N-alkane Mixtures Research Articles

The Structural Characteristics and Viscosity of Liquids within a Hole Model

Experimental X-ray or electron-diffraction research of liquid allows to reliably assess the size of a lattice seat and holes in quasi-crystalline structures. According to the results of such research, lattice constants for a series of certain n-paraffins were calculated. The author used a hole model of liquids to obtain expressions which were later used to calculate enthalpies of activation of viscous current of n-alkanes and their mixtures. It allowed to connect the experimental work on definition of temperature dependency of liquids viscosity to the calculation of structure properties of liquid mixtures of non-electrolytes. Partly, such calculation was done while solving a problem of the composition of a surface layer of n-alkanes mixtures.

Mechanism of Wax Deposition on Cold Surfaces: Gelation and Deposit Aging

To further develop an understanding of the wax deposition mechanism needed to model its occurrence in subsea oil pipelines, deposition experiments using a pure n-alkane and a binary n-alkane mixture were performed in a cold finger apparatus modified to allow for reliable and accurate visualization of the wax deposit thickness as a function of time. The deposit thickness is found to grow initially but to shrink at long times as the deposit composition enriches in the wax content and the wax concentration in the surrounding oil decreases. This non-monotonic time evolution of the deposit thickness and increase in wax composition are explained and modeled using transient heat and mass transfer kinetics. The ultimate shrinkage of the deposit thickness is traced to depletion of soluble wax in the bulk oil because soluble wax continuously diffuses from the bulk oil into the deposit and precipitates there by fast precipitation kinetics.

Molecular Dynamics Simulations of the Crystallization Process of n-Alkane Mixtures and the Resulting Thermal Conductivity

To elucidate the underlying mechanism of crystallization processes of n-alkane mixtures, molecular dynamics simulation is used to assess the effect of the morphology on thermal conductivity. Binary...

Critical Properties of n-Alkanes Binary Mixtures Based on Equations of State

The aim of this work is the parameters test of the equation of state for hard convex body chain in predicting the critical properties of binary mixtures of n-alkanes. The predicted critical properties agree closely with the experimental results and are better than the predicted values both from the hard convex body equation of state and the Guggenheim equation of state for hard spheres. The agreement between theoretical and experimental results of the critical properties of n-alkanes appears to be improved negligibly, even if the shape of the molecule is considered. However, an improvement in the accuracy of the result is obtained with the equation of state of the hard convex body chain compared to the simple hard convex body equation of state.

Vapor–Liquid Equilibria of Mixtures of Molecular Fluids Using the Activity Fraction Expanded Ensemble Simulation Method

The activity fraction expanded ensemble (AFEE) simulation technique has been extended to predict the vapor–liquid coexistence behavior of binary mixtures of molecular fluids. The systems of molecular mixtures studied are thiophene–n-hexane (a mixture of an aromatic compound with a n-alkane) and methane–n-hexane (mixture of n-alkanes with significant difference in size). Comparison with results from the grand canonical transition matrix Monte Carlo method and experimental data available in the literature has also been provided. Further, we have investigated the computational efficiency of the AFEE technique at temperatures where both compounds exhibit subcritical behavior (thiophene–n-hexane at 338.15 K) and where one of the components shows supercritical behavior (methane–n-hexane at 373 K). Canonical Monte Carlo simulations are also performed to obtain the radial distribution functions which have been used to study the structure of the coexisting liquid phases to gain insights into the molecular origins ...

Hydrogenolysis of Alkanes in a Three-Phase Slurry Reactor over Cobalt Fisher–Tropsch Catalysts: A New Product Distribution Model

Kinetic models are developed for the molecular-mass distribution of the products of hydrogenolysis of mixed long-chain n-alkanes experimentally studied in the three-phase slurry reactor over nanosized cobalt-containing Fischer–Tropsch catalysts. The models are based on different hypotheses pertaining to the ratios of probabilities for the cleavage of C–C bonds as a function of their position in n-alkane chains with allowance made for the occurrence of secondary transformations of products and the vapor-liquid equilibrium in the mixture of n-alkanes in a hydrogen medium. It is demonstrated that the experimentally observed features of this distribution cannot be described in terms of the known theories of C–C bond cleavage in the hydrogenolysis of long-chain alkanes (terminal methane splitting and uniform or normal distribution of product composition). The hypothesis of a regular increase in the probability of C–C bond cleavage on going from the center of the carbon chain to its ends is advanced. Calculations performed using combinations of the distribution following this hypothesis and the normal distribution make it possible to solve the problems mentioned above.

