Liquid N-alkanes Research Articles

Chemical heterogeneity size effects at nanoscale on interface thermal resistance of solid–liquid polymer interface via molecular dynamics simulations

The shrinking size of integrated chips poses thermal management challenges. Understanding the size effect of chemical heterogeneity on solid–liquid interfacial thermal transfer is essential for heterogeneous chip design, yet the underlying mechanisms remain lacking. The present work used the liquid n-alkanes as the thermal interface material between solid platinum substrates. To characterize chemical heterogeneity, periodic solid surface patterns composed of patches with alternating solid–liquid affinities were constructed. By using non-equilibrium molecular dynamics simulations, we investigated the size effect of chemically heterogeneous patterns on interfacial thermal resistance (ITR) at the nanoscale. At larger heterogeneity sizes, i.e., larger patch sizes, most alkane molecules directly in contact weak interaction patches cannot interact with strong interaction patches due to long atomic distances. In the case of alkanes in contact a cold substrate, alkanes in contact weak interaction patches transferred thermal energy to the substrate at a lower rate than those in contact strong interaction patches. The different rates resulted in the higher temperature of alkanes in contact weak interaction patches than those in contact strong interaction patches and, therefore, a larger disparity between temperature jump at the strong interaction areas and that at the weak interaction areas. The non-uniformity of temperature jump distribution increased ITR when compared to the heterogeneous surface system characterized by a smaller patch size with a more uniform temperature distribution in the plane perpendicular to the heat flux direction. In addition, the classical parallel thermal resistance model predicted ITR accurately for the heterogeneous surface systems with small size patches but overestimated overall thermal resistance.

Chemical additive effect on asphaltenes destabilization and deposition studied using quartz crystal resonator (QCR) sensor: From atmospheric pressure titration to isothermal depressurization of non-diluted crude oil

In this study, the destabilization of asphaltenes in a crude oil sample was analyzed under various pressure conditions using a fully immersed Quartz Crystal Resonator (QCR) sensor. Firstly, oil samples with and without a chemical additive were tested at atmospheric pressure through titration with different liquid n-alkanes (C7, C9, and C12) as antisolvents. Then, high-pressure experiments (HP) were conducted on a recombined crude oil + gas system, involving constant mass expansions from 1000 bar to the saturation pressure point at various fixed temperatures. From these high-pressure experiments, the phase diagrams, including the asphaltene pressure envelope (APE), were constructed and compared for the recombined oil with and without the chemical additive in both P vs T and P vs composition diagrams. The results regarding the impact of the chemical additive under HP conditions were compared with those obtained under atmospheric pressure conditions. The comparison shows an strong agreement between the two sets of experiments, confirming that the test conducted to evaluate the effectiveness of asphaltene inhibitors can be extrapolated to high-pressure applications.

A molecular dynamics study on the solid–liquid polymer interface: insight into the effect of surface roughness scale and polymer chain length on interfacial thermal resistance

Understanding the role of surface morphology and molecular structure interface thermal transport is essential for designing thermal management materials. In the present work, models of solid–liquid interfaces were created by placing liquid n-alkane between two platinum crystals. The effect of different levels of crystal surface roughness–flat, small, and large-scale grooves–and polymer chain lengths, under varying solid–liquid affinity, on the interface thermal resistance (ITR) were assessed using non-equilibrium molecular dynamics simulations. The overall trend confirmed that grooved surfaces have higher ITR than flat surfaces at low affinity, and lower ITR values were observed at high affinity. Large grooves enabled more favourable polymer orientations than those of small grooves, resulting in a smaller ITR. However, long chains did not facilitate heat transfer normal to the interface because they preferentially aligned parallel to it. For efficient heat transfer, a balance between the roughness scale and polymer length must be considered.

