Alkane Molecules Research Articles

A study on the reaction mechanism of microwave pyrolysis of oily sludge by products analysis and ReaxFF MD simulation

ABSTRACT The products distributions of oily sludge (OS) pyrolysis was fully explored by combining the pyrolysis experiments and molecular simulation, to help to deeply understand this complicated reaction process. The results of products analysis indicated that the main reactions include chain-breaking reactions, dehydrogenation reactions, aromatization reactions, alkylation reactions, and dehydrogenation condensation reactions. Microwave pyrolysis of model OS comprised of n-dodecane and OS sediment were conducted to further explore the specific reaction during the pyrolysis process, and the results showed that the pyrolysis of saturated alkanes begins at 350℃, and dehydrogenation condensation begins at 500℃. Specifically, saturated alkanes first dehydrogenated to form large molecules of α-alkene, then α-alkenes broke chains to form smaller molecules of alkanes. Furthermore, the pyrolysis process of n-dodecane was simulated by Reactive force field molecular dynamics (ReaxFF MD), and the molecular pyrolysis products distribution obtained by simulation was in good agreement with the experimental result.

Faceting and Flattening of Emulsion Droplets: A Mechanical Model.

When cooled down, emulsion droplets stabilized by a frozen interface of alkane molecules and surfactants have been observed to undergo a spectacular sequence of morphological transformations: from spheres to faceted liquid icosahedra, down to flattened liquid platelets. While generally ascribed to the interplay between the elasticity of the frozen interface and surface tension, the physical mechanisms underpinning these transitions have remained elusive, despite different theoretical pictures having been proposed in recent years. In this Letter, we introduce a comprehensive mechanical model of morphing emulsion droplets, which quantitatively accounts for various experimental observations, including the size scaling behavior of the faceting transition. Our analysis highlights the role of gravity and the spontaneous curvature of the frozen interface in determining the specific transition pathway.

Selectivity of the Lindlar catalyst in alkyne semi-hydrogenation: a direct liquid-phase adsorption study

Pd catalysts contain active sites that strongly adsorb alkyne and alkene molecules. The presence of the latter, alkene sites, defines the low semi-hydrogenation selectivity.

Радиолиз трансформаторного масла в присутствии трихлорбензола и нано--Al2O3

In this work, a comparative study of the kinetics of changes in the pH indicator, the formation of H2O2 and CO2 depending on the absorbed dose at the radiolysis of TCB containing transformer oil in the presence and without nano-γ-Al2O3 under the action of γ radiation was carried out. During radiolysis of both systems (TСB + transformer oil and TСB + transformer oil + 0.1 g of nano-γ-Al2O3), the radiation-chemical yield of CO2 decreases with an increase in the initial concentration of TCB, although at the presence of nano-particles, the values of the radiation-chemical riels of CO2 become less. Unlike CO2, the radiation-chemical yields of H2O2 increase with an increase in the initial concentration of TCB, but their values are less in the presence of nano-γ-Al2O3. The results obtained are explained by the reactions of active particles, radiolysis of the main components of transformer oil, such as hydrogen atoms and hydrocarbon radicals with TCB and dissolved oxygen molecules. In addition, there is a transfer of electronic excitation energy from alkane and cycloalkane molecules to aromatic hydrocarbon molecules. The effect of nano-γ-Al2O3 on the radiolysis of the mixture is discussed on the basis of the reaction of electron and hole centers with the molecules of the components of the irradiated mixture.

Temperature inversion of the action of multilayer fullerenoid structures in the oxidation of N-decan by molecular oxygen