Investigation of ultrasonic speeds of sound and excess parameters in binary liquid mixtures of N-alkanes with octan-2-ol using different empirical theories at 298.15 K

Ultrasonic velocity, density and percentage deviation in velocity were measured for mixtures of n-alkanes, namely, n-octane, n-decane, n-dodecane and n-tetradecane with octan-2-ol at 298 K. The experimental sound velocity data were compared by using three theoretical relations, namely, Nomoto relation, Vandael ideal mixing relation and Schaaffs collision factor theory to predict which one of them agrees the experimental data. It was observed that Nomoto relation was the best suited method in all the four binary systems. Hence, in the real time applications which are using the above said components can be handled without experimental expenses. The experimental data were used to calculate the interaction parameter (α), adiabatic compressibility (β), intermolecular free length (Lf), excess velocity (UE), excess impedance (ZE) and excess volume (VE) which were discussed to identify the molecular interactions in terms of non-ideality in the binary liquid mixtures. It was observed that the increase of mole fraction of octan-2-ol with different n-alkanes dipole–induced dipole interactions were supported.

Membrane Fatty Acid Composition and Cell Surface Hydrophobicity of Marine Hydrocarbonoclastic Alcanivorax borkumensis SK2 Grown on Diesel, Biodiesel and Rapeseed Oil as Carbon Sources.

The marine hydrocarbonoclastic bacterium Alcanivorax borkumensis is well known for its ability to successfully degrade various mixtures of n-alkanes occurring in marine oil spills. For effective growth on these compounds, the bacteria possess the unique capability not only to incorporate but also to modify fatty intermediates derived from the alkane degradation pathway. High efficiency of both these processes provides better competitiveness for a single bacteria species among hydrocarbon degraders. To examine the efficiency of A. borkumensis to cope with different sources of fatty acid intermediates, we studied the growth rates and membrane fatty acid patterns of this bacterium cultivated on diesel, biodiesel and rapeseed oil as carbon and energy source. Obtained results revealed significant differences in both parameters depending on growth substrate. Highest growth rates were observed with biodiesel, while growth rates on rapeseed oil and diesel were lower than on the standard reference compound (hexadecane). The most remarkable observation is that cells grown on rapeseed oil, biodiesel, and diesel showed significant amounts of the two polyunsaturated fatty acids linoleic acid and linolenic acid in their membrane. By direct incorporation of these external fatty acids, the bacteria save energy allowing them to degrade those pollutants in a more efficient way. Such fast adaptation may increase resilience of A. borkumensis and allow them to strive and maintain populations in more complex hydrocarbon degrading microbial communities.

N-Alkane and long-chain alcohol recovery in moose (Alces alces), a browsing herbivore

Habitat management for herbivores often depends on an understanding of the food habits of animals. Plant cuticular waxes containing nearly indigestible complex mixture of n-alkanes and long-chain alcohols (LCOHs) have recently shown promise for diet analyses, but the accuracy of the technique depends strongly on the efficiency of recovery of the markers in feces. Fecal recovery of n-alkanes and LCOHs from 10 browse stems or leaves and two ensiled grass hays fed to moose (Alces alces (Linnaeus, 1758)) during in vivo digestion trials was investigated. n-Alkanes and LCOHs were extracted using a single-step accelerated solvent extraction technique and the recovery of these cuticular components was calculated from the feces of the animals. n-Alkane recoveries from feces averaged 0.82, ranging from a low of 0.58 (haylage) to a high of 0.95 (browse stems). LCOH recoveries averaged 0.92 across all forages, ranging from 0.80 (haylage) to a high of 1.13 (browse stems). n-Alkane and LCOH fecal recovery increased with increasing chain length, similar to findings in other studies. Although fecal recovery of n-alkanes and LCOHs were variable, we conclude that they are inversely related to forage digestibility, are consistent within forage classes, and are therefore predictable markers for use in assessing herbivore diets.

