Increasing Carbon Number Research Articles

New insights into the effect of molecular structure on stable intermediate formation during the pyrolysis of normal and branched alkanes – I: Multi-species time history measurements

Decarbonization of energy systems that drive the transportation industry is imperative for effectively mitigating global greenhouse gas emissions. In this pursuit, the transition towards scalable and sustainable fuels will play a key role. These fuels are predominantly composed of a diverse array of hydrocarbons spanning various molecular classes. To better understand the complex chemistry of such fuels, we studied the impact of molecular structure on the distribution of pyrolysis products of C6-C12 hydrocarbons, encompassing both normal and branched alkanes, in a shock tube at combustion-relevant temperatures. An extensive suite of laser absorption spectroscopy-based diagnostics was used to simultaneously measure the time histories of key intermediates (methane, ethylene, and larger alkenes) and fuel during the pyrolysis of ten neat hydrocarbons: n-hexane, n-heptane, n-octane, n-decane, n-dodecane, 2-methylhexane, 2-methylheptane, 2-methylnonane, triptane (or 2,2,3-trimethylbutane), and iso-octane (or 2,2,4-trimethylpentane). These experiments were conducted behind reflected shock waves using 2% Fuel/Argon test mixtures at a nominal pressure of 2 atm over the temperature range of 1100–1500 K. Conducting these experiments under similar test conditions facilitated the observation of clear trends in the distribution of intermediates formed during the pyrolysis of these fuels. The current paper delineates the experimental strategy and presents the measured mole fraction time histories of the stable intermediates. A companion paper [1] delves into the observed trends and effects of molecular structure, in particular, the impact of increasing carbon number and the impact of varying degree of branching on the yields of these pyrolysis products. We also investigate the impact of fuel blending and provide insights into the role of inter-coupling on the distribution of stable intermediates. The authors anticipate that the trends and findings presented in these two papers will guide the design of sustainable fuels and play a pivotal role in modeling the combustion chemistry of the next generation of fuels. To the best of our knowledge, this work presents the first systematic, detailed pyrolysis study of several transportation-relevant hydrocarbon fuels, involving simultaneous measurements of multiple species in a shock tube using laser absorption spectroscopy.

Characteristics of carbon isotopic composition of alkane gas in large gas fields in China

Exploration and development of large gas fields is an important way for a country to rapidly develop its natural gas industry. From 1991 to 2020, China discovered 68 new large gas fields, boosting its annual gas output to 1 925×108 m3 in 2020, making it the fourth largest gas-producing country in the world. Based on 1696 molecular components and carbon isotopic composition data of alkane gas in 70 large gas fields in China, the characteristics of carbon isotopic composition of alkane gas in large gas fields in China were obtained. The lightest and average values of δ13C1, δ13C2, δ13C3 and δ13C4 become heavier with increasing carbon number, while the heaviest values of δ13C1, δ13C2, δ13C3 and δ13C4 become lighter with increasing carbon number. The δ13C1 values of large gas fields in China range from −71.2‰ to −11.4‰ (specifically, from −71.2‰ to −56.4‰ for bacterial gas, from −54.4‰ to −21.6‰ for oil-related gas, from −49.3‰ to −18.9‰ for coal-derived gas, and from −35.6‰ to −11.4‰ for abiogenic gas). Based on these data, the δ13C1 chart of large gas fields in China was plotted. Moreover, the δ13C1 values of natural gas in China range from −107.1‰ to −8.9‰, specifically, from −107.1‰ to −55.1‰ for bacterial gas, from −54.4‰ to −21.6‰ for oil-related gas, from −49.3‰ to −13.3‰ for coal-derived gas, and from −36.2‰ to −8.9‰ for abiogenic gas. Based on these data, the δ13C1 chart of natural gas in China was plotted.

