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The separation of linear from branched hydrocarbons is often required in many situations. There are several methods through which they can be separated but none provides a very high degree of purity or works without considerable expenditure of energy. Recently, a novel method was proposed to separate a mixture of neopentane and n-pentane. The present work demonstrates that the method can be used for separating other mixtures of hydrocarbons as well, by attempting the separation of a mixture of 2,2-dimethyl butane and n-pentane. Intermolecular interaction potentials have been modified to reproduce the experimental heat of adsorption and diffusivity of 2,2-dimethyl butane and n-pentane in zeolite NaY. The method involves choosing the correct host zeolite or other porous solids and introducing hot zones at appropriate positions. This result drives both the components to the opposite ends of the zeolite column, thus leading to separation. The achieved separation factors are much higher than what can be obtained with the help of existing methods. Different properties have been computed to understand the process involved in the separation of the mixture. The approach employed here uses very little energy for separation, making it suitable for green chemistry.

The intramolecular ¹H NMR dipole–dipole relaxation of molecular fluids has traditionally been interpreted within the Bloembergen–Purcell–Pound (BPP) theory of NMR intramolecular relaxation. The BPP theory draws upon Debye’s theory for describing the rotational diffusion of the ¹H–¹H pair and predicts a monoexponential decay of the ¹H–¹H dipole–dipole autocorrelation function between distinct spin pairs. Using molecular dynamics (MD) simulations, we show that for both n-heptane and water this is not the case. In particular, the autocorrelation function of individual ¹H–¹H intramolecular pairs itself evinces a rich stretched-exponential behavior, implying a distribution in rotational correlation times. However, for the high-symmetry molecule neopentane, the individual ¹H–¹H intramolecular pairs do conform to the BPP description, suggesting an important role of molecular symmetry in aiding agreement with the BPP model. The intermolecular autocorrelation functions for n-heptane, water, and neopentane also do not admit a monoexponential behavior of individual ¹H–¹H intermolecular pairs at distinct initial separations. We suggest expanding the autocorrelation function in terms of modes, provisionally termed molecular modes, that do have an exponential relaxation behavior. With care, the resulting Fredholm integral equation of the first kind can be inverted to recover the probability distribution of the molecular modes. The advantages and limitations of this approach are noted.

The effects of coarse-graining on the thermodynamic properties of molecular liquids are studied by computing the standard molar entropies of chloroform, 1,4-dioxane and neopentane using the two-pha...

A detailed knowledge on hydrophobic association and solvation is crucial in understanding the con-formational stability of proteins and polymers in osmolyte solutions. Using Molecular Dynamics simulations, we found the hydrophobic association using neopentane molecules is greater in mixed urea-TMAO-water solution in comparison to that in 8 M urea solution, in 4 M TMAO solution and in neat water. The neopentane association in urea solution is greater than that in TMAO solution or neat water. We find the association is even less in TMAO solution than pure water. From free ener-gy calculations, it is revealed that the neopentane sized cavity creation in mixed urea-TMAO-water is most unfavorable and that causes the highest hydrophobic association. The cavity formation in urea solution is either more unfavorable or comparable to that in TMAO solution. Importantly, it is found that the population of neopentane-neopentane contact pair and the free energy contribution for cavity formation step in TMAO solution are very sensitive towards the choice of TMAO force-fields. A careful construction of TMAO force-fields is important for studying hydrophobic associa-tion. Interestingly it is observed that the total solute-solvent dispersion interaction energy contribu-tion is always most favorable in mixed urea-TMAO-water. The magnitude of this interaction energy is greater in urea solution relative to TMAO solution for two different force-fields of TMAO, whereas the lowest value is obtained in pure water. It is revealed that the extent of the overall hy-drophobic association in osmolyte solutions is mainly governed by the cavity creation step and it nullifies the contribution comes from the solute-solvent interaction contribution.