Evidence for the anaerobic biodegradation of higher molecular weight hydrocarbons in the Guaymas Basin

The hydrothermal sediments of the Guaymas Basin are rich in chemically complex petroleum components, including gaseous hydrocarbons, higher molecular weight n-alkanes and aromatic compounds. Studies of indigenous deep-sea microorganisms obtained from these sediments led to novel insights on the fundamental mechanisms for the anaerobic biodegradation of gaseous hydrocarbons. However, the metabolic fate of other hydrocarbons and the requisite organisms involved in the cycling of petroleum components remain largely unexplored. Metagenomic sequencing and laboratory enrichments were used to garner evidence for the anaerobic biodegradation of liquid hydrocarbons in hydrothermal sediments and mineral concretions from three sites in the Guaymas Basin (“Megamat II”, Rebecca's Roost and Octopus Mound). Elevated sulfate consumption by microbial enrichments from the Megamat II and Rebecca's Roost sites was observed at 55 °C when sediment incubations were amended with liquid n-alkanes (C6–C12; C16–C18) or with crude oil as potential electron donors. The biodegradation of the same hydrocarbons, linked to sulfate reduction, was also evident at 31 °C by microbial consortia enriched from the “Megamat II” and Octopus Mound sites. Notably, methane was concurrently produced in enrichments from the Octopus Mound site that was covered by Ampharetid methane-oxidizing worm mats. Metagenomic sequencing revealed that Deltaproteobacteria were predominant at the three sites (up to 47.48% of the microbial community). Moreover, the genes responsible for the activation of alkanes (Ass, alkylsuccinate synthase) and aromatic hydrocarbons (Bss, benzylsuccinate synthase) were identified from all three sites. The reconstruction of high-quality draft genomes from the Desulfobacterales further confirmed their metabolic potential to degrade alkanes via fumarate addition in Guaymas Basin sediments. Collectively, our findings demonstrate that mesophilic and thermophilic microbial consortia from hydrothermal sediments and mineral concretions in different regions of the Guaymas Basin are capable of anaerobically biodegrading C6–C12- and C16–C18n-alkanes as well as crude oil under the ambient temperature regimes. Our findings highlight the importance of integrating multiple approaches to better understand the ecological functioning of microbial communities in hydrocarbon-rich hydrothermal systems.

Flexible stretchable SEBS/n-alkane phase change composite films for highly efficient thermal management and infrared stealth applications

Phase change materials (PCMs) can alleviate concerns about energy to a certain extent by reversibly storing a plenty of renewable and sustainable thermal energy. However, they do not have any flexibility due to their liquid leakage and solid rigidity, making them unsuitable for further practical wearable applications. Herein, a series of SEBS/n-alkane PCM composite films (PCMFs) were fabricated. SEBS is mainly used as the supporting substrate to prevent the leakage of liquid n-alkanes and endue the PCMFs with excellent mechanical properties. Where, the tensile strain and tensile strength of SEBS/n-HD-50% PCMF separately are 780% and 9.96 MPa, representing excellent stretchability and deformability, tailorability, and foldability. Particularly, the onset melting and crystallization temperatures (Tmo, Tco) of SEBS/n-ES-50% and SEBS/n-DS-50% PCMFs individually are 28.1 °C and 28.4 °C, 33.8 °C and 35.7 °C, which match the comfort zone for human skin and the ideal thermo-response temperature range of smart windows, and a range of experiments have verified their feasibility in the fields of thermal management, smart windows and infrared stealth. This study well solves the problems of liquid leakage and solid rigidity of PCMs themselves, endows them with excellent comprehensive performance, and greatly expanding the practical applications of PCMs.

New corresponding-state-principle based correlation for the thermal conductivity of saturated liquid refrigerants and n-alkanes

In this work, we propose a new corresponding state principle based correlation based on the novel ideas published very recently. The new proposed correlation well stands in a wider temperature range from the triple point temperature (Ttr) to about 0.98 times the critical temperature (Tc), beyond which the thermal conductivity exhibits completely different behaviors. It requires two temperatures, i.e., the triple point temperature and T0 at which the thermal conductivity experimentally takes a minimal value, and the corresponding two thermal conductivity values as inputs. For the 23 refrigerants and 11 n-alkanes considered here, it can reproduce the REFPROP data with AAD<3% for 26 liquids, AAD<5% for 31 liquids, and AAD<10% for all the 34 liquids.