Mesomorphic behaviour and photoluminescence study of novel homologous series of Schiff’s base derived from cholesteryl carbonate and thiadiazole moiety

ABSTRACT The steroidal derivatives are widely known for their ability to display a variety of mesophases, including frustrated phases, depending on the structure of the steroidal skeleton and the substituents attached. In this report, thirteen new homologues Schiff’s base derivatives were synthesised by condensing 4-formyl phenyl cholesteryl carbonate with 5-(4’-n-alkoxy phenyl)-2-amino-1,3,4-thiadiazole. All the synthesised derivatives were characterised using elemental analysis, FT-IR, 1H-NMR and 13C-NMR. Optical texture studies were carried out using a polarising optical microscope in heating and cooling cycles to examine the liquid crystalline behaviour of the synthesised compounds. The derivatives displayed a variety of mesophases, including chiral nematic (N*), twist grain boundary-A (TGBA), smectic A (SmA) and chiral smectic C (SmC*) phases. The isotropic temperature of all the compounds within the homologous series seems to decline with the increase in carbon numbers on flexible chains. The thermal behaviour of all the synthesised compounds was checked using differential scanning calorimetry and thermogravimetric analysis. All the synthesised compounds are UV-active and exhibit photoluminescence in the blue emission band with a remarkable quantum yield. The radical-scavenging activity of the synthesised mesogenic derivatives was also evaluated using the DPPH assay.

Adsorption of per- and polyfluoroalkyl substances (PFAS) by ionic liquid-modified clays: Effect of clay composition and PFAS structure

Organically modified clays have been reported as a promising class of adsorbents for the treatment of per- and polyfluoroalkyl substances (PFAS), a group of emerging contaminants of widespread concerns. Here, we reported the development and evaluation of ionic liquid (IL)-modified clays prepared with various natural clays to explore the role of clay substrate in the adsorption of eight persistent perfluoroalkyl acids (PFAAs). Based on detailed adsorption isotherm study, we found that the adsorption capacities of PFAAs were closely related to the cation exchange capacities of the raw clays and correspondingly the IL loadings of the modified clays. Additionally, a positive correlation was observed between the adsorption affinity of PFAAs onto IL-modified clays and the octanol–water distribution coefficient (Dow) of PFAAs. Adsorption free energy analysis suggested that both electrostatic and hydrophobic interactions played important roles in the adsorption of PFAAs onto IL-modified clays. Although electrostatic interactions were more predominant, the contribution of hydrophobic interactions increased with the increasing carbon number of perfluoroalkyl moiety of PFAAs, resulting in more favorable adsorption of long-chain PFAAs than their short-chain homologs. The performance of IL-modified clays was further demonstrated for the removal of PFAA mixtures under environmentally relevant conditions. Overall, results of this work can provide important insights into guiding the design of organically modified clay adsorbents for PFAS treatment.

Spectrophotometric investigation on interactions of dye with surfactant in aqueous as well as alcoholic media

The interaction of the methyl orange (MO) dye with cetyltrimethylammonium bromide (CTAB) in propanol, butanol, and water was studied using spectrophotometry method. The NLREG approach was used to compute the distribution constant which is the lower as carbon number increases which resembles that value of distribution constant 0.07161476, 0.00060913, 0.00010865 is of water, 1-propanol, 1-butanol media respectively. The Benesi-Hilderbrand and Hashemi and Sun equations were also used to determine the binding constant (Kb) and Gibbs free energy of binding (ΔG°). As the alkyl chain lengthened, the ΔG° value shifted more negatively in comparison to water. The spontaneous nature of CTAB binding with MO was suggested by the negative value of ΔG°. As the concentration of CTAB in the water & alcoholic media increased, the MO absorption dramatically blue-shifted from 464 nm (water) to 440–450 nm (propanol, butanol). These findings showed that the alkyl chain plays a role in reducing absorbance. The MO absorbance in the water, 1-propanol or 1-butanol media decreased with increasing CTAB concentration (hyperchromic shift).

An alkylation route for developing novel liquid aviation fuels from α-pinene and mixed isobutane/isobutene

As a naturally rigid polycyclic biomass platform compound without oxygen, α-pinene has always been expected to develop high-energy–density fuel with both good combustion performance and cryogenic properties by increasing carbon number in a high atom economical way. The present work has explored the screening of alkylation blocks for α-pinene over H3PW12O40 (HPW). Here, a novel pinene-based blended fuel was prepared through cross-alkylation of α-pinene with mixed isobutane/isobutene, the common low-cost feedstock of alkylated gasoline. The reaction conditions including feed composition, reaction time, catalyst dosage, and reaction temperature were optimized. The mechanism of the hybrid alkylation process was further computationally speculated and experimentally verified. Produced liquid hydrocarbon products after hydrogenation and vacuum distillation possessed higher net heat of combustion and flash point than those of pinane, and lower freezing point and viscosity than those of dimers fuel from pinene. These favorable performances indicate that alkylated pinanes have promising potential as high-energy aviation fuel.