The pulse radiolysis of gaseous neopentane has been investigated in the absence and presence of electron scavengers (SF(6), CD(3)I, CCl(4)). Deuterium labeling experiments show that the stable product molecules can be accounted for by (a) radical combination reactions involving mainly CH(3) and H; (b) hydride ion transfer reactions involving C(2)H(3)(+), C(2)H(5)(+), and C(3)H(5)(+); (c) neutralization reactions of C(4)H(9)(+) and C(5)H(11)(+); and (d) unimolecular dissociation of the parent ion (C(5)H(12)(+)) and of electronically excited neopentane. Neutralization of the t-C(4)H(9)(+) ion, which is the major positive ion in the system occurs as follows: (a) t-C(4)H(9)(+) + e → i-C(4)H(8) + H and (b) t-C(4)H(9)(+) + e → 2CH(3) + C(3)H(6). It is shown that C(5)H(11)(+) produced in hydride ion transfer reaction C(n)H(m)(+) + neo-C(5)H(12) → C(n)H(m+1) + C(5)H(11)(+) (where C(n)H(m)(+) = C(2)H(3)(+), C(2)H(5)(+), and C(3)H(5)(+)) rearranges to the CH(3)C(+)(CH(3))CH(2)CH(3) structure prior to neutralization. A detailed accounting of all products produced in the unimolecular and bimolecular reactions led to the conclusion that the ratio of neutral electronically excited molecules to parent ions (N(ex)/N(+)) is 0.28.

The rate constants of ethynyl (C2H) radical reaction with isobutane (kiso) and neopentane (kneo) were calculated for the first time using canonical variational transition state theory (CVT) with small-curvature tunneling (SCT) in the temperature range of 150–5000 K. The geometries and frequencies of all the stationary points were calculated at the M06-2X/Aug-cc-pVTZ level of theory. Thermodynamics (ΔH°298 and ΔG°298) results govern that the title reactions are highly exothermic and spontaneous in nature. The rate constants obtained over the temperature range of 150–300 K were used to derive the modified Arrhenius expressions: kiso = 6.84 × 10–19 T2.5 exp[1496/T] and kneo = 1.72 × 10–17 T2.0 exp[938/T] cm3 molecule−1 s−1. Branching ratio calculation for the reaction of C2H radical with isobutane shows that the tertiary-H abstraction channel is dominant (> 95%) over the complete temperature range.

The extremely large latent heat exchanged in phase transitions involving strong molecular orientational disordering has recently led to the proposal of plastic crystals as a feasible solution for solid-state barocaloric eco-friendly cooling technologies. Here we determine the reversible barocaloric response of four plastic crystals derived from neopentane [C(CH3)4]: (NH2)C(CH2OH)3 (TRIS for short), (NH2)(CH3) C(CH2OH)2 (AMP), (CH3)C(CH2OH)3 (PG) and (CH3)3C(CH2OH) (NPA). All of them display colossal entropy changes at their ordered-plastic phase transition, which is a primal requirement for competitive barocaloric materials. However, we show that it is also important to verify that the large barocaloric effects can be achieved using pressures that, while being moderate, are large enough to overcome the pressure-dependent hysteresis. From this quantity and using the quasi-direct method, we determine the minimum pressure needed to achieve reversible barocaloric effects, prev, for each compound. Specifically, we find a small and moderate prev for PG and NPA, respectively, which therefore display colossal reversible barocaloric effects comparable to harmful fluids used in current refrigerators and thus confirm the potential of plastic crystals as excellent alternatives. Instead, in TRIS and AMP, the obtained prev is excessive to yield reversible barocaloric effects useful for cyclic applications.

Chromium(VI) dialkyls are remarkably acidic, yielding a new set of anionic chromium alkylidenes upon deprotonation with KN(TMS)2. We describe the characterization of three anionic chromium alkylidenes of the type [(ArN)2Cr(=CHR)(CH2R]- (R = tBu, SiMe3, Ph; Ar = 2,6-diisopropylphenyl). NEt4[(ArN)2Cr(=CHSiMe3)(CH2SiMe3)] has been structurally characterized by X-ray diffraction. We have also studied the C-H activation of cyclohexane effected by the transient neopentylidene (ArN)2Cr(=CHCMe3). This reaction generated a tri-nuclear chromium(IV) complex, namely ‘[Cr(NAr)2]3’, as well as the two organic products cyclohexene and neopentane. A probable intermediate in this reaction could be trapped by PPh3 to form (ArN)2Cr(PPh3)2. The latter undergoes ligand substitution reactions with ethylene and CO to produce p-acid complexes of tetravalent chromium.