Simultaneous compressed liquid viscosity and density measurements of n-alkanes at temperatures between (291 and 353) K and pressures up to 50 MPa

Compressed liquid density (ρ) and dynamic viscosity (η) were simultaneously measured for pure liquid n-alkanes (n-hexane, n-heptane, n-octane, n-nonane, and n-decane) in the temperature range from (291 to 353) K and pressure up to 50 MPa by an experimental system using a coil capillary tube viscometer (CCTV) coupled with a vibrating tube densimeter (VTD). The reliability and validation of this measuring system were verified by determining and comparing both dynamic viscosity and density data of ethanol published in the international literature. The maximum viscosity deviation was 8 μPa ∙ s for viscosity and 0.87 kg ∙ m−3 for density. The measurements were carried out with a relative expanded uncertainty (k=2) of 1.00 % for the measurements of dynamic viscosity and 0.20 % for the measurements of density considering the impurities of the chemical compounds). Both dynamic viscosity and density data were represented using two empirical models, obtaining a maximum deviation of 2.49 % for the dynamic viscosity and 0.12 % for the density with the experimental data. Finally, the isothermal compressibility and isobaric thermal expansivity were calculated from the empirical models at the reported conditions.

Dissecting the Chain Length Effect on Separation of Alkane-in-Water Emulsions with Superwetting Microchannels.

Oil/water separation is an essential process in the petrochemical industry, environmental remediation, and water treatment. Alkanes are the major components of crude oil and are difficult to separate once they form emulsions in water. Much less attention has been focused on the feature of liquid alkanes that could, in turn, influence the separation process. The role of chain length is systematically studied herein by separating the alkane-in-water emulsions with superwetting titanium microchannels of 14-55 μm. The chain length covers the entire liquid alkane spectrum with carbon numbers ranging from 6 to 16. The separation efficiency decreases while the TOC content increases with the chain length of liquid alkanes for a given channel. This is attributed to the small Ostwald ripening rate with the long chains, which stabilize the oil droplets of small sizes that could pass through the zigzag channels. Accordingly, a high separation efficiency of >99.97% and a low TOC content of <5 ppm are achieved with superhydrophilic channels of 14 μm for alkanes with less than 12 carbons. The metallic microchannels surpass the conventional organic membranes and inorganic frameworks over the entire liquid n-alkane spectrum, paving the way for the future development of oil/water separation using porous metals.

Solubility of xenon in liquid n-alkanes and cycloalkanes by computer simulation. Towards the perfect anaesthetic

The solubility (Henry’s constant) of xenon in a series of n-alkanes (n-heptane, n-octane, n-nonane, n-dodecane and n-hexadecane) and in two cycloalkanes (cyclopentane and cyclohexane) has been obtained by Monte Carlo computer simulations as a function of temperature, at a reference pressure of 100 kPa and compared with experimental results from literature. The n-alkanes and cycloalkanes were modelled with the united atom TraPPE force field, using optimized non-bonded parameters in a transferable fashion for each solvent family. Standard enthalpies of solvation were calculated from the temperature dependence of the Henry’s constants. Solute-solvent interaction energies were also estimated for all systems by Molecular Dynamics. The agreement between the simulated Henry’s constants and experimental data from the literature is excellent in all cases. For all systems involving n-alkanes, the temperature dependence of the standard enthalpies of solvation displays a maximum at very similar reduced temperatures, 0.51 < TR < 0.55. These results confirm the behaviour previously observed experimentally for n-pentane and n-hexane. Furthermore, the simulation results provide a large coherent set of data that allows extending the analysis to a large number of longer n-alkanes, including those for which no experimental data is available.Structural details of the solutions were also studied calculating the radial distribution functions xenon/CHn for all the systems at similar thermodynamic states. The results confirm the enrichment of methyl groups within xenon’s first coordination sphere relatively to methylene groups. The effect is more pronounced the longer the n-alkane chain.

Density, Enthalpy of Vaporization and Local Structure of Neat N-Alkane Liquids

The properties of alkanes are consequential for understanding many chemical processes in nature and industry. We use molecular dynamics simulations with the Amber force field GAFF2 to examine the structure of pure liquids at each respective normal boiling point, spanning the 15 n-alkanes from methane to pentadecane. The densities predicted from the simulations are found to agree well with reported experimental values, with an average deviation of 1.9%. The enthalpies of vaporization have an average absolute deviation from experiment of 10.4%. Radial distribution functions show that short alkanes have distinct local structures that are found to converge with each other with increasing chain length. This provides a unique perspective on trends in the n-alkane series and will be useful for interpreting similarities and differences in the n-alkane series as well as the breakdown of ideal solution behavior in mixtures of these molecules.