It was established that at low temperatures MFS inhibit the oxidation of n-decan, and at temperatures close to the boiling point of the hydrocarbon, on the contrary, accelerate the transformation of the original alkane molecules. The composition of alkane transformation products in the high-temperature two-phase (gas-liquid) oxidation regime was analyzed by gas-liquid chromatography. It is shown that the transformation of n-decan molecules occurs according to the same schemes both in the case of oxidation without the additive of MFS, and in the presence of these compounds in a liquid. The work is devoted to the actual problem of increasing the energy efficiency of liquid motor fuels (gasoline, diesel and jet fuels) in transport power plants. One of the most acceptable ways to solve this problem at the present stage, which does not require capital expenditure, is to improve the processes of chemical transformations of fuel molecules in engines under the action of additives. The use of multilayer fullerene-like structures (MFS) as additives to motor fuels is proposed. The influence of additives modified MFS on the conversion of reagents in the processes of liquid-phase oxidation of n-decan by molecular oxygen at low (70°C) and high (150°C) temperatures has been studied. The change in the direction of the MFS action on chemical transformation of initial reagents depending on process temperature is experimentally revealed. It was established that at low temperatures MFS inhibit the oxidation of n-decan, and at temperatures close to the boiling point of hydrocarbons, on the contrary, accelerate the transformation of the original alkane molecules. The composition of alkane transformation products at high-temperature two-phase (gas-liquid) oxidation regime was analyzed by gas-liquid chromatography. It is shown that the transformation of n-decan molecules occurs according to the same schemes both in the case of oxidation without the additive of MFS, and in the presence of these compounds in a liquid.

First-Principles-Based Multiscale Modelling of Nonoxidative Butane Dehydrogenation on Cr2O3(0001).

Propane (C3H8) and butane (C4H10) are short straight-chain alkane molecules that are difficult to convert catalytically. Analogous to propane, butane can be dehydrogenated to butenes (also known as butylenes) or butadiene, which are used industrially as raw materials when synthesizing various chemicals (plastics, rubbers, etc.). In this study, we present results of detailed first-principles-based multiscale modelling of butane dehydrogenation, consisting of three size- and time-scales. The reaction is modelled over Cr2O3(0001) chromium oxide, which is commonly used in the industrial setting. A complete 108-step reaction pathway of butane (C4H10) dehydrogenation was studied, yielding 1-butene (CH2CHCH2CH3) and 2-butene (CH3CHCHCH3), 1-butyne (CHCCH2CH3) and 2-butyne (CH3CCCH3), butadiene (CH2CHCHCH2), butenyne (CH2CHCCH), and ultimately butadiyne (CHCCCH). We include cracking and coking reactions (yielding C1, C2, and C3 hydrocarbons) in the model to provide a thorough description of catalyst deactivation as a function of the temperature and time. Density functional theory calculations with the Hubbard U model were used to study the reaction on the atomistic scale, resulting in the complete energetics and first-principles kinetic parameters for the dehydrogenation reaction. They were cast in a kinetic model using mean-field microkinetics and kinetic Monte Carlo simulations. The former was used to obtain gas equilibrium conditions in the steady-state regime, which were fed in the latter to provide accurate surface kinetics. A full reactor simulation was used to account for the macroscopic properties of the catalytic particles: their loading, specific surface area, and density and reactor parameters: size, design, and feed gas flow. With this approach, we obtained first-principles estimates of the catalytic conversion, selectivity to products, and time dependence of the catalyst activity, which can be paralleled to experimental data. We show that 2-butene is the most abundant product of dehydrogenation, with selectivity above 90% and turn-over frequency above 10–3 s–1 at T = 900 K. Butane conversion is below 5% at such low temperature, but rises above 40% at T > 1100 K. Activity starts to drop after ∼6 h because of surface poisoning with carbon. We conclude that the dehydrogenation of butane is a viable alternative to conventional olefin production processes.

Ab Initio Multiscale Process Modeling of Ethane, Propane and Butane Dehydrogenation Reactions: A Review

Olefins are among the most important structural building blocks for a plethora of chemical reaction products, including petrochemicals, biomaterials and pharmaceuticals. An ever-increasing economic demand has urged scientists, engineers and industry to develop novel technical methods for the dehydrogenation of parent alkane molecules. In particular, the catalysis over precious metal or metal oxide catalysts has been put forward as an alternative way route to thermal-, steam- and fluid catalytic cracking (FCC). Multiscale system modeling as a tool to theoretically understand processes has in the past decade period evolved from a rudimentary measurement-complementing approach to a useful engineering environment. Not only can it predict various experimentally obtained parameters, such as conversion, activity, and selectivity, but it can help us to simulate trends, when changing applicative operating conditions, such as surface gas temperature or pressure, or even support us in the search for the type of materials, their geometrical properties and phases for a better functional performance. An overview of the current set state of the art for saturated organic short chain hydrocarbons (ethane, propane and butane) is presented. Studies that combine at least two different dimensional scales, ranging from atomistic-, bridging across mechanistic mesoscale kinetics, towards reactor- or macroscale, are focused on. Insights considering reactivity are compared.