Palladium-containing catalyst based on binder-free granular sulfated zirconium oxide for n-butane isomerization has been investigated. It has been found that Pd content of 0.2–1.0 wt % slightly influences textural characteristics and other physicochemical properties of bifunctional catalysts; however, it determines their activity and selectivity in the reaction studied, with the optimal palladium content being 0.5 wt %. Parameters of the isomerization process have been studied depending on the composition of industrial n-butane fractions. It has been shown that impurities of isobutane, propane, neopentane, isopentane and pentane in an amount of no more than 2% do not exert a effect on isobutane production; nonetheless, the conversion of n-butane and selectivity for isobutane both increase when more pure n-butane fractions are used. It has been found that the process for isobutane production by isomerization of the n-butane fraction under the optimal conditions at H2 /n-C4 = 0.1 and 140–150°C makes it possible to obtain a high isobutane yield (up to 52 wt %) and avoid the undue formation of С1–С3 alkanes.

The understanding of major zeolite applications is partially based on diffusion of molecules inside or outside microporous networks. However, it is still a challenge to measure such phenomena. The diffusion ordered nuclear magnetic resonance spectroscopy (DOSY) technique has been reported to measure a probe molecule's diffusion inside porous solids. Pulsed-field gradient (PFG)-NMR has been used herein to measure the self-diffusivity of different probe molecules, such as neopentane, benzene, toluene and 1-dodecene with increasing dynamic diameter, respectively, on a series of H-ZSM-5 zeolites. The latter materials exhibit different crystal sizes, Si/Al ratios and the presence (or absence) of crystalline defects. In addition, shaped zeolite bodies representing industrial catalysts were compared with the afore-mentioned samples.

International audience; The oxidation of neopentane was studied in jet-stirred reactors at atmospheric pressure over a temperature range 500–850 K and ϕ = 0.5. The products were analyzed with chromatographic, mass spectrometric, and photoelectron spectroscopic setups complemented with theoretical calculations. This combination provides a comparison of photo-ionization mass spectrometry and gas chromatography for the quantification of mole fractions and highlights the relevant differences between them, while mass-tagged photoelectron spectroscopy sheds light onto the isomeric distribution. The new data and corresponding analyses are expected to provide valuable guidance for an extension of the kinetic model and the choice of experimental methods. The main first and second O2-addition products were observed in agreement with the literature (e.g., 3,3-dimethyloxetane, acetone, isobutene, and γ-ketohydroperoxide). The simulated mole fractions of the products using a literature kinetic model were compared to the experimental results. Even though the kinetic model has been validated previously, significant discrepancies between the measured and simulated mole fractions of 2-methylpropanal and methacrolein, two fuel-specific low-temperature oxidation products, were found. Furthermore, some experimentally observed species related to γ-ketohydroperoxide decomposition were not predicted indicating that the model is incomplete. The detection of 2-methylpropanal and formic acid highlighted the importance of the Korcek-type pathway.

We reported the characteristics of hydrate-bound hydrocarbons in lake-bottom sediments at the Kedr mud volcano in Lake Baikal. Twenty hydrate-bearing sediment cores were retrieved, and methane-stable isotopes of hydrate-bound gases (δ13C and δ2H of − 47.8‰ to − 44.0‰ V-PDB and − 280.5‰ to − 272.8‰ V-SMOW, respectively) indicated their thermogenic origin accompanied with secondary microbial methane. Powder X-ray diffraction patterns of the crystals and molecular composition of the hydrate-bound gases suggested that structure II crystals showed a high concentration of ethane (around 14% of hydrate-bound hydrocarbons), whereas structure I crystals showed a relatively low concentration of ethane (2–5% of hydrate-bound hydrocarbons). These different crystallographic structures comprised complicated layers in the sub-lacustrine sediment, suggesting that the gas hydrates partly dissociate, concentrate ethane and form structure II crystals. We concluded that a high concentration of thermogenic ethane primarily controls the crystallographic structure of gas hydrates and that propane, iso-butane (2-methylpropane) and neopentane (2,2-dimethylpropane) are encaged into crystals in the re-crystallisation process.