Self-diffusion coefficients of heavy water in low n-alkanes

The self-diffusion coefficients of D2O (i.e., heavy water or 2H2O) in eight n-alkanes at 298 K were investigated using 2H NMR diffusometry. D tended to decrease in the n-alkanes with increasing carbon number and be inversely proportional to the n-alkane viscosity to a fractional power. The hydrodynamic radius of D2O in the n-alkanes, calculated from Stokes-Einstein-Sutherland equation with stick boundary conditions, decreased with increasing n-alkane size and was smaller in the n-alkanes than in the bulk phase due to the absence of hydrogen bonds. This study provides fundamental data on the diffusion properties of water molecules dissolved in n-alkanes with applications to, for instance, molecular dynamics simulations or interpretation of Ostwald ripening.

Solubility study of hydrogen in direct coal liquefaction solvent based on quantitative structure–property relationships model

Direct coal liquefaction (DCL) is an important and effective method of converting coal into high-value-added chemicals and fuel oil. In DCL, heating the direct coal liquefaction solvent (DCLS) from low to high temperature and pre-hydrogenation of the DCLS are critical steps. Therefore, studying the dissolution of hydrogen in DCLS under liquefaction conditions gains importance. However, it is difficult to precisely determine hydrogen solubility only by experiments, especially under the actual DCL conditions. To address this issue, we developed a prediction model of hydrogen solubility in a single solvent based on the machine-learning quantitative structure–property relationship (ML-QSPR) methods. The results showed that the squared correlation coefficient R2 = 0.92 and root mean square error RMSE = 0.095, indicating the model’s good statistical performance. The external validation of the model also reveals excellent accuracy and predictive ability. Molecular polarization (α) is the main factor affecting the dissolution of hydrogen in DCLS. The hydrogen solubility in acyclic alkanes increases with increasing carbon number. Whereas in polycyclic aromatics, it decreases with increasing ring number, and in hydrogenated aromatics, it increases with hydrogenation degree. This work provides a new reference for the selection and proportioning of DCLS, i.e., a solvent with higher hydrogen solubility can be added to provide active hydrogen for the reaction and thus reduce the hydrogen pressure. Besides, it brings important insight into the theoretical significance and practical value of the DCL.

A year-round observation of δ13C of dicarboxylic acids and related compounds in fine aerosols: Implications from Central European background site

Isotopic analysis of specific compounds in aerosols can be a useful tool when studying atmospheric processes. Here, we present the results of stable carbon isotope ratio (δ13C) measurements performed on a one-year set (n = 96, Sep. 2013–Aug. 2014) of dicarboxylic acids and related compounds in PM1 at a rural Central European background site, Košetice (Czech Republic).The most 13C enriched acid was oxalic (C2, annual average = −16.6 ± 5.0‰) followed by malonic (C3, avg. = −19.9 ± 6.6‰) and succinic (C4, avg. = −21.3 ± 4.6‰) acids. Thus, δ13C values decreased with an increase in carbon numbers. Azelaic acid (C9, avg. = −27.2 ± 3.6‰) was found to be the least 13C enriched.A comparison of δ13C of dicarboxylic acids from other background sites, especially in Asia, shows similar values to those from the European site. This comparison also showed that C2 is more 13C enriched at background sites than at urban ones. In general, we did not observe significant seasonal differences in δ13C values of dicarboxylic acids at the Central European station. We observed statistically significant differences (p value < 0.05) between winter and summer δ13C values solely for C4, glyoxylic acid (ωC2), glutaric acid (C5) and suberic acid (C8).The only significant correlations between δ13C of C2 and δ13C of C3 were found in spring and summer, suggesting that the oxidation of C3 to C2 is significant in these months with a strong contribution from biogenic aerosols. The strongest season-independent annual correlation was observed in δ13C values between C2 and C4, the two dominant dicarboxylic acids. Therefore, C4 appears to be the main intermediate precursor of C2 throughout the whole year.