Study on the influence of the external conditions and internal components on foam performance in gas recovery

In the lifting process of drainage gas recovery, external conditions and internal components of the foam are complex. We used molecular dynamics simulation to construct a series of fatty alcohol polyoxyethylene ether sulfate (AES) foam models that could represent various foams in different lifting stages from well to ground. The effect of temperature and pressure on foam stability was investigated. We found that there are two main reasons for foam instability in the first-half stage of the lifting process. Firstly, high temperature aggravated the molecule movement; some CH4 molecules entered the foam film and formed a molecular transport channel. Secondly, the interaction between the CH4 phase and condensate oil leads to some alkane molecules entering the gas–liquid interface. The calculation results and theoretical analysis will help to deepen the understanding of the performance of oily foams under harsh conditions.

Enhanced Resonant Positron Annihilation due to Nonfundamental Modes in Molecules.

Positrons attach to most molecules through Feshbach resonant excitation of fundamental vibrational modes, and this leads to greatly enhanced annihilation rates. In all but the smallest molecules, vibrational energy transfer further enhances these annihilation rates. Evidence is presented that in alkane and cycloalkane molecules, this can occur by the excitation of other than fundamental vibrations and produce roughly comparable annihilation rates. These features are compared to infrared absorption spectra. A possible mechanism is discussed that involves combination and overtone vibrations.

Structure–Property Correlation for Calculating the Critical Pressures of Liquid–Vapor Phase Transitions from the Topological Characteristics of Alkene Molecules

A multidimensional QSPR model is proposed for calculating the critical pressure of normal and substituted alkenes from combinations of the topological descriptors of molecular graphs, i.e., the Wiener and Randic indices and function of the eigenvalues of the topological matrix, and indices that consider the differences between cis- and trans-isomers. It is shown that the QSPR model adequately describes the critical pressure of olefins for the liquid–vapor phase transition. It is concluded that the obtained results can be recommended for determining the critical properties of known and novel alkenes. They can be used when making scientific and engineering calculations in petroleum chemistry and the technology of supercritical fluids.

Influence of Physicochemical Properties on Gas Transport Properties of Silver-Containing Ionic Liquid Mixtures for Olefin/Paraffin Membrane Separation

Olefin/paraffin separation by cryogenic distillation is one of the most energy-consuming processes not only among the entire chemical processes but also among all the energy-consuming activities by human beings. The purification of propylene and ethylene accounts for 0.3% of global energy use (1). Membrane separation is an attractive alternative, owing to its high energy-efficiency compared to conventional distillation processes. Liquid membranes that utilize gas transport through the liquid phase confined in the pore structures have shown promising performance due to the faster transport compared to solid membrane materials (2).Since the liquid phase is where the transport of olefin/paraffin molecules occurs, the liquid membrane performance in terms of permeability, selectivity, and stability mainly relies on the properties of the liquid component. Ionic liquids are a suitable material since the liquid component in the membranes provide stable separation performance owing to their extremely low vapor pressure and good thermal/chemical stability. Moreover, the limitless turnability of ionic liquids can be manipulated to enhance the molecular interaction with certain gas molecules to result in better gas solubility. For olefin/paraffin separation, in addition to physical solubility of the olefin in the ionic liquid, silver ions are commonly added to further improve olefin solubility. The silver ions can complex with olefin molecules via interaction between the double bonds of olefins and the orbitals of silver ions.Here we have investigated the effect of the anion, concentrations of the silver salt, and temperatures on the physicochemical properties of the silver-containing ionic liquid mixtures. The macroscopic physicochemical properties, such as viscosity and density, affect the filling of the membrane pores and stability to transmembrane pressure. However, we show that they are also indicators of ion aggregation in the mixtures, which can be correlated with relevant membrane properties, including solubility, diffusivity and silver ion reactivity with contaminant gases. The physiochemical viewpoint on the silver-containing ionic liquid mixture will provide appropriate insight for understanding the olefin/paraffin gas transport in the ionic liquid mixture, which leads to a design idea for better separation performance.(1) D. S. Sholl, R. P. Lively, Seven chemical separations: to change the world: purifying mixtures without using heat would lower global energy use, emissions and pollution--and open up new routes to resources. Nature 532, 435 (2016).(2) C. M. Sanchez, T. Song, J. F. Brennecke, B. D. Freeman, Hydrogen Stable Supported Ionic Liquid Membranes with Silver Carriers: Propylene and Propane Permeability and Solubility. Industrial & Engineering Chemistry Research 59, 5362-5370 (2020).