A radically different approach for separation of molecular mixtures is proposed. A judicious combination of levitation effect observed in zeolites with a counter intuitive Landauer blow torch effect provides driving forces for the two components of the mixture to move in opposite directions. Using nonequilibrium Monte Carlo simulations, we illustrate the efficacy of the method for separating real mixtures of both linear $n$-pentane and its branched isomer, neopentane, and linear $n$-hexane and its branched isomer, 2,2-dimethylbutane. The method yields several orders of magnitude improvement in separation factor and relative energy efficiency by using submicron zeolite column. The extremely high purity of the resulting single components makes the method best suited for green chemistry.

This work aims at the calculation of various inelastic cross sections for three pentane isomers, namely normal pentane, isopentane and neopentane. The direct ionisation, positronium formation, tota...

A highly promising class of three-dimensional polyaromatic hydrocarbons comprises the centropolyindanes. The characteristic feature of these compounds is the mutual fusion of several molecules of indane along the saturated C-C bonds of their cyclopentane rings. Among the polycyclic aromatic hydrocarbons, the centropolyindanes are special because of the saturated core of sp(3)-hybridised carbon atoms embedded in a three-dimensional environment of aromatic building blocks. While the centropolyindanes and their numerous derivatives have been studied in detail by NMR spectroscopy, mass spectrometry and X-ray diffraction, investigation of their vibrational features, and especially those of the neopentane core present in most cases, have not been performed so far. In the present paper, we report the first systematic study of a set of centropolyindanes by vibrational spectroscopy, using inelastic neutron scattering (INS), infrared and Raman spectroscopies.

High resolution infrared absorption spectra of neopentane (2,2-dimethylpropane, C5H12) have been recorded in the mid-infrared region at room temperature and 232 K. Neopentane is a spherical top with Td symmetry. The high symmetry and low temperature allow for detailed comparison of theory and experiment for the analysis of the fundamental vibrations. Four strong bands with characteristic rotational structure of t2 modes were observed at 1257.6, 1369.4, 1472.5, and 1489.0 cm-1, and a fifth very weak band was found near 924.2 cm-1. Quantum chemical calculations (B3LYP/6-311++(d,p)/VPT2 and harmonic CCSD(T)-pVTZ) were carried out in both normal and local mode representations to help with the vibrational assignments and elucidate the couplings. The local mode representation combined with the experimental observations highlights the important potential couplings between neighboring methyl groups and their influence on observed transitions. We have analyzed spectral regions where the models failed to provide agreement and have identified those couplings responsible for the differences.

The GERG-2008 equation of state is the approved ISO standard (ISO 20765-2) for the calculation of thermophysical properties of natural gas mixtures. The composition of natural gas can vary considerably due to the diversity of origin. Further diversification was generated by adding hydrogen, biogas, or other non-conventional energy gases. In this work, high-precision experimental (p, ρ, T) data for two gravimetrically prepared synthetic natural gas mixtures are reported. One mixture resembled a conventional natural gas of 11 components (11 M) with a nominal mixture composition (amount-of-substance fraction) of 0.8845 for methane as the matrix compound with the other compounds being 0.005 for oxygen, 0.04 for nitrogen, 0.015 for carbon dioxide, 0.04 for ethane, 0.01 for propane, 0.002 each for n- and isobutane, and ultimately 0.0005 each for isopentane, n-pentane, and n-hexane. The other mixture was a 13-component hydrogen-enriched natural gas with a low calorific value featuring a nominal composition of 0.7885 for methane, 0.03 for hydrogen, 0.005 for helium, 0.12 for nitrogen, 0.04 for carbon dioxide, 0.0075 for ethane, 0.003 for propane, 0.002 each for n- and isobutane, and 0.0005 each for neopentane, isopentane, n-pentane, and n-hexane. Density measurements were performed in an isothermal operational mode at temperatures between 260 and 350 K and at pressures up to 20 MPa by using a single-sinker densimeter with magnetic suspension coupling. The data were compared with the corresponding densities calculated from both GERG-2008 and AGA8-DC92 equations of state to test their performance on real mixtures. The average absolute deviation from GERG-2008 (AGA8-DC92) is 0.027% (0.078%) for 11 M and 0.095% (0.062%) for the 13-component H2-enriched mixture, respectively. The corresponding maximum relative deviation from GERG-2008 (AGA8-DC92) amounts to 0.095% (0.127%) for 11 M and 0.291% (0.193%) for the H2-enriched mixture.