Multitunable LCST and UCST Behaviors of Y-Junction-Bearing Polyacrylamides

Rational design of thermoresponsive polymers allows facile control over LCST/UCST and nano-object shapes. Despite tremendous progress, it remains a challenge to monitor chain conformations as the solvent isotope affects types of phase transitions. This study aims at addressing the challenge by construction of thermoresponsive Y-junction-bearing polyacrylamides with nontraditional intrinsic luminescence. With an increasing carbon number of substituents connecting with ester groups (x = 1, 2, 3, 4, 6, 8, 10, and 12), copolymers transform from hydrophilic (x = 1) to LCST (x = 2) and dual LCST/UCST (x ≥ 3) in H2O, while no UCST is available in D2O due to more stable amide–solvent hydrogen bonding and strengthened intra-/intermolecular interactions. Meanwhile, copolymer aqueous solutions can exhibit substituent/pH-dependent evolution orders of single, dual, and triple phase transitions, and asymmetric V-shaped evolution of LCST/UCST values with increasing pH is usually observed. Although 1H NMR analysis can only reveal the solvation status of subunits in the LCST region, fluorescence analysis allows to elucidate intra-/intermolecular hydrogen bonding interactions in LCST/UCST regions. Thermoinduced self-assembly in water renders sphere-to-nanocapsule-to-lamella-to-nanocapsule transitions. These important findings provide us with considerable insight into hydrogen bonding-related UCST formation by rational macromolecular design. Our study may open new avenues for regulating phase transitions and exploring solvent isotope effects.

Microemulsion and interfacial properties of anionic/nonionic surfactant mixtures based on sulfonate surfactants: The influence of alcohol

The influence of alcohols on the microemulsion and interfacial properties of sulfonate and nonionic surfactant mixtures (LAS-IPA/AEO9 mixture) were explored. Surface properties and interaction parameters were investigated to determine the optimum molar ratio of the LAS-IPA to AEO9, and the subsequent experimental studies in this paper were based on the system of mixtures (nLAS-IPA: nAEO9 (4:6)). The microemulsion phase behaviors of LAS-IPA / AEO9 / alcohol / n-decane / water were investigated by constructing a pseudo-ternary phase diagram. Results suggest that the microemulsion systems with n-butanol and n-pentanol as cosurfactants behave have optimal solubilization capacity when the corresponding alcohol to mixed surfactant (Km value) mass ratios are 1:1 and 1:1 ∼ 1:2, respectively. The solubilization capacity of the two systems reached their maximum in the temperature range of 35 °C–40 °C. The hydrodynamic diameters of microemulsion were determined by employing dynamic light scattering (DLS), and the average hydrodynamic diameters of microemulsion increased with the carbon number of alcohol, which ranges from 12 nm to 21 nm. Moreover, the equilibrium oil–water interfacial tension, the dynamic adsorption mechanism, and the dilational viscoelasticity of the oil–water interfacial film were studied using spinning-drop method and drop shape analysis, respectively. The results shows that equilibrium oil–water interfacial tension decreased with increased carbon number of the regular alcohol in the system. However, the decrease of interfacial tension with decreased Km is not significant when the carbon numbers of regular alcohol are 5 and 6. At the initial stage, diffusion-controlled adsorption processes were followed with n-propanol and n-butanol as cosurfactants when the Km values were 1:2, but systems of the other two cosurfactants yielded mixed kinetics-diffusion control. The dilatational modulus of oil–water interfacial film increased with the carbon number increase in regular alcohol or the decreased Km value. The contact angles of n-butanol based microemulsion system at the hydrophilic interface and the lipophilic interface reached 20° and 18°, which had excellent bi-phasic wettability property. At the same time, the oil film removal efficiency of the n-butanol based microemulsion was the highest, which was close to 100 % at 24 h.

Impact of lighter alkanes on the formation and dissociation kinetics of methane hydrate in oil-in-water dispersions relevant for flow assurance