Application of LSSVM algorithm as a novel tool for prediction of density of bitumen and heavy n-alkane mixture

ABSTRACTThe most of oil reservoirs in the world are heavy oil and bitumen reservoirs. Due to high viscosity and density of these types of reservoirs the production has problems so importance of enhanced oil recovery (EOR) processes for them is clear. The injection of solvents such as tetradecane is known as one of methods which improve oil recovery from bitumen reservoirs. In the present investigation, the Least squares support vector machine (LSSVM) algorithm was used to estimate density of Athabasca bitumen and heavy n-alkane mixture in term of temperature, pressure and weight percent of the solvent. The Root mean square error (RMSE), average absolute relative deviation (AARD) and the coefficient of determination (R2) for total dataset are determined 0.033466, 0.0025686 and 1 respectively. The predicted results indicate that the LSSVM algorithm has potential to be a predicting machine for the bitumen-heavy alkane mixture density prediction.

High pressure phase equilibria of carbon dioxide + n-alkanes mixtures: Experimental data and modeling

Experimental phase equilibrium data were measured for systems containing a mixture of heavy n-alkanes (C22H46, C23H48 and C24H50) and a light n-alkane (C12H26) in the presence of 20, 40, 60 and 80% mole fraction of CO2. The experiments were carried out in the range of 290–353 K and up to 70 MPa. The measured phase equilibrium data presented regions of vapor-liquid, solid-liquid and solid-liquid-vapor coexistence. To model the data obtained, the solid phase was described using the multiple solid solution approach, which employs the modified UNIQUAC equation to calculate the activity coefficients. The Poynting correction factor was used to take into account the pressure effect in the solid-liquid equilibrium. The liquid and vapor phases were described using the Peng-Robinson equation of state with classical mixing rule. Further, a correlation was developed for the calculation of the molar volumes difference between the liquid and the solid phases. The phase equilibrium predictions were in good agreement with the measured phase transitions data, indicating that the set of models employed is adequate to describe the phase equilibrium behavior of mixtures containing paraffins and CO2 at low and high pressures.

Application of fuzzy c-means algorithm as a novel method to predict density of mixtures of Athabasca bitumen and heavy n-alkane

The significant number of oil reservoir are bitumen and heavy oil. One of the approaches to enhance oil recovery of these types of reservoir is dilution of reservoir oil by injection of a solvent such as tetradecane into the reservoirs to modify viscosity and density of reservoir fluids. In this investigation, an effective and robust estimating algorithm based on fuzzy c-means (FCM) algorithm was developed to predict density of mixtures of Athabasca bitumen and heavy n-alkane as function of temperature, pressure and weight percent of the solvent. The model outputs were compared to experimental data from literature in different conditions. The coefficients of determination for training and testing datasets are 0.9989 and 0.9988. The comparisons showed that the proposed model can be an applicable tool for predicting density of mixtures of bitumen and heavy n-alkane.

Microaerophilic alkane degradation in Pseudomonas extremaustralis: a transcriptomic and physiological approach.

Diesel fuel is one of the most important sources of hydrocarbon contamination worldwide. Its composition consists of a complex mixture of n-alkanes, branched alkanes and aromatic compounds. Hydrocarbon degradation in Pseudomonas species has been mostly studied under aerobic conditions; however, a dynamic spectrum of oxygen availability can be found in the environment. Pseudomonas extremaustralis, an Antarctic bacterium isolated from a pristine environment, is able to degrade diesel fuel and presents a wide microaerophilic metabolism. In this work RNA-deep sequence experiments were analyzed comparing the expression profile in aerobic and microaerophilic cultures. Interestingly, genes involved in alkane degradation, including alkB, were over-expressed in micro-aerobiosis in absence of hydrocarbon compounds. In minimal media supplemented with diesel fuel, n-alkanes degradation (C13-C19) after 7days was observed under low oxygen conditions but not in aerobiosis. In-silico analysis of the alkB promoter zone showed a putative binding sequence for the anaerobic global regulator, Anr. Our results indicate that some diesel fuel components can be utilized as sole carbon source under microaerophilic conditions for cell maintenance or slow growth in a Pseudomonas species and this metabolism could represent an adaptive advantage in polluted environments.