Effects of paraffin, fatty acid and long alkyl chain phenol on the solidification of n-hexadecane under harsh subcooling condition: A molecular dynamics simulation study

Information about the solidification of n-alkanes at low temperature is of great value to understand relevant phenomena that impose severe technological problems in the oil industry. In order to better understand the roles of different compounds on the structuration of n-alkanes, several molecular dynamics simulations were performed at strong subcooling condition. The analyzed systems consisted of pure n-hexadecane, pure n-triacontane and their equimolar mixtures, as well as the mixture of n-hexadecane with a fatty acid or with a long alkyl chain phenol. The occurenceof different patterns of molecular organization were observed along the formation of solid-like structures of n-alkanes. The presence of both the fatty acid and the phenol limit the fraction of alkane molecules in solid nuclei in, approximately, 10 and 40 %, respectively, when compared to a system composed only of hexadecane. Moreover, the systems containing alkanes and fatty acids organized themselves in closely packed solid nuclei, whilst the presence of the phenol led to smaller and sparser nuclei. In systems containing organic acids or phenols, cluster analysis revealed different and complex interaction network, connecting the small solid-like nuclei.

Structure and electronic structure of van der Waals interfaces at a Au(1 1 1) surface covered with a well-ordered molecular layer of n-alkanes

The structure and electronic structure of a system comprising molecular layers of n-alkane adsorbed on Au(111) were investigated to understand the origin of the interfacial electric dipole layer. These alkane molecules are inert and thus van der Waals (vdW) interaction is the primary adsorptive force. Although these vdW interfaces are regarded as ideal physical adsorption systems unlikely to chemically interact with the metal surface, a large interfacial electric dipole layer over 1 eV is formed. It is important to elucidate the mechanism underlying the generation of such large dipole layers to understand the electrode interface in organic semiconductor devices. Thus, this paper elucidates the details of the vdW interface, in particular between tetratetracontane (TTC) and Au(111). First, the mechanism of growth of the TTC layer up to monolayer thickness was revealed using a low-energy electron-diffraction method. Second, the interface states were newly formed, as determined using angle-resolved photoelectron spectroscopy, X-ray photoemission spectroscopy, and near-edge absorption fine-structure spectroscopy. Our findings indicate, unexpectedly, that a relatively strong inter-orbital interaction governs this vdW interface, similar to a weak chemisorption system rather than a physisorption system.

Ring opening in cycloheptane and dissociation of 1-heptene at high temperatures

Cycloalkanes and alkenes are important components of real fuels but there is little kinetic and mechanistic data on the dissociation of most large cyclic and olefinic molecules at elevated temperatures. We present here the first experimental and theoretical investigation of dissociation of cycloheptane and the initial product from ring opening, 1-heptene. Experiments were performed in a diaphragmless shock tube using laser schlieren densitometry. Pyrolysis of cycloheptane (0.5–4% in Kr) was studied over 1450–2000 K and 30–120 Torr. Experiments with 1-heptene (1–4% in Kr) covered 1200–1650 K and 30–120 Torr. A newly developed chemical kinetic mechanism for pyrolysis of cycloheptane and 1-heptene is presented herein. Simulations are in very good agreement with the experimental measurements. Rate coefficients for the initial ring-opening process in cycloheptane, k1, and dissociation of 1-heptene, k2, were determined from the experiments. Both k1 and k2 are in falloff, and the pressure and temperature dependencies were well reproduced by theoretical calculations allowing extrapolation to conditions beyond the scope of this work. These calculations yielded the following expressions for k1 and k2 with the uncertainties estimated as ±40% and ±50% respectively:k1,∞=5.94×1017exp(−44,521T)s−1 and k2,∞=8.86×1016exp(−35,887T)s−1. The results of this study indicate that cycloheptane dissociates similarly to cyclopentane and cyclohexane, i.e. ring-opening via CC scission to a diradical that rapidly isomerizes to a conjugate 1-alkene. The secondary chemistry is dominated by the dissociation products of the 1-alkenes i.e. allyl and n-alkyl radicals. Furthermore, rates of dissociation of the cycloalkanes are size dependent and kcyclopentane << kcyclohexane < kcycloheptane.