Effective and isotropic potentials of three hydrocarbon refrigerants were determined from an iterative inversion procedure, including ethylene (R1150), isobutane (R600a), and neopentane (R601b). By employing the inverted potentials, predictions of transport properties were performed with the aid of the kinetic theory of dilute gases. The viscosity coefficient, self-diffusion coefficient, and thermal diffusion factor of pure R1150, R600a, and R601b were presented over the temperature range from 273.15 K to 973.15 K at low density. Comparisons of the theoretically calculated values with the literature data were discussed. It is shown that the potentials obtained by the inversion scheme were able to predict accurate transport properties for these slightly polar ozone-safe hydrocarbon refrigerants.

We use first-principles calculations to explore the change of the separation properties of strained porous graphene membranes. Small to moderate lateral strain, biaxial (1% - 2%) or uniaxial (1% to 7%, depending on the direction), always increases the percolation barriers of the same passing molecules (e.g. methane, cyclopropane, neopentane) regardless of the pore size, shape and functionalization, when compared with their strain-free values. The pore size expansion under such strain is no match for the electronic structure redistribution, which leads to more rigid pore plane (against the out-of-pore-plane bending). Larger strain will eventually make the geometric enlargement dominant over the electronic effect and the barrier falls. The energy barrier in response to biaxial strain can rise by 0.2 - 0.3 eV, corresponding to a substantial drop of gas transport rate by three to five orders of magnitude. The barrier-to-strain response is highly anisotropic for uniaxial strain. Strain (6% - 7%) in the direction of the longest pore diameter can cause the barrier to rise even more by 0.3 - 0.4 eV (gas percolation rate slashes by five to seven orders of magnitude), which can effectively shut down the molecules’ percolation. Our results demonstrate that there is plenty space for strain engineering the separation performance of porous graphene membranes.

In the present article, electron scattering cross sections for n-pentane and its isomers, viz., isopentane (butane-2-methyl), and neopentane (propane-2-2-dimethyl) are reported. The presence of these molecules along with abundant energetic electrons in the atmosphere of Titan make it favorable for many scattering events. Hence, to study the physio-chemical processes taking place in this environment, the cross section data presented here are inevitable. In this work, the cross sections are calculated for a wide energy range. Elastic and momentum transfer cross sections are calculated using group additivity method implemented through spherical complex optical potential formalism, whereas the ionization cross sections are calculated employing the complex scattering potential ionization contribution method. Total cross section is the sum of elastic and ionization cross section. Present calculation includes geometric screening correction to alleviate the overestimation of cross section values arising due to the overlap of atomic electronic charge densities. A reasonable agreement was found between the present values and previous experimental and theoretical results, wherever available.

Single-layer membranes of porous graphene, graphyne derivatives (α/α2/β-graphyne), and porous boron nitride (BN) with similar pore sizes (approximately 8 × 6 Å) have been evaluated for separating pentane isomers using first-principles calculations. In spite of their slightly bigger pore sizes, graphyne derivatives only allow linear pentane molecules to go through their native pores, while in contrast porous graphene and BN membranes only block dibranched isomers, i.e., neopentane molecules. Analyses of the geometric changes reveal that the structural flexibility of the membrane determines the penetration barrier. During the penetration of molecules, rigid membranes like graphyne derivatives may exhibit similar distortion to flexible porous graphene and BN; however the energy increase for the former is twice that for the latter. More importantly, the passing molecules experience about two times geometry distortion and four times energy barrier increase when going through rigid membranes compared with flexible membranes. The more deformed passing molecule and the less deformed rigid membrane can result in a much higher penetration barrier. Our results show that the flexibility of porous BN is comparable to that of porous graphene while graphyne derivatives are much more rigid.

Direct (solute-water) and indirect (water-water) contributions to adsorption at an air-water interface are identified using the Widom potential distribution theorem and quantified using molecular dynamics simulations of a liquid water droplet containing either neopentane or iodide-like solutes with charges of 0 or ±1. The results are used to quantitatively compare direct and indirect energetic and entropic contributions to adsorption, as well as to critically test surface capillary wave, linear response (LR), and mean field (MF) predictions. The negative signs of the total adsorption energies and entropies of both the anionic and cationic solutes are found to result from indirect adsorption induced changes in water-water interactions, rather than from surface capillary wave perturbations, which are found to be asymmetric with respect to solute charge. The LR and MF approximations both accurately describe the adsorption of neutral (hydrophobic) solutes, while for ionic solutes the MF approximation is entirely inappropriate and LR predictions are qualitatively (but not quantitatively) accurate.