Thermoconductive n-alkane enables ultra-high shape/thermal stability, durability, and ambient thermal energy harvesting

Thermal energy storage using phase change materials (PCMs) has received significant attention in the field of sustainable energy development. However, extremely low thermal conductivity and seepage issues are two long-standing drawbacks limiting PCM-based applications. In this study, an alternative strategy is used to construct composite PCMs by introducing hybrid functional materials as support and liquid n-alkane as energy storage material through a facile vacuum impregnation method. The hybrid functional material, obtained from a commercially available natural mineral, montmorillonite (Mt), and boron nitride, possesses high specific surface area and physicochemical stability and can endow the n-dodecane (DA) with beneficial characteristics. Hybrid-functional-material-supported DA is suitable for ambient energy harvesting in the form of latent heat, with a 309% growth rate in energy storage capacity compared with that of Mt/DA. The thermal conductivity reached 0.795 W/m·K, which is 2.01 and 5.89 times higher than those of Mt/DA and pristine DA, respectively. In addition, the composite PCMs exhibited ultra-high leakage resistance at up to 120 °C owing to the presence of a favorable interconnected network structure, strong surface tension, and capillary forces. The materials also exhibited high durability after 50 thermal cycles with a high latent heat retention capacity (>98%). Because of such thermal properties, the application scope of composite PCMs can be extended to the development of various human comfort thermal management systems.

Conversion of Polyolefin Waste to Liquid Alkanes with Ru-Based Catalysts under Mild Conditions.

Chemical upcycling of waste polyolefins via hydrogenolysis offers unique opportunities for selective depolymerization compared to high temperature thermal deconstruction. Here, we demonstrate the hydrogenolysis of polyethylene into liquid alkanes under mild conditions using ruthenium nanoparticles supported on carbon (Ru/C). Reactivity studies on a model n-octadecane substrate showed that Ru/C catalysts are highly active and selective for the hydrogenolysis of C(sp3)–C(sp3) bonds at temperatures ranging from 200 to 250 °C. Under optimal conditions of 200 °C in 20 bar H2, polyethylene (average Mw ∼ 4000 Da) was converted into liquid n-alkanes with yields of up to 45% by mass after 16 h using a 5 wt % Ru/C catalyst with the remaining products comprising light alkane gases (C1–C6). At 250 °C, nearly stoichiometric yields of CH4 were obtained from polyethylene over the catalyst. The hydrogenolysis of long chain, low-density polyethylene (LDPE) and a postconsumer LDPE plastic bottle to produce C7–C45 alkanes was also achieved over Ru/C, demonstrating the feasibility of this reaction for the valorization of realistic postconsumer plastic waste. By identifying Ru-based catalysts as a class of active materials for the hydrogenolysis of polyethylene, this study elucidates promising avenues for the valorization of plastic waste under mild conditions.

Effect of chain length on the near edge X-ray absorption fine structure spectra of liquid n-Alkanes

The carbon 1s near edge X-ray absorption fine structure (NEXAFS) spectra of liquid phase n-alkanes have been measured for the first time. Clear trends are observed in the liquid phase spectra as a function of chain length. Specifically, the ‘C-H band’ in the NEXAFS spectra shifts to lower energy as the chain length increases. Characteristic differences between the gas, liquid and solid phase spectra are observed. Differences in the liquid phase n-alkane NEXAFS spectra are examined through molecular dynamics simulations coupled with density functional theory simulations of the NEXAFS spectra.

Prediction of thermal conductivities for n-alkanes in liquid and supercritical phase

In this paper, a new model for thermal conductivity was proposed and applied for predicting thermal conductivities of n-alkanes in compressed liquid and supercritical phase. The new model was based on the modified Enskog theory and the Peng-Robinson Equation of State, with modifications made to improve the predictive accuracy of the former. Moreover, the new model can be utilized over a wide range of temperatures and pressures. The newly derived equation was then used to calculate the thermal conductivities of 16 n-alkanes (methane to n-hexadecane) in liquid and supercritical phase to check its accuracy. A comparison between the calculated data and the corresponding literature data was performed, yielding good agreement between values and an uncertainty of 6.2% (at the 95% confidence level). In addition, predicted performance of the present method was compared with that of previously reported models in the literature and the results indicated that the present model is generally superior to the conventional models, with respect to the accuracy. This suggests that the proposed model may be a useful tool for accurately calculating the thermal conductivities of liquid and supercritical n-alkanes.

