spectra. The second model considers a simple statistical distribution of methyl and methylene groups populating a three dimensional, interfacial lattice. This statistical picture implies that the VSF signal arises from a region extending several functional groups into the bulk liquid, and that the growing fraction of methylene groups in longer chain alkanes bears responsibility for the observed spectral changes. The data and resulting interpretations provide clear benchmarks for emerging theories of molecular structure and organization at liquid surfaces, especially for liquids lacking strong polar ordering.

Squeezing Molecularly Thin Alkane Lubrication Films: Layering Transitions and Wear

The properties of alkane lubricants confined between two approaching solids are investigated by a model that accounts for the curvature and the elastic properties of the solid surfaces. We consider linear alkane molecules of different chain lengths, C3H8, C4H10, C8H18, C9H20, C10H22, C12H26, and C14H30 confined between smooth gold surfaces. We observe well-defined molecular layers develop in the lubricant film when the width of the film is of the order of a few atomic diameters. An external squeezing-pressure induces discontinuous changes in the number n of lubricant layers. We find that with increasing alkane chain length, the transition from n to n - 1 layers occurs at higher pressure, as expected based on the increasing wettability with increasing chain length. We obtain good correlation between our theoretical results and wear experiments.