Mechanical C-C Bond Formation by Laser Driven Shock Wave.

Mechanically induced C−C bond formation was demonstrated by the laser driven shock wave generated in liquid normal alkanes at room temperature. Gas chromatography mass spectrometry analysis revealed the dehydrogenation condensation between two alkane molecules, for seven normal alkanes from pentane to undecane. Major products were identified to be linear and branched alkane molecules with double the number of carbons, and exactly coincided with the molecules predicted by supposing that a C−C bond was formed between two starting molecules. The production of the alkane molecules showed that the C−C bond formation occurred almost evenly at all the carbon positions. The dependence of the production on the laser pulse energy clearly indicated that the process was attributed to the shock wave. The C−C bond formation observed was not a conventional passive chemical reaction but an unprecedented active reaction.

Thermal resistance of an interfacial molecular layer by first-principles molecular dynamics.

The approach-to-equilibrium molecular dynamics (AEMD) methodology is applied in combination with first-principles molecular dynamics to investigate the thermal transfer between two silicon blocks connected by a molecular layer. Our configuration consists of alkanes molecules strongly coupled to the silicon surfaces via covalent bonds. In phase 1 of AEMD, the two Si blocks are thermalized at high and low temperatures to form the hot and cold reservoirs. During phase 2 of AEMD, a transfer between reservoirs occurs until thermal equilibrium is reached. The transfer across the interface dominates the transient over heat conduction within the reservoirs. The value of the thermal interface conductance is in agreement with the experimental data obtained for analogous bonding cases between molecules and reservoirs. The dependence on the length of the thermal interface resistance features two contributions. One is constant (the resistance at the silicon/molecule interface), while the other varies linearly with the length of the molecular chains (diffusive transport). The corresponding value of the thermal conductivity agrees well with experiments.

Decane structure on a graphite surface with sodium dodecyl sulfate and betaine surfactant mixtures: A molecular dynamics study

Computer simulations of anionic and zwitterionic surfactants were carried out to study decane molecules arrangement on a graphite surface. Systems were constructed with different amount of decane molecules deposited on top of the graphite surface by forming two and four structured layers. Then, Sodium dodecyl sulfate (SDS) and two betaine surfactants, cocoamidopropyl (CAPB) and the N-Dodecyl-N,N-dimethyl- 3-ammomio-1-propanesulfonate (SB3-12), with their mixtures were used to investigate removal of the alkane molecules where different features were observed. Arrangement was analyzed in terms of density profiles and isotherm curves at different surfactant concentrations. It was observed that all surfactants promoted the formation of an additional decane layer suggesting they could produce detachment or removal from the graphite surface. The anionic surfactant present better removal from the surface than the betaine ones whereas in the case of the mixtures the SDS/CAPB one was slightly better than the SDS/SB3-12 one.

C[sbnd]H functionalization of alkanes, bactericidal and antiproliferative studies of a gold(III)-phenanthroline complex

This research article demonstrates the synthesis, structural characterization, CH functionalization, bactericidal activity and anti-proliferative studies of a mononuclear Au(III) complex, [Au(phen)Cl2]NO3 (1) [phen = 1,10-phenanthroline]. X-ray structural analysis of 1 reveals that the Au(III) complex crystallises in a monoclinic system with P21/c space group and adopts a perfect square planar geometry. The Au(III) complex has been evaluated as an efficient catalytic system towards CH activation of a series of alkane molecules in presence of TBHP. The catalyst exhibits moderate to excellent reactivity with good selectivity toward aldehyde or ketone when aryl alkanes are used, and ketone is formed when cyclic alkanes are tested. This catalytic reaction recommends the involvement of freely diffusing hydroxyl radicals rather than metal-based oxidant for this course of catalysis. The cytotoxic activity of the Au(III) complex have been investigated against the A549 human lung cancer cell line that induces apoptosis mode of cell death and loss of mitochondrial membrane potential are prominent characteristics as an anti cancer drug as well as antibacterial activity against Staphylococcus aureus.