Tetrakis(2-pyridylmethyleneimino)neopentane (L) was designed to form a spiro-structure after complex formation, where L plays a role of a double tetradentate bridging ligand. The X-ray diffraction study of [Cu2L(CF3SO3)4] clarified that the molecular structure was topologically spiro but the two coordination basal planes were not orthogonal with the dihedral angle of 49.8(1)°. The χmT value of [Cu2L(CF3SO3)4] showed a small increase on cooling below 10 K, indicating the presence of ferromagnetic coupling. Fitting to a singlet–triplet model gave 2J/kB = +0.293(7) K. The density-functional-theory calculation of the [Cu2L]4+ core reproduced the ferromagnetic coupling. Furthermore, from another calculation after removal of the neopentyl skeleton, through-bond interaction is clarified to be major in the exchange mechanism. The intervening sp3-hybridized carbon atoms may be spin-polarized.

Catalysts prepared from industrial wastes rich in Fe, Ca, Si, and Al were used in catalytic upgrading of pyrolysis vapour derived from durian shell and their effect on product yield and properties were compared. With same silica-to-alumina ratio, catalyst prepared from oil palm ash (AS-OPA) with lower Fe and Ca contents gave higher liquid yield (8.32 wt%) with alcohols (28.90%), hydrocarbons (46.00%), and nitrogen-containing compounds (21.46%) while catalyst prepared from electric arc furnace slag (AS-EAF) with higher Fe and Ca contents produced lower liquid yield (50.21 wt%) with high amount of esters (25.80%) and hydrocarbons (72.82%). The presence of AS-OPA and AS-EAF catalysts enhanced deoxygenation degree of bio-oil to 81.13% and 85.49%, respectively. The catalytic performance of AS-EAF at different temperatures (400–600 °C) and AS-EAF/durian shell ratios (1:30, 2:30, 3:30) was investigated. Increasing catalytic temperature enhanced production of bio-oil, reduced oxygenates and enhanced formation of esters. The liquid yield and yield of esters decreased with increasing catalyst loading. Hydrocarbons (mainly neopentane) were the major chemical compounds found in bio-oil produced over AS-EAF. Besides that, AS-EAF showed good deoxygenation performance with highest selectivity of hydrocarbons at 500 °C and AS-EAF/durian shell ratio of 2:30. Catalytic fast pyrolysis of durian shell using waste-derived catalysts is an effective waste management strategy as the bio-oil produced can be a potential alternative source of energy or chemical feedstocks.

Understanding the fundamental forces such as hydrophobic interactions in a crowded intracellular environment is necessary to comprehensively decipher the mechanisms of protein folding and biomolecular self-assemblies. The widely accepted entropic depletion view of crowding effects primarily attributes biomolecular compaction to the solvent excluded volume effects exerted by the "inert" crowders, neglecting their soft interactions with the biomolecule. In this study, we examine the effects of chemical nature and soft attractive energy of crowders on the water-mediated hydrophobic interaction between two non-polar neopentane solutes using molecular dynamics simulations. The crowded environment is modeled using dipeptides composed of polar and non-polar amino acids of varying sizes. The results show that amongst the non-polar crowders, Leu2 strengthens the hydrophobic interactions significantly, whereas the polar and small-sized non-polar crowders do not show significant strengthening. Distinct underlying thermodynamic driving forces are illustrated where the small-sized crowders drive hydrophobic interaction via a classic entropic depletion effect and the bulky crowders strengthen it by preferential interaction with the solute. A crossover from energy-stabilized solvent-separated pair to entropy-stabilized contact pair state is observed in the case of bulky non-polar (Leu2) and polar (Lys2) crowders. The influence of solute-crowder energy in affecting the dehydration energy penalty is found to be crucial for determining the neopentane association. The findings demonstrate that along with the entropic (size) effects, the energetic effects also play a crucial role in determining hydrophobic association. The results can be extended and have implications in understanding the impact of protein crowding with varying chemistry in modulating the protein free energy landscapes.