Various crude oil fractions (saturates, aromatics, resins, and asphaltene) affect the hydrate formation cumulatively during the multiphase phase flow in offshore flowlines. This study investigates the impact of chain length of saturated hydrocarbons (nC5, nC6, nC7, and nC10) on methane hydrate formation and dissociation kinetics in oil-in-water dispersions at 275.15 K and 8 MPa. Sodium dodecyl sulfate (SDS) has been added (at 0, 500, 1000, and 1500 ppm concentration) to mimic the natural surfactants in the crude oil. Methane hydrate formation kinetics without surfactant does not correlate well with methane solubility trend in liquid alkanes (this study) due to narrow methane solubility difference along with poorly dispersed oil droplets without surfactant and stochastic hydrate induction behaviour. Increased SDS concentration (up to ∼1000 ppm) enhances the hydrate formation during initial stages due to enhanced oil–water interface following a decrease for higher concentration (∼1500 ppm) due to possible disruptions in the structure of local water by the hydrophilic surfactant part. At fixed surfactant concentration (∼1000 ppm), the hydrate formation is enhanced with increasing carbon number (nC6 < nC7 < nC10) during initial stages (∼10 h) due to lower methane solubility (increased methane availability in water) along with synergistic mechanism of alkane and SDS surfactant, before achieving similar formation kinetics during later stages. During dissociation, the gas release has been observably delayed at higher concentrations (∼1500 ppm) compared to lower (∼1000 ppm and below), possibly due to hydrate crystals trapping by surfactant molecules and methane adsorption on the hydrophobic surfactant part. A faster gas release has also been observed for systems with higher alkane at fixed surfactant concentration, possibly aided by lower methane solubility upon gaining enough thermal energy.

Complementary Mass Spectral Analysis of Isomeric O-bearing Organic Compounds and Fragmentation Differences through Analog Techniques for Spaceborne Mass Spectrometers

Mass spectrometers on board spacecraft typically use either impact ionization or electron ionization (EI) as ion sources. Understanding the similarities and differences in the spectral signatures and fragmentation patterns produced by different techniques in mass spectrometry could elucidate the composition of organic compounds. Here we present a comparison between the mass spectra obtained through laser-induced liquid beam ion desorption (LILBID; proven to simulate the impact ionization mass spectra of ice grains) and EI mass spectra of pairs of low-mass, isomeric aldehydes and ketones. Our comparison confirms that EI produces more fragmentation of carbonyl compounds, particularly aldehydes, than LILBID. We find protonated molecular ions [M+H]+ in LILBID but molecular ions [M]+ in EI spectra. From the evaluated species, LILBID generally produces oxygen-carrying fragment ions (e.g., [CHO]+ and [C2H3O]+) in the mass ranges 26–30 and 39–44 u, while in EI, most ions in these ranges correspond to hydrocarbon fragments. The LILBID spectra additionally show mostly protonated oxygen-bearing fragments [CH3O]+ and [C2H5O]+ at m/z 31 and 45, less commonly observed in EI spectra. We observe a decrease in the relative intensities of cation fragment mass lines between m/z 26 and 33 and an increase between m/z 39 and 45, with an increasing carbon number for ketones and aldehydes with LILBID and EI, respectively. Our study provides a basis for complementary compositional analysis to identify the structural properties of organic species in a space environment using different spaceborne mass spectrometers (e.g., SUrface Dust Analyzer and MAss Spectrometer for Planetary EXploration) on board NASA’s future Europa Clipper space mission.

Assessment of the Intestinal Absorption of Higher Olefins by the Everted Gut Sac Model in Combination with In Silico New Approach Methodologies.

To reduce the number of animals and studies needed to fulfill the information requirements as required by Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) (EC no. 1907/2006), a read-across approach was used to support approximately 30 higher olefins. This study aimed to assess the absorption potential of higher olefins through the gut wall as the experimentally determined bioavailability which would strengthen the read-across hypothesis and justification, reducing the need for toxicity studies on all of the higher olefins. The absorption potential of a series of higher olefins (carbon range from 6 to 28, with five configurations of the double bond) was determined in the in vitro everted rat small intestinal sac model and subsequently ranked. In addition, in silico approaches were applied to predict the reactivity, lipophilicity, and permeability of higher olefins. In the in vitro model, everted sacs were incubated in “fed-state simulated small intestinal fluid” saturated with individual higher olefins. The sac contents were then collected, extracted, and analyzed for olefin content using gas chromatography with a flame ionization detector. The C6 to C10 molecules were readily absorbed into the intestinal sacs. Marked inter-compound differences were observed, with the amount of absorption generally decreasing with the increase in carbon number. Higher olefins with ≥C14 carbons were either not absorbed or very poorly absorbed. In the reactivity simulation study, the reactivity is well described by the position of the double bond rather than the number of carbon atoms. In the lipophilicity and permeability analysis, both parameter descriptors depend mainly on the number of carbon atoms and less on the position of the double bond. In conclusion, these new approach methodologies provide supporting information on any trends or breakpoints in intestinal uptake and a hazard matrix based on carbon number and position of the double bond. This matrix will further assist in the selection of substances for inclusion in the mammalian toxicity testing programme.