LIQUID- SOLID AND LIQUID-VAPOR PHASE EQUILIBRIUM IN SECONDARY ALCOHOL - n-ALKANE SYSTEM

Primary and secondary alcohols, obtained as a product of processing of plant raw materials, can be used as additives in fuel. Mixtures of n-alkanes, cyclic alkanes and aromatic hydrocarbons can act as a model for gasoline and diesel fuel. Therefore, it is necessary to study the characteristics of mixtures of alcohols with normal, cyclic and aromatic hydrocarbons. To simulate liquid-solid and liquid-vapor phase equilibria, a method is used to minimize excess Gibbs energy by the solvation parameter. The authors developed the PCEAS (Phase Charts Eutectic and Azeotropic Systems) software. The input data in the case of constant pressure are the temperature T 0 and the enthalpy of the phase change H 0 of the pure components. Prediction of the thermodynamic parameters of secondary alcohols is used to calculate the eutectic and azeotropic parameters of the secondary alcohol - n-alkane mixture: composition, temperature, melting enthalpy and evaporation. The model makes it possible to determine the average value of the association parameter in the liquid phase k . Experimental data for azeotropic mixtures made it possible to establish the association parameter in the vaporphase  of the systems under study. The results of calculations can be used to select the optimal composition and obtain the requiredcharacteristics of biofuel.

Modeling binary mixtures of n-alkanes and water using PC-SAFT

Modeling and measuring the mutual solubility in binary n-alkane + water mixtures is very challenging due to their low order of magnitude. Consequently, experimental data regarding mutual solubilities of these systems scatter remarkably. In this work, the PC-SAFT equation of state has been applied to model liquid-liquid and vapor-liquid-liquid equilibria of binary n-alkane + water mixtures. For this purpose, temperature-dependent binary interaction parameters have been fitted to the n-alkane solubility in the aqueous phase for n-alkanes ranging from n-pentane to n-undecane. Furthermore, these binary interaction parameters have been correlated with the carbon number of the n-alkane in order to predict phase equilibria of binary n-alkane + water mixtures for n-alkanes ranging from n-propane to n-pentadecane. Excellent agreement between modeling results and available experimental data has been observed for the liquid-liquid equilibria including the description of the minimum of n-alkane solubility in water as a function of temperature. Even the prediction of the vapor-liquid-liquid equilibria of the respective mixtures showed remarkably good results compared to experimental data.

Viscosity estimation of mixed oil using RBF-ANN approach

ABSTRACTDiluting the bitumen and heavy oil with a liquid solvent such as tetradecane is one way to decrease the viscosity. The accurate estimation for the viscosity of the aforesaid mixture is serious due to the sensitivity of enhanced oil recovery method. The main aim of this study was to propose an impressive relation between the viscosity of heavy n-alkane and Athabasca bitumen mixtures based on pressure, temperature, and the weight percentage of n-tetradecane using radial basis function artificial neural network (RBF-ANN). Also, this model has been compared with previous equations and its major accuracy was evidenced to estimate the viscosity. The amounts of mean relative error (MRE %) and R-squared received 0.32 and 1.00, respectively. The endeavors confirmed amazing forecasting skill of RBF-ANN for the approximation of the viscosity as a function of temperature, pressure, and the weight percentage of n-tetradecane.

Characterization of cuticular hydrocarbons according to colony duties in the stingless bee Tetragonisca angustula

In social insects, task-related recognition plays an important role in the coordination and cohesion between members of the colony. Tetragonisca angustula is an eusocial stingless bee that presents a sophisticated system of defense involving two complementary groups of guards: hovering and standing guards. We identified, quantified, and compared the cuticular compounds of worker bees captured within the nest, and bees performing tasks outside: foragers and guards. In addition to cuticular hydrocarbons (CHCs), we identified abundant di- and triterpenes. Among the CHCs, we found a mixture of n-alkanes, methyl-branched alkanes, alkenes, and alkadienes. Significant differences in the relative abundance of CHCs between behavioral groups were found. Particularly, guards present high amounts of branched alkanes relative to nest bees and foragers. Differential CHC profiles associated with behavioral groups could imply a mechanism for caste recognition.