Static and dynamic properties of mid-size liquid n- alkanes, C12∼C400: a molecular dynamics simulation study

ABSTRACTIn this paper, we have extended our previous study of the static and dynamic properties (self-diffusion coefficient Dself and friction coefficient ζ) of liquid n-alkane systems up C400 at several temperatures (∼2300 K) using molecular dynamics (MD) simulations in the canonical ensembles. For the small n-alkanes with n ≤ 120 (n: the chain length), the chains are clearly ⟨R2ee⟩/6⟨R2g⟩ ≥ 1 (1.06 ∼ 1.44), which leads to the conclusion that the liquid n-alkanes are far away from the ideal chain regime. But for the n-alkanes of n ≥ 160, the chains are ⟨R2ee⟩/6⟨R2g⟩ ≈ 1, indicating that they are Gaussian. It is found that the long chains of these n-alkanes at high temperatures show abnormalities in density and friction coefficient. We observed a clear transition in the power law dependence of n-alkane self-diffusion coefficient on the molecular weight (M) of n-alkane, Dself ∼ M−γ, occurs in the range C120∼C160 at temperatures of 318, and 618 K, corresponding to a crossover from the ‘oligomer’ to the ‘Rouse’ regime. The entanglement lengths (Ne) are calculated by the Z1 code and discussed shortly.

Diffusion and Friction Dynamics of Probe Molecules in Liquid n-Alkane Systems: A Molecular Dynamics Simulation Study

We present a molecular dynamics simulation study of the probe diffusion and friction dynamics of Lennard-Jones particles in a series of liquid n-alkane systems from C12 up to C400 at 318 K, 418 K, 518 K, and 618 K, to investigate the power law dependence of self-diffusion of polymer liquids on their molecular weights. Two LJ particles MY1 with a mass of 114 g/mol and MY2 with a mass of 225 g/mol are used as probes to model methyl yellow. We observed that a clear transition in the power law dependence of n-alkane self-diffusion on the molecular weight (M) of n-alkane, Dself∼M−γ, occurs in the range C120∼C160 at temperatures of 318 K, 418 K, and 518 K, corresponding to a crossover from the “oligomer” to the “Rouse” regime. We also observed that a clear transition in the power law dependence of the diffusion coefficient DMY2 on the molecular weight (M) of n-alkane, DMY2∼M−γ, occurs at low temperatures. The exponent γ for DMY2 shows a sharp transition from 1.21 to 0.52 near C36 at 418 K and from 1.54 to 0.60 near C36 at 318 K. However, no such transition is found for the probe molecule MY2 at temperatures of 518 K and 618 K and for MY1 probe at temperatures of 418 K, 518 K, and 618 K, but the power law exponent γ for MY1 at 318 K shows instead a linear or a rather slow transition. The dependence of the probe diffusion (DMY2) on the matrix molecular weight (M) reflects a significant change of the matrix dynamics associated with the probe diffusion: a crossover from the “solvent-like” to the “oligomer” regime. As the molecular weight of n-alkane increases, the ratio of Dself/DMY2 becomes less than 1 and the probe molecules encounter, in turn, two different microscopic frictions depending on MMY/Mmatrix and the temperature. It is believed that a reduction in the microscopic friction on the probe molecules that diffuse at a rate faster than the solvent fluctuations leads to large deviations of slope from the linear dependence of the friction of MY2 on the chain length of the n-alkane at 318 K and 418 K.

Quantum nuclear effects in water using centroid molecular dynamics

The quantum nuclear effects are studied in water using the method of centroid molecular dynamics (CMD). The aim is the calibration of CMD implementation in LAMMPS. The calculated intramolecular energy, atoms gyration radii and radial distribution functions are shown in comparison with previous works. The work is assumed to be the step toward to solution of the discrepancy between the simulation results and the experimental data of liquid n-alkane properties in our previous works.