Treatment of naphthenic acids in oil sands process-affected waters with a surface flow treatment wetland: mass removal, half-life, and toxicity-reduction

This study is the first to investigate the removal of naphthenic acids in a full-scale constructed wetland within the Alberta Oil Sands region. The average mass-removal efficiency for all O2-naphthenic acids measured in three separate deployments in the wetland ranged from 7.5% to 68.9% and appeared sensitive to physicochemical properties of the naphthenic acids, environmental conditions, and water quality. Treatment efficiency of individual naphthenic acids was found to increase with increasing carbon number and decreasing number of double bond equivalents in the molecule. Treatment efficiency was also found to increase with both higher initial turbidity in OSPW entering the wetland, and warmer average OSPW temperatures during wetland operation. Half-life times of naphthenic acids in the treatment wetland ranged between 8.9 and 39 days and were substantially lower than those in tailings ponds (i.e., 12.9–13.6 years) and laboratory studies focussed on bench-scale aerobic microbial biodegradation (i.e., 44–315 days). Using published dose-response data, biomimetic extraction measurements using solid phase microextraction fibers indicate that 14 days of wetland treatment resulted in a reduction in (4 d) deformity of Danio rerio from 50 to 16%, while exhibiting less than 1% toxic response for less sensitive toxic endpoints. The study concludes that wetland treatment is a feasible and productive treatment method for naphthenic acids in oil sands process-affected water due to a combination of sorption and biodegradation.

Condensability sieving porous coordination polymer membranes for preferential permeation of C1–C4 alkanes over H2

Refinery gas contains abundant H2 and a small amount of C1–C4 hydrocarbons. Here, we propose a condensability sieving strategy to realize preferential permeation of hydrocarbons over H2 by developing halogen-induced porous coordination polymer (PCP) mixed matrix membranes (MMMs) that display condensability sieving gas transport. The 4-Cl-PCP, 5-Cl-PCP and 5-Br-PCP are synthesized by using Zr4+ and X-isophthalic acid (where X ​= ​4-Cl or 5-Cl or 5-Br) exhibit increased gas adsorption capacity with the increase in carbon number of the feed gas, but with almost no H2 adsorption. MMMs containing the PCPs with different charge distributions enhance condensability sieving selectivity and inhibit diffusion selectivity. The permeances of the MMMs originated from condensability sieving are consistent with the polarizability-dependent adsorption of the PCP. The selectivity of the obtained MMMs for n-C4H10/H2, C3H8/H2, C2H6/H2, and CH4/H2 achieve ∼40, ∼15, ∼5, and ∼2, respectively, exhibiting promising applications in refinery gas purification owing to their lower energy consumption compared with H2-preferential permeation membranes.

Guerbet alcohol esters: Practical synthesis and applications

Guerbet alcohols are primary alcohols with beta branching and have lower melting point than their linear counterpart. Due to presence of branching, the products are liquid at lower temperatures; they have low volatility and exhibit better color and oxidation stability. The main advantage of the Guerbet branching material is their biodegradability. Present research work was carried out on synthesis of branch chain alcohols with varying hydrocarbon chain lengths. The main purpose was to study the effects of branching and varying chain length with performance properties. Branch chain esters with mono and di-carboxylic acids were synthesized with varying hydrocarbon chain lengths. The major limitation of Guerbet products is their cost. Guerbet alcohols were esterified with various monobasic and dibasic acids and found to have lower pour points. Load carrying capacity of prepared ester increased with increase in carbon chain. Wear scar of the prepared ester decreased with the increase in carbon number of ester molecule. These properties indicated their potential use as lubricating oil base stock which are environment friendly as they are biodegradable and with excellent liquidity.

Molecular Simulation Study on the Density Behavior of n-Alkane/CO2 Systems.