A method for the separation of a mixture of n-pentane and neopentane using a nano-crystallite of zeolite Y is reported. This method judiciously combines two well-known, counter-intuitive phenomena, the levitation and the blowtorch effects. The result is that the two components are separated by being driven to the opposite ends of the zeolite column. The calculations are based on the non-equilibrium Monte Carlo method with moves from a region at one temperature to a region at another temperature. The necessary acceptance probability for such moves has been derived here on the basis of stationary solution of an inhomogeneous Fokker–Planck equation. Simulations have been carried out with a realistic and experimentally relevant Gaussian hot zone and also a square hot zone, both of which lead to very good separation. Simulations without the hot zones do not show any separation. The results are reported at a loading of 1 molecule per cage. The temperature of the hot zone is just ∼30 K higher than the ambient temperature. The separation factors of the order of 1017 are achieved using single crystals of zeolite, which are less than 1 μm long. The conditions for including the hot zone may be experimentally realizable in the future considering the rapid advances in nanoscale thermometry. The separation process is likely to be energetically more efficient by several orders of magnitude as compared to the existing methods of separation, making the method very green.

We propose a ‘composite sphere’ model for molecules of tetrahedral symmetry. In particular, we choose as an example the hydrocarbon neopentane. We disassemble the molecule into five moieties: four ...

The influence of the energy of low-voltage discharges in the liquid phase on the directions of fragmentation of toluene is studied. The discharges were generated by a 60 V DC source with a capacitor of 90 μF, 20090 μF, and 40090 μF. Fragmentation of toluene leads to the formation of carbon structures on the surface of graphite electrodes and in a liquid medium. It was revealed that an increase in the power of electric discharges leads to the growth of carbon structures on the surface of electrodes, reduces the output of the gas phase and finely dispersed carbon structures. The morphology and composition of solid phase products were determined by scanning electron microscopy and energy dispersive X-ray spectroscopy. Nanosized carbon structures are obtained in the form of aggregates - carbon nanohorns, which actively adsorb oxygen (content 0.9-3.6 at%). The composition of gaseous products was determined by gas chromatography. It was revealed that with an increase in the power of electric discharges, the hydrogen content slightly increases from 74.8 to 75.15 mol%, methane from 5.86 to 6.55 mol%, neopentane from 0.02 to 0.55 mol%. At the same time, the acetylene content in gaseous products decreases from 18.14 to 16.36 mol%.

We demonstrate by molecular dynamics simulation that co-non-solvency manifests itself in the solvent-induced interaction between three hydrophobes, methane, propane and neopentane, in methanol-water mixtures. Decomposition of the potential of mean force, based on the potential distribution theorem, clearly shows that the solute-solvent entropic change is responsible for stabilizing the aggregation of these hydrophobic molecules. Furthermore, we show that the entropic change pertains to the excluded volume effect.

This study explores the autoignition characteristics of three C5 isomers, namely n -pentane, 2-methylbutane ( iso -pentane) and 2,2-dimethylpropane ( neo -pentane). These measurements are intended to enhance understanding of C5 autoignition chemistry, and provide experimental data to guide improvements to a general hydrocarbon oxidation mechanism. To that end, the autoignition behavior of these three C5 isomers was investigated in a modified CFR engine at an intake temperature of 120 °C and a fixed engine speed of 600 rpm to determine the critical compression ratio (CCR) at which hot ignition occurs. To find the critical compression ratio, the engine compression ratio (CR) was gradually increased to the point where CO in the engine exhaust rapidly decreased and significant high temperature heat release was observed, while holding equivalence ratio constant. Fundamental ignition behaviors such as the CCR and the calculated percentage of low temperature heat release (%LTHR) demonstrate the impact of chain length and methyl substitutions on ignition reactivity. The %LTHR shows a stronger two stage heat release for n- pentane than for neo- pentane observed at critical ignition conditions. In contrast, single stage heat release is observed for iso- pentane, leading to the weakest overall oxidation reactivity of the three isomers. Key reaction paths forming conjugate alkenes and C 5 oxygenated species control the autoignition reactivity of n- pentane and iso- pentane within the low temperature and NTC regimes. However, neo- pentane forms no conjugate alkene due to its unique molecular structure, and instead produces iso -butene to retard its oxidation.