Heat capacities and thermal diffusivities of n-alkane acid ethyl esters—biodiesel fuel components

The heat capacities and thermal diffusivities of ethyl esters of liquid n-alkane acids C n H2n–1O2C2H5 with the number of carbon atoms in the parent acid n = 10, 11, 12, 14, and 16 are measured. The heat capacities are measured using a DSC 204 F1 Phoenix heat flux differential scanning calorimeter (Netzsch, Germany) in the temperature range of 305–375 K. Thermal diffusivities are measured by means of laser flash method on an LFA-457 instrument (Netzsch, Germany) at temperatures of 305–400 K. An equation is derived for the dependence of the molar heat capacities of the investigated esters on temperature. It is shown that the dependence of molar heat capacity C p,m (298.15 K) on n (n = 1–6) is close to linear. The dependence of thermal diffusivity on temperature in the investigated temperature range is described by a first-degree polynomial, but thermal diffusivity a (298.15 K) as a function of n has a minimum at n = 5.

Comparison of the Biodegradation of n-alkanes and Readily Biodegradable Substrates Using Open Mixed Culture under Aerobic, Anoxic and Anaerobic Conditions

This study has investigated the biodegradation of n-alkanes using open mixed cultures in batch tests. Biodegradation of n-C12, C14, C16, C18, C20 was investigated using a respirometric method and compared with the biodegradation of the readily biodegradable substrates glucose, acetic acid and ethanol. Experiments were performed in small-scale bioreactors under various conditions, i.e. aerobic, anoxic with nitrate and completely anaerobic conditions, using two different sources of open mixed microbial cultures. Under aerobic conditions all the readily biodegradable substrates and hydrocarbons were removed, although the acclimation time was longer for the hydrocarbons (3-5 days) than for the readily biodegradable substrates (1-2 days). No significant effect on the hydrocarbon concentration on biodegradation was observed in the concentration range 0.5-5 g/l. Under anoxic conditions, both the readily biodegradable substrates and the hydrocarbons were removed using nitrate as electron acceptor. However, the acclimation time for the hydrocarbons under anoxic conditions (20-25 days) was much longer than under aerobic conditions. Under both aerobic and anoxic conditions, once acclimation with the hydrocarbons was completed, the microorganisms were immediately able to remove a second spike of the substrate without acclimation. Under anaerobic conditions, no activity was observed with the hydrocarbons over a period of 150 days, while the mixed culture was able to remove glucose and convert it to volatile fatty acids. Under aerobic conditions, the dissolved oxygen consumption data was mathematically modelled using Monod kinetics to obtain biokinetic parameters. Good fittings between the model and the experimental data was obtained and the biodegradation of hydrocarbons was characterised by higher values of the parameter KS compared to the readily biodegradable substrates. The results of this study showed that the open mixed microbial cultures contained diverse microorganisms capable of utilizing both liquid and solid n-alkanes under aerobic and anoxic conditions.

Predicting phase behavior of metallic mercury in liquid and compressed gaseous hydrocarbons

This study presents the first predictive approach for estimating phase behavior of metallic mercury in hydrocarbons and compressed gases. This approach is based on the recently developed CP-PC-SAFT EoS attached by a universal value of k12=0.3. The CP method of solving SAFT parameters is not applicable for metallic mercury. Therefore it has been treated as a monoatomic substance, while σ and ε/k have been adjusted to the experimental vapor pressure and density data. It has been demonstrated that the proposed approach accurately predicts the solubility enhancement of metallic mercury in the compressed gases up to ∼400bar. The solubility data in liquid n-alkanes, aromatic and oxygenated hydrocarbons in wide range of temperatures have been truthfully estimated as well. The available binary diffusion coefficients of mercury in gases can also be accurately predicted by the Chapman–Enskog model when applied with the model’s molecular parameters. This study also shows that the analogous implementation of the original version of PC-SAFT results in a slightly lesser over-all accuracy, which could probably be attributed to the not entirely systematic practice of evaluating its molecular parameters for various hydrocarbons. A doubtless advantage of both considered versions of PC-SAFT over Peng–Robinson EoS is demonstrated as well.