The density and volumetric behavior of three typical n-alkanes (hexane, octane, and decane) influenced by different mole fractions of CO2 injected in them at temperatures from 303 to 363 K and pressures from 3.8 to 8.67 MPa were investigated by performing molecular dynamics simulations. It is shown that the mass density first increases and then decreases with increasing CO2 mole fraction. Correspondingly, the system volume only slightly swells at low CO2 contents while suddenly expanding when the CO2 mole fraction exceeds a value of ∼60%. The calculations of structural properties and interaction energies indicate that at low CO2 mole fractions, there are a few CO2 molecules existing in the gap of alkane molecules, resulting in poor compressibility, while at higher CO2 concentrations, the CO2 molecules begin to separate from the CO2-saturated alkane phase and form a gas phase, leading to higher compressibility. Therefore, at high CO2 mole fractions, the system density and volume can more easily be changed by temperature and pressure than that at low CO2 mole fractions. In addition, since it is harder for alkanes with longer chains to separate from each other, the volume swelling decreases and the density increases with increasing carbon number of n-alkane chains. Finally, we found that the increase in CO2 mole fraction, temperature, and the decrease in alkane chain length would promote the diffusion of both CO2 and alkane molecules. However, the influence of pressure on molecular diffusion is very limited except when P = 8.67 MPa and T = 333 K, where CO2 is in the supercritical state. This work is helpful for understanding the density and volumetric behavior of n-alkane/CO2 mixtures at a molecular level and provides useful information for guiding carbon sequestration and CO2-enhanced oil recovery.

Relationship of color change to permeation of target compound in polydiacetylene vesicle system

AbstractPolydiacetylene (PDA) systems, which showed color changes due to the permeation of target molecules, were reported previously by our research group. To use the systems for controlled drug delivery systems, the relationship of the color change to the permeation time of the PDA vesicle must be characterized precisely. Therefore, this relationship was investigated and characterized in this study. Methotrexate (MTX) was used as the target compound and the detection of MTX is an important process in anticancer study. N‐(2‐aminoethyl)pentacosa‐10,12‐diynamide (AEPCDA) was used as the diacetylene surfactant. Dimethyldioctadecylammonium bromide (DOAB) was used as an assistant surfactant. The color change occurred when the mixed surfactant vesicles, with DOAB, were used. When a lower ratio of DOAB was added to the AEPCDA vesicle, the color change rate was slower than that when using the higher ratio of DOAB. The color change rate constants were estimated for several different ratios (AEPCDA:DOAB). Surfactants with different carbon numbers to DOAB were used as the assistant surfactants in this study. The results showed that the color change rate constant decreased with the increasing carbon number of the assistant surfactant. This means that the color change rate can be controlled by changing the assistant surfactant.

The effect of slight to moderate biodegradation on the shale soluble organic matter composition of the upper triassic Yanchang formation, Ordos Basin, China

Biodegradation greatly affects the physical properties and economic value of oil and gas reserves. Here, the composition of a suite of 27 samples of shale soluble organic matter from typical biodegraded shale profiles in the Upper Triassic Yanchang Formation, Ordos Basin, China, was analyzed using GC/MS/MS and ESI FT-ICR MS technology. The effects of slight to moderate biodegradation on the compositions of saturated hydrocarbons and polar nitrogen, sulfur, oxygen (NSO) compounds were assessed, revealing three key effects as biodegradation increases (1) Chloroform asphalt "A" (i.e. soluble organic matter). and saturated hydrocarbons gradually decrease, aromatic hydrocarbons gradually increase, non-hydrocarbons increase, and there is no regular change in asphaltene content. (2) The relative content of pristane (Pr) and phytane (Ph) to their corresponding n-alkanes increases gradually, indicating the n-alkanes decrease gradually. However, the resistance of the n-alkanes to biodegradation may be related to the carbon number and odd-even distribution. As the carbon number increases, the ability of n-alkanes to resist biodegradation increases, and even carbon number n-alkanes may be more resistant to biodegradation than odd carbon number n-alkanes. (3) No obvious changes in the relevant biodegradation indices of steranes and polar NSO compounds were observed in the entire profile. Hopane biodegradation indices were variable and sometimes contradictory with depth throughout the sediment profile. However, overall the data suggest the hopanes were not affected by biodegradation.Our results indicate that shale oil can also be biodegraded, and due to the tightness of shale reservoirs, slight to moderate biodegradation is common. Changes in shale oil content in the profile are the result of the primary migration and biodegradation together, with primary migration occurring mainly from the shale to the upper sandstone reservoirs. The above evidence shows that slight to moderate biodegradation has a relatively small impact on shale oil. However, in previous work we have shown that biodegradation has significant impacts on the shale gas content and its geochemical characteristics.