The effects of urea and taurine osmolytes on the hydrophobic interactions of methane and neopentane have been studied using molecular dynamics simulations. From the study of potential of mean force, it is observed that both urea and taurine enhance the association of methane and neopentane. The hydrophobic association of methane molecules is stabilized by entropy and destabilized by enthalpy in the mixtures of osmolytes at contact minima while the hydrophobic association of neopentane is stabilized by enthalpy and entropy. In these mixtures, hydrophobic solvation of methane molecules is enthalpy favorable and entropy unfavorable at SSM. The hydrophobic solvation of neopentane is stabilized by entropy and enthalpy. The study of radial distribution functions (RDFs), running coordination numbers, excess coordination numbers of water, urea and taurine molecules around hydrophobic molecules shows that methane shows salting-out (less soluble) and neopentane shows salting-in (more soluble) behavior in aqueous-urea. Methane and neopentane show salting-in behavior in aqueous-taurine solution because of preferential solvation by taurine. Salting-out behavior of methane has been observed in water-urea-taurine mixture. Neopentane shows salting-in behavior in aqueous solution of urea and taurine because of preferential binding with urea. These observations are supported by solvation free energies and spatial density maps.

Previously published experimental viscosity data at low density, originally obtained using all-quartz oscillating-disk viscometers for 12 gases and vapors in the temperature range between 297 K and 691 K, were re-evaluated after an improved re-calibration. The relative combined expanded (k = 2) uncertainty of the re-evaluated data is 0.2% near room temperature and increases to 0.3% at higher temperatures. The re-evaluated data for sulfur hexafluoride, methanol, n-pentane, n-hexane, n-heptane, neopentane, cyclohexane, benzene, toluene, p-xylene, phenol, and triethylamine were arranged in approximately isothermal groups and converted into quasi-isothermal viscosity data using a first-order Taylor series in temperature. Then, they were evaluated by means of a series expansion truncated at first order to obtain the zero-density and initial density viscosity coefficients, η(0) and η(1). When the number of isothermal data or their quality was not adequate, the Rainwater–Friend theory for the initial density dependence of the viscosity was additionally used to derive η(0) and η(1) values. Finally, reliable η(0) and η(1) values, preferably obtained from the isotherms, were recommended as reference values for the 12 gases and vapors in the measured temperature range to be applied when generating any new viscosity formulation.

In order to investigate the decomposition mechanism of hydrocarbons, pyrolysis processes of 11 typical hydrocarbons (isobutane, isopentane, isohexane, n-butane, n-pentane, n-hexane, cyclobutane, cyclopentane, cyclohexane, benzene and toluene) are performed by using ReaxFF MD and DFT method. The results show that the initial pyrolysis reactions of these hydrocarbons can be divided into two types: homolytic cleavage of C–H bond and C–C bond. The bond dissociation energies of C–H bonds are higher than that of C–C bonds in these hydrocarbons except for toluene. The thermal decomposition rates of branched-chain hydrocarbons are faster than that of straight-chain hydrocarbons. The thermal decomposition rates of chain hydrocarbons gradually increase with the increases of C atom number. The main product molecules of hydrocarbon pyrolysis are H2, CH4, C2H2 and C2H4. The apparent activation energies of 4 hydrocarbons (n-pentane, isohexane, neopentane and cyclopentane) pyrolysis are calculated by the kinetic analysis. In further reactions, CH3, C2H5 and H radicals are collided with hydrocarbons to undergo H-abstraction reactions. The energy barriers of H-abstraction reactions are calculated by DFT.

The paper presents the results of studies on a mesoscopic self-assembling occurring in liquid state of hydrogen-bonded n-, sec-, and tert- butanols. In the first part of the paper it was revealed (basing on the literature data) that an unexpectedly high melting point of tert-butanol does not result from some extraordinary way of intermolecular clustering in that alcohol, but from an exceptional packing of its globular-like molecules. The conclusion arises from a similar behavior of neopentane – the non-polar analogue of tert-butanol. Our results of the static dielectric studies on butanol isomers, in particular the Kirkwood correlation factor and the orientation entropy increment show that the spatial arrangement of the hydrocarbon moiety surrounding –OH group, essentially determines the structure of emerging molecular clusters. The form of clusters are evolving from a chain-like in n-butanol to a great variety of branched entities (including the cyclic ones) in tert-butanol.