A high-throughput computing procedure for predicting vapor-liquid equilibria of binary mixtures – Using carbon dioxide and n-alkanes as examples

An automatic high-throughput computing (HTC) procedure is implemented for calculating vapor-liquid equilibrium (VLE) curves of binary systems using molecular dynamics simulation and coarse-grained force field. The HTC procedure builds simulation models, carries out the simulations, and validates the simulations automatically. The procedure is demonstrated by calculating the VLE curves for 16 binary mixtures of carbon dioxide and n-alkanes on 856 state points in the temperature range of 277.2–420.0 K and pressure range of 0.3–25.0 MPa. The averaged uncertainties in predictions are 0.119 MPa for pressure, 0.007 and 0.029 for liquid and vapor CO2 molar fractions, and 0.005 and 0.010 for liquid and vapor densities respectively. The Validation against experiment data on 10 binary systems and 316 state points shows that the predictions are accurate with average deviation of about 5% for CO2 mole fraction and 3.5% for saturated density at pressure range to P < 0.9Pc. This automatic procedure can only be used for the prediction of the vapor-liquid equilibrium. The computed data can be obtained from http://sun.sjtu.edu.cn/msd.

Predicting the viscosity of n-alkane liquid mixtures based on molecular description

A new model has been developed to predict the viscosity of liquid, n-alkane mixtures. It represents a mixture by a single pseudo-component characterized by an appropriate molecular weight and calculates the viscosity by means of the modified, extended hard-sphere model (EHS) that makes use of an universal function relating reduced viscosity to reduced volume. For mixtures that contain n-alkanes with a similar number of carbon atoms, the molecular weight of the pseudo-component is simply given by the molecular weight of the mixture. For more asymmetric mixtures, the choice of the molecular weight is a function of the difference in the number of carbon atoms, between the longest and the shortest chain. The proposed model is a precursor of a new family of models that do not require the knowledge of detailed composition of the mixture, but still take advantage of the underlying molecular description. The developed model, named 1-component Extended Hard-Sphere (1-cEHS), predicted, in general, the viscosity of binary and multicomponent n-alkane mixtures with uncertainty of 5%, even when the mixtures contain very long n-alkanes. For highly asymmetric binary mixtures of alkanes the predictions deteriorated, but improved for highly asymmetric multicomponent mixtures indicating that the presence of the intermediate alkane species leads to a better prediction.We have also tested two other viscosity models, the extended hard sphere (EHS) and Vesovic-Wakeham (VW), that also rely on kinetic theory to provide the molecular description, but require a full compositional specification of the mixture. They can also predict the viscosity within 5%, but the presence of the long chain n-alkanes in a mixture as well as the high asymmetry, leads to deterioration of the prediction.

Thermodiffusion in multicomponent n-alkane mixtures

Compositional grading within a mixture has a strong impact on the evaluation of the pre-exploitation distribution of hydrocarbons in underground layers and sediments. Thermodiffusion, which leads to a partial diffusive separation of species in a mixture due to the geothermal gradient, is thought to play an important role in determining the distribution of species in a reservoir. However, despite recent progress, thermodiffusion is still difficult to measure and model in multicomponent mixtures. In this work, we report on experimental investigations of the thermodiffusion of multicomponent n-alkane mixtures at pressure above 30 MPa. The experiments have been conducted in space onboard the Shi Jian 10 spacecraft so as to isolate the studied phenomena from convection. For the two exploitable cells, containing a ternary liquid mixture and a condensate gas, measurements have shown that the lightest and heaviest species had a tendency to migrate, relatively to the rest of the species, to the hot and cold region, respectively. These trends have been confirmed by molecular dynamics simulations. The measured condensate gas data have been used to quantify the influence of thermodiffusion on the initial fluid distribution of an idealised one dimension reservoir. The results obtained indicate that thermodiffusion tends to noticeably counteract the influence of gravitational segregation on the vertical distribution of species, which could result in an unstable fluid column. This confirms that, in oil and gas reservoirs, the availability of thermodiffusion data for multicomponent mixtures is crucial for a correct evaluation of the initial state fluid distribution.