Влияние модификации изотактического полипропилена на его транспортные свойства

Модификацией промышленных полимеров можно создать материалы с определенным набором эксплуатационных свойств. В данной работе проведена модификация структуры пленок изотактического полипропилена марки 01030 (ПП) путем обработки их жидкими алканами с увеличивающимся числом атомов углерода (гексан, гептан, н-нонан), которая приводит к увеличению сорбции и проницаемости воды в процессе первапорации. Эксперименты проводили по четырем маршрутам, как при изучении набухания ПП, так и при первапорации. Показано, что при проведении эксперимента по маршруту № 1 с увеличением числа атомов углерода в молекуле алкана степень набухания ПП растет, а величина плотности первапорационного потока падает. При модификации пленок ПП алканами по маршрутам №№ 3-4 происходит рост подвижности сегментов макромолекулярных цепей и увеличение расстояний между ними. При десорбции алканов образовавшаяся структура, по-видимому, сохраняется. После полного удаления ранее растворенного вещества (гексан и гептан) остаются «пустоты», через которые проникает вода (маршрут № 3) и наблюдается рост равновесной степени набухания ПП, а н-нонан полностью не удаляется, поэтому вода не может проникнуть в ПП. Аналогичное поведение наблюдается и при первапорации воды по маршруту №3. В случае маршрута № 4, когда десорбцию алканов не проводили, вода выталкивает алканы из полимера и проникает вслед за ними в пленку по образовавшимся каналам. С повышением температуры в изучаемом интервале плотность потока алканов возрастает (для гексана в 5 раз). Увеличение плотности потока воды после модификации происходит для всех изучаемых алканов, но она уменьшается при переходе от гексана к н-нонану. Показано, что в маршруте № 2 происходит поверхностная модификация пленки, в маршрутах № 3 и № 4 − объемная модификация. Таким образом, модификация полимерных пленок с использованием гидрофобных веществ приводит к увеличению сорбции и проницаемости гидрофильных веществ (воды).

Selective Adsorption of C6, C8, and C10 Linear α-Olefins from Binary Liquid-Phase Olefin/Paraffin Mixtures Using Zeolite Adsorbents: Experiment and Simulations

The adsorption separation of gaseous olefin/paraffin using porous materials has been extensively studied from both experimental and molecular simulation perspectives, while the adsorption separation of liquid-phase olefin/paraffin has been much less studied. One of the most important reasons for this is that it is difficult to measure the actual adsorption capacity of liquid-phase adsorption separation directly through experiments, and the simulation results of most studies are compared to gas-phase measurements. In this paper, the selective adsorption of linear α-olefins from three binary liquid-phase olefin/paraffin mixtures, 1-hexene/n-hexane (C6), 1-octene/n-octane (C8), and 1-decene/n-decane (C10), by zeolite adsorbents was systematically investigated using batch adsorption experiments and configurational-bias grand canonical Monte Carlo (CB-GCMC) simulations. In the batch experiments, based on the liquid-phase measurement method of the actual adsorption capacity that we developed, a modified commercial 5A zeolite with a relatively large pore volume and surface area was used for adsorption. The results showed that the modified 5A zeolite had larger actual adsorption capacities for C6 and C8 linear α-olefins, which increased by 51% and 56%, respectively, than the standard 5A zeolite that was used in our previous work. The adsorption isotherms of C6, C8, and C10 in the 5A and 13X zeolites were calculated by CB-GCMC simulations. The visualized results of density profiles showed that the olefin molecules were densely distributed at the edge of the zeolite cages and that there were cases where a single molecule was adsorbed over two adjacent cages. The good agreement between the experimental and simulated data proves the completeness of the liquid-phase measurement method that we developed and the reliability of the simulation prediction.